Abstract:To investigate the effect of different extrusion temperatures (350 and 200 °C) on the tensile properties of backward extruded Zn-6Al alloys at room temperature, the microstructure and mechanical properties were studied using scanning electron microscope (SEM), electron back-scattered diffraction (EBSD), and electronic universal testing machine. The results show that with the decrease of extrusion temperature from 350 °C to 200 °C, the elongation of backward extruded Zn-6Al alloys increases from 98% to 198% at the strain rate of 10^-3 s^-1 due to the fine grains, high Schmid factor and non-lamellar structure.

Abstract:Six kinds of Cu-Ni alloys with different sulfur contents were investigated at room temperature for tensile properties. The effects of tensile rate and sulfur content on the yield strength, tensile strength, elongation, and reduction of area of the alloys were studied. The changes of metallographic structure with sulfur content were studied by scanning electron microscope (SEM), energy disperse spectroscopy (EDS) and metallographic structure analysis. The distribution and deformation of sulfur precipitate and the influence law for the plasticity of Cu-Ni alloy were analyzed. The origin and occurrence of alloy fracture process and the influence mechanism of sulfur content on plasticity were analyzed, providing a theoretical basis for subsequent cold deformation process.

Abstract:Fe-Cr-C/TiCN composites with different carbon contents were prepared via mechanical alloying followed by spark plasma sintering. The effects of carbon black content on the microstructure and wear properties of Fe-Cr-C/TiCN composites were systematically investigated by scanning electron microscopy, X-ray diffraction, Vickers hardness test, and ball-on-disk type tribotest. The results show that the (Cr, Fe)₇C₃ carbides form in the sintered specimens with 1wt%~5wt% carbon, but (Cr, Fe)₃C phases appear when the carbon black content reaches 4wt%~5wt%. Carbon black content plays a significant role in the microstructure uniformity and densification of the Fe-Cr-C/TiCN composites. When the sintering temperature is ~1000 °C, the relative density of specimen without carbon addition increases from 95.0% to 99.7% of the specimen with carbon addition of 3wt%, indicating that the full densification is realized. High Vickers hardness of 11 940 MPa is achieved for the specimen with carbon addition of 3wt%. Furthermore, adding an appropriate amount of carbon (3wt%) contributes to the excellent wear properties with narrow fluctuation ranges of friction coefficient, suggesting an average friction coefficient of 0.320 and wear rate of 6.8×10^-4 mm³·N^-1·m^-1.

Abstract:To improve the wear resistance of brake disks, the Ni60A coating was prepared on 20CrNiMo steel using laser cladding by optical fiber-based laser system. The microstructure, composition uniformity, hardness, dry-sliding wear performance, and friction and wear mechanism of the Ni-based alloy coating were investigated. The results show that the coating consists of γ-Ni, M₂₃C₆, Ni-Cr-Fe, Ni₃B, [Fe, Ni], FeNi₃, NiC, FeNi, and other phases. The average microhardness HV_0.3 of Ni-based alloy coating is 4600 MPa, which is 2.63 times higher than that of the 20CrNiMo steel substrate. Compared with the substrate, the coating exhibits lower average friction coefficients under working condition of high load and high temperature, and the wear resistance significantly improves. When the load is 150 N, the wear resistance of the coating increases by 15.3 and 22.0 times at room temperature and 400 °C, respectively. With the increase of temperature and load, the wear mechanism of the coating changes from abrasive and adhesive wear to oxidative and abrasive wear.

Abstract:Lanthanum (La) thin film was electrodeposited at room temperature (298 K) using lanthanum nitrate, ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate (BMIMPF₆) and cosolvent acetone as the electrolyte. Results show that the reduction from La³⁺ to La⁰ involves the transformation of La³⁺→La²⁺ occurring at around -1.7 V vs. Pt and La²⁺→La⁰ occurring at around -2.1 V vs. Pt. The electrolyte BMIMPF₆ exhibits an electrochemical window from -2.5 V vs. Pt to 1.5 V vs. Pt. The low hygroscopic property of BMIMPF₆ allows La electrodeposition under air atmosphere. The precipitate films were observed by scanning electron microscopy and metallographic microscope, showing a dense texture. Then the films were characterized by energy dispersive spectrometry and X-ray photoelectron spectroscopy, confirming therein a large amount of La. The electrochemical tests of changing voltage scan rate and the concentration of lanthanum nitrate reveal that the reduction of La³⁺ is an irreversible process. The diffusion coefficient of La³⁺ in BMIMPF₆ is calculated as 1.47×10^-9 cm²·s^-1. This research provides a simple approach to obtain La thin film, which can be used for the electrodeposition of other lanthanides thin film.

Abstract:Graphene nanosheets (GNSs) of different mass fractions (0wt%, 0.025wt%, 0.05wt%, 0.075wt%, 0.1wt%, and 0.2wt%) were added into the Sn-58Bi low-temperature solder. The influences of GNSs on melting characteristics, wettability, shear properties, microstructure and interfacial reaction were investigated. Results show that adding GNSs has the positive effect on the wettability and shear strength of Sn-58Bi solder joint, and a slight influence on the melting temperature. After the addition of GNSs, a finer microstructure of Sn-58Bi solder is obtained. The thickness of intermetallic compound (IMC) at solder/Cu interface reduces significantly and the IMC morphology becomes flat after adding GNSs. In addition, with the addition of GNSs, the shear fracture mode of Sn-58Bi low-temperature solder converts from brittle into a mixed mode of brittle and ductile fracture, which is coincident with the changing situation of shear strength. In general, adding GNSs may be conducive to the improvement of solder joint reliability.

Abstract:The Ti-6Al-4V alloy T-joints were prepared by double-sided synchronized laser beam welding with homologous filler wires. Influence of heat input on the stability of welding process, weld formation, microstructure, and mechanical properties of Ti-6Al-4V alloy T-joints was investigated through the high-speed camera during double-sided laser beam welding process. Results show that the heat input has a significant effect on molten pool behavior and droplet transition, which influences the appearance and welded quality of the T-joints. With the increase of heat input, the morphologies of welded T-joints change and the grain size increases. Martensite forms at the heat affected zone (HAZ) and fusion zone (FZ), resulting in the fact that the microhardness of HAZ and FZ is higher than that of the skin. Moreover, the tensile strength of welded T-joints along the directions of skin and stringer increases with increasing the welding heat input. The fractures occur at the base metal part of all the specimens, which is correlated with the martensitic strengthening effect of the joints.

