Abstract:In order to study the effect of Ru on the microstructure stability of high generation single-crystal superalloys, two single-crystal superalloys D1 and D2 containing 6wt.%Ru and 4.5wt.%Ru respectively were prepared. After complete heat treatment, they were long-term aged at 980℃ and 1160℃ for 200h. The alloy microstructure of different scales, compositions of topologically close-packed (TCP) phase and TCP crystal structures were detected. Results show that after long-term aging at 980℃ for 200h, the precipitation of TCP in D1 alloy containing more Ru is significantly higher than that in D2 alloy; after long-term aging at 1160 ℃ for 200h, no TCP phase is observed in D1 alloy, while a small amount of TCP phase is observed in D2 alloy; the TCP phases in both alloys are of the same type, and Ru is one of the main forming elements. The experimental results are analyzed combining with d-electrons concept and thermodynamic calculation. It is shown that the influence of Ru on the TCP precipitation of single crystal superalloys has two sides. On the one hand, adding Ru can increase the d-electron energy level of single crystal superalloys, which increase the TCP precipitation tendency. On the other hand, the increase of Ru content can reduce the segregation of refractory elements in γ phase, thus reducing the amount of TCP phase precipitation caused by the supersaturation of refractory elements. At different temperatures, the main influencing factors are different.

Abstract:This paper discussed the intermetallic compounds (IMCs) in the copper-aluminum brazed joints during formation and application through reviewing some recent research on brazing copper to aluminum. The review indicated that it was difficult to avoid the formation and growth of the IMCs, which depends on the mutual diffusion between Cu substrate and Al substrate as well as substrates and filler metals. Thermodynamics and kinetics are critical for the nucleation and growth of the IMCs respectively. Besides, defects (voids, cavities and cracks) in the joint mainly result from the formation and growth of the brittle IMCs because it always results in stress concentration as the source of cracks and accelerates the excessive consumption of the diffused atoms to form voids and cavities. Properties of copper-aluminum joints were severely deteriorated when the thickness of the IMCs exceeds 2~5μm. Finally, numerous factors (melting point, thermal conductivity, joint design, heat input and chemical composition) strongly impact the formation and growth of the IMCs through changing the mutual diffusion process. Moreover, these factors also have distinct effects on the defects. At present, some efficient methods used to control the IMCs in the copper-aluminum joints are heat input controlling, optimization of joint design and the addition of the third element into filler metals.

Abstract:The cold deformation and recrystallization behavior of Inconel 625 superalloy were studied by using compression deformation at room temperature and recrystallization annealing. The strain distribution, grain size change, microstructure and texture evolution during cold deformation, as well as recrystallization fraction, grain sizes, microstructure and texture evolution of cold deformed Inconel 625 superalloy during recrystallization annealing were analyzed by EBSD technique. Studies have shown that Inconel 625 superalloy has good plasticity when the deformation is 35%~65%. With the increase of deformation, the grain size decreases and the strain distribution is more uniform, {111}<112> texture and {110} <001> texture is gradually weakened, while the {001}<110> texture and the {112}<111> texture are slightly enhanced. After recrystallization annealing treatment of cold deformed Inconel 625 superalloy, the recrystallization fraction increases with the increase of annealing temperature and holding time. With the increase of deformation, the annealing temperature decreases when complete recrystallization with finer grains occurs. When the deformation is 35%, the recrystallization process is mainly {112}<111> texture and {123 <634> texture transformed into {110}<112> texture, {001}<100> texture and {124}<211> texture. With the increase of deformation amount to 50% and 65%, the {123}<634> texture produced by cold deformation transforms into {124}<211> texture during recrystallization.

Abstract:Micro segregation of Mg and Mn in a Al-Mg5.0-Mn0.5 aluminum alloy homogenized annealing at 470°C was evaluated by computational simulation in DICTRA? software, using MOB2 diffusion database and Al-based database. The segregation factor was used to predict the distribution of Mg and Mn at 470°C annealing temperature for different annealing time. Simulation results were compared with microstructure observations. After homogenizing at 470 oC for 8.3h, the segregation factor of Mg was about 0.94, close to 1.0; while, the segregation factor of Mn varied from 0.78 to 1.3. After homogenization annealing at 470 oC for 11.1h, the segregation factor of Mg was close to 1.0, and concentration of Mg was basically uniform, the range of segregation factor of Mn was almost unchanged. However, almost the same segregation factor of 0.8~1.3 was observed for Mn at the annealing temperature of 470 °C and annealing time of 27.8h. According to the DICTRA calculation results, after homogenizing at 470oC/11.1h, the micro-segregation of Mg was nearly eliminated. While the micro-segregation of Mn could not be eliminated, even if the annealing holding time extended to 27.8 h and 30h. This provides a reference for the selection of annealing process of Al-Mg5.0-Mn0.5 aluminum alloy.

Abstract:The hot deformation behavior of pure titanium in EB furnace process (EB-Ti) with centimeter scale original grain size at different deformation temperature and deformation rate was studied by thermal compression experiment, and the recrystallization mechanism of EB-Ti was discussed based on the electron back scattering diffraction (EBSD) technology. The results show that the hardening behavior of EB-Ti in the process of hot deformation has typical "three-stage" characteristics. In the start stage, the hardening ability is rapid linearly declined; in the middle stage, it rapidly recovers to a peak; in the final stage, it re-declines from the peak. The three-stage phenomenon is related to twinning in the deformation process. EBSD results also show that the recrystallization mechanism of EB-Ti in the process of hot deformation is mainly a discontinuous dynamic recrystallization.

Abstract:In the present study, the Density Functional Theory (DFT) implemented in Vienna Ab-initio Simulation Package(VASP) code was employed to investigate the β phase stability and elastic properties of Ti-xMo-Sn (x=1-5) alloys. The structural properties were investigated after geometrical optimization. The general elastic properties (such as bulk modulus B, shear modulus G, Young"s modulus E) were estimated by Voigt-Reuss-Hill approximation. In addition, the valence electron criterion for design of low Young"s modulus Ti-xMo-Sn alloys was proposed. The calculated cohesive energy indicate that Mo can increase the β phase stability of Ti-xMo-Sn alloys. The Pugh ratio B/G and Poisson"s ratio ν suggest that all these alloys exhibit ductile properties. For Ti-xMo-Sn alloys, the smaller tetragonal shear constant C′ may induce the lower Young’s modulus. Ti-3Mo-Sn possess the lowest Young’s modulus (48.47 GPa) and best ductility, showing great potential for biomedical applications. The elastic anisotropy A of Ti-xMo-Sn alloys is sensitive to Mo concentration, the lowest Young’s modulus always oriented in the <100> crystallographic direction. In the end, detailed analysis of total and partial DOS explained the calculated results.

Abstract:The bars of Ti-53Nb alloy were prepared by room temperature Equal Channel Bending Channel Deformation (ECAP) with cold rolling and rotating and followed by forging combined deformation method. The evolutions of microstructure and b-crystal growth were systematically studied by metallographic microscope (MM), scanning electron microscope(SEM) and uniaxial tensile test after preparing process. The effects of work hardening and fine grain strengthening were analyzed with dislocation strengthening theory and Hall-Petch theory. The results show that the tensile strength increases from 380MPa to 553MPa before and after deformation and heat treatment, it shows that the preparing technology enhances significant tensile strength and elongation with the increase ratio of 45.53% and 16%, respectively. The growing speed of b-crystal is accelerated with increasing solid solution temperature, and the grain size dependence of strengthen follows Hall-Petch equation. The microstructure exhibits uniform with fine iso-axial shape by annealing at 700℃for 60 mins, which can match the requirement of strong plastic characteristics for the application.

