Abstract:Under high temperature conditions, the crystal WS₂ is easily oxidized to WO₃, which has a great impact on the tribological properties of WS₂ solid lubrication films. In order to improve the tribological properties of WS₂ solid lubricating films at high temperatures, the co-doped La-Ti/WS₂ composite films were prepared by unbalanced magnetron sputtering. The effects of target power on the structure and tribological properties of La-Ti/WS₂ composite films were studied. The micromorphology, composition, mechanical properties and microstructure of the films were analyzed by scanning electron microscopy (SEM), X-ray diffraction (XRD), nano indentation and X-ray photoelectron spectroscopy (XPS). The high temperature tribological properties of composite films were researched by high temperature friction tester. The results show that La-Ti/WS₂ composite films show excellent tribological properties when the target power is 20 W at high temperature. At this time, the H/E value of the composite film is the largest, the friction coefficient is the smallest with the average value of 0.012, and the wear rate is the lowest, which is 1.56×10^-8 mm³/N·m. This is mainly due to the production of rare earth oxides at the friction interface at high temperatures, which change the friction and wear mechanism of La-Ti/WS₂ composite film, so that WS₂ still has excellent tribological properties when it is damaged at high temperature, further expanding the scope of engineering application of WS₂ composite films.

Abstract:The effect of Cr addition on the corrosion resistance of the laser-cladding Ni-Cr-Mo coatings was evaluated in chloride solution with thiosulfate by microstructure observation and electrochemical measurements. Results show that very similar microstructures and phase compositions are tested by scanning electron microscope and X-ray diffraction. Both eutectic and dendrite structures are observed, and the coatings are mainly composed of the γ-Ni solid solution of Cr, Mo, W, Fe, and Cr0.19Fe0.7Ni0.11 solid solution. The electrochemical results confirm that the laser-cladding coating with the special Cr addition behaves better corrosion resistance. The coating C28 performs higher values in open circuit potential and lower passive current density, especially the larger modulus of the impedance and charger transfer resistance. With increasing Cr content, the passive film is much thicker and the defects of the films are less in chloride solution with thiosulfate. The Mott-Schottky reveals that the passive film formed on the top surface of the laser-cladding coatings in solution behaves as n-type and p-type semiconductors.

Abstract:To improve the high-temperature oxidation resistance performance of Nb-Hf alloys, Si-Ti-Cr silicide coatings were prepared on Nb-Hf alloy by slurry sintering and high-temperature permeation methods. The high-temperature oxidation resistance performance of Si-Ti-Cr silicide coating on Nb-Hf alloys in high-temperature constant oxidation and high-temperature thermal shock was analyzed, and the failure mechanism of Si-Ti-Cr coating in high-temperature constant oxidation and high-temperature thermal shock was determined. The results show that the mass gain of the coating is 7 mg/cm² after constant oxidation at 1800 °C for 5 h. The mass gain of the coating in atmosphere is less than 1.8 mg/cm² after thermal shock cycles for 50 cycles followed by constant oxidation at 1700 °C for 5 h. Therefore, the silicide coating exhibits excellent oxidation resistance at 1800 °C in constant oxidation and at 1700 °C in thermal shock/constant oxidation.

