Volume 53,Issue 10,2024 Table of Contents
2024, 53(10):2723-2734.
DOI: 10.12442/j.issn.1002-185X.20240245
Abstract:
Ni-P-SiCP coatings were deposited on 42CrMo steel by electroless plating. The surface morphologies and phase structures of the Ni-P-SiCP coatings processed under different SiCP concentrations at different heat treatment temperatures were analyzed. The microhardness, corrosion resistance, and wear resistance of the Ni-P-SiCP coatings were studied. Results show that Ni-P-SiCP coatings exhibit cauliflower-like morphology. Increasing the SiCP concentration can reduce the size of cellular structure. The microhardness and corrosion resistance are initially increased and then decreased with the increase in SiCP concentration. The maximum microhardness and corrosion potential are 7379 MPa and -0.363 V, respectively, when the SiCP concentration is 5 g/L. The Ni-P-SiCP coatings exhibit an amorphous structure, and the width of the diffuse diffraction peak becomes narrower with the increase in SiCP concentration. It is suggested that SiCP inhibits the deposition of P and promotes the microcrystalline transformation. After heat treatment at 350 °C, the Ni-P-SiCP coatings are crystallized, resulting in the precipitation of Ni3P phase. Heat treatment at 400 °C for 1 h maximizes the structure. The synergistic effect of the Ni3P precipitate phase and SiCP dispersion phase promotes the densification of the cellular structure, leading to the optimal microhardness (13 828 MPa), optimal corrosion resistance (-0.277 V), and excellent wear resistance. The wear mechanism is dominated by micro-cutting abrasive wear with slight adhesive and oxidative wear.
Ni-P-SiCP coatings were deposited on 42CrMo steel by electroless plating. The surface morphologies and phase structures of the Ni-P-SiCP coatings processed under different SiCP concentrations at different heat treatment temperatures were analyzed. The microhardness, corrosion resistance, and wear resistance of the Ni-P-SiCP coatings were studied. Results show that Ni-P-SiCP coatings exhibit cauliflower-like morphology. Increasing the SiCP concentration can reduce the size of cellular structure. The microhardness and corrosion resistance are initially increased and then decreased with the increase in SiCP concentration. The maximum microhardness and corrosion potential are 7379 MPa and -0.363 V, respectively, when the SiCP concentration is 5 g/L. The Ni-P-SiCP coatings exhibit an amorphous structure, and the width of the diffuse diffraction peak becomes narrower with the increase in SiCP concentration. It is suggested that SiCP inhibits the deposition of P and promotes the microcrystalline transformation. After heat treatment at 350 °C, the Ni-P-SiCP coatings are crystallized, resulting in the precipitation of Ni3P phase. Heat treatment at 400 °C for 1 h maximizes the structure. The synergistic effect of the Ni3P precipitate phase and SiCP dispersion phase promotes the densification of the cellular structure, leading to the optimal microhardness (13 828 MPa), optimal corrosion resistance (-0.277 V), and excellent wear resistance. The wear mechanism is dominated by micro-cutting abrasive wear with slight adhesive and oxidative wear.
2024, 53(10):2735-2746.
DOI: 10.12442/j.issn.1002-185X.E20240311
Abstract:
A combined process of molten salt electro-deoxidation and vacuum hot-pressing sintering was proposed to prepare AlCrFeNiTix high-entropy alloy (HEA)-TiN ceramic coating composites on low-carbon steel surfaces, where nitrides were introduced from BN isolater between graphite mold and HEA powders. The effect of Ti content on the microstructure, ultimate tensile strength, hardness, and wear resistance of the composites was investigated, and the bonding mechanism was elucidated. Results demonstrate that the composites have excellent hardness and wear resistance. The hardness of composites is significantly increased with the increase in Ti content. The extremely high wear resistance is attributed to the extremely high melting point and high thermal hardness of TiN, which can effectively prevent oxidation deformation of the worn surface.
A combined process of molten salt electro-deoxidation and vacuum hot-pressing sintering was proposed to prepare AlCrFeNiTix high-entropy alloy (HEA)-TiN ceramic coating composites on low-carbon steel surfaces, where nitrides were introduced from BN isolater between graphite mold and HEA powders. The effect of Ti content on the microstructure, ultimate tensile strength, hardness, and wear resistance of the composites was investigated, and the bonding mechanism was elucidated. Results demonstrate that the composites have excellent hardness and wear resistance. The hardness of composites is significantly increased with the increase in Ti content. The extremely high wear resistance is attributed to the extremely high melting point and high thermal hardness of TiN, which can effectively prevent oxidation deformation of the worn surface.
2024, 53(10):2747-2754.
DOI: 10.12442/j.issn.1002-185X.20240095
Abstract:
FeCrAlCu, FeCrAlCuNi, FeCrAlCuCo, and FeCrAlCuNiCo high-entropy alloy (HEA) coatings were synthesized on the surface of 45# steel through cold spraying-assisted laser remelting. Results reveal that all four HEA coatings are composed of face-centered cubic+body-centered cubic phases. Additionally, the microstructure of the coatings consists of columnar dendrites. With the simultaneous addition of both Ni and Co elements, the columnar dendritic grains are gradually refined in the coating. Moreover, the FeCrAlCuNiCo HEA coating exhibits excellent friction performance with the coating hardness of 5847.7 MPa, friction factor of 0.45, and wear rate of 3.72×10-5 mm3·N-1·m-1. The predominant wear mechanism is the adhesive wear and abrasive wear.
FeCrAlCu, FeCrAlCuNi, FeCrAlCuCo, and FeCrAlCuNiCo high-entropy alloy (HEA) coatings were synthesized on the surface of 45# steel through cold spraying-assisted laser remelting. Results reveal that all four HEA coatings are composed of face-centered cubic+body-centered cubic phases. Additionally, the microstructure of the coatings consists of columnar dendrites. With the simultaneous addition of both Ni and Co elements, the columnar dendritic grains are gradually refined in the coating. Moreover, the FeCrAlCuNiCo HEA coating exhibits excellent friction performance with the coating hardness of 5847.7 MPa, friction factor of 0.45, and wear rate of 3.72×10-5 mm3·N-1·m-1. The predominant wear mechanism is the adhesive wear and abrasive wear.
Deng Zhenzhen
,
Dai Zhengfei
,
Wu Weibo
,
Lai Ruisi
,
Feng Qing
,
Jia Bo
,
Wang Chen
,
Lv Yuanjiang
,
Ma Fei
2024, 53(10):2755-2765.
DOI: 10.12442/j.issn.1002-185X.20240194
Abstract:
To improve the corrosion resistance of titanium (Ti) bipolar plate, titanium nitride (TiN) film was prepared on the surface of commercial TA1 pure titanium by magnetron reactive sputtering and pulse laser deposition (PLD) techniques, and the film prepared under different process parameters were evaluated. Results show that dense and complete TiN film can be obtained on TA1 surface under different preparation processes, and the corrosion current density of Ti substrate significantly increases. However, the composition of the film prepared by magnetron reactive sputtering is affected by the oxygen competition reaction, and its homogeneity is inferior to that of the film prepared by PLD. The comprehensive performance of the PLD-prepared film shows excellent characteristics in the terms of low corrosion current density (0.025 μA·cm-2), moderate corrosion overpotential (-0.106 V), and good hydrophobicity.
To improve the corrosion resistance of titanium (Ti) bipolar plate, titanium nitride (TiN) film was prepared on the surface of commercial TA1 pure titanium by magnetron reactive sputtering and pulse laser deposition (PLD) techniques, and the film prepared under different process parameters were evaluated. Results show that dense and complete TiN film can be obtained on TA1 surface under different preparation processes, and the corrosion current density of Ti substrate significantly increases. However, the composition of the film prepared by magnetron reactive sputtering is affected by the oxygen competition reaction, and its homogeneity is inferior to that of the film prepared by PLD. The comprehensive performance of the PLD-prepared film shows excellent characteristics in the terms of low corrosion current density (0.025 μA·cm-2), moderate corrosion overpotential (-0.106 V), and good hydrophobicity.
Zhang Ge
,
Tao Xipeng
,
Jafri Syed Muhammad Abbas
,
Wang Xinguang
,
Zhang Song
,
Zhang Chunhua
,
Liang Jingjing
,
Li Jinguo
,
Sun Xiaofeng
,
Zhou Yizhou
2024, 53(10):2766-2776.
DOI: 10.12442/j.issn.1002-185X.20240015
Abstract:
The influence of applied temperatures on the creep rupture life of the third-generation low-cost single crystal (SX) superalloy with Pt-Al coating was evaluated. The creep damage was observed under the conditions of 1100 °C/137 MPa, 1120 °C/137 MPa, and 1140 °C/137 MPa. Results show that the properties of bare superalloy outperform those of coated superalloy under all test conditions. The most significant reduction in creep life reaches 50% when the test condition is 1100 °C/137 MPa. At higher temperatures (1120 and 1140 °C), the crack propagation rate in Pt-Al coatings to SX superalloy substrate decreases, thereby reducing the degradation degree of mechanical properties. Instead of the penetration into SX substrate, tip oxidation and Al diffusion of the coating cracks cause the formation of oxides, therefore leading to the slow degradation in microstructures of the substrate beneath the coating. At 1100 °C, however, the microstructure of coating/SX superalloy substrate degrades due to the Al internal diffusion. This diffusion mechanism promotes the formation of harmful topologically close packed phases around 1100 °C. At 1120 and 1140 °C, the dislocation of SX superalloy substrate beneath the coating is relatively unchanged, compared to that in the inner superalloy. In contrast, the dislocation network of the substrate beneath the coating becomes sparse, and the number of superdislocations cutting into γ′ phases increases at 1100 °C.