Abstract:The effect of Mn addition on the microstructure and corrosion behavior of extruded Mg-Zn-Y-Nd alloy immersed in 3.5 wt.% NaCl solution were studied by optical microscope, scanning electron microscope equipped with energy dispersive spectroscope, X-ray diffraction, immersion, and electrochemical measurements. Results suggest that the Mn addition in the studied Mg-Zn-Y-Nd alloy can induce Mg3Y2Zn3 (I-phase) precipitation which may inhibit dynamic recrystallizaiton (DRX) grain coarsening during hot extrusion. Meanwhile, its corrosion resistance was improved owing to the addition of Mn. The corrosion rates of free and 1.0 wt.% Mn containing Mg-5.6Zn-1Y-0.4Nd alloys were 18.78 and 9.89 mm·y?1, respectively. The improvement of corrosion resistance is mainly due to an enhanced protectiveness of the corrosion product layer.

Abstract:Different micro-arc oxidation coatings were fabricated on ZL108 alloy in the silicate electrolyte without and with In2S3. Scanning electron mi-croscope (SEM), Optical Profiler, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and electrochemical workstation and so on were used to study the influence of In2S3 on the microstructure, phase composition, corrosion resistance，micro-hardness and thickness of the MAO coating. The results showed that the addition of In2S3 can increase the voltage of the MAO, promote the MAO coating formation rate and increase the coating thickness. The coating formed containing In2S3 was denser and the micro-hardness of the coating was increased. Therefore, the corrosion resistance of the coating with In2S3 was improved. The main phases of all the MAO coating were α-Al2O3, γ-Al2O3 and SiO2. The XPS result showed that In2O3 was formed on the coating surface. As a consequence, adding In2S3 can optimize the structure of the MAO coating and enhance its comprehensive properties.

Abstract:AgCuOSnO₂ electrical contact materials with different SnO₂ contents were prepared by reaction synthesis. In this paper, FQR-7501 eddy current conductivity meter is used to measure the conductivity of the polished AgCuOSnO₂. The erosion morphology of the surface of the AgCuOSnO₂ electrical contact is observed and studied by Scanning Electron Microscope (SEM). The JF04C DC digital resistance tester is used to carry out 10000 dot tests. The results show that the contact resistance of AgCuO(10)SnO₂(5) and AgCuO(10)SnO₂(8) electric contact materials is lower than 1.3mΩ at U = 12V and I = 15A, and the fluctuation is the smallest; when I = 10A, the welding force of AgCuO(10)SnO₂ (x, x = 2,5,8) is less than 8cN, and the welding force of AgCuO(10)SnO₂(5) electric contact is small and stable when the current increases; when the arc erosion of AgCuOSnO₂ electric contact materials occurs, the material transfer way is from anode to cathode. With the increasing of SnO₂ content, the loss in the process of material transfer is restrained and reduced. There are little pores and microcracks on the surface of the transferred electrical contact, and the surface morphology is relatively flat.

Abstract:In this study, nickel matrix composite coatings reinforced by nano WC were prepared by pulse current (PC) electrodeposition. The effects of surfactant sodium dodecyl sulfate (SDS) concentration and wet-milling treatment of WC particles on surface morphologies, distribution of particles, microstructures and microhardness values of Ni/nano-WC composite coatings were all investigated and the results were discussed. The results revealed formation of compact coatings with high contents of embedded WC particles and uniform distribution in presence of SDS and under wet-milling treatment of WC particles. The microhardness of the composite coatings also improved. The optimal coating was obtained by adding 0.15 g/l SDS under wet-milling for 10 h.

Abstract:Ti6Al4V and Inconel 718 alloys are both extensively used in the aerospace industry. However, TC4 or Inconel 718 is difficult to meet the demand of both light weight and high temperature resistance. In this paper, the composites of different Ti6Al4V/Inconel 718 ratios were prepared by direct laser deposition. The phase, microstructure and element distribution were analyzed by X-ray Diffraction, scanning electron microscope and energy dispersive spectrometer, respectively. The microhardness, friction and wear properties were also investigated. With Inconel 718 increasing, Ti2Ni and Ni3Ti intermetallic compound were formed. The forming mechanism of Ti2Ni is: β→α+Ti2Ni and L→β-Ti+Ti2Ni, and the segregation mechanism of Ti2Ni intermetallic compound was intergranular segregation. As the doping of Inconel 718 increased, the microhardness of the composites increased gradually. When the volume fraction of Inconel 718 was 50%, the average microhardness value was 770 HV, which was 85.5% higher than that of 100% Ti6Al4V. The reason for the increase of microhardness was directly related to Ti2Ni intermetallic compound precipitation strengthening. Wear experiments showed that the composites were dominated by abrasive wear and accompanied by adhesive wear. As Inconel 718 increased, the adhesion was weakened, and when Inconel 718 reached 50% volume fraction, the wear volume was just 36.9% of that of 100% Ti6Al4V.

Abstract:In order to obtain the metal-coated fiber with high temperature resistance and long service life, Cu-based coating was plated on quartz fiber surface by electroless plating and studied by material characteristic parameters measurement. SEM, EDS, XPS and Raman were used to characterize the microstructure of graphene sheet and cu-based coating. Electrochemical workstation and nano indentation instrument were used to test the properties of metal coating. The bonding properties of Cu-based coating and fiber substrate were analyzed by thermal shock method. The results show that compared with Cu coating, Cu-graphene coating has more compact structure, better quality and fine grain, with the hardness and elastic modulus increased by 33.5% and 34.0% respectively. The corrosion potential Ecorr of Cu-graphene coating increased by 32.3%, and the corrosion current icorr decreased by 22.5%. The corrosion resistance of Cu-graphene coating is obviously improved. The surface of quartz fiber is electroless coated with Cu metal coating, which can overcome the problem of burning out due to excessive local temperature of optical fiber cladding optical filter in practical application. The coating has no blocking on signal transmission inside the optical fiber. Graphene can improve the forming quality of optical fiber surface coating, improve corrosion resistance and other properties, which is of great significance to improve the service life of optical fiber.

Abstract:The Al-Cu alloy walls (ZL205A) produced by wire + arc additive manufacturing (WAAM) have good mechanical properties, but toxic cadmium oxide is generated during production. Therefore, to prevent the generation of cadmium oxide, we replaced the Cd in the Al-Cu alloy (ZL205A) with Sn. The microstructural and mechanical properties of the newly developed alloy with Sn and the ZL205A alloy before and after T6 heat treatment were investigated and compared by conducting metallographic, scanning electron microscopy, energy dispersive spectroscopy, transmission electron microscopy, and tensile tests. The surface of the Al-Cu-Sn alloy wall was smooth and exhibited a silver-white luster, and the burning loss rate of Sn was 5.9%. The wall of the WAAM Al-Cu-Sn alloy was fine and contained grains with a size of approximately 30 μm, which is smaller than that of the ZL205A alloy wall. The main precipitated phase was uniformly distributed among the grains or on the grain boundaries. Following T6 heat treatment, the θ phase was completely dissolved in the Al matrix, and the re-melted T phase and small co-phases of Sn and Al2Cu were uniformly distributed on the grain boundaries. The TEM results show that a large number of θ" phases were dispersed among the grains. The mechanical properties of the Al-Cu-Sn alloy after heat treatment were as follows: tensile strength – 493 MPa; yield strength – 434 MPa; elongation rate – 9.5%. The alloy shows excellent performance in WAAM process and has broad application prospects.