Abstract:In order to study the influence of Cu element on the corrosion resistance of directional structure coating of Ni-based alloy, 5%Cu element was added to Ni60 alloy powder, and the directional structure Ni60/Cu composite coating was prepared. The electrochemical corrosion properties and immersion corrosion properties of the coatings in different concentrations of H₂SO₄ solutions were evaluated by electrochemical tests and immersion tests, and the corrosion behavior of the coatings in different concentrations of H₂SO₄ solutions was discussed. The results showed that the corrosion of the coatings in different concentrations of H₂SO₄ solution shows the process of activation -passivation-overpassivation, and the electrochemical impedance spectroscopy has typical capacitive reactance characteristics in the whole time constant. The charge transfer resistance decreased firstly and then increased, and the corrosion resistance of the coating showed a trend of first decreasing and then increasing when the concentration increased from 5% to 80%. With the increase of H₂SO₄ concentration, the corrosion degree of the coating surface first intensified and then gradually slowed down, and the corrosion potential shifted to the most negative and the corrosion current density increased to the maximum when the concentration of H₂SO₄ solution was 40%. However, the surface of the coating is accompanied by the formation of a dense and uniform corrosion reaction passivation film mainly composed of NiO, Cr₂O₃ and Cu₂O when the concentration of H₂SO₄ solution reaches 80%. These reactive passivation films effectively prevent the H₂SO₄ solution on the coating surface, making the coating exhibit good corrosion resistance in high concentrations of acid.

Abstract:Supersonic laser deposition is an innovative surface treatment technology, which combines supersonic cold spray technology and laser irradiation heating technology. It has the advantages of preparing hard metal composite coating with high deposition efficiency. In this paper, composite coatings of hard 7075 Al alloy and Al2O3 ceramic particles were prepared on 7B04 Al alloy substrate by supersonic laser deposition technology. The effect of laser power on the deposition characteristics and mechanical properties of coatings was systematically studied. The microstructure, phase composition and microhardness of the coating were characterized and analyzed by field emission electron microscope (SEM), energy dispersive analyzer (EDS), X-ray diffractometer (XRD) and microhardness tester. The results showed that with the increase of laser power, the thickness, density, deposition efficiency, and the dispersion uniformity & deposited amount of Al2O3 particles in the coating were increased. When the laser power was 600W, the coating thickness reaches to 1543μm, the coating porosity is only 0.05%, the relative deposition efficiency of Al2O3 particles is 65%, and the coating hardness rises to 195HV. However, when the laser power was enhanced to 900W, the thickness and deposition efficiency of the coating slowed down, and the porosity increased significantly. The oxidation of coating materials was found, and the relative deposition efficiency of Al2O3 particles and the coating hardness decreased significantly. In summary, the appropriate amount of laser input is beneficial to improve the plastic deformation of aluminum alloy particles, resulting in significant enhancement of coating quality, while the excessive laser input leads to softening of aluminum alloy particles and even oxidation of powder materials, which deteriorate the quality of deposited coatings.

Abstract:In view of the high photonic thermal conductivity of thermal barrier coatings, a Gd-doped YSZ-NiCr₂O₄ composite (GYSZ-NCO) was designed, and its sintering parameters, thermal stability and thermal conductivity were analyzed. The results show that tetragonal GYSZ can be obtained when the sintering temperature is 1600 ℃, and the GYSZ-NCO series materials have high thermal stability at 1500 ℃, and no phase transition occurs after holding for 300 h. After adding NiCr₂O₄, the thermal conductivity of GYSZ did not rebound significantly at high temperature, showing excellent thermal conductivity against photons. The thermal conductivity of the GYSZ-5%NCO material has the lowest thermal conductivity, which is only 2.23 W/(m.K) at 1200 °C.

Abstract:The FeCrNiCoMoCuBSi high-entropy alloy coating was prepared on the surface of 316L stainless by laser cladding technology. The microstructure, hardness, wear, electrochemical and tribocorrosion properties of the coating were studied. The results show that the cladded coating is well formed with no defects such as cracks and pores on the surface. The cladded coating is mainly composed of FCC solid solution phase, the microstructure is dominated by “wicker-like” dendrites, and the bonding area is planar crystals, which have a good metallurgical bond with the 316L stainless. The average hardness of the coating is 700 HV_0.2, which is about 3.5 times that of the substrate. The cladded coating shows significantly better wear resistance than the substrate under different loads with the lower friction coefficient and the less wear amount. In 3.5wt% NaCl solution, the self-corrosion current density of the coating is 4.74 × 10^_-8A.cm^_-2, which is two orders of magnitude lower than that of the substrate, showing excellent corrosion resistance. Under the coupling effect of friction load and corrosion, the open circuit potential of the coating shifted negatively and the corrosion tendency increased. With the increase of friction load, the free-corrosion potential moves negatively, the free-corrosion current density increases, and the effect of friction promoting corrosion increases.