The influence of applied temperatures on the creep rupture life of the third-generation low-cost single crystal (SX) superalloy with Pt-Al coating was evaluated. The creep damage was observed under the conditions of 1100 °C/137 MPa, 1120 °C/137 MPa, and 1140 °C/137 MPa. Results show that the properties of bare superalloy outperform those of coated superalloy under all test conditions. The most significant reduction in creep life reaches 50% when the test condition is 1100 °C/137 MPa. At higher temperatures (1120 and 1140 °C), the crack propagation rate in Pt-Al coatings to SX superalloy substrate decreases, thereby reducing the degradation degree of mechanical properties. Instead of the penetration into SX substrate, tip oxidation and Al diffusion of the coating cracks cause the formation of oxides, therefore leading to the slow degradation in microstructures of the substrate beneath the coating. At 1100 °C, however, the microstructure of coating/SX superalloy substrate degrades due to the Al internal diffusion. This diffusion mechanism promotes the formation of harmful topologically close packed phases around 1100 °C. At 1120 and 1140 °C, the dislocation of SX superalloy substrate beneath the coating is relatively unchanged, compared to that in the inner superalloy. In contrast, the dislocation network of the substrate beneath the coating becomes sparse, and the number of superdislocations cutting into γ′ phases increases at 1100 °C.
2024, 53(10):2777-2785.
DOI: 10.12442/j.issn.1002-185X.20240014
Abstract:
High-performance yttrium oxide-phenolic resin (Y2O3-PF) alternating coating was prepared on epoxy resin-based composite material using supersonic plasma spraying and dual-channel powder feeding technique. Y2O3-coated PF (Y2O3/PF) powder was firstly sprayed onto the substrate, forming a transition layer, and then the spherical Y2O3 powder and Y2O3/PF powder were alternately deposited to form the composite alternating coating. Results show that the alternating coating is mainly composed of deposited Y2O3/PF powder. The bonding strength between coating and substrate is as high as 26.48 MPa with the single-test maximum bonding strength of 28.10 MPa, and shear strength reaches 24.30 MPa. Additionally, the heat transfer effect caused by external Y2O3 particles gradually softens and even melts PF, thus effectively avoiding the damage of high temperature to molecular structure and thereby promoting the crosslinking and curing effects of resin during the deposition process. In the meantime, the unmelted Y2O3 powder results in the shot peening effect, which washes out and eliminates the powder particles with inferior deposition effect, ultimately improving the physical and chemical properties of the alternating coating.
High-performance yttrium oxide-phenolic resin (Y2O3-PF) alternating coating was prepared on epoxy resin-based composite material using supersonic plasma spraying and dual-channel powder feeding technique. Y2O3-coated PF (Y2O3/PF) powder was firstly sprayed onto the substrate, forming a transition layer, and then the spherical Y2O3 powder and Y2O3/PF powder were alternately deposited to form the composite alternating coating. Results show that the alternating coating is mainly composed of deposited Y2O3/PF powder. The bonding strength between coating and substrate is as high as 26.48 MPa with the single-test maximum bonding strength of 28.10 MPa, and shear strength reaches 24.30 MPa. Additionally, the heat transfer effect caused by external Y2O3 particles gradually softens and even melts PF, thus effectively avoiding the damage of high temperature to molecular structure and thereby promoting the crosslinking and curing effects of resin during the deposition process. In the meantime, the unmelted Y2O3 powder results in the shot peening effect, which washes out and eliminates the powder particles with inferior deposition effect, ultimately improving the physical and chemical properties of the alternating coating.
7 Study of high-temperature oxidation behavior of electrodeposited Ni/Cr coatings on Zr alloy surfaces
2024, 53(10):2805-2800.
DOI: 10.12442/j.issn.1002-185X.20240037
Abstract:
After the Fukushima nuclear accident in Japan, accident tolerant fuel (ATF) cladding technology has attracted widespread attention in the industry. The cladding of Cr coatings on zirconium (Zr) alloys for nuclear fuel cladding in nuclear reactor cores is considered to be the most likely technology to be commercially available in the near future. At present, most of the preparation methods for Cr coatings have the disadvantages of expensive equipment, low deposition rate and weak shape adaptability. And the molten salt electrodeposition technology has the advantages of high cathodic current efficiency, fast electrodeposition speed, and strong adaptability of substrate shape, which is expected to solve the problem of efficient and low-cost preparation of high-quality Cr coatings on the surface of cladding Zr alloys. In order to realize the preparation of Cr coating on the surface of Zr alloy by molten salt electrodeposition, this paper adopted aqueous solution electrodeposition and molten salt electrodeposition methods to prepare Ni transition layer and Cr coating on the surface of Zr alloy substrate sequentially, and carried out the characterization of the organization structure, the bonding force and nano-hardness test as well as the study of the high-temperature oxidation behavior of the Zr/Ni/Cr specimens obtained from the preparation. The results showed that the Ni/Cr coating on the surface of Zr alloy was uniform and dense, and the bonding force between the coating and the substrate was about 151N. The hardness and modulus of elasticity of Zr/Ni/Cr increased gradually from inner to outer layers with a quasi-gradient transition. The surface roughness of the Cr coating was about 2 μm, and the hardness and modulus of elasticity were 2.86 GPa and 172.86 GPa, respectively. The Zr/Ni/Cr specimens showed nearly parabolic and nearly linear patterns during steam oxidation at high temperatures of 1000°C and 1200°C, respectively, indicating that the Ni/Cr coatings were able to provide good protection to the Zr alloy matrix at 1000℃. The high-temperature oxidation failure mechanism of Ni/Cr coatings on Zr alloy surfaces was closely related to the rapid diffusion of the Ni transition layer, the oxidation and diffusion depletion of the Cr layer, and the weakening of the Cr layer due to the rapid diffusion of Zr along the Cr grain boundaries.
After the Fukushima nuclear accident in Japan, accident tolerant fuel (ATF) cladding technology has attracted widespread attention in the industry. The cladding of Cr coatings on zirconium (Zr) alloys for nuclear fuel cladding in nuclear reactor cores is considered to be the most likely technology to be commercially available in the near future. At present, most of the preparation methods for Cr coatings have the disadvantages of expensive equipment, low deposition rate and weak shape adaptability. And the molten salt electrodeposition technology has the advantages of high cathodic current efficiency, fast electrodeposition speed, and strong adaptability of substrate shape, which is expected to solve the problem of efficient and low-cost preparation of high-quality Cr coatings on the surface of cladding Zr alloys. In order to realize the preparation of Cr coating on the surface of Zr alloy by molten salt electrodeposition, this paper adopted aqueous solution electrodeposition and molten salt electrodeposition methods to prepare Ni transition layer and Cr coating on the surface of Zr alloy substrate sequentially, and carried out the characterization of the organization structure, the bonding force and nano-hardness test as well as the study of the high-temperature oxidation behavior of the Zr/Ni/Cr specimens obtained from the preparation. The results showed that the Ni/Cr coating on the surface of Zr alloy was uniform and dense, and the bonding force between the coating and the substrate was about 151N. The hardness and modulus of elasticity of Zr/Ni/Cr increased gradually from inner to outer layers with a quasi-gradient transition. The surface roughness of the Cr coating was about 2 μm, and the hardness and modulus of elasticity were 2.86 GPa and 172.86 GPa, respectively. The Zr/Ni/Cr specimens showed nearly parabolic and nearly linear patterns during steam oxidation at high temperatures of 1000°C and 1200°C, respectively, indicating that the Ni/Cr coatings were able to provide good protection to the Zr alloy matrix at 1000℃. The high-temperature oxidation failure mechanism of Ni/Cr coatings on Zr alloy surfaces was closely related to the rapid diffusion of the Ni transition layer, the oxidation and diffusion depletion of the Cr layer, and the weakening of the Cr layer due to the rapid diffusion of Zr along the Cr grain boundaries.
2024, 53(10):2823-2830.
DOI: 10.12442/j.issn.1002-185X.20240390
Abstract:
The fatigue crack propagation rate (da/dN) of bimodal structure Ti55531 titanium alloy before and after laser shock peening（LSP）was investigated. The fracture, microstructure and residual stress of fatigue crack propagation samples were analyzed. The results show that after laser shock, the fatigue crack growth rate da/dN decreased. When △K < 22.84MPa?√m, the sample BM-LSP has a lower fatigue crack growth rate than the sample without laser shock BM. When △K=22.84 the crack growth rates of the two samples were similar that is 3.92×10-4mm/cycle. After LSP, the length dispersion and thickness dispersion of the secondary α layer decreased by 22.9%, 38.9%, and the polar density of α and β phases decreased by 37% and 16%, respectively. The passivity of the lamer α tip and microstructure homogenization alleviated the stress concentration, resulting in a decrease in da/dN. In addition, the laser shock process introduces a residual compressive stress layer to a depth of about 900μm on the surface of the material. Residual compressive stress is also an important factor to offset tensile stress at crack tip, enhance crack closure and slow down crack propagation.