Abstract:In this study, the effect of vacuum heat-treatment on the micro-structure evolution and properties of W-80Cu sheets was investigated. The micro-structure and fracture?appearance of W-80Cu sheet were observed by scanning electron microscope (SEM) and transmission electron?microscopy (TEM). The electrical conductivity and mechanical properties were investigated. The results indicated that the electrical conductivity and elongation of the?specimen?after?heat-treatment was higher than those of the un-heated while the hardness and room temperature tensile strength was lower. The maximum electrical conductivity and elongation of W-80Cu sheet after ageing at 600℃ for 1h were achieved and the dimples appeared?more deep and compact, and its?size and distribution became uniform. The tensile fracture of W-80Cu sheet was the?main manner?of?the intergranular brittle?fracture with?dimple?fracture. When raising the heat-treatment temperature around and above 800℃, the size and depth of the dimples become?different and ?the local?emergence of the steps and quasi-cleavage appeared. Once the time was above 1h, the local dimples became big and the tearing ridges of copper got longer due to the recrystallization growth of copper grains. During the heat-treatment, tungsten phase in W-80Cu sheet has not an obvious change, but a lot of dislocations around tungsten particles and grain boundary decrease. Both tungsten nano-partials and copper matrix have a good interface relation, which benefits to enhance the strength.

Abstract:The magnetic properties of the soft magnetic sensitive film are the key factors to determine the performance of the magnetic sensor. In order to ensure process compatibility, the sensitive film is usually fabricated by magnetron sputtering, and its performance is generally poor, which greatly restricts the development of magnetic sensors. Therefore, how to fabricate thin sensitive film on silicon substrate which meets the performance requirements of magnetic sensor and is compatible with the process of MEMS is an urgent problem to be solved. The correlation research indicated, change of microstructure is conducive to improving the magnetic performances of sensitive film. In this paper, nanoporous thin films were prepared by standard MEMS technology. The related characterization and testing of sensitive films with different apertures were carried out, and the influence of aperture size on the soft magnetic properties of thin films was analyzed. The porous structure with more than 50nm pore size can reduce the Hs and Hc of sensitive film, and the effect of 100nm structures is the most obvious to improve the soft performance of sensitive film. The conclusion of the experimental analysis provides support for the determination of preparation scheme and the performances improvement of sensitive film.

Abstract:Using the molecular dynamics method, we apply tensile loads in different directions to a preset-microcracks α-Ti model. Through the observation of the changes in the pores and dislocations of the α-Ti model, we reveal the mechanism of the pore growth and the potential energy distribution. We found that: under the tensile load along [0001], the perpendicular direction of the close-packed plane, the preset crack in the model closes up, the clusters on both sides occupy the gap of crack defect, showing obvious necking phenomenon, and part of the HCP lattice transform into the FCC lattice to plane, which derive a variety of dislocations with higher density in the crystal. Therefore, it can bear more press. Under the tensile load along [12-30], the dislocation types are mainly 1/3 [1-210] with less total length than in [0001]. The crack grows into a circular cavity. The cavity and sliding band divided the absorption energy regions into four parts. The lattice transformations are mainly from HCP to amorphous structure. The direction of the slip band depends on the material lattice and the position depends on the initial crack. Load on [0001] makes the necking phenomenon of the model prominent, and the crack defect vacancies are occupied by the clusters on left and right sides. Therefore, when loaded on [0001] the α-Ti have better plasticity and ductility than loaded on [12-30].

Abstract:Different from the traditional size model, this paper is based on the phenomenological phonon confinement model. The phonon wave vector q, standard deviation σ and confinement coefficient β were comprehensively considered and their relative functional relationship was established. The discussions focused on the Raman shift and asymmetry broadening of the amorphous coated silicon nanocrystals brought by the size effect. The results showed that, for the silicon nanocrystals embedded in amorphous matrix, the confinement coefficient β involved the influence of the limitation barrier height to the Raman shift. As the size of the silicon nanocrystals decreased, the q changed from quasi-continuous form to discrete form participating the scattering and this discrete q can more accurately fit the Raman spectral lines of small-sized silicon nanocrystals. Standard deviation σ was further changed to precisely adjust the asymmetry of Raman peaks. Finally, the theoretical model established in this paper was compared with the experimental results and literature data of the research group, and found that the comprehensive consideration of the synergistic effect of the q, σ and β was conducive to evaluating the size effect, crystal morphology and relative proportion of amorphous coated silicon nanocrystals.

Abstract:In this paper, the effects on the microstructure and mechanical properties of twin-roll casting 6061 aluminum alloy plates with Mn addition were investigated. The microstructure of 6061 cast-rolled plates were analyzed by means of thermodynamic simulation and Optical microscope (OM), scanning electron microscope (SEM) and transmission electron microscopy (TEM). The mechanical properties of 6061 cast-rolled plate with different Mn contents were tested using tensile tests. The results showed that, with the increase of Mn content of the 6061 cast-rolled plate, the iron-rich phase at the edge of 6061 cast-rolled plates gradually transformed from acicular β-Al5FeSi phase to granular α-Al12(FeMn)3Si phase, a large number of irregular blocks and a petal-like α-Al15（FeMn）3Si2 phase aggregated in the core（ω(Mn)=0.54 wt.%）; When ω(Mn)=0.36 wt.%, the mechanical properties of 6061 cast-rolled plate were the best. At this time, the tensile strength, yield strength and elongation of cast-rolled plates were 195.93 MPa, 170.36 MPa and 17.96%,

Abstract:_{:In the use of clean energy conversion devices such as fuel cells and metal-air batteries, the oxygen reduction reaction process has proven to be exceedingly crucial. Therefore, the design and synthesis of efficient and stable cathodic oxygen reduction catalysts have been an indispensable task at present. In order to achieve accurate synthesis of materials, and the maximum utilization of platinum, anodic aluminum oxide (AAO) template was used to accurately synthesize bimetallic one-dimensional Pt3Co nanowires in a certain concentration of solution. Subsequently, the alloy nanowires underwent a high-temperature phase transition in the template under vacuum, which effectively prevented material agglomeration. The disordered and ordered Pt3Co nanowires were obtained by phase transition annealing at 400 ℃and 650 ℃ respectively and were confirmed by structural characterizations for order phase transition. As expected, compared to disordered Pt3Co, ordered Pt3Co exhibited better mass activity and half-wave potential, confirming the advantages of ordered bimetal alloy nanowires in composition and structure. After the accelerated durability cycle tests, the ordered and disordered Pt3Co nanowires were still more stable than Pt/Cparticles, indicating the advantage of one-dimensional nanowires. It can be seen that the ordered Pt3Co, as an acceptable catalytic material with potential commercial value, has become alternative materials for future fuel cell catalysts.}

Abstract:This manuscript focused on the effect of processing technology and microalloying addition on the microstructure and mechanical properties of Ni-W coatings that were prepared by electrodeposition. For this reason, the surface morphology, microstructure, and tensile properties of Ni-W coatings were studied within a small W addition of less than 2.0 at.%. The experimental results showed that the Ni-W coatings have a single-phase FCC structure. By increasing the W content, the surface morphology of the coatings varied from the grooves between the coarse pyramid structures to uniformly distributed micropores. At the same time, the intensity of Ni(220) diffraction peak of the coatings also gradually weakened, with the surface roughness and the grain size reduced. There was a critical W addition of about 1.0 at.%, where the yield strength of Ni-W coating increased from ~ 1.0 GPa at the W addition regime <1.0 at.% sharply to ~ 2.0 GPa at the W addition regime >1.0 at.%. However, the tensile elongation was insensitive to the W content, which kept almost unchanged within the studied W addition range. In addition, strain hardening capacity of the coatings was also stable with the W content. In this work, the mechanical properties of Ni-W coating with micro-addition of W were optimized through manipulation of microalloying effect on the surface morphology and microstructure.