Abstract:High-strength and high-porosity tricalcium phosphate (TCP) scaffolds were prepared by 3D gel-printing (3DGP) technique. The microstructure of the scaffolds was observed by scanning electron microscopy (SEM) and the biocompatibility was evaluated by animal experiments. The results show that the optimal concentration of solid loading of slurry for printing is 34vol%, and the shrinkage of printing scaffolds along length, width, and height directions is 11.44%±0.20%, 9.41%±0.23%, and 10.57%±0.20%, respectively. After the scaffolds are sintered at 1150 °C for 2 h, the compressive strength of the scaffolds is 22.6±0.12 MPa and the porosity is ~62.1%. The animal implantation experiment shows that the porous TCP scaffolds do not cause significant tissue rejection in rabbit femoral condylar defects, and there is no inflammatory reaction or chronic inflammatory reaction at the bone-to-scaffold junction. In conclusion, the porous TCP scaffolds prepared by 3DGP technique have good biocompatibility and excellent strength properties, which are expected to meet the implantation requirements of cancellous bone.

Abstract:The effects of percentage reduction per pass (PRPP) on the effective strain, microstructure, mechanical properties and through-thickness homogeneity of AA7055 alloy plates were investigated through experiments and numerical simulations. Results show that with consistent total strain, the difference between the effective strain values in the surface and middle layer of AA7055 alloy plates decreases with the increase of PRPP. In the plate rolled with small PRPP, the surface layer of plate contains higher recrystallization fraction, while the middle layer comprises of large recrystallized grains. In contrast, the plate rolled with large PRPP has consistent recrystallized grain size with consistent recrystallization fraction along the thickness direction. Thus, an improved homogeneity of the microstructure and mechanical properties along the plate thickness direction can be obtained through the rolling process with large PRPP.

Abstract:A new kind of Al-5Ti-0.8C master alloy was fabricated using a self-propagating combustion reaction method and dilution treatment, and the effects of different Al-5Ti-0.8C master alloy contents (0wt%, 0.1wt%, 0.3wt%, 0.5wt%) on the microstructure and elevated temperature mechanical properties of Al-Cu-Mn alloy were investigated. The results show that the Al-5Ti-0.8C master alloy refines the Al-Cu-Mn alloy, increases the amount of θ′(Al₂Cu) precipitates, and reduces their size during heat treatment, resulting in the grain refinement. Moreover, this new master alloy obviously improves the elevated temperature mechanical properties of Al-Cu-Mn alloy, mainly due to the precipitation strengthening caused by the uniform distribution of second phases and fine θ′(Al₂Cu) precipitates, and the formation of Al₃(Ti, Zr) nanoparticles with high thermal stability. Furthermore, the microstructure and mechanical properties of Al-Cu-Mn alloy with 0.3wt% Al-5Ti-0.8C master alloy show the optimal status.

Abstract:An artificial neural network model with high accuracy and good generation ability was developed to predict and optimize the mechanical properties of Al-7Si alloys. The results show that Al-7Si alloys with tensile strength of 310~350 MPa, elongation of 3%~12%, and different microstructures are obtained by controlling the holding pressure (85~300 kPa) and cooling rate (1~10 k/s) of the casting process. The quantitative correlation relationships of the mechanical properties with microstructures of the secondary dendrite arm spacing (18.56~33.04 μm), area of eutectic Si phase (6.37~13.37 μm²), area fraction of porosity defects (0%~0.363%),and area fraction of maximum Fe-rich intermetallics (0%~0.06%) in the alloy were established. The individual and combined influences of these microstructure characteristics on the mechanical properties were simulated. Both tensile strength and elongation are inversely related to the above-mentioned structural characteristics, and the presence of defects and Fe-rich intermetallics have great adverse effects on the properties of the alloy. Therefore, narrowing the dendrite spacing (<20 μm), modifying the eutectic Si phase (<12 μm²), and controlling the porosity defects (<0.35%) and the morphology of the Fe-rich intermetallics are keys to prepare high-performance aluminum alloys.

Abstract:FeCoNiCr high entropy alloy coatings were prepared by electrodeposition in sulfate system with citric acid and sodium citrate as the complexing agent. The effects of current density, bath temperature, and pH value on the composition, morphology, crystal structure and hardness of the coatings were studied. The results show that the prepared FeCoNiCr high entropy alloy coatings are amorphous and uniform. The optimized process parameters are: pH=2.5, temperature of 25 ℃, and current density of 25 A·dm^-2.

Abstract:VMoTi catalyst was prepared separately by impregnation method (IM) and sol-gel method, and the alkali metal K poisoning of the catalyst was simulated. The X-ray diffraction, BET specific surface area test, NH₃-temperature programmed desorption (TPD), H₂-temperature programmed reduction (TPR), and X-ray photoelectron spectroscopy (XPS) methods were used to analyze the physical and chemical properties of the VMoTi catalyst, and the reaction and deactivation mechanisms of the vanadium-titanium-based catalyst were discussed. The results show that compared with the catalyst prepared by IM, i.e., VMoTi (IM) catalyst, the catalyst prepared by the sol-gel method, i.e., VMoTi (Sol-gel) catalyst, has a smaller grain size, a larger specific surface area and pore volume, a larger amount of surface acid, a stronger redox capacity, and a higher content of V⁴⁺, Mo⁴⁺, and surface active oxygen. Therefore, VMoTi (Sol-gel) catalyst shows a good denitration efficiency stabilized at ~100% in the temperature range of 180~320 °C. The addition of potassium (alkali metal) leads to catalyst poisoning, and the poisoning effect of the catalysts prepared by different methods is different. The K salt deposition has a great influence on the denitration efficiency of the VMoTi (IM) catalyst. The VMoTi (Sol-gel) catalyst has good resistance to K poisoning. Through the characterization of the catalyst, it is found that K salt weakens the interaction between the active ingredient and the carrier, enhances the intensity of the diffraction peak of anatase TiO₂, and reduces the acidity and redox of the catalyst surface. At the same time, the content of chemical adsorption of oxygen and active metals, such as V⁴⁺ and Mo⁴⁺, decreases. These factors are the main reasons of the catalyst inactivity.