Abstract:A FeCrCoNiNb high entropy alloy (HEA) coating was deposited by laser cladding, aiming at studying the influence of Nb addition on hardness and wear resistance. The formed phases, microstructural evolution, nano-hardness and wear behavior of the FeCrCoNiNb HEA coating was clarified by using XRD, SEM, nano-hardness measurement and friction-wear measurement. The results showed that the FeCrCoNiNb high-entropy alloy coating were composed by FCC solid solution and Nb-Laves phase. The nano-hardness (H), elastic modulus (H), H/E and H3/E2 of FeCrCoNiNb coating were 6.066GPa, 231.54GPa, 0.0262 and 0.0042, respectively. Which were much higher than FeCrCoNi coating of 3.456GPa, 209.48GPa, 0.0165 and 0.00094. With the increased of nano-hardness, the friction coefficient and specific wear rate of FeCrCoNiNb coating also decreased, which were 0.519 and 2.54×10-6mm3/N.m, respectively. The addition of Nb can effectively improve the nano-hardness and wear resistance of FeCrCoNi high-entropy alloy coating.

Abstract:The effects of different strain rates and cathodic protection potential on the stress corrosion cracking (SCC) behavior of new-developed 1200 MPa Ti-35421 (Ti-3Al-5Mo-4Cr-2Zr-1Fe) alloy have been investigated by using slow strain rate test combined with in-situ electrochemical monitoring. The results indicate that Ti-35421 alloy has the highest SCC susceptibility in 3.5% NaCl solution at the strain rate of 1.67×10-5 mm s-1. The plastic loss and stress corrosion index of Ti-35421 alloy are confirmed to be 27.27% and 0.273, respectively. The passivating ability of the passivation films in the crack tips is considered to be weaker than active dissolution under the combined interaction of applied stress and corrosive media especially with strain rate of 1.67×10-5 mm s-1, which results in the intensification of SCC. When the cathodic protection potential is set at -600 mV, the SCC susceptibility of Ti-35421 alloy in 3.5% NaCl solution is the lowest. The range of the optimal cathodic protection potential is measured to be from -450 to -600 mV. The reduction of the plastic loss and stress corrosion index of Ti-35421 alloy down to 1.01% and 0.113 is ascribed to the slower conjugated anodic reaction kinetics under the cathodic protection.

Abstract:The thermal conductivity and expansion properties of materials are important factors affecting their application. The effects of W, B addition on the thermo-physical properties such as thermal diffusion rate, thermal conductivity and thermal expansion of Ti-42Al-5Mn alloy (at.%, the same below) with low cost and good hotworkability were systematically studied. The results show that, with the increase of W content to 1.0 at.%, the thermal diffusivity of the alloy decreases slightly, on the contrary, after the B content increases to 0.3 at.%,that of the alloy increases slightly. The promotion of βo phase in microstructure by W addition is the main reason for decreasing the thermal conductivity of the alloy. It is observed that these phases in β-solidifying γ-TiAl alloys are followed by γ, α2, and βo in deceasing order of thermal conductivity. On the other hand, B improving the thermal conductivity of the alloy might be related to the B-containing precipitates in the alloy. W addition (0.5~1.0 at.%) has little effect on the average linear expansion coefficient of Ti-42Al-5Mn alloy. In the range of 100 ~ 300 ℃, with W content increase to 1.0 at.%, the average linear expansion coefficient of the alloy decreases slightly, on the contrary, the influence decreases gradually at higher temperature. The thermal expansion coefficient of TiAl alloy is equivalent to that of cast iron, and lower than that of steel, nickel base superalloy and other materials. It would have certain application value in components requiring very low thermal expansion coefficient such as piston.