Abstract:The (Sr1-xMex)1.95SiO4：0.05Eu phosphor powders were synthesized by high temperature solid-state reaction. The effects of solid solution of different large (Ba2+) and small (Mg2+) ionic on the phase, the coordination crystal structure and the valence state of Eu ions were investigated firsly, and then regulation mechanism in the luminscent spectra was disccused. With increasing temperature, α-Sr2SiO4 increases and β-Sr2SiO4 phase decreases in Sr2SiO4 powder. Mg2+ ion dopant would increase the stability of α-Sr2SiO4 phase. Ba2+ ion dopant would lead the phase tranformation as β-Sr2SiO4+α-Sr2SiO4→α-Sr2SiO4→α-Sr2SiO4+Ba2SiO4→Ba2SiO4, in the sequence as β-Sr2SiO4, α-Sr2SiO4, Ba2SiO4, the Si–O–Me(I)–O–Me(II) chain changes from zigzag to straight chain, and the Me-O length increases. Under the excitation of 254nm (365nm), Eu-activated β-Sr2SiO4, α-Sr2SiO4, and Ba2SiO4 powders have bright green fluorescence emission (in the same sequence, the intensity increases and the overall spectrum is slightly blue shifted) and weak red light emission. For β-Sr2SiO4 →α-Sr2SiO4, Eu (I) emission peak is blue-shifted while the one of Eu (II) is red-shifted (Si–O–Me(I)–O–Me(II) chain changes from zigzag to straight, Me-O length increases). For α -Sr2SiO4 →Ba2SiO4, both emission peaks of Eu (I) and Eu (II) are blue-shifted (Me-O bond is enlonged). In the thermoluminescence spectra, there exit Eu2+ and Eu3+ defect energy levels in all these phosphors, and Eu2+ concentration looks larger. The high resolution XPS spectrum of Eu3d indicates that there are higher possibilities for Eu2+ in the sequence as β-Sr2SiO4 → α-Sr2SiO4 → Ba2SiO4, which is confirmed by Eu ion ESR spetra. By Ba2+ ions solid solution into Sr2SiO4 crystal, phase transforamtion as β-Sr2SiO4 → α-Sr2SiO4 → Ba2SiO4 would occurs, which would means the adjustmens in Si–O–Me(I)–O–Me(II) chain type and Me-O bond length. These would lead to the regulation in the coordination environment and valence state (Eu2+/ Eu3+ ratio) of Eu ion, and result to regular in emission wavelength and intensity.

Abstract:Based on the powder-binder two-fluid model, the filling process was simulated by CFX commercial software, especially for the ultra-fine WC/10Co round bar with large aspect ratio by powder injection molding (PIM). The results indicated that the numerical simulation results are almost consistent with the experimental filling process, which proves that the hypothesis and parameter settings are reasonable and the two-fluid model is feasible. Also there is no great difference in temperature distribution between powder and binder. There is no solidification for melting feedstock, which due to that the lowest temperature valued 330 K of melting feedstock is higher than the vitrification temperature of binder. In addition, there is great difference in the viscosity between powder and binder, valued 50.0 ~379.4 Pa·s, 2.9~9.2 Pa·s, respectively, which is one cause for segregation. Finally, it is also another main cause for segregation that the relative velocity difference between powder and binder increases up remarkably, such as 0.2% up 1.8% from gate to die wall, 0.1% up 1.6% from gate to far end.

Abstract:In this paper, single-phase cementite powders are prepared by mechanical alloying and vacuum annealing heat treatment methods. Combined with first-principles calculations, the effects of Mn, Cr, and Si on the phase formation ability and magnetic properties of cementite are analyzed. It has been found that single-phase cementite can be obtained by mechanical alloying + 600 ° C vacuum heat treatment. The addition of Si completely inhibited the formation of cementite, while the addition of Mn and Cr could promote the formation of cementite. The saturation magnetization and coercive force of Cr and Mn alloyed cementite are lower than those of pure Fe3C when unalloyed, and the effect of the reduction range caused by the Cr element is greater.

Abstract:Zr_1-xCoNb_x (x = 0, 0.05, 0.1, 0.15, 0.2) alloys were prepared via vacuum arc-melting method. The effects of substituting Zr with Nb on the structure, hydrogen absorb/desorb properties and anti-disproportionation performance of the afore-mentioned alloys were systematically investigated. The results showed that Zr_1-xCoNb_x (x = 0-0.2) alloys exhibited ZrCo and ZrCo₂ phases, and their corresponding hydrides consisted of ZrCoH₃ and ZrCo₂ phase. As the Nb content was increased, the activation time decreased significantly from 6790 s for ZrCo to 380 s for Zr_0.8CoNb_0.2. The activation energy for hydrogenation decreased from 44.88 kJ mol^_-1 H₂ for ZrCo to 32.73 kJ mol^_-1 H₂ for Zr_0.8CoNb_0.2 alloy. DSC measurement results showed that the desorption temperature decreased from 597.15 K for ZrCo to 541.36 K for Zr_0.8CoNb_0.2 and the activation energy for dehydrogenation decreased from 100.55 kJ mol^_-1 H₂ for ZrCo to 84.58 kJ mol^_-1 H₂ for Zr_0.8CoNb_0.2 alloy, which was beneficial to the anti-disproportionation properties. Additionally, the extents of disproportionation of alloys after disproportionated at 798 K for 10 h decreased from 83.68% for ZrCo to 8.71% for Zr_0.8CoNb_0.2. The positive effect of Nb substitution on improving the anti-disproportionation propertis of ZrCo alloys was attributed to the reduction of hydrogen atoms in 8f₂ and 8e sites, which decreases the driving force of the disproportionation reaction.

Abstract:The anisotropic oxidation characteristics is an important issue that needs to be focused on during the corrosion process of zirconium alloys, and it is of great significance for studying the corrosion mechanism of zirconium alloy. Based on the finite element method, the stress state of the oxide film of zirconium alloy with (11-20) oriented grain and (0001) oriented grain in superheated steam at 500 °C/10.3 MPa was simulated in the paper. The simulation results show as follows: The change of stress distributions of the oxide films on zirconium alloy with (11-20) oriented grain and (0001) oriented grain exhibits the same trend with the increase of the oxide film thickness. The stress of the oxide film is distributed in a gradient. And in the thickness direction of oxide film, the stress decreases from the inner surface to the outer surface of the oxide film. The compressive stress in the oxide film decreases first, then increases and then decreases with the oxide film thickness increasing, and after the oxide film reaches 10 μm, the stress no longer has a significant change trend. There are obvious differences in the stress magnitude and stress gradient of the oxide films on the surfaces of (11-20) oriented grain and (0001) oriented grain, which is one of the reasons for the different corrosion resistance.