Abstract:The influence of Pr addition on the microstructure, phase transformation, and hardness of Ni₅₀Ti_50-xPr_x (x=0, 0.1, 0.3, 0.5, 0.7, 0.9, at%) shape memory alloys was investigated. Results show that Ni₅₀Ti_50-xPr_x alloys consist of NiTi matrix and NiPr precipi-tates. Ni₅₀Ti_49.5Pr_0.5 alloy has the optimal properties of martensitic transformation start temperature of 73 °C, the thermal hysteresis as narrow as 37 °C, and the Vickers hardness of 2850 MPa. Pr addition obviously decreases the martensitic transformation temperature of NiTi alloys, but the composite alloy maintains a relatively narrow thermal hysteresis and relatively high Vickers hardness, compared with other NiTi-based shape memory alloys.

Abstract:With the novel dual heat source model for pulsed laser-gas tungsten arc (GTA) hybrid welding by COMSOL Multiphysics, the temperature distribution was analyzed at several selected points along the weld line. The influences of laser pulse parameters and electric arc current on the welding pool morphology were investigated. The results show that the influence of different process parameters on the depth of molten pool ranked in order is as follows: laser excitation current>arc current>laser pulse width>laser pulse frequency. The influence of different process parameters on the width of molten pool ranked in order is as follows: arc current>laser pulse width or laser excitation current>laser pulse frequency. A database of molten weld pool characteristics for laser-induced arc welding of magnesium alloy was established by classifying the composite heat source parameters and used to realize the precise control of the molten pool shape. The precise control of the actual welding molten pool of a T-shaped weld is achieved with accuracy of 95.1%.

Abstract:The grain selection process during single-crystal casting of a Ni-base superalloy DD5 in a spiral grain selector was simulated by a macroscale ProCAST coupled with a mesoscale cellular automaton finite element (CAFE) model, and the simulation results were validated by experimental observations. The results show that at the same withdrawal rate, the number of dendrites decreases gradually, and the primary dendrite arm spacing increases gradually with the increase of the distance from the chill surface. With increasing the withdrawal rate from 2 mm/min to 8 mm/min, the primary dendrite arm spacing decreases, the number of dendrite stems increases, the dendrite spacing decreases and the dendrite structure is refined gradually. During the simulation process, the quantity, area, and color of the solid tissue are similar at the three withdrawal rates of the spiral selector starter block. In the spiral part, the microstructures at 5 mm/min are less than those at the other two withdrawal rates, with larger area and lighter color. The grain selection efficiency at the intermediate withdrawal rate is better than that at the other two withdrawal rates, which is obtained from the results of the grain microstructure evolution and metallographic microstructure analysis of crystal selector.

Abstract:Cold-rolled Ti/Al laminated composites were annealed at 675~750 °C for different time with superfluous Ti and Al, and the interfacial microstructure evolution in Ti/Al laminated composites during annealing was investigated. The results indicate that the interfacial layer between Ti and Al consists of two sub-layers: a compact TiAl₃ sub-layer with the microstructure of many randomly oriented cracks filled with Al, and a granular TiAl₃ sub-layer with the microstructure of granular particles distributed in Al matrix. The thickness of the compact TiAl₃ sub-layer is stable at different annealing temperatures for different durations, but the thickness of the granular sub-layer increases with increasing the annealing temperature and duration. Furthermore, the average volume fraction of TiAl₃ phase in the interfacial layer at different temperatures decreases with increasing the duration. A reaction diffusion model, in which the TiAl₃ phase is regarded as the result of diffusion and chemical reaction, was established to evaluate the formation mechanism of the interfacial layer. Additionally, the dissolution of TiAl₃ phase into liquid Al was considered in the model. The calculated results indicate that the formation of TiAl₃ phase is governed by the chemical reaction, and the equivalent thickness of TiAl₃ phase in the interfacial layer obeys a linear relationship with annealing time, which is attributed to the rapid diffusion of Ti and Al atoms through the thin TiAl₃ compact sub-layer.

Abstract:The high-temperature deformation behavior of Ni60Ti40 alloy and the related mechanisms were investigated by thermocompression simulation experiments. The results of high-temperature compression tests were analyzed to reveal the effects of deformation temperature and strain rate on the structural properties and microstructure of alloys. Subsequently, the changing laws of the strain rate sensitivity index m, and the activation energy Q of alloys under different deformation conditions were obtained by calculation. Thermal processing maps based on the dynamic material model and the deformation mechanism maps revealing the dislocation quantity were plotted based on five plastic instability criteria, namely, Prasad, Gegel, Malas, Murty, and Semiatin, to analyze the physical significance of the parameters. The preferred forming zone and the rheological instability zone of the alloys were predicted using the thermal processing theories. The dislocation evolution laws and deformation mechanisms of the grain size with Burgers vector compensation were reported. With the aid of deformation maps, the rheological stress combined with modulus compensation during the high-temperature superplastic deformation was predicted.

Abstract:In this paper, the emission spectra of a high color rendering phosphors, mixed with the Yttrium Aluminium Garnet, Silicon based Oxynitride and Nitride based phosphors, were predicted by using the Lambert-Beer theory and Back Propagation Neural Network (BP NN). Firstly, the modified Lambert-Beer model was used to calculate the proportional coefficient of the emission spectra of the mixed phosphors in ratios. Next, the BP NN was implemented to train and predict the proportional coefficients. Finally, the prediction of the emission spectra of the mixed phosphors were estimated and verified by the experimental measurements. The results show that: (1) The prediction error percentage of the scale factor can be controlled within 5%; (2) The predicted emission spectra by BP NN keep high agreement with the experimental measurements with lower RMSE andΔxy as 0.019 and 0.0016, respectively.