The fatigue crack propagation rate (da/dN) of bimodal structure Ti55531 titanium alloy before and after laser shock peening（LSP）was investigated. The fracture, microstructure and residual stress of fatigue crack propagation samples were analyzed. The results show that after laser shock, the fatigue crack growth rate da/dN decreased. When △K < 22.84MPa?√m, the sample BM-LSP has a lower fatigue crack growth rate than the sample without laser shock BM. When △K=22.84 the crack growth rates of the two samples were similar that is 3.92×10-4mm/cycle. After LSP, the length dispersion and thickness dispersion of the secondary α layer decreased by 22.9%, 38.9%, and the polar density of α and β phases decreased by 37% and 16%, respectively. The passivity of the lamer α tip and microstructure homogenization alleviated the stress concentration, resulting in a decrease in da/dN. In addition, the laser shock process introduces a residual compressive stress layer to a depth of about 900μm on the surface of the material. Residual compressive stress is also an important factor to offset tensile stress at crack tip, enhance crack closure and slow down crack propagation.
2024, 53(10):2831-2842.
DOI: 10.12442/j.issn.1002-185X.20230506
Abstract:
In this paper, the fatigue properties of Zr705 alloy in original state and ultrasonic rolling state after pre-corrosion in 1mol/L LiOH solution, 3.5% NaCl solution and 5% HCl solution for 30 days were studied. The results show that the corrosion degree of the original Zr705 alloy is the most serious in 3.5% NaCl solution, followed by 5% HCl solution and the least in 1mol/L LiOH solution. This is related to the different corrosion mechanism of Zr705 alloy in different media: when Zr705 alloy is in LiOH solution, mainly O2- and OH- participate in the corrosion reaction, while Li+ does not participate in the corrosion reaction, but is adsorbed on the pore wall of oxide film and the grain boundary of ZrO2 to accelerate the corrosion; When Zr705 alloy is in NaCl solution, a large amount of Cl- plays a leading role in the corrosion reaction. When Zr705 alloy is in HCl solution, both H+ and Cl- participate in the corrosion process of Zr705 alloy in HCl solution. USRP-Zr705 alloy is more easily corroded than the original Zr705 alloy because of the high density dislocation defects in the surface gradient structure. After immersion corrosion treatment, the fatigue life of the original Zr705 alloy decreased obviously, which was mainly caused by corrosion damage on the surface of the sample during immersion corrosion. After immersion corrosion treatment, the fatigue life of USRP-Zr705 sample in 1mol/L LiOH solution is higher than that of the original Zr705 alloy, but it is lower in 3.5% NaCl solution and 5% HCl solution. There is a competitive relationship between the corrosion environment and the surface gradient structure on the fatigue properties of zirconium alloys: when the corrosion medium is weak, the surface gradient structure is the main factor affecting the fatigue properties of zirconium alloys. When the corrosive medium is strong, the surface gradient structure is still the main factor affecting the fatigue properties of the alloy under high stress cyclic loading. Under low stress cyclic loading, corrosion environment is the main factor affecting the fatigue properties of the alloy.
In this paper, the fatigue properties of Zr705 alloy in original state and ultrasonic rolling state after pre-corrosion in 1mol/L LiOH solution, 3.5% NaCl solution and 5% HCl solution for 30 days were studied. The results show that the corrosion degree of the original Zr705 alloy is the most serious in 3.5% NaCl solution, followed by 5% HCl solution and the least in 1mol/L LiOH solution. This is related to the different corrosion mechanism of Zr705 alloy in different media: when Zr705 alloy is in LiOH solution, mainly O2- and OH- participate in the corrosion reaction, while Li+ does not participate in the corrosion reaction, but is adsorbed on the pore wall of oxide film and the grain boundary of ZrO2 to accelerate the corrosion; When Zr705 alloy is in NaCl solution, a large amount of Cl- plays a leading role in the corrosion reaction. When Zr705 alloy is in HCl solution, both H+ and Cl- participate in the corrosion process of Zr705 alloy in HCl solution. USRP-Zr705 alloy is more easily corroded than the original Zr705 alloy because of the high density dislocation defects in the surface gradient structure. After immersion corrosion treatment, the fatigue life of the original Zr705 alloy decreased obviously, which was mainly caused by corrosion damage on the surface of the sample during immersion corrosion. After immersion corrosion treatment, the fatigue life of USRP-Zr705 sample in 1mol/L LiOH solution is higher than that of the original Zr705 alloy, but it is lower in 3.5% NaCl solution and 5% HCl solution. There is a competitive relationship between the corrosion environment and the surface gradient structure on the fatigue properties of zirconium alloys: when the corrosion medium is weak, the surface gradient structure is the main factor affecting the fatigue properties of zirconium alloys. When the corrosive medium is strong, the surface gradient structure is still the main factor affecting the fatigue properties of the alloy under high stress cyclic loading. Under low stress cyclic loading, corrosion environment is the main factor affecting the fatigue properties of the alloy.
10 Fretting wear behavior of Cr coated Zr-1Nb alloy cladding in high temperature high pressure water
Liao Yehong
,
Dai Gongying
,
Yan Jun
,
Lin Xiaodong
,
Peng Zhenxun
,
Liang Xue
,
Li Yifeng
,
Xue Jiaxiang
,
Li Qiang
2024, 53(10):2843-2851.
DOI: 10.12442/j.issn.1002-185X.20230530
Abstract:
The fretting wear behaviors of Cr-coated Zr-1Nb cladding tube with different griding pairs in simulated PWR primary water environment at 290 °C and 310 °C were studied by using three-dimensional optical surface profilometer, scanning electron microscope, electron back scattered diffraction and energy dispersive X-ray spectrometer. The results showed that the fretting wear behaviors between the Cr-coated Zr-1Nb cladding and griding pairs (i.e., Zr-4 dimple or Inconel 718 spring) were both dominated by the adhesive wear mechanism, accompanied by material transfer from the grinding pair to the Cr-coated cladding. With the increase of temperature, the fretting wear resistance of the Cr-coated cladding was decreased, as manifested by increased surface wear depth and volume. However, the fretting wear mechanism still remained unchanged within the temperature range tested in this work. In addition, the wear degree of the Cr-coated cladding with Zr-4 dimple was greater than that with Inconel 718 spring, which was thoughted to be related to the hardness and contact mode of the grinding pair.
The fretting wear behaviors of Cr-coated Zr-1Nb cladding tube with different griding pairs in simulated PWR primary water environment at 290 °C and 310 °C were studied by using three-dimensional optical surface profilometer, scanning electron microscope, electron back scattered diffraction and energy dispersive X-ray spectrometer. The results showed that the fretting wear behaviors between the Cr-coated Zr-1Nb cladding and griding pairs (i.e., Zr-4 dimple or Inconel 718 spring) were both dominated by the adhesive wear mechanism, accompanied by material transfer from the grinding pair to the Cr-coated cladding. With the increase of temperature, the fretting wear resistance of the Cr-coated cladding was decreased, as manifested by increased surface wear depth and volume. However, the fretting wear mechanism still remained unchanged within the temperature range tested in this work. In addition, the wear degree of the Cr-coated cladding with Zr-4 dimple was greater than that with Inconel 718 spring, which was thoughted to be related to the hardness and contact mode of the grinding pair.
2024, 53(10):2852-2859.
DOI: 10.12442/j.issn.1002-185X.20230511
Abstract:
Using Ni3Al+Cr3C2 mixed powder with different amounts of Cr3C2, laser cladding was carried out on 45 steel to prepare Ni3Al-based alloy cladding layer. By means of scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), and wear tests, the content and average size of in situ-formed carbides under different amounts of Cr3C2 were calculated, and the effects of carbides on the microstructure, microhardness and wear resistance of Ni3Al-based alloy cladding layer were analyzed. The results indicate that the microstructure of the Ni3Al-based alloy cladding layer contains mainly Ni3Al matrix and in situ-formed Cr7C3 carbides. With the increase of Cr3C2 content, the proportion of in situ-formed carbides in cladding layer increases from 6.8% to 32.3%, the average size increases from 0.10μm to 0.78μm, and the microhardness of the cladding layer increases from 471HV to 609HV. When the content of Cr3C2 is 35%, the carbide particles are dispersed, and uniform wear is produced in the process of wear test, so that the wear less of cladding layer is as low as 0.19 mg, and the wear loss of the disk is relatively the lowest, about 1.23 mg. However, when the content of Cr3C2 is 45%, the carbide content is 32.3%, but the large size particles are mainly. In the process of wear test, the large particles of carbide fracture and spalling, which accelerates the wear of the disk.
Using Ni3Al+Cr3C2 mixed powder with different amounts of Cr3C2, laser cladding was carried out on 45 steel to prepare Ni3Al-based alloy cladding layer. By means of scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), and wear tests, the content and average size of in situ-formed carbides under different amounts of Cr3C2 were calculated, and the effects of carbides on the microstructure, microhardness and wear resistance of Ni3Al-based alloy cladding layer were analyzed. The results indicate that the microstructure of the Ni3Al-based alloy cladding layer contains mainly Ni3Al matrix and in situ-formed Cr7C3 carbides. With the increase of Cr3C2 content, the proportion of in situ-formed carbides in cladding layer increases from 6.8% to 32.3%, the average size increases from 0.10μm to 0.78μm, and the microhardness of the cladding layer increases from 471HV to 609HV. When the content of Cr3C2 is 35%, the carbide particles are dispersed, and uniform wear is produced in the process of wear test, so that the wear less of cladding layer is as low as 0.19 mg, and the wear loss of the disk is relatively the lowest, about 1.23 mg. However, when the content of Cr3C2 is 45%, the carbide content is 32.3%, but the large size particles are mainly. In the process of wear test, the large particles of carbide fracture and spalling, which accelerates the wear of the disk.