Abstract:Si and Mn are usually added into austenitic stainless steels to improve their corrosion resistance by improving the oxide film forming ability and increasing the stability of austenite matrix. However, the additions of Si and Mn can significantly affect the microstructure and mechanical properties of the cold-worked material. In this study, austenitic stainless steels with different Si and Mn contents are designed. The microstructure of the alloys is characterized by SEM, EPMA, and TEM, and the mechanical properties are evaluated by tensile tests at room temperature. As Si increases from 1.0 wt.% to 2.0 wt.%, the volume fraction of deformation twins increases from 4.98% to 8.33%, the yield strength increases from 620MPa to 682 MPa, and the elongation basically remains constant; as Mn increases from 1.5 wt.% to 2.0 wt.%, the volume fraction of the deformation twins decreases from 8.33% to 7.22%, the yield strength decreases from 682MPa to 627 MPa, and the elongation increases from 16.0% to 21.3 %; Si addition increases the quantity of deformation twins in the alloy, improves the strength of the alloy and maintains plasticity; Mn addition reduces the number of the deformation twins in the alloy, reduces the strength of the alloy and enhances plasticity.

Abstract:The Ta-25Ti-18Al-6.5W alloy was prepared by vacuum suspension melting method. The aim of this study was to investigate the oxidation behavior of Ta-Ti-Al-W alloy at 1000℃. The phase composition and microstructure of specimens as-sintered and oxidized were characterized by XRD, SEM, and EDS. It was found that the oxidation kinetics of the alloy followeds the parabolic law at first,and then, changed into the linear law. During the oxidation process, Ta can be oxidized preferentially, and the enrichment areas of TiO2 and Al2O3 were observed in the surface of oxide scale,because of the higher diffusion rates of Ti and Al. In the initial stage,the oxidation was controlled by external diffusion of alloying elements. The oxidation layer mainly composed of the TiO2 and Ta2O5 solid solution of WO3, TiO2, Al2O3. With the increasing of oxidation duration, the oxides scale which controlled the oxidation process shows different layer structure: an outer layer mainly composed of TiO2 and Al2O3, a Ta2O5 solid solution inner layer and a transition layer with less oxygen content.

Abstract:The different Mg alloys before and after Cu and/or Zn addition were used as the experimental material. The effects of Cu and/or Zn addition on the microstructures and grain sizes of Mg alloys were firstly discussed and the mechanism of grain refinement after Cu and/or Zn addition was explained. What’more, the phase compositions of different Mg alloys before and after Cu and/or Zn addition were revealed. The results show that after Zn, Cu and Cu+Zn addition in the pure Mg, the grain sizes of the alloys decreased from 1270μm (pure Mg) to 470μm, 120μm and 85μm, respectively and the crystal morphology changed from columnar grain to equiaxed grain. The Cu and Zn addition had the best grain refinement effect on pure Mg, then the Cu addition followed and the Zn addition was the worst. After Zn addition, Mg-3Zn alloy was composed of α-Mg and MgZn phases. The secondary phases were mainly in the morphology of tiny particles. After Cu addition, Mg-5Cu alloy was composed of α-Mg and CuMg2 phases. The secondary phases were mainly in the morphology of discontinuous herringbone structure. After Cu and Zn addition, Mg-5Cu-3Zn alloy was composed of α-Mg, CuMg2 and CuMgZn phases. It was found that CuMg2 phases were in the shape of continuous bulk and the CuMgZn phases were in the in the morphology of discontinuous herringbone structure. The grain refinement of Zn addition on pure Mg was mainly due to the effect of solute Zn element. And the mechanism of the grain refinement of Cu addition was the effect of solute Cu element and pinning effect of CuMg2 phases on the grain boundaries of α-Mg. However, after Cu and Zn addition, the grain size was finer than Mg-3Zn and Mg-5Cu alloys. This was mainly due to composite solute effect of Cu and Zn element and stronger pinning effect of the secondary phases.

Abstract:In this paper, the thermal compression test of as-cast GH4169 alloy is performed on a Gleeble-1500 thermo-mechanical simulator. The deformation parameters are: temperature (1193~1373 K), strain rate (0.01~10 s_^-1), and deformation 50%. By analyzing the true stress and true strain curve, the hot deformation behavior of as-cast GH4169 alloy was studied; the correlation coefficients (R) and average relative errors (AARE) of the three constitutive models of Johnson-Cook (JC), modified Johnson-Cook (MJC) and strain-compensated Arrhenius model are compared and analyzed. The results show that the flow stress of as-cast GH4169 alloy decreases with the increase of deformation temperature and the decrease of strain rate. The correlation coefficients (R) of the JC model, MJC model and strain-compensated Arrhenius constitutive model were 0.891, 0.956, and 0.961, and the average relative errors (AARE) were 29.02%, 11.16%, and 9.31%, respectively. Therefore, the strain-compensated Arrhenius model can describe the thermal deformation behavior of as-cast GH4169 more accurately.

Abstract:The permeation and retention of hydrogen isotopes in tungsten-copper composites were studied. The permeability, diffusion coefficient, solubility and activation energy of deuterium in tungsten and tungsten-copper composites were obtained by gas driven permeation and thermal desorption spectroscopy, and the permeation and retention properties of deuterium in tungsten-copper composites were also analyzed. The results show that the permeability of deuterium in tungsten-copper composite material is 2-3 orders of magnitude larger than that of pure tungsten, and the diffusion coefficient of deuterium in tungsten-copper composite material is 5-6 orders of magnitude larger than that of pure tungsten. With the increase of copper content in the composite, the permeability and diffusion coefficient of deuterium increased. The phase interface between tungsten-copper compound material acts as a deuterium fast diffusion channel. The solubility of deuterium in tungsten-copper compound material is much smaller than that of pure tungsten, and the dissolution activation energy is also larger, indicating that copper may have a weakened effect on the solid solution of deuterium in tungsten, which is consistent with the conclusion that deuterium diffuses rapidly in tungsten-copper compound material. The apparent retention of deuterium in tungsten-copper compound material is approximately 1 order of magnitude higher than that in pure tungsten because the deuterium trapped in the tungsten-copper compound material cannot be released in time due to rapid cooling in the gas absorption experiment.

Abstract:Abstract: It is a powerful and efficient method for materials development and process optimization by gasping the thermodynamic and kinetic information of studied materials and further performing simulations. The quality of CALPHAD-type calculations is strongly dependent on the quality of the thermodynamic and diffusivity databases. Based on previously developed thermodynamic database (CSUTDCC1) and diffusivity database (CSUDDCC1), some simulations concerned during the research and development of cemented carbides, like sintering “carbon window” and cubic phase composition, were performed. Several gradient cemented carbides sintered under vacuum and various partial pressures of N2 have been studied. The microstructure and element concentration in the gradient layer were investigated via SEM and EPMA. Thermodynamic and kinetic simulations were performed and agreed well with experimental data. Examples of thermodynamic and kinetic simulation applications in design and manufacture for gradient cemented carbides were shown, which provides theoretical basis for the development of novel and high-performance gradient cemented carbides.