Abstract:Stress corrosion cracking (SCC) endangers structural integrity of the nickel-base alloy 600 components widely used in the water environment of high temperature and high pressure in pressurized water reactors (PWRs). Due to the complexity of the interweaving influences, the existing prediction models developed for SCC are limited for engineering assessment by accuracy. In this study, a non-algebraic model with multi-dimensional data associations was developed for predicting the SCC growth rate of the Ni-base alloy 600, which utilized the TPE-XGBoost machine learning algorithm to describe the correlation between the multiple characteristic parameters including stress intensity factor, temperature, yield strength, dissolved hydrogen content, crack propagation direction, load type, heat treatment process and SCC growth rate. It was found that the TPE-XGBoost algorithm could achieve rapid global optimization of multi-dimensional data sets rather than the local optimal values. The obtained SCC model with sound generalization ability demonstrates potential engineering application on SCC growth rate prediction of Ni-base alloy 600 components in PWRs.

Abstract:In this paper, full-atom models of O2-/CaCl2 were constructed and the systems were described by Born-Mayer-Huggins (BMH) potential function to investigate the dynamic behavior of O2- in CaCl2 molten salt based on molecular simulations. The calculated diffusion coefficient at 1073 K is about 2.01 × 10-5 cm2/s, which is consistent with the reported value of F.D.Ferro"s literature. At the same time, the diffusion coefficient of O2- is closely related to temperatures. When the temperature is increased from 1073 K to 1473 K, the diffusion coefficient is 5.66 × 10-5 cm2/s. The activation energy for diffusion of O2- in CaCl2 molten salt is 15.6 kJ/mol by fitting diffusion coefficients at various temperatures. In terms of the microstructure, Ca2+ can form a positive coordination layer to inhibit the diffusion of O2- due to the electrostatic attraction. Further calculations found that the energy barrier that O2- needs to escape from the Ca2+ coordination layer is about 1.7 J. This article not only reveals the dynamic behaviors of O2- in CaCl2, but also provides guide to research and improvement of molten salt compounds.

Abstract:In this investigation, the Ti-Al-V flat ingots were fabricated by electron beam cold hearth melting (EBCHM), the chemical composition and melting process of the flat ingots were compared and analyzed. The experimental results showed that the stability of chemical composition in the longitudinal direction was significantly affected by melting speed. As the melting speed increased, the Al content in the longitudinal direction was also increased and vice versa. The chemical compositions of the flat ingots were all uniform and the segregation of element Al was not found in this experimental condition. Through the analysis of the flowing characteristics of melt in three stages of EBCHM, it showed that the Machlin model was not applicable to the mass transfer of melt boundary layer in cold hearth and crystallizer. The calculation method of aluminum volatilizing flux in three stages including the melting of raw materials, cold hearth melting and the solidification process of molten alloy in mould were established. Results of calculation are in good agreement with that of experiment.

Abstract:This paper takes the solid Cu-9wt%P alloy as the research object, and studies the dissolution process of solid Cu-9wt%P in molten aluminum at 973 K. Through static dissolution and water quenching experiments, the solidification structure that retains the dissolution process information is obtained. ZEISS Axio Vert.A1 optical metallographic microscope and scanning electron microscope (Scaning electron microscope, SEM) were used to analyze the solidified structure. The study found that when the solid Cu-9wt%P alloy is dissolved in molten aluminum, with the extension of the dissolution time, single-phase Cu3P is easily formed on the side of the Cu-9wt%P alloy on the solid-liquid interface, and the front of the solid-liquid interface is enriched with particles and Layered AlP. The dissolution process of solid Cu-9wt%P alloy in aluminum melt is summarized, and the root cause of the slow dissolution rate is revealed.

Abstract:The as-quenched (AQ) and after alternating current magnetic field (ACMF) treatment Fe78Si9B13 amorphous ribbons have investigated by XRD, DSC and VSM. The XRD and VSM results show that the nearest neighbor distance (d) and coercivity (Hc) of the ACMF treatment samples first decrease and then increase with increasing alternating current, however, the saturation magnetization varies little with the alternating current. The changes of d and Hc are attributing to the interaction of inhomogeneous characteristics structures in present alloys in the structural magnetic relaxation process. The apparent activity energies, local activity energies and local Avrami exponents of AQ and ACMF treatment samples deduced from DSC curves show that ACMF treatment increased the onset crystallization activity energy and local Avrami exponent and decrease the apparent growth activity energy of the crystallization reactions. The changes of crystallization behavior are ascribe to atomic pair ordering in atomic clusters and diffusion of free volume resulted by the magnetic aftereffect.

Abstract:Based on the Schaeffler diagram, the solidification cracking susceptibility of austenitic alloys during laser welding was investigated systematically. Specimens with different chemical compositions were made up by laser welding with hot different Nickel-based wires. Brittleness temperature range (BTR) could be obtained by combining the result of solidification crack from laser Trans-Varestraint test with the temperature profile of weld bead during laser welding. Then the solidification cracking susceptibility was studied quantitatively using BTR. With the increase of the ratio of Cr equivalent to Ni equivalent (Creq / Nieq) from 0.1 to 1.2, the BTR tended to increase firstly and then decrease. This showed that the solidification cracking susceptibility had a tendency of increasing and decreasing with increasing Creq / Nieq. While, the solidification cracking susceptibility was relatively higher in the middle region, and the susceptibility was lower at the sides of the single phase austenite region in the single phase austenite region of the Schaeffler diagram. When the contents of P + S, Nb and Si alloy elements were relatively higher, the low melting point eutectic compound – segregated liquid film could be formed at the grain boundary and sub-grain boundary, leading to increase the solidification cracking susceptibility. In addition, the effect of Nb on the solidification cracking susceptibility was much higher than that of P + S under a certain condition.