12 Tribological Properties of Electroless Ni-Mo-P/(h)BN Composite Coatings in Wide Temperature Range
2024, 53(10):2860-2872.
DOI: 10.12442/j.issn.1002-185X.20240138
Abstract:
Ni-Mo-P and Ni-Mo-P/(h)BN composite coatings were prepared on the surface of GH4169 nickel-based high-temperature alloy by chemical composite plating technology. The tribological behaviour of the coatings at different temperatures and the microstructures of the coatings after friction wear at different temperatures were investigated. The tribological properties of the coatings at room temperature, 300℃, 500℃ and 700℃ were investigated by utilising a ball-disc friction and wear test. The chemical composition and organisational structure of the plated layer following the friction test at different temperatures were analysed by scanning electron microscope, energy spectrometer and X-ray diffractometer. The mechanical properties of the coatings were characterised by microhardness tester and Rockwell indentation tester following tribological tests at different temperatures.The results demonstrate that the deposited Ni-Mo-P and Ni-Mo-P/(h)BN composite coatings are predominantly amorphous structure containing small amounts of nancrystalline. The coatings transformed from amorphous to nanocrystalline structure with the increase of the friction test temperature. As the friction test temperature is increased, the plating layer undergoes a transformation from an amorphous to a nanocrystalline structure, accompanied by an increase in crystallinity. At temperatures exceeding 500℃, the The precipitation of the Ni3P hard phase in the plating layer occurs concurrently with the oxidative volatilisation of the Mo and P elements, resulting in the formation of pores within the plating layer and a reduction in its densification. As the temperature increased, the hardness of the plated layer exhibited a fluctuating trend, initially rising and then declining. Concurrently, the bonding strength of the film base exhibited a gradual decline, progressing from an HF1 grade to an HF6 grade. As the test temperature increased, the abrasive wear and oxidation of the plating layer became more pronounced. The highest wear rate was observed at 500℃. However, further increases in temperature resulted in a reduction in friction at the interface, with the average coefficient of friction of the Ni-Mo-P plating layer decreasing from 1 to 0.60. The coefficient of friction of the Ni-Mo-P/(h)BN composite layer was reduced from 0.88 to 0.53, which improved the friction reduction and wear-resistant performance of the plating layer at high temperatures. The incorporation of (h)BN particles into the plating layer enhances the P content, thereby increasing the toughness of the Ni-Mo-P/(h)BN composite plating layer, improving the hardness of the composite plating layer, and strengthening the film-base bonding. Furthermore, the composite plating layer exhibits superior wear resistance within the temperature range of room temperature to 700℃.
Ni-Mo-P and Ni-Mo-P/(h)BN composite coatings were prepared on the surface of GH4169 nickel-based high-temperature alloy by chemical composite plating technology. The tribological behaviour of the coatings at different temperatures and the microstructures of the coatings after friction wear at different temperatures were investigated. The tribological properties of the coatings at room temperature, 300℃, 500℃ and 700℃ were investigated by utilising a ball-disc friction and wear test. The chemical composition and organisational structure of the plated layer following the friction test at different temperatures were analysed by scanning electron microscope, energy spectrometer and X-ray diffractometer. The mechanical properties of the coatings were characterised by microhardness tester and Rockwell indentation tester following tribological tests at different temperatures.The results demonstrate that the deposited Ni-Mo-P and Ni-Mo-P/(h)BN composite coatings are predominantly amorphous structure containing small amounts of nancrystalline. The coatings transformed from amorphous to nanocrystalline structure with the increase of the friction test temperature. As the friction test temperature is increased, the plating layer undergoes a transformation from an amorphous to a nanocrystalline structure, accompanied by an increase in crystallinity. At temperatures exceeding 500℃, the The precipitation of the Ni3P hard phase in the plating layer occurs concurrently with the oxidative volatilisation of the Mo and P elements, resulting in the formation of pores within the plating layer and a reduction in its densification. As the temperature increased, the hardness of the plated layer exhibited a fluctuating trend, initially rising and then declining. Concurrently, the bonding strength of the film base exhibited a gradual decline, progressing from an HF1 grade to an HF6 grade. As the test temperature increased, the abrasive wear and oxidation of the plating layer became more pronounced. The highest wear rate was observed at 500℃. However, further increases in temperature resulted in a reduction in friction at the interface, with the average coefficient of friction of the Ni-Mo-P plating layer decreasing from 1 to 0.60. The coefficient of friction of the Ni-Mo-P/(h)BN composite layer was reduced from 0.88 to 0.53, which improved the friction reduction and wear-resistant performance of the plating layer at high temperatures. The incorporation of (h)BN particles into the plating layer enhances the P content, thereby increasing the toughness of the Ni-Mo-P/(h)BN composite plating layer, improving the hardness of the composite plating layer, and strengthening the film-base bonding. Furthermore, the composite plating layer exhibits superior wear resistance within the temperature range of room temperature to 700℃.
2024, 53(10):2873-2881.
DOI: 10.12442/j.issn.1002-185X.20240187
Abstract:
In order to enhance the high-temperature antioxidant protection provided by glass coating on titanium alloy, this study introduces the Ti3AlC2 reinforcing phase into pure glass coating slurry by ball milling method, and scrapes the slurry onto the surface of TC4 alloy and conducts antioxidant test. The results show that when 5 wt.% Ti3AlC2 (TAC5 coating) was added, the α-contamination layer thickness of the TC4 alloy substrate is minimized, measuring approximately 65.78 μm. In comparison to the pure glass coating under similar test conditions, the α-contamination layer thickness of the TAC5 coating is reduced by about one quarter. This reduction occurs as the Ti3AlC2 reinforcing phase reacts with the infiltrated oxygen in the coating, thereby diminishing contact between the substrate and oxygen and improving the coating’s ability to safeguard the TC4 alloy against oxidation at elevated temperatures.
In order to enhance the high-temperature antioxidant protection provided by glass coating on titanium alloy, this study introduces the Ti3AlC2 reinforcing phase into pure glass coating slurry by ball milling method, and scrapes the slurry onto the surface of TC4 alloy and conducts antioxidant test. The results show that when 5 wt.% Ti3AlC2 (TAC5 coating) was added, the α-contamination layer thickness of the TC4 alloy substrate is minimized, measuring approximately 65.78 μm. In comparison to the pure glass coating under similar test conditions, the α-contamination layer thickness of the TAC5 coating is reduced by about one quarter. This reduction occurs as the Ti3AlC2 reinforcing phase reacts with the infiltrated oxygen in the coating, thereby diminishing contact between the substrate and oxygen and improving the coating’s ability to safeguard the TC4 alloy against oxidation at elevated temperatures.
2024, 53(10):2968-2974.
DOI: 10.12442/j.issn.1002-185X.20230680
Abstract:
Yb2Si2O7 and high entropy double silicate powders (Yb0.25Y0.25Lu0.25Er0.25)2Si2O7, (Yb0.2Y0.2Lu0.2Er0.2Sc0.2)2Si2O7, and (Yb0.2Y0.2Lu0.2Er0.2Ho0.2)2Si2O7 were prepared through solid-state reaction. The phase composition, thermal expansion coefficient, thermal conductivity, and elastic modulus of their ceramic blocks and insulation treatment were studied. The results show that due to the addition of rare earth elements Y, Lu, and Er, the thermal expansion coefficient and thermal conductivity of high entropy (Yb0.25Y0.25Lu0.25Er0.25)2Si2O7 are similar to those of Yb2Si2O7, but the elastic modulus decreases the least, at 10.28%; Due to the addition of Scelements, high entropy (Yb0.2Y0.2Lu0.2Er0.2Sc0.2)2Si2O7 has lower thermal expansion coefficient and thermal conductivity compared to (Yb0.25Y0.25Lu0.25Er0.25)2Si2O7, and the elastic modulus is reduced by 18.74%; Compared with (Yb0.25Y0.25Lu0.25Er0.25)2Si2O7, the high entropy (Yb0.2Y0.2Lu0.2Er0.2Ho0.2)2Si2O7 doped with Ho element has a higher thermal expansion coefficient and lower thermal conductivity, but its elastic modulus decreases the most, reaching 24.78%. After insulation at 1200 ℃ and 1300 ℃ for 10, 30, and 50 hours, Yb2Si2O7, (Yb0.25Y0.25Lu0.25Er0.25)2Si2O7, (Yb0.2Y0.2Lu0.2Er0.2Sc0.2)2Si2O7, and (Yb0.2Y0.2Lu0.2Er0.2Ho0.2)2Si2O7 all exhibited good high-temperature stability, and their elastic modulus increased with the increase of insulation time, while their thermal expansion coefficient gradually decreased. After high entropy double silicate insulation treatment, it still exhibits good high-temperature phase stability and has a similar coefficient of thermal expansion to the substrate, indicating that the prepared high entropy double silicate is suitable for thermal environment barrier coating materials of high thrust weight ratio aviation engines.