Abstract:In order to determine the composition of the novel γ′ strengthened Co-Al-W-based wrought superalloy of the Co-Al-W-Ni-Ta-Ti system and the corresponding heat treatment process, using Pandat calculation software and the thermodynamic database of cobalt-based superalloys, The influence of alloying elements on the precipitation behavior of the equilibrium phase was calculated. The calculations showed that: W, Ni, Ta, and Ti can improve the stability of γˊ, W, Ta can increase the precipitation tendency of the harmful phase χ-D0₁₉, and Ti and Ni can be suppressed the precipitation of the harmful phases χ-D0₁₉ and B2 phase respectively, the alloy composition was determined as Co-9Al-3W-30Ni-2Ta-3.5Ti (at%). The phase transition law of this alloy was calculated, and the results showed that the equilibrium precipitation phases of the alloy were γ, γˊ, χ-D0₁₉ and Co₇Ta₂, and the initial precipitation temperatures were 1355 °C, 1169 ° C, 700 ° C, and 288 ° C, respectively. The alloy heat treatment process was formulated: 1250℃/12h homogenization, 1150℃/6h solution treatment, 900℃/4h + 750℃/16h two-step aging treatment. The alloy samples were prepared by vacuum induction melting. After the above heat treatment, the DSC analysis results are consistent with the calculated phase transition rules. SEM and XRD results show that the equilibrium phase of the alloy is typical γ + γˊ two-phase structure.

Abstract:Investigation of the impact resistance of Al-Zn-Mg-Cu alloys as aerospace materials is of great significance to expanding its extreme applications in engineering.In this paper, taking 7A04-T6 as the specimen material, the experimental study of dynamic mechanical response of materials at different temperatures and strain rates is carried out withthe split Hopkinson pressure bar device.The results show that,undertheexperimental temperature within 25℃-150℃, the thermal softening effect in the high-speed impacted material takes advantage of the competition with the work hardening, resulting in the decrease of the material"s flow stress. With the increase of average strain rate, both the flow stress and the yield strength of the material increase, which indicates an obviousstrain rate hardening effect.Adiabatic shear phenomenon can occur in the material under high-speed impacting, accompanied by macroscopic cracks. When the adiabatic temperature rise is superimposed on the experimental temperature, it fulfills the solid dissolution condition for the reinforcementphases in local adiabatic shear bands, and the fracture failure of the material occurs when it is much lower than the phase transition temperature.

Abstract:Radially graded porous titanium / tantalum orthopedic implants fabricated by additive manufacturing technology have golden prospects. A cylindrical radially graded porous scaffold with an average porosity of 70% was built by using the triply minimal surfaces (TPMS) modeling methods, and the porosity gradually decreases from the central axis (90%) to the circumferential surface (30%). Selected laser melting (SLM) process was used to fabricate this scaffold. Optical microscopy, scanning electron microscopy, and Micro-CT results show that the SLM titanium/tantalum were consistent with the design models. The porosities of the SLM radially graded porous titanium / tantalum are 73.18% and 68.18% respectively. The mechanical test results show that the elastic modulus of radially graded porous titanium / tantalum are 3.96 ± 0.19GPa and 3.47 ± 0.25GPa respectively, and the compressive strength are 90.83 ± 3.35MPa, 93.27 ± 1.24MPa respectively. Both of them are significantly higher than those of homogeneous porous titanium / tantalum respectively. (Homogeneous porous titanium with an average porosity of 70.11% has an elastic modulus of 2.34 ± 0.48GPa and a compressive strength of 67.63 ± 1.33MPa; Homogeneous porous tantalum with a porosity of 65.39% has an elastic modulus of 1.69 ± 0.49GPa and a compressive strength of 68.56 ± 0.41MPa). In vitro cytocompatibility experiments show that both radially graded porous titanium and tantalum have good biocompatibility and they are suitable for the adherent and growth of mesenchymal stem cells and muscle cells. The radially graded porous titanium / tantalum fabricated by the SLM process has more similar structure and properties to natural bone tissue than homogeneous porous titanium / tantalum, and both of them are an ideal substitute for bone defect repair.

Abstract:This paper studies for the effect of solution-aging (SA), homogenization + solution aging (H+SA), Hot isostatic pressing + solution-aging (HIP + SA) three different heat treatments on the microstructure and mechanical properties of selective laser melting (SLM) formed Inconel 718 alloy. The as-built Inconel 718 has a large number of dendritic structures, and there are many brittle Laves phase precipitating among the interdendritic region. The δ phase was prone to precipitate when treated by proper homogenization, but the material can not be strengthened without γ"and γ " phases. Hot isostatic pressing(1080 ℃×1480 bar/2 h) can considerably removed Laves phase and micro pores of the as-fabricated samples, and combine with the solution aging treatment subsequently, it’s conductive to refine the grain size of the as-built samples, flat the grain boundaries, and promote the precipitation of γ "、γ " phase, so HIP+SA treatment significantly increases the strength of Inconel 718 alloy, the mechanical properties of Inconel 718 alloy reached their optimum combination at UTS=1361 MPa, 0.2% YS=1191 Mpa, and HV0.2 =490, and the elongation after breaking is 13.30%.

Abstract:The AlCoCrFeNiTi_0.2 alloy was designed and prepared by the arc melting method. It was found that the as-cast alloy formed the B2 phase and the BCC phase, and showed good room temperature compressibility, compressive plasticity of 32.6%, yield strength of 1530.4 MPa, and compressive strength of 4035.0 MPa. The hardness is about 600 HV. It was heat-treated at 550°C, 800°C and 1050°C, and the high-temperature phase was preserved by water cooling. The phase composition corresponding to the three temperatures was BCC + B2, BCC + B2 + FCC + σ, and BCC + B2 + FCC. The brittleness and hardness of the alloy increase after heat treatment. A bulk AlCoCrFeNiTi_0.2 alloy was prepared by magnetic levitation melting. The alloy has a relatively uniform composition distribution, forming a BCC + B2 + σ three-phase structure. The compressive plasticity is 35.0% at 600°C, and it can still maintain a yield strength of 1486.7 MPa which is good at high temperature.

Abstract:The phase transformation process of U-2Nb alloy under isothermal condition and the mechanical properties corresponding to the morphological changes were studied within 450℃~635℃.By applying the Optical Microscope、Scanning Electron Microscope techniques, tensile and compression tests, the relationship between structure and performance was discussed. The results show that U-2Nb alloy has two distinct microstructure features during isothermal heat treatment from 550℃ to 635℃. The main factor affecting the strength and plasticity was the lamellar spacing of the dual-phase in the range of 550℃~635℃.The lamellar spacing was mainly determined by the formation temperature. The higher the temperature, the greater the lamellar spacing, and so, the lower the strength and the higher the plasticity. The isothermal time is positively correlated to the lamellar spacing. The best overall properties we obtained were elongation of 22%, reduction area of 27.4%, tensile strength of 875Mpa and yield strength of 410Mpa.The rest samples were quenched and annealed at 450℃~500℃.The main factors influencing the mechanical properties within this temperature range are speculated to be the texture of the acicular martensite and the distribution or size of the granular structure. All samples with quenching+annealing treatment show overall strength higher than 1000Mpa, but with low plasticity. Elongation and reduction of area were within 5%. The annealing temperature affect the strength much more than plasticity. The plasticity was improved slightly by extending the annealing time.