Abstract:The microstructure and texture evolution of the center of the adiabatic shear band (ASB), transition region and substrate of the dual-phase TB6 titanium alloy under detonation loading at ultra-high strain rates were investigated by electron backscatter diffraction (EBSD). The results show that the grain size of α and β phases decreases after detonation. The α phase produces {102} twins. The β phase grains in the central region of ASB undergo dynamic recrystallization, the grain size is 400 nm, most of them are high-angle grain boundaries, and the dislocation density is reduced. The α→β phase transition occurs in the ASB center. {100}⊥AD, <0001>//RD or ND, {100}<110> rotating cubes are present in all α or β phases except the detonation matrix; {100}<0001>, {100}<110> texture exists in the α phase of the original structure, and there are {100}<0001>, {100}<110>, {110}<0001> three textures in the transition region, {100}<001> pseudo cubic texture exists only in the β phase of the detonation matrix. {100}//SD is a common feature of ASB organization, <0001>//AD texture exists in the detonation matrix, {110}//SD, <0001>//SD texture exists in the ASB center. The {110} plane, <0001> orientation of α phase and the {110} plane of β phase are parallel to ASB direction, which are not belong to close-packed planes and dense-packed directions, which are not conducive to the alloy"s mechanical properties.

Abstract:The effects of compressive stresses on the breakdown and self-healing of the surface passivation films on Ti-35421 (Ti-3Al-5Mo-4Cr-2Zr-1Fe) alloy after damaging by the Al2O3 ceramic needles have been investigated on a self-made scratching tester by using the in-situ electrochemical monitoring. The passivation potential of Ti-35421 alloy in 3.5% NaCl solution is determined to be -0.27~0.01 V. Without the compressive stress, the potential recovers to the initial leverl shortly. When the scratching experiments carry out under the passivation polarization of -0.13 V, the increase of compressive stress leads to the decrease of the atomic binding forces, the increase of metallic dissolution rates, and the slow down of repassivation rates. In-situ electrochemical data show that the potential drops and the currents rise, and the self-healing duration times become longer. The growth and sel-healing of the passive films in the transient stage basically conform to the linear high-field model. Observation of scratch morphology shows that the scratching generates the higher residual stresses at the bottom of the grooves. It is found that microcracks appear in the scratch grooves under the compressive stresses basing on the scratch morphology, indicating that the damages of the scratches under high compressive stresses are partialy unrecoverable, which results from the synergetic effects of the residual stresses and environmental corrosion.

Abstract:In this investigation, NiTi alloys were prepared by high-energy milling and spark plasma sintering (SPS) at 1000℃. The effects of the Ni content and sintering pressure on the density, microstructure, microhardness and tribological properties of NiTi alloys were also investigated. The experimental results showed that the particle sizes of the powders were decreased after high-energy ball milling, and the diffraction peaks of Ni phase were shifted to the high angle with the increase of nickel contents. As the sintering pressure increased, the relative densities of NiTi alloys were increased. At the sintering pressure of 5MPa, the relative densities of NiTi alloys were decreased from 94.7% to 84.6% with the increase of nickel contents. When the sintering pressure was higher than 5MPa, the relative densities of NiTi alloys were firstly increased and then decreased as nickel content increased. However, the lowest value of the relative density of NiTi alloys was happened at nickel content of 45 wt.%. NiTi phase, NiTi2 phase and Ni3Ti phase were presented in the microstructures of NiTi alloys. The microhardness of the alloy were firstly increased and then decreased as the nickel contents increased from 0 wt.% to 65 wt.%. The microhardness of the NiTi alloy has the biggest value at nickel content of 45 wt.%. The wear rates of NiTi alloys were reduced as the nickel content and sintering pressure increased and the wear resistance of the alloys were significantly improved. The wear mechanisms of NiTi alloys at room temperature were mainly abrasive wear and adhesive wear.