Yb2Si2O7 and high entropy double silicate powders (Yb0.25Y0.25Lu0.25Er0.25)2Si2O7, (Yb0.2Y0.2Lu0.2Er0.2Sc0.2)2Si2O7, and (Yb0.2Y0.2Lu0.2Er0.2Ho0.2)2Si2O7 were prepared through solid-state reaction. The phase composition, thermal expansion coefficient, thermal conductivity, and elastic modulus of their ceramic blocks and insulation treatment were studied. The results show that due to the addition of rare earth elements Y, Lu, and Er, the thermal expansion coefficient and thermal conductivity of high entropy (Yb0.25Y0.25Lu0.25Er0.25)2Si2O7 are similar to those of Yb2Si2O7, but the elastic modulus decreases the least, at 10.28%; Due to the addition of Scelements, high entropy (Yb0.2Y0.2Lu0.2Er0.2Sc0.2)2Si2O7 has lower thermal expansion coefficient and thermal conductivity compared to (Yb0.25Y0.25Lu0.25Er0.25)2Si2O7, and the elastic modulus is reduced by 18.74%; Compared with (Yb0.25Y0.25Lu0.25Er0.25)2Si2O7, the high entropy (Yb0.2Y0.2Lu0.2Er0.2Ho0.2)2Si2O7 doped with Ho element has a higher thermal expansion coefficient and lower thermal conductivity, but its elastic modulus decreases the most, reaching 24.78%. After insulation at 1200 ℃ and 1300 ℃ for 10, 30, and 50 hours, Yb2Si2O7, (Yb0.25Y0.25Lu0.25Er0.25)2Si2O7, (Yb0.2Y0.2Lu0.2Er0.2Sc0.2)2Si2O7, and (Yb0.2Y0.2Lu0.2Er0.2Ho0.2)2Si2O7 all exhibited good high-temperature stability, and their elastic modulus increased with the increase of insulation time, while their thermal expansion coefficient gradually decreased. After high entropy double silicate insulation treatment, it still exhibits good high-temperature phase stability and has a similar coefficient of thermal expansion to the substrate, indicating that the prepared high entropy double silicate is suitable for thermal environment barrier coating materials of high thrust weight ratio aviation engines.
Li Hushan
,
Ding Chaogang
,
Ding Ziheng
,
Zhang Hao
,
Wang Fanghui
,
Chen Yuxi
,
Bao Jianxing
,
Xu Jie
,
Guo Bin
,
Shan Debin
2024, 53(10):2713-2717.
DOI: 10.12442/j.issn.1002-185X.20240485
Abstract:
The mechanical properties and fracture morphologies of Cu/Nb multilayer composites under electric-assisted tension (EAT) were investigated. Results show that the generated Joule-heat leads to obvious stress softening with the increase in current density. However, the elongation decreases, which is closely related to the characteristic fracture behavior of Cu/Nb multilayer composites during EAT. The fracture pattern is gradually transformed from ductile fracture to melt fracture with the increase in current density.
The mechanical properties and fracture morphologies of Cu/Nb multilayer composites under electric-assisted tension (EAT) were investigated. Results show that the generated Joule-heat leads to obvious stress softening with the increase in current density. However, the elongation decreases, which is closely related to the characteristic fracture behavior of Cu/Nb multilayer composites during EAT. The fracture pattern is gradually transformed from ductile fracture to melt fracture with the increase in current density.
2024, 53(10):2718-2722.
DOI: 10.12442/j.issn.1002-185X.20220918
Abstract:
The dimensional change, residual stress, grain orientation difference, dislocation density, and dislocation distribution of beryllium after different hot isostatic pressing treatments were analyzed by laser length meter, Raman spectrometer, nanoindentation meter, electron backscattered diffractometer, and transmission electron microscope, and the influence of thermal-cold cycling treatment on the dimensional stability of beryllium was analyzed. Results show that the size of the hot isostatic pressed beryllium tends to be stable after 6 cycles of thermal-cold cycling treatment from -100 °C to 150 °C, and it has good dimensional stability. The dimensional stabilization mechanism of beryllium is mainly the homogenization of dislocations within the grain and the homogenization of orientation difference caused by micro-plastic deformation.
The dimensional change, residual stress, grain orientation difference, dislocation density, and dislocation distribution of beryllium after different hot isostatic pressing treatments were analyzed by laser length meter, Raman spectrometer, nanoindentation meter, electron backscattered diffractometer, and transmission electron microscope, and the influence of thermal-cold cycling treatment on the dimensional stability of beryllium was analyzed. Results show that the size of the hot isostatic pressed beryllium tends to be stable after 6 cycles of thermal-cold cycling treatment from -100 °C to 150 °C, and it has good dimensional stability. The dimensional stabilization mechanism of beryllium is mainly the homogenization of dislocations within the grain and the homogenization of orientation difference caused by micro-plastic deformation.
17 Coarsening Behavior of γ′ Precipitates and Compression Performance of Novel Co-Ni-Al-W Superalloy
2024, 53(10):2786-2793.
DOI: 10.12442/j.issn.1002-185X.20240244
Abstract:
The coarsening behavior of γ? precipitate phase at different temperatures and the compressive performance of novel Co-Ni-Al-W superalloy were investigated. Experiment results show that the evolution of the mean radius and volume fraction of the γ? phase obeys the classical Lifshitz-Slyozov-Wagner model. The coarsening rate of the γ? phase exhibits a significant dependence on the aging temperature, which increases from 1.30×10-27 m3/s at 800 °C to 9.56×10-27 m3/s at 900 °C. The activation energy of γ? phase is mainly influenced by the W diffusion in the γ matrix, presenting as 210 kJ/mol. The prepared Co-Ni-Al-W alloy possesses superb comprehensive properties, particularly the good combination of high γ? solvus temperature (1221 °C) and low density (8.7 g/cm3). Besides, the compressive yield strength of the Co-Ni-Al-W alloy at ambient and high temperatures are higher than that of other γ?-strengthened Co-based superalloys. The compressive yield strength of the Co-Ni-Al-W alloy at 850 °C is as high as 774 MPa.
The coarsening behavior of γ? precipitate phase at different temperatures and the compressive performance of novel Co-Ni-Al-W superalloy were investigated. Experiment results show that the evolution of the mean radius and volume fraction of the γ? phase obeys the classical Lifshitz-Slyozov-Wagner model. The coarsening rate of the γ? phase exhibits a significant dependence on the aging temperature, which increases from 1.30×10-27 m3/s at 800 °C to 9.56×10-27 m3/s at 900 °C. The activation energy of γ? phase is mainly influenced by the W diffusion in the γ matrix, presenting as 210 kJ/mol. The prepared Co-Ni-Al-W alloy possesses superb comprehensive properties, particularly the good combination of high γ? solvus temperature (1221 °C) and low density (8.7 g/cm3). Besides, the compressive yield strength of the Co-Ni-Al-W alloy at ambient and high temperatures are higher than that of other γ?-strengthened Co-based superalloys. The compressive yield strength of the Co-Ni-Al-W alloy at 850 °C is as high as 774 MPa.
2024, 53(10):2794-2804.
DOI: 10.12442/j.issn.1002-185X.20240299
Abstract:
The microstructure and corrosion behaviour of hot-rolled Mg-3Zn-1Y-xCu alloys (x=0, 1, 3, 5, wt%) were investigated. Results show that all Mg-3Zn-1Y-xCu alloys mainly consist of α-Mg matrix and Mg3Zn6Y phases. The addition of Cu element promotes the formation of MgZnCu phase, and the amount of MgZnCu phase is increased with the increase in Cu content. Electrochemical and immersion test results show that the corrosion resistance of Mg-3Zn-1Y-xCu alloys is deteriorated after Cu addition, which can be attributed to the influence of the microstructure of alloys and the properties of the formed corrosion product film. The MgZnCu phase with high electrochemical potential accelerates the micro-galvanic corrosion as strong cathodic sites, and the decreased protection effect of the corrosion product ?lm results from the variation in PBR value of the related compounds.
The microstructure and corrosion behaviour of hot-rolled Mg-3Zn-1Y-xCu alloys (x=0, 1, 3, 5, wt%) were investigated. Results show that all Mg-3Zn-1Y-xCu alloys mainly consist of α-Mg matrix and Mg3Zn6Y phases. The addition of Cu element promotes the formation of MgZnCu phase, and the amount of MgZnCu phase is increased with the increase in Cu content. Electrochemical and immersion test results show that the corrosion resistance of Mg-3Zn-1Y-xCu alloys is deteriorated after Cu addition, which can be attributed to the influence of the microstructure of alloys and the properties of the formed corrosion product film. The MgZnCu phase with high electrochemical potential accelerates the micro-galvanic corrosion as strong cathodic sites, and the decreased protection effect of the corrosion product ?lm results from the variation in PBR value of the related compounds.
2024, 53(10):2882-2890.
DOI: 10.12442/j.issn.1002-185X.20240088
Abstract:
The W-25Re alloy was prepared by selective laser melting (SLM) using spherical W-25Re (mass fraction, %, hereinafter) alloy powder as the raw material. The effects of process parameters on the relative density, microstructure and micro-Vickers hardness of W-25Re alloy were investigated. The relative density, microstructure, phase composition, and micro-Vickers hardness of W-25Re alloy were characterized by analytical balance, field emission scanning electron microscope (FE-SEM), X-ray diffractometer (XRD), microhardness tester. The results show that there are no obvious spheroidization, warping, deformation, delamination or non-forming phenomena during the preparation of W-25Re alloy by SLM. There are no obvious defects such as holes and cracks on the surface and side of the specimens, and W-25Re alloy formability is good. With the increase of Ev, the grain morphology in the vertical plane of W-25Re alloy specimens gradually changes from the mixture of equiaxed and columnar grains to coarse columnar grains. W-25Re alloy specimens only contain the cubic W13Re7 phase, and the change in the leftward shift of the diffraction peak 2θ angle is mainly caused by residual stress during the forming process. The influence of laser power and scanning speed on the relative densityof W-25Re alloy is significant. When Ev is 1050 J/mm3, that is, the laser power is 210 W and the scanning speed is 200 mm/s, the W-25Re alloy specimen with a relative density of up to 98.49% can be obtained. At this time, the microhardness of the specimen in the horizontal and the vertical plane is as high as 525.9 HV0.2 and 520.6 HV0.2, respectively, which is close to the hardness value of the rolled W-25Re alloy.