Abstract:The stress-strain curves obtained by thermal simulation compression experiments show that the powder TC4 titanium alloy has the characteristics of work hardening and continuous dynamic softening during deformation at the temperature of 850~950℃ and the strain rate of 0.1~10s_^-1. The constitutive equation of the material was established, which well describes the rheological behavior of the powder TC4 titanium alloy. Furthermore, the dynamic softening behavior was analyzed, and the influence degree of various factors on softening was calculated. The results show that with the decrease of deformation temperature and the strain rate, the flow softening degree increases. When the strain rate is 1s_^-1 and 10s_^-1, the flow softening is mainly caused by the deformation heat. When the strain rate is 0.1s_^-1 and the temperature are 850 and 900℃, there are three softening factors: deformation heat, dynamic phase transformation and α phase morphology evolution. As temperature decreases, the softening proportion caused by morphological evolution of αphase increases. With the increase of temperature, the softening proportion of dynamic phase transformation increases. When the strain rate is 0.1s_^-1 and the deformation temperature is 950℃, there are two softening factors : deformation heat and dynamic phase transformation. With the increase of deformation, the proportion of dynamic phase transformation softening increases.

Abstract:Powder metallurgy (P/M) Ni-based superalloy has been the most important material for high-temperature structural application in turbine disc owing to its good tensile and creep properties. However, the inclusions in P/M superalloy have an important impact on the safety and reliability of superalloy. By means of implanting Al2O3 and SiO2 inclusions artificially, the Low Cycle Fatigue (LCF) samples containing different sizes of inclusions were prepared. LCF tests with different strain amplitudes were carried out at 650 ℃. By observing and analyzing statistically the fracture of samples, the effect of size, location, types of inclusions and strain amplitude on the LCF lifetime were studied, the relationship between inclusion characteristics and LCF lifetime was constructed. The results showed that fatigue source areas were mainly internal inclusions or surface inclusions when the strain amplitude was 0.8% or 0.9%, and the inclusions greatly reduced the LCF lifetime. When the strain amplitude was 1.0% or 1.2%, the fatigue source areas had no inclusions, and the inclusions had no influence on LCF lifetime. Moreover, with the increase of strain amplitude, the locations of fatigue source were transferred from internal inclusions to surface inclusions and sample surface without inclusions gradually. With the increase of inclusions area, the LCF lifetime decreased at low strain amplitude, and the relationship between the inclusion area and the LCF lifetime was constructed. The effect of the distance from inclusions to the surface (L) on the LCF lifetime had no obvious rules when the inclusion area was uncertain. With the increase of L, the LCF lifetime increases linearly when the inclusion area was fixed. The effect of SiO2 inclusions on the LCF lifetime was more detrimental than Al2O3 inclusions when the inclusion area was within a certain range.

Abstract:The phase transformation temperature, microstructure of 10%Co-WC cemented carbide, pure Co powder were analyzed using in situ X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscope(TEM) in the paper. The results showed that, shearing martensite phase transformation was the main type in Co, the crystal orientation relationship was {111}_α//{0002}_β,<110>_α//<110>_β. and lamellar structure was formed as the stacking fault induced at the {0002} crystal plane during phase transformation. Compared with powder, the A_s and A_f were up about 80℃,the supercooling degree was increased as the slipping drag strengthened as the W and C atoms solid solution and precipitation.

Abstract:The effect of hatching distance (h) on the microstructure, dynamic recrystallization (DRX) behavior, texture evolution and mechanical properties of Inconel 738 alloy formed by selective laser melting (SLM) were systematically investigated by electron backscatter diffraction (EBSD) technique. The results show that the aspect ratio of the elonged columnar grains parallel to the build direction decreases and the grainsmorphology changes from coarse elonged columnar grains to fine equiaxed grains, with the increase of h. And leading to orientation of the grains becomes more random. With the increase of h, the dynamic recrystallization volume fraction increases, and the dislocation density and strain in the recrystallized region are lower than those in the unrecrystallized region. With the increase of h, the type of casting texture changes, the texture is mainly transformed from Rotated-Goss texture {110}<110> to Rotated-Goss texture {110}<110> + Cube texture {001}<100>, and the intensity of Cube texture gradually increases, while the intensity of the Rotated-Goss texture is gradually weaken. Excellent room temperature mechanical properties (σ_y=933 MPa, σ_uts=1209 MPa, ε_f=38%) of the as-deposited Inconel 738 alloy used appropriate hatching distance (h=70 μm) can be obtained, thereby achieving good match of strength and ductility.

Abstract:BaTa(O,N)3 nano-powder was fabricated within minutes with urea as nitrogen source and pressure-less spark plasma sintering technique as a calcination tool. The effects of urea content, heating rate, synthesis temperature and dwell time on the purity of the products were studied and optimized. Experimental results show that excessive urea and proper synthesis temperature benefit the synthesis reaction. The purity of BaTa(O,N)3 powder can be significantly improved by applying a higher heating rate and an intermediate dwell time. Based on the processing optimization of 8 times molar(urea content), 300℃/min(heating rate), 1000℃(synthesis temperature) and 0~1min(dwell time), the obtained BaTa(O,N)3 powder possesses an average particle size of 50~150nm, a uniform Ba/Ta/O/N element as well as a good purity.

Abstract:Mg-Zn-Ca alloys are expected to become a new generation of internal fixation materials because of their high specific strength and excellent degradability. However, the relatively poor bio-corrosion resistance of magnesium alloys limits its clinical application. The microstructure, physical structure and element distribution of the Mg67Zn28Ca5 alloy modified by laser melting treatment were studied. The bio-corrosion performance of that in simulated body fluid was also investigated. The results show that a melted layer with an average thickness of about 508 μm was formed on the surface of the alloy after laser surface melting treatment of Mg67Zn28Ca5 alloy; the average grain size of the melted layer is about 10 μm. Compared with the as-cast and solid-solution alloys, the corrosion potential of the melted layer in the simulated body fluid was positively shifted by 76 mV and 60 mV, respectively; and the corrosion rate of the melted layer is 0.0468 mm/a, which is reduced by 82% and 78%, respectively. The oxide film on the surface of the alloy was denser, which improves the corrosion resistance of magnesium alloy at the early stage. With the decrease of MgZn2 content and the size of the second phase, the degree of galvanic corrosion was reduced and the corrosion of α-Mg matrix phase was inhibited.