Abstract:Shape memory alloy (SMAs) springs have the ability to perform giant reversible strain, which is of great importance to the energy absorption buffer and vibration control applications. In this paper, the influence of structure design on the performance of NiTi SMAs springs is studied. Ti-52.5at.%Ni alloy wires with diameters of 1.2mm were prepared by cold drawing and subsequent annealing, and springs with spring index C of 6.0, 7.7, and 9.3 were prepared by mandrel wound molding and subsequent high temperature annealing, respectively. The energy absorption performances of the springs were studied by testing the superelastic curves of the alloy wires and springs. The results show that, based on the superelastic processes, the energy absorption capacity per unit volume of the three types of springs at room temperature (298K) is 4618, 2225 and 1143kJ/m3 at a maximum displacement amplitude of 120mm, respectively, where the spring with spring index C of 6.0 has the best energy absorption capacity. Furthermore, the energy absorption per unit volume of spring with spring index C of 6.0 reaches 6662kJ/m3 at 318K due to its full austenite state, which is 192 times higher than that of the alloy wire (34.7kJ/m3) under the same load (47N), meaning that under same condition, the spring structure has better energy absorption capacity than that of the alloy wire. Therefore, superelastic SMAs springs may show great potential in the future application of damping structures.

Abstract:xTiC/FeMnCu(x=2.5, 5, 7.5, 10, vol%) composites were fabricated by vacuum induction melting and then annealed. X-ray diffraction (XRD), scanning electron microscope (SEM) and energy dispersive spectrum (EDS) were used to analyze the phase constitution and microstructure, and the tensile properties of the samples were investigated by the universal tensile testing machine. The results show that the xTiC/FeMnCu(x=2.5, 5, 7.5, 10, vol%) composites exhibit a biphasic face-centred cubic structure. With the increase in x value, the matrix structure of the composites is significantly refined and the tensile strength gradually increases, which is due to the combined effect of fine grain strengthening, thermal mismatch strengthening and Orowan strengthening. After 10TiC/FeMnCu is annealed at 600 °C for 4 h and 800 °C for 4 h, the structure does not change significantly, and carbides are precipitated in the matrix. The tensile strength of the sample increases but the elongation decreases slightly.

Abstract:A CoCrCuFeNi high-entropy alloy (HEA) was diffusion welded using a Co filler at 850, 950, 1050, and 1100 °C, and the microstructure and diffusion mechanism of the joints were examined. Results show that firm connections are achieved at each temperature, no intermetallic compound forms in the joints, and some Kirkendall voids are remained on the HEA side around the interface. The diffusion coefficients of Cr, Fe, Ni, and Cu in the Co filler at 850 and 950 °C are calculated, ranked as follows: Cu>Cr>Fe>Ni. The diffusion rates of all elements are at the same level. The diffusion between the CoCrCuFeNi HEA and Co filler occurs under the combined action of the vacancy and grain boundary diffusion mechanisms.

Abstract:A bcc-structured Ti₂ZrNbV (at%) high entropy alloy was prepared by vacuum arc melting. The stability of the solid solution phase was studied, and the improvement of tensile property via V₂Zr phase precipitation was investigated. The results show that the homogenous solid solution phase is stable above 900 °C, and Laves phase V₂Zr easily precipitates below this temperature. The instability of the solid solution phase can be used for enhancing the Ti₂ZrNbV alloy. After solid solution and aging treatment, the tensile yield strength of the alloy can reach 1145 MPa with a promising elongation of 8.3%.