Abstract:In view of the waste of W-Re alloy, the electrochemical dissolution method was used to make W, Mo and Rre completely dissolved in the alkaline solution of sodium hydroxide, and then the selective precipitation separation of the electrolytic solution were performed.by using calcium chloride to precipitate W-Mo and potassium chloride to precipitate Re. The results show that: (1)The suitable process parameters for electrochemical dissolution of W-Re alloy waste are: cell voltage 2.5V, NaOH concentration 100g/L, electrolysis temperature 30-40℃, electrode distance 20-30mm, and the total W-Re ion concentration is controlled at 30-35g/L. Under these conditions, the dissolution rate of W, Mo and Re are all more than 99%, the current efficiency is over 99%, and the wire waste is better than the block waste to be eletrochemically dissolved. (2)The optimum technological parameters for the selective chemical precipitation separation of W-Re electrolytic solution are: reaction temperature 80℃, CaCl₂ dosage 3 times of theoretical dosage, OH^_- concentration 9.5g/L, W ion concentration 23.18g/L, reaction time 2h. Under these conditions, the precipitation rates of W and Mo are 99.86% and 99.55%, respectively. (3)After the above two processes, the recovery rates of W and Mo are 98.86% and 98.55%, respectively. The morphology of CaWO₄/CaMoO₄ mixture is spherical, and KReO₄ white crystals are obtained.

Abstract:Cu@Ag coated powder was prepared by electroless plating and sintered by spark plasma sintering technology (SPS). The scanning electron microscope and transmission electron microscope were used to study the microstructure of the coated powder and sintered samples. The phases and densities of the samples were characterized. The results showed that there is obvious coating on the surface of Cu@Ag powder prepared by electroless plating. By using SPS, a high-density Cu-Ag sintered block can be obtained. At 550 ° C, the density reached a maximum of 96.76%. At low temperatures, the necking of nano-silver promotes the sintering; at high temperatures, solid solution between Cu and Ag promotes sintering.

Abstract:Hot dip Al-Si alloy coating is an efficient corrosion resistant technology. However, there are serious Al-Si corrosion problems in some parts of the production line, such as sunk rolls, which are in direct contact with the Al-Si alloy melt. In this paper, YSZ/NiCrAlY protective coating system was prepared by air plasma spraying (APS). The influence of main gas flow on the microstructure, mechanical properties, high-temperature stability and Al-Si alloy corrosion resistance of YSZ coating were also investigated. The results showed that the spreading uniformity, coating density and mechanical properties of the droplet firstly increased and then decreased with the main gas flow rising. The coating exhibited the best surface smoothness, maximum density and optimal mechanical properties when the main flow is 40 L/min. The interface structure of YSZ coating is stable, the porosity is decreased, and the density is significantly increased after heat treatment at 1000°C for 100 h. In addition, no diffusion or reaction zone was found at the interface between YSZ coating and Al-Si alloy melt when the coated sample was immersed in the Al-Si alloy melt for 50 h. Al-Si melt did not penetrate into the coating, but was blocked on the YSZ coating surface, indicating that APS YSZ/NiCrAlY coating can effectively resist Al-Si melt corrosion, which can be used as one of the most potential protective coatings for parts contacting with high temperature Al-Si melt.

Abstract:The effects of post-weld heat treatment on the microstructure and mechanical properties of Ti650 alloy electron beam welding (EBW) samples were studied. The results indicated that metastable martensite α′ is the main phase in the fusion zone of welding seam. During 700℃/2hAC heat-treatment, a phase transition α′→α occurred, and a large number of short aciculate secondary α were precipitated in the fusion zone. After 1010℃/1.5hWC+650℃/2hAC heat treatment, α was obviously coarsened and equiaxed. The microstructure contains the original coarse layer and the secondary short acicular alpha can effectively improve the strength and prevent the crack growth of welded joint. The welded joint has better strength and plasticity under the condition. After subsequent treatment at 700℃/2hAC, some equiaxed alpha can be found gradually precipitated at the grain boundary, resulting in a decrease in strength and plasticity of the grain boundary. In conclusion, 1010℃/1.5hWC+650℃/2hAC is the most suitable post-welding heat treatment for Ti650 EBW welded joint to make the properties of weld and matrix be well matched.

Abstract:_{:For traditional magnetron sputtering, the sputtered species possessed low kinetic energy and ionization rate, which give rise to the metal coating formed columnar structure with micro pores, the coating therefore has poor compactness and adhesion strength. Aiming at this problem, the electric current through the anode and cathode was adjusted into the arc discharge transition region between the glow region and arc region of the gas discharge voltammetry curve in plasma physics. The escape energy of electron at the grain boundary and defect of the target is lower than that inside the grain, then the“self-enhancing effect”of electron escape is formed in grain boundary which induces the arc discharge phenomenon. Arc discharge melts some micro regions of the target surface, the plating particles in these regions will leave the target in the form of melt splashing. The high yield of melt splashing can improve the collisional ionization rate of the plating particles, which establish a foundation for the control of the coating structure. Experimental results show that: In the case of high frequency oscillating pulsed electric field, when the target current was gradually increased, the micro-morphology of the target surface gradually changed from Irregular pit-like morphology to round pit and curved ravine morphology, indicating that the off-target mode of the plating material changed from collision sputtering to melt splashing. When the target current was 2A, the species left the target by means of collision sputtering. The microstructure of the aluminum coating presented typical columnar structure with voids. When the target current increased to 14A, the off-target mode of the target particles was mainly melt splashing, massive ionized plating particles were accelerated under the negative bias of substrate. These ions with high kinetic energy enhanced bulk diffusion and weakened the tendency for column growth,which helped the coating form a dense structure. At the same time, the adhesion and the deposition rate of the coating were also significantly improved.}

Abstract:In order to improve the electrochemical corrosion and wear performance of MgF₂+MgO MAO (micro-arc oxidation) coating on AZ61 simultaneously, composite dielectric ordinal discharge thought was used to weaken the eruption of breakdown melt and hence densify the coating and enhance its performance. α (MgF₂-MgO mass ratio), microstructure, electrochemical corrosion and wear performance of coatings were investigated. The results show that the weakening effect on eruption of breakdown melt for coating with α=1.2 is obviously better than that with α=0.1 and 11.8. The thickness of inner dense layer is thickened to 3.6 μm, which is about three times as thick as that of the existing MAO coating. The impedance of outer loose layer is enhanced to 13555 Ω cm^₂, which is about 30% larger than that of α=0.1 and 11.8. Ecorr (corrosion potential) of AZ61 is increased from -1.912 to -0.455 V_SCE, Icorr (corrosion current density) is decreased from 378.6 to 0.453 (10^_-6 A/cm^₂) and the wear rate is reduced from 921 to 0.5 (10^_-5 mm^₃/N.m) by this densified micro-arc oxidation coating. This investigation provides a novel processing mode for outstanding MAO coating.