Abstract:In this work, to study the effect of Y on the high temperature oxidation resistance of alloy, different doses of rare earth Y were implanted on the surface of alloy by means of ion implantation. The characteristics of oxide scales were investigated by scanning electron microscopy (SEM), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) methods. The oxidation process was observed in situ by VL200DX ultra high temperature confocal laser scanning microscope. The results show that the weight gain per unit area and the amount of spalling of Y-implanted samples reduced by 39.4% and 77.8% respectively, compared with the un-implanted Y samples. Y irons on the alloy surface were oxidized to Y2O3 preferentially, which promotes the formation of oxide film and inhibits the grain growth. In addition, Y2O3 at the grain boundary hinders the diffusion of metal cations through the grain boundary. Importantly, Y substituted for Mn2+and Cr3+ in MnCr2O4 spine, resulting in the information of vacancy defect. It relieve the internal stress of oxide layer and reduce the generation of cracks and holes that make oxide layer bond with the matrix closely.

Abstract:The hot compression experiment of 6061 aluminum alloy was carried out by using Gleeble-3500 thermal simulator. The hot deformation and dynamic recrystallization behavior of the studied alloy at a deformation temperature of 340℃-490℃ and a strain rate of 0.001s-1-1s-1 by metallographic microscope and transmission electron microscope to study. The results show that the dynamic recrystallization behavior of the studied alloy is very sensitive to deformation temperature and strain rate. The increase of temperature and the decrease of strain rate will promote the occurrence of dynamic recrystallization. Based on the peak stress, the constitutive equation is established, and the thermal deformation activation energy is calculated to be 235.155kJ·mol-1. The work hardening rate and flow stress curve is used to determine the relationship model between the critical stress (strain), peak stress (strain) and the Z parameter during the hot deformation process. As the temperature increases and the strain rate decreases, the critical stress (strain) and peak stress (strain) of DRX decrease. According to the Avrami equation, the dynamic recrystallization volume fraction model of the studied alloy is established. With the increase of strain, the dynamic recrystallization volume fraction first slowly increases, then rapidly increases and then slowly increases. The dynamic recrystallization volume fraction model can predict the dynamic recrystallization behavior of the studied alloy more accurately.

Abstract:Using graphene as the carrier and ethylene glycol as the reducing agent, an oil bath method was used to synthesize a Pt(100) crystal face preferential orientation catalyst by adding different additives as shape directing agents, and the performance of the catalyst was discussed. Use X-ray diffractometer (XRD), transmission electron microscope (TEM), inductively coupled plasma atomic emission spectrometry (ICP-AES) and scanning electron microscope (SEM) to microscopically characterize the synthesized catalyst, and use electrochemical workstation to analyze the synthesized catalyst Conduct electrochemical performance tests. The results show that the Pt(100) crystal plane orientation catalyst added with KBr has the most regular cubic morphology and the most complete formation. At the same time, its electrocatalytic performance is the best. The electrochemically active surface area is 42.43m2/g, the peak current density for ethanol oxidation is 417.67A/g, and the steady-state current density value for 1100s is 149.50A/g, which is catalytic oxidation reaction for ethanol. The activation energy is the lowest, and the retention rate of the peak current density of ethanol oxidation is 82.26%.

Abstract:After solving the material model, geometric model, mesh generation and other key technical problems in the FE model of GH5188 sheet with densely holes, the 3D FE model of asymmetric three - roll bending of the sheet with densely holes was established. The simulation results of the FE model agree well with the experimental results, and the model is reliable. And then, a representation method for the deformation of the holes on the sheet with densely holes is proposed. The deformation rule of the holes on the sheet with densely holes is analyzed. The results show that the expansion of the outside face is slightly greater than the compression of the inside face after the hole bend, and the deformation of the holes fluctuates slightly and increases slightly during the rolling process.The deformation difference of the holes along the same axis direction of the forming part is teeny.The deformation of the holes along the same circumference direction of the forming part fluctuates, but the difference is very small.

Abstract:The technology of laser deposited repair was used to repair TA15 alloy forgings,and the fracture toughness of substrate,shaped component,body-repaired sample and surface-repaired sample were investigated. Microstructure, fracture surface and longitudinal section morphology of sample were examined by OM and SEM.The results show that the substrate presents duplex microstructure, the repaired zone presents basket weave, and the heat-affected zone shows continuous microstructure transition from duplex microstructure to basket weave.The fracture toughness of shaped component,body-repaired sample and surface-repaired sample are lower than that of substrate, which are 76.4%, 81.0% and 83.1% of substrate respectively.The fracture toughness increases with the increase of the yield difference. When the increase of the yield difference is the same, the fracture toughness of repaired samples increases more significantly than that of substrate, and the increase of the shaped component is the most significant.The cracks expand in a straight line inside the cluste. When the α lamellar cluster with different orientations is encountered, the crack deflects and propagates along the boundary of α lamellar cluster. The smaller the cluster size is, the more serious the deflection is.

Abstract:The quasi-static tensile behavior and mechanism of TA2 pure titanium with three grain sizes of 41 μm, 63 μm, and 323 μm has been studied using OM, SEM, EBSD, etc. The results show that the coarsening of the grains results in a higher uniform deformability of TA2. The reason is that the larger the grain size, the stronger the twinning activity during deformation. The twin boundaries divide the grains and reduce the effective sliding distance and hinder the movement of dislocations, so it has a positive effect on the strain hardening rate of the material. When the grain size increases from 41 μm to about 323 μm, the strain hardening rate curve changes from a continuous decreasing trend to a three-stage change trend of decreasing-increasing-decreasing. The high strain hardening rate induced by twins in the coarse grains is the root cause of TA2"s high uniform deformability.