Abstract:Five machine learning (ML) approaches, i.e. K-Nearest Neighbor (KNN), Support Vector Machine (SVM), Decision Tree (DT), Random Forest (RF) and Artificial Neural Network (ANN) were used to classify and to predict the combination of phases, i.e. solid solutions (SS) and mixed solid solution and intermetallic (SS+IM) in refractory high-entropy alloys (RHEAs). Five input characteristic phase predicting parameters and 139 RHEAs were selected to train these models. Results show that ANN model has the highest accuracy of 90.72%. Experimental results of 9 quaternary and (TiVTa)_xCr_1–x RHEAs verify the accuracy of prediction and indicate that RF and ANN can predict more accurately, successfully predicting 11 SS and 3 SS+IM. SHAP (SHapley Additive exPlanations) model was used to interpret the ANN model which exhibits the highest accuracy and to investigate the contribution of each feature to phase formation. The order of importance of five features is enthalpy of mixing (ΔH_mix), atomic size difference (δ), valence electron concentration (VEC), entropy of mixing (ΔS_mix), and electronegativity difference (Δχ), where the mean SHAP value of ΔH_mix is approximately 5 times higher than that of ?χ and 4 times higher than that of ΔS_mix. Less negative ΔH_mix, smaller δ and VEC may contribute to the formation of SS in RHEAs.

Abstract:Hot workability, microstructure evolution, and phase composition of dual-phase Mg-Li alloy were investigated via hot compression test at 250?400 °C with strain rates of 0.1?10 s^-1. The optimum hot workability window integrating processing and α-Mg content maps was established. Results show that the established Arrhenius constitutive model can accurately predict the stress flow behavior during work softening. In addition, the microstructure of the alloy shows that dynamic recovery (DRV), dynamic recrystallization (DRX) and α-Mg phase transformation are the main softening mechanisms. α-Mg phase is transformed into β-Li phase in forms of both spheroidization and internal precipitation of α-Mg phase, especially above 300 °C. Meanwhile, the DRX process can easily occur in β-Li phase, whereas in the α-Mg phase it is retarded. Based on the dynamic materials model and microstructure analysis, the optimal processing window can be obtained as 300?350 °C/0.1?1 s^-1 and 250 °C/0.1 s^-1.

Abstract:The relationship between the twin behavior, the evolution law of texture and the plastic anisotropy of AZ31 magnesium alloy during tensile deformation was studied by combining room temperature uniaxial tensile experiment with crystal plastic finite element through tensile orientation control. Based on the rate-dependent crystal plastic constitutive theory, a plastic constitutive model of crystals with different orientations coupled by slip and twin mechanisms was established, and the effect of twins on the structural evolution and mechanical properties of AZ31 magnesium alloy during plastic deformation was studied by introducing twin crystal integrals. Results show that the specimens with two different orientations show significantly different texture evolution laws during the plastic deformation process, and exhibit obvious anisotropy. When the specimen is axially stretched, the twin is suppressed, and the twin activation volume fraction is low. The twin crystal is easily generated when the specimen is radially stretched, and the twin activation volume fraction is high. The axial specimen has a small shift in the {0001} polar map throughout the plastic deformation process, and the radial specimen has a significant shift in the polar density of the {0001} prismatic surface texture gradually towards the positive and negative directions of RD due to the activation of a large number of tensile twins.

Abstract:The relationship of microstructure evolution with subzero treatment time and number of Inconel 617 alloy was studied. The results indicate that subzero treatment has an obvious influence on the microstructure of Inconel 617 alloy. With the increase in subzero treatment time, the grain size decreases. With the increase in subzero treatment number, the grain size increases gradually, and the high stress is retained at the boundaries of the refined grains. The lattice constant varies inversely with the grain size. The simple and complex carbides of MC, M₆C and M₂₃C₆ are precipitated from the samples after subzero treatment, which leads to the accumulation of dislocations. The geometrically necessary dislocation density of the samples increases after subzero treatment for 24 h, and decreases significantly with two times of subzero treatment for 24 h. In addition, after subzero treatment, the rotated cube texture and rotated copper texture transform to brass texture, P texture and goss texture.