The W-25Re alloy was prepared by selective laser melting (SLM) using spherical W-25Re (mass fraction, %, hereinafter) alloy powder as the raw material. The effects of process parameters on the relative density, microstructure and micro-Vickers hardness of W-25Re alloy were investigated. The relative density, microstructure, phase composition, and micro-Vickers hardness of W-25Re alloy were characterized by analytical balance, field emission scanning electron microscope (FE-SEM), X-ray diffractometer (XRD), microhardness tester. The results show that there are no obvious spheroidization, warping, deformation, delamination or non-forming phenomena during the preparation of W-25Re alloy by SLM. There are no obvious defects such as holes and cracks on the surface and side of the specimens, and W-25Re alloy formability is good. With the increase of Ev, the grain morphology in the vertical plane of W-25Re alloy specimens gradually changes from the mixture of equiaxed and columnar grains to coarse columnar grains. W-25Re alloy specimens only contain the cubic W13Re7 phase, and the change in the leftward shift of the diffraction peak 2θ angle is mainly caused by residual stress during the forming process. The influence of laser power and scanning speed on the relative densityof W-25Re alloy is significant. When Ev is 1050 J/mm3, that is, the laser power is 210 W and the scanning speed is 200 mm/s, the W-25Re alloy specimen with a relative density of up to 98.49% can be obtained. At this time, the microhardness of the specimen in the horizontal and the vertical plane is as high as 525.9 HV0.2 and 520.6 HV0.2, respectively, which is close to the hardness value of the rolled W-25Re alloy.
Wang Xianjun
,
Yang Junzhou
,
Wang Shichen
,
Wang Zhixuan
,
Hu Boliang
,
Wang Li
,
Bai Run
,
Gao Xuanqiao
,
Zhang Wen
,
Hu Ping
2024, 53(10):2891-2896.
DOI: 10.12442/j.issn.1002-185X.20230509
Abstract:
The constant strain rate compression experiments were conducted on Mo-14Re alloy by the Gleeble-3500 thermal simulation testing machine, the high-temperature were selected at 1400℃, 1500℃, 1600℃, and strain rates of 0.01 s-1, 0.1 s-1, 1 s-1, and 10 s-1.During the hot deformation process, the flow stress decreases with the increase of deformation temperature and the decrease of strain rate, which is due to the relative effect of work hardening and dynamic softening under different conditions. Based on the Arrhenius model and Zener Hollomon function, a constitutive equation for the flow stress of Mo-14Re alloy was established, and the activation energy for hot deformation of Mo-14Re alloy was obtained to be 588.31 kJ . mol-1. According to the established Hot processing map, the reasonable forming process parameters of Mo-14Re alloy are that the temperature is 1400℃~1600℃, the strain rate is 0.0089~0.14s-1, and the power dissipation coefficient Not less than 0.22, which is a reasonable process parameter for Mo-14Re alloy.
The constant strain rate compression experiments were conducted on Mo-14Re alloy by the Gleeble-3500 thermal simulation testing machine, the high-temperature were selected at 1400℃, 1500℃, 1600℃, and strain rates of 0.01 s-1, 0.1 s-1, 1 s-1, and 10 s-1.During the hot deformation process, the flow stress decreases with the increase of deformation temperature and the decrease of strain rate, which is due to the relative effect of work hardening and dynamic softening under different conditions. Based on the Arrhenius model and Zener Hollomon function, a constitutive equation for the flow stress of Mo-14Re alloy was established, and the activation energy for hot deformation of Mo-14Re alloy was obtained to be 588.31 kJ . mol-1. According to the established Hot processing map, the reasonable forming process parameters of Mo-14Re alloy are that the temperature is 1400℃~1600℃, the strain rate is 0.0089~0.14s-1, and the power dissipation coefficient Not less than 0.22, which is a reasonable process parameter for Mo-14Re alloy.
Yin Tao
,
Wang Baojian
,
Hu Zhongwu
,
Zhang Weiwei
,
Bai Wei
,
Ren Guangpeng
,
Guo Linjiang
,
Liu Yan
,
Zhang Wen
,
li jianfeng
2024, 53(10):2897-2905.
DOI: 10.12442/j.issn.1002-185X.20240190
Abstract:
Mo-based single crystal is a key material for nuclear power generation components in deep space exploration ships. Optimizing alloy composition is an important way to the applied property improvement of single crystal materials, and also can improve the power generation efficiency and service life of nuclear power sources. In this paper, a novel Mo-Nb-W single crystal was prepared by electron beam suspension zone melting method, and the hardness (H), contact stiffness (S) and elastic modulus (E) in the (110), (111) and (112) orientation crystal planes were investigated by nanoindentation technology. The results showed that there was no pop-in phenomenon in the load-displacement (P-h) curves of the (111) crystal plane, while the pop-in step appeared in the P-h curves of both (110) and (112) crystal plane during nanoindentation. The hardness in the measured oriented crystal planes gradually gone up with the increase of strain rate due to the shortened relaxation time, while the contact stiffness and elastic modulus slowly decreased as strain rate increased. There was significant anisotropy in the mechanical properties of Mo-Nb-W single crystal, and the hardness ranked: H(111)>H(110)>H(112), while the order of contact stiffness and elastic modulus were as follow: S(111)>S(112)>S(110) and E(111)>E(112)>E(110). The hardness in these mentioned orientation crystal planes gradually decreased with the rising of indentation depth, and the (111) oriented crystal plane had the most obvious indentation size effect.
Mo-based single crystal is a key material for nuclear power generation components in deep space exploration ships. Optimizing alloy composition is an important way to the applied property improvement of single crystal materials, and also can improve the power generation efficiency and service life of nuclear power sources. In this paper, a novel Mo-Nb-W single crystal was prepared by electron beam suspension zone melting method, and the hardness (H), contact stiffness (S) and elastic modulus (E) in the (110), (111) and (112) orientation crystal planes were investigated by nanoindentation technology. The results showed that there was no pop-in phenomenon in the load-displacement (P-h) curves of the (111) crystal plane, while the pop-in step appeared in the P-h curves of both (110) and (112) crystal plane during nanoindentation. The hardness in the measured oriented crystal planes gradually gone up with the increase of strain rate due to the shortened relaxation time, while the contact stiffness and elastic modulus slowly decreased as strain rate increased. There was significant anisotropy in the mechanical properties of Mo-Nb-W single crystal, and the hardness ranked: H(111)>H(110)>H(112), while the order of contact stiffness and elastic modulus were as follow: S(111)>S(112)>S(110) and E(111)>E(112)>E(110). The hardness in these mentioned orientation crystal planes gradually decreased with the rising of indentation depth, and the (111) oriented crystal plane had the most obvious indentation size effect.
2024, 53(10):2906-2912.
DOI: 10.12442/j.issn.1002-185X.20230531
Abstract:
Zirconium alloys are used as fuel cladding materials in commercial reactors, which suffer from synergetic effects of irradiation and corrosion degradations. In order to evaluate the effects of irradiation on the corrosion behavior of the Zr-1Nb alloy, the alloy has been irradiated with 6.37 MeV Xe ions. The pre- and post-irradiation corrosion property modifications have been evaluated. The current paper have also reported the micro-hardness, surface roughness and phase composition modifications. After the Xe ion irradiation, unraveling surface has been observed due to the ion sputtering effect. The surface roughness and the microhardness are increased with increasing irradiation dose. The post-irradiation corrosion under LiOH solution result with lath shaped surface microstructures on the Zr-1Nb samples, which become more pronounced at higher irradiation doses. The polarization current density for the 0.5 dpa dose irradiated sample is increased by 18 times over that of the unirradiated sample, while it is about 72 times for the 2.7 dpa irradiated sample. After the ion irradiation tests, the polarization potentials are lowered (increased negatively) and the polarization resistance values are increased, compared with the unirradiated sample. The electro-chemical impedance spectra (EIS) results show that, the lower-frequency impedance values are decreased, the curvature radius of the capacitance curve is decreased and the phase angle peak is moving rightward with increasing irradiation doses. The polarization curves and the EIS results show that the ion-irradiation has increased the corrosion tendency of the Zr-1Nb alloy, and its corrosion resistance is decreased with increasing irradiation doses. The reduced corrosion resistance after the ion irradiation tests are considered to be mainly caused by the irradiation induced damages on the alloy matrix material.