Abstract:The microstructure evolution and mechanical properties of 51.1Zr-40.2Ti-4.5Al-4.2V alloy during tensile deformation at room temperature were studied. The results show that the phase transformation from β to α" phase were observed in the process of tensile deformation at room temperature, and the volume fraction of the α" phase decreases with the increase of the tensile rate. The existence of the α" phase has an obvious effect on the mechanical properties of the alloy. At the tensile rate of 0.3 mm/min, the trigger stress (TS), ultimate tensile strength (UTS), elongation (EL) and elastic modulus (EM) were 770.06 MPa, 1168.60 MPa, 14.96% and 64 GPa, respectively. TS and EM increased with the increase of tensile rate, while UTS and EL decreased. Three different stages were presented in the curve of work hardening rate. Especially, the second stage was obviously affected by the α" phase. At a given strain, the work hardening rate at the second stage is gradually decreased with increasing tensile rate. When the tensile rate was 0.3 mm/min, the fracture morphology of the alloy was composed of a large number of dimples and a small number of quasi-cleavage planes, which show a typical feature of plastic fracture. With the increase of the tensile rate, the fracture mode of the alloy changed from plastic fracture to brittle fracture. This is mainly due to that the volume fraction of the α" phase decreases with the increase of the tensile rate.

Abstract:In order to improve the performance of Sn-58Bi lead-free solder, the Sn-58Bi-0.1Ti nanometer reinforced composite solder was prepared by incorporating 0.1% Ti nanoparticles into the Sn-58Bi solder. In this paper, the effect of adding Ti nanoparticles on the growth behavior of intermetallic compounds (IMC) in Sn-58Bi/Cu solder joints during thermal cycling was studied. The results showed that a scallop-like Cu₆Sn₅ IMC layer was formed at Sn-58Bi /Cu and Sn-58Bi-0.1Ti/Cu interface after reflow soldering. After 300 thermal cycles, a layer of Cu₃Sn IMC was formed at the Cu₆Sn₅/Cu interface. The thickness of IMC layer of Sn-58Bi/Cu solder joint and Sn-58Bi-0.1Ti/Cu solder joint is proportional to the square of thermal cycling time. However, the IMC thickness of Sn-58Bi-0.1Ti/Cu solder joint is significantly lower than that of Sn-58B/Cu solder joint, which indicated that the addition of Ti nanoparticles can effectively inhibit the excessive growth of interfacial IMC during the thermal cycle process. In addition, the IMC layer diffusion coefficients of these two solder joints were calculated, and it was found that the diffusion coefficients of IMC layer in Sn-58Bi-0.1Ti/Cu solder joint (overall IMC, Cu₆Sn₅ and Cu₃Sn IMC) were smaller than that of Sn-58Bi/Cu solder joint, which explained the inhibitory effect of Ti nanoparticles on the interface IMC layer to some extent.

Abstract:High-entropy alloys, which usually composed of 4 or more elements in equiatomic or near equiatomic ratio with a solid solution structures, have emerged as a new kind of metallic materials for a recent decade. The proposed philosophy of high-entropy alloys has broken through the paradigm of traditional alloy design and largely expanded the scope of alloy exploration. Meanwhile, high-entropy alloys exhibit several unique properties, such as high strength and hardness, unusual low-temperature toughness, high corrosion resistance and radiation resistance, due to the large lattice distortion, high mixing entropy, slow diffusion of atoms and cocktail effects. In this paper, we made a brief summary of the present research on high-entropy alloys, and discussed the potential applications of high-entropy alloys in extreme environments as new-emerged structural materials. In particular, the possibility of high-entropy alloys used in the key components of petroleum industries, e.g. drill pipe joint belt, bushing and high-performance riser, etc., was emphatically analyzed.

Abstract:Among the existing anode materials for lithium-ion capacitors (LICs), Nb-based oxides are considered as one of the most promising anode materials. This review takes Nb2O5, M-Nb-O (M = Ti, Cr, Ga, Fe, Zr, Mg, Li, Na, K, etc.) and (H, Li, K)-Ti-Nb-O group anode materials as examples, and introduces the advantages of niobium-based oxides as anode materials for LICs, the energy storage mechanism, synthetic methods. Moreover, the existing problems in each material currently and corresponding solutions are proposed, which will promote their further development and applications in the field of emerging energy storage devices.

Abstract:SiC fiber reinforced metal-base composite is more and more widely used in aerospace field for the higher temperature capability, lower density. SiC fiber reinforced Ti, Al, Mg based composites have proved to be great success. But the usage temperature of these composites has been limited by the usage temperature of base metal. In order to further increase the temperature capability of SiC fiber reinforced metal-base composite and obtain high-temperature structural material with better properties, there are some attempts of SiC fiber reinforced superalloy-base composite at home and aboard. However, the development of SiC fiber reinforced superalloy-base composite is in slow development and there has not been breakthrough success. The bottleneck for the development of SiC fiber reinforced superalloy-base composite is the interface reaction between SiC fiber and superalloy base. Many attempts (such as a variety of interface coatings) have been made to conquer this challenge, however, no mature solution has been found. Hence, it is necessary to systematically analyze the feasibility of SiC fiber reinforced superalloy-based composite. In this paper, the origin and development of SiC fiber reinforced superalloy-based composites in past decades were narrated. The failure cases and reasons were summarized. Moreover, the attempts of interface coating and disadvantages of this method were analyzed. Experiments and simulations were carried out to investigate the interface reaction between SiC fiber and major superalloy elements. The results show that the reaction between SiC fiber and major superalloy elements is severe and cannot be avoided. Further analysis on the essence of severe reaction between SiC fiber and superalloy was made. The experiment and analysis show that SiC fiber and superalloy are intrinsically incompatible, and the interface reaction trend is severe. Interface coating can hinder the reaction in some extent. But the reaction trend is so severe that any minor failure of coating will result in catastrophic result. The above reasons indicate that it is difficult for SiC fiber reinforced superalloy-base composite to be used commercially in the near future.

Abstract:The great potential for applications in automotive, aerospace and electronic industries of magnesium alloys can be attributed to their desirable properties such as low density, high specific strength and stiffness, superior damping capacity and good electromagnetic interference shielding. Meanwhile, the alloys are also finding broad medical applications and receiving extensive scientific research due to their biocompatibility and biodegradability in physiological media. However, the Achilles heel of magnesium is that it corrodes too fast in solutions. Alloying is one of the most important approaches to slow down corrosion rates of magnesium alloys. It facilitates the creation of new Mg alloys by optimizing the composition and content of alloying elements in the stage of materials design, so that the new alloys acquire desired properties to meet the requirements of various applications. During alloying, the elements, secondary phases, gain size and defects greatly influence corrosion kinetics and electrochemistry of magnesium alloys. In terms of corrosion kinetics, most alloying elements can affect the activity of anodic and/or cathodic reactions of Mg, though they have negligible effects on the chemical stability. The secondary phases always serve as cathodes in the micro-corrosion couples, such that the micro-galvanic corrosion is possible and the dissolution of Mg is accelerated. Microstructural homogeneity and grain refinement are responsible for the decrease of corrosion rates of Mg alloys. It is believed that alloys with relatively high grain boundary densities tend to exhibit an analogous relationship between grain size and corrosion rate like the ‘Hall-Petch’ relationship, which can quantitatively reveal the relationship between corrosion rates and grain size. In addition, the defects including dislocations, pores, cracks and stresses are ready to trigger the dissolution of Mg since these locations have high free energy. In this article, the influences of alloying on the corrosion rates of Mg alloys were reviewed from the electrochemical viewpoint, on the basis of the corrosion nature of magnesium metal. Then the possibility of an improved anti-corrosion performance of Mg alloys by some alloying-related methods such as multi-elemental alloying, micro-alloying and alloying control was analyzed. At last, it was pointed out that the future development directions of electrochemical corrosion of magnesium alloys under the influences of alloying, to contribute much broader applications in the future.