Abstract:The isothermal constant strain rate compression test of the Laves phase NbCr₂/Nb dual-phase alloy prepared by mechanical alloying and hot pressing was investigated in the temperature range of 800~1200℃ and the strain rate range of 0.001~0.1s^_-1 by a Gleeble3500 thermal simulation tester. The flow stress behavior and the constitutive relations based on the hyperbolic sinusoidal function Arrhenius equation and the stepwise regression method were studied. The results show that the ductile to brittleness transition temperature (DBTT) of Laves NbCr₂/Nb dual-phase alloy is about 950~1000℃. The alloy breaks into pieces directly without yield below 950℃. While, it shows good plastic deformation ability above 1000℃. The flow stress of the alloy decreases with the increase of deformation temperature and the decrease of strain rate. It is characterized by steady-state flow under the deformation conditions of 1050~1200℃/0.001s^_-1 and 1150~1200℃/0.01s^_-1. While, it shows the flow softening under the deformation conditions of 1000℃/0.001s^_-1, 1000~1100℃/0.01s^_-1 and 1000~1200℃/0.1s^_-1. The AARE of the peak flow stress constitutive relation and the strain-compensated constitutive relation, which are established based on hyperbolic sinusoidal function Arrhenius equation, is 9.89% and 13.859%, respectively. The AARE of the constitutive relation under all experimental conditions, the steady-state flow stress curve constitutive relation and the softening flow stress curve constitutive relation, which are established based on stepwise regression method, is 8.63%, 5.28% and 6.83%, respectively. The established constitutive relation can provide theoretical guidance and basic data for forging process design, forging equipment tonnage selection and forging process finite element numerical simulation of the Laves phase NbCr₂/Nb dual-phase alloy.

Abstract:In present work, a non-isothermal simulated hot compression test is designed to investigate the effect of final forging temperature on hot deformation behavior of GH4738 superalloy. Microstructure observation is carried out to explore the effect of final forging temperature on homogeneity of microstructure and microstructure heredity in following heat treatment process. The results show that in the condition of same initial forging temperature, the dynamic recrystallization of GH4738 superalloy will be inhibited when the final forging temperature is too low. The fraction of dynamic recrystallization is relatively low and the flow stress keeps increasing during hot compression. The less developed dynamic recrystallization microstructure tends to develop into mischcrystal structure in the following heat treatment process and can influence the homogeneity of microstructure. Hence, the final forging temperature should be rational controlled to improve the microstructure homogeneity of forgings during hot deformation.

Abstract:The new Ti-6Al-4V-0.5Ni-0.05Ru titanium alloy was designed for oil country tubular goods (OCTG) in the rigorous oil gas exploration environment of China. However, the hot working technology and heat treatment of this new titanium alloy are unclear. The effect of hot rolling process and heat treatment on microstructure and tensile properties of Ti-6Al-4V-0.5Ni-0.05Ru Titanium alloy were investigated by using optical microscopy, mechanical performance test, electron backscatter diffraction (EBSD) analysis and transmission electron microscope (TEM) observation in this paper. The results showed that the hot rolled plate had good deformation ability after 80% deformation rolling in α+β two-phase zone (940℃) andβphase zone (1000℃), no macroscopic cracks were obseved. After hot rolling inα+βphase zone, the single annealing treatment homogenizes the microstructure to a certain extent, but the grain size is still large, and the longitudinal and transverse microstructure of the rolled plate is still quite different. After hot rolling in theβphase, the microstructure is smaller and uniform distribution than that of 940℃ hot rolling, and the morphology of the longitudinal and transverse microstructure is basically the same.With the increase of single annealing temperature, the tensile strength of hot rolled plate decreased and the impact energy increased, when using double annealing treatment, the strength can be improved but the toughness of the plate is reduced.In the same heat treatment process, a good match of strength and toughness can be obtained by increasing the hot rolling temperature.

Abstract:The microstructural evolution including γ′ phase, carbide and Topologically Close-Packed (TCP) Phase of GTD111 and designed alloy WZ-D2 has been researched in directional solidification condition, heat treatment condition and ruptured at 980 ℃/190 MPa condition. The effects of these microstructural evolution on stress rupture property have also been studied. The size and volume fractions of eutectic phase in WZ-D2 are both significantly less than that in GTD111. The γ′ phase area fraction of WZ-D2 is apparently more than that of GTD111 after heat treatment, and the γ′ phase cubic degree of WZ-D2 is slightly higher than GTD111. The morphology of MC carbides in GTD111 is mostly presented as Chinese characters and is more unstable. The stress rupture lives of GTD111are obviously shorter than that of WZ-D2 when the work temperature is above 900 ℃, which is closely related to the difference in quantity and size of eutectic phase, the morphology and decomposition of MC carbide, and the evolution of γ′ phase in the two alloys.

Abstract:Surface mechanical attrition treatment (SMAT) was conducted on a Mg-Gd-Y alloy to obtain a gradient structure. Vickers micro-hardness tests and transmission electron microscopy were employed to study the age hardening behavior and the mechanisms. The gradient structure in the SMATed alloy can be classified into three layers: the severely deformed layer, the moderately deformed layer and the undeformed layer. The different layers exhibited distinct age hardening behaviors when aged at 225°C. The aging times for peak hardness increased in the order of the severely deformed layer, the moderately deformed layer and the undeformed layer; however, the hardness increments at the peak aging times decreased in the same order. This was attributed to the different distributions of the precipitates and their variable interactions with dislocations in the different layers. The severely deformed layer exhibited the shortest aging time and the highest value for peak hardness, which indicated that the surface nanocrystallization had remarkable effect on promoting age hardening for the Mg-Gd-Y alloy.