Zirconium alloys are used as fuel cladding materials in commercial reactors, which suffer from synergetic effects of irradiation and corrosion degradations. In order to evaluate the effects of irradiation on the corrosion behavior of the Zr-1Nb alloy, the alloy has been irradiated with 6.37 MeV Xe ions. The pre- and post-irradiation corrosion property modifications have been evaluated. The current paper have also reported the micro-hardness, surface roughness and phase composition modifications. After the Xe ion irradiation, unraveling surface has been observed due to the ion sputtering effect. The surface roughness and the microhardness are increased with increasing irradiation dose. The post-irradiation corrosion under LiOH solution result with lath shaped surface microstructures on the Zr-1Nb samples, which become more pronounced at higher irradiation doses. The polarization current density for the 0.5 dpa dose irradiated sample is increased by 18 times over that of the unirradiated sample, while it is about 72 times for the 2.7 dpa irradiated sample. After the ion irradiation tests, the polarization potentials are lowered (increased negatively) and the polarization resistance values are increased, compared with the unirradiated sample. The electro-chemical impedance spectra (EIS) results show that, the lower-frequency impedance values are decreased, the curvature radius of the capacitance curve is decreased and the phase angle peak is moving rightward with increasing irradiation doses. The polarization curves and the EIS results show that the ion-irradiation has increased the corrosion tendency of the Zr-1Nb alloy, and its corrosion resistance is decreased with increasing irradiation doses. The reduced corrosion resistance after the ion irradiation tests are considered to be mainly caused by the irradiation induced damages on the alloy matrix material.
2024, 53(10):2913-2925.
DOI: 10.12442/j.issn.1002-185X.20230508
Abstract:
Numerical simulation and experimental verification were used to study the atomization process of aluminum alloy powder by rotating disk, systematically study the spreading motion characteristics of melt on different disk surfaces, the breaking law of melt thin liquid film, and the flight cooling of droplets formed after crushing. The results showed that: The slip of liquid film on the surface of the spherical disk is smaller, the liquid film spreads more evenly, and the heat transfer of the disk is more stable. Under the same working conditions, the continuous liquid film boundary diameter of the spherical disk increases by about 40%, the maximum liquid film velocity increases by about 19%, the median diameter D50 of atomized droplets decreases by about 14%, and the droplet size distribution is more concentrated, the control of particle size and particle size distribution is more efficient.
Numerical simulation and experimental verification were used to study the atomization process of aluminum alloy powder by rotating disk, systematically study the spreading motion characteristics of melt on different disk surfaces, the breaking law of melt thin liquid film, and the flight cooling of droplets formed after crushing. The results showed that: The slip of liquid film on the surface of the spherical disk is smaller, the liquid film spreads more evenly, and the heat transfer of the disk is more stable. Under the same working conditions, the continuous liquid film boundary diameter of the spherical disk increases by about 40%, the maximum liquid film velocity increases by about 19%, the median diameter D50 of atomized droplets decreases by about 14%, and the droplet size distribution is more concentrated, the control of particle size and particle size distribution is more efficient.
2024, 53(10):2926-2933.
DOI: 10.12442/j.issn.1002-185X.20230525
Abstract:
Nuclear materials are exposed to high temperature, high pressure and strong irradiation for a long time, and are subjected to strong neutron irradiation, which will produce a large number of point defects under the action of cascade collision, and then form radiation voids. Irradiation swelling caused by irradiation voids is responsible for the failure of austenite steel serve in the reactor core. The external stress introduced in the process of material processing and service and the elastic stress field generated by crystal defects such as dislocation have an important influence on diffusion and phase transformation. The phase field method at mesoscale can not only couple the physical fields such as temperature, irradiation and stress, but also simulate the dynamics and morphology evolution of the microstructure of materials during irradiation. A mesoscale phase field model coupled with rate and micro-elastic theory is used to survey the stress effects on void microstructures for Fe-Cr austenite; the global applied stress and the local dislocation stress field are considered. The applied stress promotes vacancies aggregate, nucleate, and growth, and the voids evolve into fusiform eventually. Voids in the stressed state have a larger size and lower density compared with a stress-free state. The larger the applied stress, the larger the average size and volume fraction, the smaller the number, and the more significant the morphology reconstruction is. The local elastic stress field of dislocation absorbs vacancies to reduce the elastic energy, and the concentrated vacancies accelerate the voids preferentially nucleate and grow around the dislocation. Compared with the dislocation-free system, the voids are fine and denser when dislocations exist; but the volume fraction and the morphologies of voids persist. In contrast, the applied stress should probably cause server swelling than dislocations in Fe-Cr alloys. The studying benefits the properties evaluation of in-core reactor components.
Nuclear materials are exposed to high temperature, high pressure and strong irradiation for a long time, and are subjected to strong neutron irradiation, which will produce a large number of point defects under the action of cascade collision, and then form radiation voids. Irradiation swelling caused by irradiation voids is responsible for the failure of austenite steel serve in the reactor core. The external stress introduced in the process of material processing and service and the elastic stress field generated by crystal defects such as dislocation have an important influence on diffusion and phase transformation. The phase field method at mesoscale can not only couple the physical fields such as temperature, irradiation and stress, but also simulate the dynamics and morphology evolution of the microstructure of materials during irradiation. A mesoscale phase field model coupled with rate and micro-elastic theory is used to survey the stress effects on void microstructures for Fe-Cr austenite; the global applied stress and the local dislocation stress field are considered. The applied stress promotes vacancies aggregate, nucleate, and growth, and the voids evolve into fusiform eventually. Voids in the stressed state have a larger size and lower density compared with a stress-free state. The larger the applied stress, the larger the average size and volume fraction, the smaller the number, and the more significant the morphology reconstruction is. The local elastic stress field of dislocation absorbs vacancies to reduce the elastic energy, and the concentrated vacancies accelerate the voids preferentially nucleate and grow around the dislocation. Compared with the dislocation-free system, the voids are fine and denser when dislocations exist; but the volume fraction and the morphologies of voids persist. In contrast, the applied stress should probably cause server swelling than dislocations in Fe-Cr alloys. The studying benefits the properties evaluation of in-core reactor components.
2024, 53(10):2934-2940.
DOI: 10.12442/j.issn.1002-185X.20230513
Abstract:
Spinel MgxCo1-xFe2O4 was prepared by hydrothermal method. The effects of the proportion of Mg and Co doping on the crystal structure, microstructure and absorption properties of magnesia cobalt ferrite were studied by X-ray diffraction (XRD), transmission electron microscopy (TEM) and vector network analyzer (VNA). The electromagnetic wave absorption mechanism of magnesia cobalt ferrite was summarized. The results show that under the conditions of pH=10, crystallization temperature 180℃ and crystallization time 8 h, Mg-Co ferrite with irregular quadrilateral morphology was successfully prepared. When the ratio of Mg2+ and Co2+ is 5:5 and the thickness of the absorbing layer is 3.5mm, the reflection loss value at the frequency 9.50 GHz reaches -40.78 dB, and the effective absorption frequency band is 3.65 GHz (8.06~11.71 GHz), covering the X-band. The excellent absorbing properties are attributed to the combined action of natural resonance, exchange resonance and eddy current loss.
Spinel MgxCo1-xFe2O4 was prepared by hydrothermal method. The effects of the proportion of Mg and Co doping on the crystal structure, microstructure and absorption properties of magnesia cobalt ferrite were studied by X-ray diffraction (XRD), transmission electron microscopy (TEM) and vector network analyzer (VNA). The electromagnetic wave absorption mechanism of magnesia cobalt ferrite was summarized. The results show that under the conditions of pH=10, crystallization temperature 180℃ and crystallization time 8 h, Mg-Co ferrite with irregular quadrilateral morphology was successfully prepared. When the ratio of Mg2+ and Co2+ is 5:5 and the thickness of the absorbing layer is 3.5mm, the reflection loss value at the frequency 9.50 GHz reaches -40.78 dB, and the effective absorption frequency band is 3.65 GHz (8.06~11.71 GHz), covering the X-band. The excellent absorbing properties are attributed to the combined action of natural resonance, exchange resonance and eddy current loss.
2024, 53(10):2941-2951.
DOI: 10.12442/j.issn.1002-185X.20230524
Abstract:
The presence of needle α′ martensite in the coarse columnar β grains is the main reason for the poor ductility of TC11 titanium alloys for wire-fed electron beam additive manufacturing (EBAM). In order to achieve the engineering fabrication of high-strength and ductile TC11 titanium alloy, a novel coaxial electron beam wire additive manufacturing (C-EBAM) process was used to improve the interaction state of electron beam, wire, and substrate during the EBAM process, and to improve the heat distribution of the melt pool. A detailed comparison between EBAM and C-EBAM was further made in terms of microstructure, grain morphology and mechanical properties. The effects of the transition state of the wire on the process stability, the martensitic transformation process, and the reasons for the difference and anisotropy of the tensile properties were discussed. The results show that C-EBAM achieves a strong lamellar α+β microstructure with almost no evaporation of Al elements via the pathway of slow cooling of the β phase field and in situ martensite decomposition at a lower cooling rate. Compared to EBAM, the improvement in ductility of C-EBAM can be attributed to a bi-lamellar microstructure and discontinuous grain boundaries α. This indicates the direction for further optimization of the beam source characteristics.
The presence of needle α′ martensite in the coarse columnar β grains is the main reason for the poor ductility of TC11 titanium alloys for wire-fed electron beam additive manufacturing (EBAM). In order to achieve the engineering fabrication of high-strength and ductile TC11 titanium alloy, a novel coaxial electron beam wire additive manufacturing (C-EBAM) process was used to improve the interaction state of electron beam, wire, and substrate during the EBAM process, and to improve the heat distribution of the melt pool. A detailed comparison between EBAM and C-EBAM was further made in terms of microstructure, grain morphology and mechanical properties. The effects of the transition state of the wire on the process stability, the martensitic transformation process, and the reasons for the difference and anisotropy of the tensile properties were discussed. The results show that C-EBAM achieves a strong lamellar α+β microstructure with almost no evaporation of Al elements via the pathway of slow cooling of the β phase field and in situ martensite decomposition at a lower cooling rate. Compared to EBAM, the improvement in ductility of C-EBAM can be attributed to a bi-lamellar microstructure and discontinuous grain boundaries α. This indicates the direction for further optimization of the beam source characteristics.