Abstract:In order to develop a new type of amorphous alloy whose composition is far away from the eutectic point of Cu56Zr44 and explore a piston material used biomass fuel new energy vehicle. In this paper, (Cu56Zr44)1-xYx (x=0, 1, 3 and 9 at.%) samples were prepared by the single-roller rapid quenching, the phases, thermodynamic parameters and nano-hardness of the samples were checked, as well as the tribological properties of the samples under ethanol-gasoline diluted engine oil were measured. The results showed: (Cu56Zr44)1-xYx samples are completely composed of amorphous structure, with Y content increasing from 1 at.% to 9 at.%, the ΔTx and Trg of the (Cu56Zr44)1-xYx amorphous sample decreases from 61K to 51K and 0.670 to 0.658, but are still higher than 49K and 0.644 of Cu56Zr44 amorphous sample, i.e., the glass forming ability (GFA) and thermal stability of Cu56Zr44-based alloy are enhanced by Y doping. With Y content increasing from 1at.% to 9at.%, the nano-hardness of (Cu56Zr44)1-xYx amorphous sample decreases from 8.83GPa to 7.33GPa (higher than 6.82GPa of Cu56Zr44). The friction coefficient and wear rate at 10N and 20N loads increase (lower than the ones of Cu56Zr44), i.e., the mechanical and tribological properties of Cu56Zr44-based alloy are significantly improved by Y doping. At the same experimental conditions, the friction coefficient and wear rate of (Cu56Zr44)1-xYx amorphous samples are lower than those of ZL109 Al alloy. The highest reduction of wear rates are as high as 98.62% and 97.79% at the two loads, namely (Cu56Zr44)1-xYx amorphous alloy possesses very excellent anti-wear performance than ZL109 Al alloy under ethanol-gasoline dilution engine oil lubricantion, which also provides a certain theoretical and experimental guidance for the research and development of a new piston material used in biomass fuel-fueled new energy automobile.

Abstract:The Fe-15Mn-5Si-14Cr-0.2C amorphous matrix composite rod sample was prepared from industrial raw materials by the coating agent (CaO-Fe₂O₃-SiO₂), and the rare earth elements Ce, Dy and Ce+Dy were added, and the rare earths were studied by XRD ;the influence of elements on the microstructure; the electrochemical workstation three-electrode system was used to test the corrosion behavior of the sample in 1mol/L HCl and 1mol/L NaOH. The results show that the alloy with rare earth elements is still amorphous composite material (undercooled austenite phase CFe_15.1 + ferrite phase Fe-Cr), and the sample with 1% Ce is resistant to corrosion in HCl and NaOH .The self-corrosion potential in HCl is -0.16205V, the self-corrosion current density is 7.699×108A?cm^_-2, and the polarization resistance reaches 9.5774×108Ω?cm^₂. In NaOH the self-corrosion potential and self-corrosion current density is -0.1839V, 1.7453×10^_-8A?cm^_-2, and the polarization resistance value is 7.1574×10^₈Ω?cm2. The corrosion resistance is much better than 304 stainless steel. It is a corrosion-resistant material with great potential.

Abstract:A new type of high strength and tough powder titanium alloy for Marine use was prepared by hot isostatic pressing (HIP) near net forming process using pre-alloyed powder. The interface reaction between titanium alloy and low carbon steel cladding was studied. Results show that there is a wavy interface between titanium alloy and low carbon steel capsule and the thickness of interfacial reaction layer is 8 microns. Alloying elements Al, Mo and V in titanium alloy diffused into low carbon steel to a certain extent, while matrix elements Ti and Fe of the two materials diffused significantly less than the former. After selective chemical washing, The capsule was removed, and the thickness of interfacial reaction layer was reduced by 2.5μm, but the interface was still wavy. Subsequent sand blast could not only reduce the thickness of the interfacial reaction layer but also make the interface flat.

Abstract:Due to the intriguing intrinsic mechanical and functional properties, graphene has attracted extensive attention in the metal matrix composites as a novel ideal inforcement. In this work, the preparation methods of graphene reinforced Cu matrix composites are firstly reviewed, then the research status of improving the graphene dispersivity along with the interface bonding between graphene and copper matrix is summerized. At last, the potential applications and future research directions of graphene reinforced copper matrix composites are pointed out.

Abstract:This paper describes the application advantages of titanium alloy in aviation engine and the problems of "titanium fire", and introduces the solutions to "titanium fire", such as flame retardant titanium alloy, flame retardant coating and flame retardant abrasion coating.The research status of flame-retardant and wearability coatings, including the evaluation criteria of their flame-retardant and wearability, and the mechanism research of flame-retardant and wearability coatings were emphatically introduced.Finally the research trend and development direction of flame-retardant and wearability coatings for titanium alloys in the range of 600-750℃ in the future were pointed out.

Abstract:On account of their excellent adaptability of mechanical properties with hard tissue bone, biocompatibility and biodegradability, magnesium and its alloys are considered as a new type of surgical metal-based implant material with the most potential application, however, its rapid degradation rate limits its rapid application and popularization. Hydroxyapatite(HA) has an excellent bioactivity, it can enhance the corrosion resistance and bioactivity of magnesium alloys, and decrease the degradation of magnesium alloys when fabricated as a coating on magnesium alloys. Nevertheless, pure HA coating still exist some problems of brittleness, insufficient toughness and poor adhesion between coating and magnesium alloy surface, therefore, to explore a HA composite coating on magnesium alloys is of great scientific and practical value. This paper reviews the development of HA composite coating on magnesium alloy and its application in bone repair in recent years, and forecasts the development trend of HA composite coating on magnesium alloys.

Abstract:Selective laser melting (SLM) 3D printing technology is a rapid development of metal additive manufacturing technology in recent years. Because of its designability, rapid net forming of complex components, high surface quality and other advantages, it has a wide range of application prospects. Titanium matrix composites based on SLM technology can usually obtain nano ceramic reinforcing phase, which has better performance than titanium alloy, and the mechanical properties of formed components are better than that of castings and forgings. In this paper, the development status of titanium matrix composite based on SLM technology at home and abroad in recent years is reviewed, the selection of ceramic reinforcements is used as an entry point to describe its typical microstructure characteristics and evolution laws, it also discusses its properties and analyzes its unique strengthening mechanism. And on this basis, the key academic problems need to be solved and development direction in the future are prospected.

Abstract:As a kind of strategic nuclear materials, uranium plays an important role in the human story. In the demand of nuclear industry, the forming and manufacturing technology of uranium and its alloy parts is also developing. This paper reviews the development of uranium material preparation and uranium parts processing technology from the view of engineering, specifically introduces the uranium alloy preparation and uranium material purification technology, and mainly describes the manufacturing methods of uranium parts from two aspects of plastic forming and casting forming. In view of the particularity of uranium products manufacturing, it points out that the technology facing future will pay more attention to safety, environmental protection and intelligence.