2024, 53(10):2952-2959.
DOI: 10.12442/j.issn.1002-185X.20230527
Abstract:
In this paper the effects of different cooling speeds on the organization evolution of second-generation nickel-based single-crystal superalloy DD6 are revealed by high-resolution transmission electron microscopy and scanning electron microscopy. Under air-cooling conditions, a large number of secondary γ" precipitates are distributed at the matrix channels, and the secondary γ" precipitates progressively evolve in shape from spherical to cuboidal and then to butterfly-like shapes, and the size also increases with time; sharp crevices appear at the edges of the γ" precipitates and gradually evolve into serrated grooves. Under furnace-cooling conditions, a large number of fine spherical secondary γ" precipitates are distributed in the collective channel, and the width of the matrix channel increased and is positively correlated with the holding time. Under water-cooling conditions, there is no secondary γ" precipitates distribution in the matrix channel, the cubicity of γ" precipitates is complete, and there is no significant change in morphology with the extension of the holding time. γ" precipitates produces a large number of positive-negative edge-type dislocations between the two-phase interfaces in the process of selective decomposition, and the positive-negative edge-type dislocations on the two sides of the phase boundary meet to produce annihilation, reduce the surrounding energy, and promote the selective decomposition of the γ" precipitates.
In this paper the effects of different cooling speeds on the organization evolution of second-generation nickel-based single-crystal superalloy DD6 are revealed by high-resolution transmission electron microscopy and scanning electron microscopy. Under air-cooling conditions, a large number of secondary γ" precipitates are distributed at the matrix channels, and the secondary γ" precipitates progressively evolve in shape from spherical to cuboidal and then to butterfly-like shapes, and the size also increases with time; sharp crevices appear at the edges of the γ" precipitates and gradually evolve into serrated grooves. Under furnace-cooling conditions, a large number of fine spherical secondary γ" precipitates are distributed in the collective channel, and the width of the matrix channel increased and is positively correlated with the holding time. Under water-cooling conditions, there is no secondary γ" precipitates distribution in the matrix channel, the cubicity of γ" precipitates is complete, and there is no significant change in morphology with the extension of the holding time. γ" precipitates produces a large number of positive-negative edge-type dislocations between the two-phase interfaces in the process of selective decomposition, and the positive-negative edge-type dislocations on the two sides of the phase boundary meet to produce annihilation, reduce the surrounding energy, and promote the selective decomposition of the γ" precipitates.
2024, 53(10):2960-2967.
DOI: 10.12442/j.issn.1002-185X.20230528
Abstract:
In this paper, the effect of Cu content on the tensile properties of Al-Si-Mg-Er-Zr alloy at room temperature and high temperature was studied. They were α-Al, Si, β, Q and θ phases in the as-cast Al-Si-Mg-Er-Zr alloys with different Cu contents. With the increase of Cu content, the eutectic microstructure of the alloy increases, and it is bone-shaped, which is conducive to improving the casting performance of the alloy. With the increase of Cu content, the yield strength of as-cast alloys increases. Three Al-Si-Mg-Er-Zr alloys with different Cu content (0.6Cu, 1.0Cu and 1.0Cu) were heat treated under 500°C/4h+540°C/2h+180°C/xh, and they reached peak aging at 10h, 12h and 12h, respectively, and the peak hardness was 137.2HV, 139.2HV and 142.7HV, respectively. With the increase of Cu content, the room temperature tensile strength of the alloys under T6 temper increases, which is due to the fact that the alloy containing 1.4Cu has the most strengthening phase, including β ? ? phase, Q ? phase and θ ? phase. After 44 hours of soaking at 300°C, the hardness of the alloy containing 1.4Cu decreased the least, this is because, at 300 ℃，with the increase of the Cu level, the amount of the Q-Al5Mg8Cu2Si6 precipitates increases, and the Q-Al5Mg8Cu2Si6 phase is the main thermo-dynamically stable precipitate at 300 ℃ and improved the heat resistance of the alloy. The elongation at 300°C of the three Cu alloys under T6 temper was higher than that of room temperature tensile, and the fracture form also changed from brittle fracture at room temperature to ductile fracture at 300℃.
In this paper, the effect of Cu content on the tensile properties of Al-Si-Mg-Er-Zr alloy at room temperature and high temperature was studied. They were α-Al, Si, β, Q and θ phases in the as-cast Al-Si-Mg-Er-Zr alloys with different Cu contents. With the increase of Cu content, the eutectic microstructure of the alloy increases, and it is bone-shaped, which is conducive to improving the casting performance of the alloy. With the increase of Cu content, the yield strength of as-cast alloys increases. Three Al-Si-Mg-Er-Zr alloys with different Cu content (0.6Cu, 1.0Cu and 1.0Cu) were heat treated under 500°C/4h+540°C/2h+180°C/xh, and they reached peak aging at 10h, 12h and 12h, respectively, and the peak hardness was 137.2HV, 139.2HV and 142.7HV, respectively. With the increase of Cu content, the room temperature tensile strength of the alloys under T6 temper increases, which is due to the fact that the alloy containing 1.4Cu has the most strengthening phase, including β ? ? phase, Q ? phase and θ ? phase. After 44 hours of soaking at 300°C, the hardness of the alloy containing 1.4Cu decreased the least, this is because, at 300 ℃，with the increase of the Cu level, the amount of the Q-Al5Mg8Cu2Si6 precipitates increases, and the Q-Al5Mg8Cu2Si6 phase is the main thermo-dynamically stable precipitate at 300 ℃ and improved the heat resistance of the alloy. The elongation at 300°C of the three Cu alloys under T6 temper was higher than that of room temperature tensile, and the fracture form also changed from brittle fracture at room temperature to ductile fracture at 300℃.
2024, 53(10):2975-2986.
DOI: 10.12442/j.issn.1002-185X.20230505
Abstract:
2D materials are widely used in optics, biology, materials science and semiconductor fields owing to their large specific surface area, high carrier mobility and high thermal conductivity. Mechanical ball milling method is widely used in the stripping of 2D materials because of its advantages of low cost, environmental protection, and large-scale production. Starting from the mechanism and related models of mechanical ball milling, this paper reviews the research status of nanosheets of 2D materials, such as graphene, boron nitride, molybdenum disulfide and so on, by mechanical ball milling. The advantages and existing problems of this method in preparing 2D nanomaterials were summarized, and the development directions of 2D materials prepared by mechanical ball milling were prospected.
2D materials are widely used in optics, biology, materials science and semiconductor fields owing to their large specific surface area, high carrier mobility and high thermal conductivity. Mechanical ball milling method is widely used in the stripping of 2D materials because of its advantages of low cost, environmental protection, and large-scale production. Starting from the mechanism and related models of mechanical ball milling, this paper reviews the research status of nanosheets of 2D materials, such as graphene, boron nitride, molybdenum disulfide and so on, by mechanical ball milling. The advantages and existing problems of this method in preparing 2D nanomaterials were summarized, and the development directions of 2D materials prepared by mechanical ball milling were prospected.
2024, 53(10):2987-3000.
DOI: 10.12442/j.issn.1002-185X.20230518
Abstract:
Proton exchange membrane fuel cells (PEMFCs) are potential solutions for the dual problems of energy shortage and environmental pollution, due to their high efficiency, low temperature, and eco-friendliness. However, the slow kinetic process in its cathodic oxygen reduction reaction (ORR) has to rely on scarce and expensive Pt-based catalysts, which hinders the further development and application of PEMFC technology. In order to reduce the cost and ensure efficient catalytic performance, researchers have developed various technological strategies in recent years, and alloying with Pt through the introduction of transition metals is one of the main strategies, especially PtCo bimetallic catalysts, which exhibit superior ORR catalytic performance. This paper reviews the research results and current status of PtCo alloy catalysts for PEMFCs in recent years. Firstly, it summarizes the effects of modulation strategies such as catalyst component control, particle size modulation, crystal surface modulation, and doping on the catalytic activity of fuel cells. Then, it introduces the most promising PtCo alloy structures, such as polyhedral, core-shells, nano-frames, and ordered intermetallic structure, etc. It also discusses the research on catalyst supports. Finally, it identifies the existing challenges and future prospects of PtCo alloy catalysts for their applications.
Proton exchange membrane fuel cells (PEMFCs) are potential solutions for the dual problems of energy shortage and environmental pollution, due to their high efficiency, low temperature, and eco-friendliness. However, the slow kinetic process in its cathodic oxygen reduction reaction (ORR) has to rely on scarce and expensive Pt-based catalysts, which hinders the further development and application of PEMFC technology. In order to reduce the cost and ensure efficient catalytic performance, researchers have developed various technological strategies in recent years, and alloying with Pt through the introduction of transition metals is one of the main strategies, especially PtCo bimetallic catalysts, which exhibit superior ORR catalytic performance. This paper reviews the research results and current status of PtCo alloy catalysts for PEMFCs in recent years. Firstly, it summarizes the effects of modulation strategies such as catalyst component control, particle size modulation, crystal surface modulation, and doping on the catalytic activity of fuel cells. Then, it introduces the most promising PtCo alloy structures, such as polyhedral, core-shells, nano-frames, and ordered intermetallic structure, etc. It also discusses the research on catalyst supports. Finally, it identifies the existing challenges and future prospects of PtCo alloy catalysts for their applications.