Abstract:The wettability and interface microstructures of Al-8Si/stainless steel, Al-8Si/MgO, and Al-8Si/TiO₂ systems were investigated by a modified sessile drop method. The formation of interface products of three systems was discussed from the view of thermodynamics. Results show that the interface microstructure of Al-8Si/stainless steel is composed of Fe(Al,Si)₃, Al_7.2Fe_1.8Si and Fe₂Al₅ phases, while that of Al-8Si/MgO and Al-8Si/TiO₂ systems consists mainly of the Al₂O₃ phase with different morphologies and roughness. The wettability results indicate that the Al-8Si/MgO system exhibits a better non-wettability compared with the stainless steel and TiO₂ substrates, whose equilibrium wetting angle is 124°. The wettability differences of the three systems are mainly related to the roughness and properties of interface products. The interface roughness tests show that the interface of Al-8Si/MgO system has the largest roughness of 1.46 μm, which is mainly due to the evaporation of Mg that destroys the morphology of the interface reaction layer during the interface reaction process. Furthermore, the existence of Ti promotes the interface reaction and increases the thickness of interface reaction layer and thus reduces the equilibrium wetting angle of Al-8Si/TiO₂ system.

Abstract:Laminated metal composites (LMCs) of 1060Al/AlSn20Cu/1060Al/steel were fabricated by cold roll bonding, and the effects of rolling reductions on the microstructure and mechanical properties were characterized. The microstructure was observed by scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD), and the mechanical properties were examined by tensile tests. The initial rolling reduction was 17%, and the minimum stable rolling reduction was 40%. Results show that the increase in rolling reduction causes an elongation of the Sn phases in the AlSn20Cu layer and lengthening of grains in the steel layer along the rolling direction, whereas the 1060Al layers shows equiaxed grains. The tensile strength and interfacial bonding strength of the composite sheets increase while the elongation decreases with increasing rolling reduction. The fracture of the AlSn20Cu layer is related to the Sn phase.

Abstract:To improve its dimensional stability, the microstructure and residual stress of hot isostatically-pressed beryllium were regulated by low-temperature aging. Results show that after low-temperature aging, the dimensional shrinkages of hot isostatically-pressed beryllium, annealed beryllium, and thermal-cold cycled beryllium are evidently reduced. Various stabilizing mechanisms, including dislocation homogenization and coordinated grain micro-deformation, are observed during low-temperature aging, which effectively improve the dimensional stability of hot isostatically-pressed beryllium.

Abstract:The SPH-FEM coupling algorithm was applied to simulate four typical explosive composite combinations including titanium-steel, stainless steel-steel, copper-steel and titanium-aluminum. The ranges of strain rate applicable to the Johnson-Cook strength equation and the Steinberg-Guinan strength equation were analyzed theoretically. Besides, the effects of the thickness of the flyer plate and base plate, impact velocity and impact angle on the temperature, pressure and microstructure of the interface during explosive welding were investigated. The growth mechanism of the interface wave, vortex and a small amount of splashing molten blocks were explored through numerical simulation. Results show that the interface temperature, pressure and waveform size increase with the rise in flyer plate thickness and impact velocity, while the peak of interface pressure decreases with the increase in impact angle. The change in the thickness of the base plate cannot directly affect the temperature and pressure of the interface, where the material behaves as an incompressible liquid and reciprocates, producing sinusoidal waveforms, vortex, and splash molten blocks.

Abstract:Nanometer-sized zirconia (ZrO₂) powder was synthesized from ZrOCl₂·8H₂O through a hydrothermal method. The aqueous suspension stability of ZrO₂ powder was studied by zeta potential measurement and particle size analysis. Results show that ZrO₂ nanoparticles are ellipsoidal with uniform particle size, and the particle size is mainly in the range of 40–100 nm. The isoelectric point (IEP) occurs at pH=9.0. ZrO₂ particles are well dispersed far from IEP and severely agglomerated near IEP.

Abstract:Ti/IrO2+MnO2 composite electrodes were prepared by thermal decomposition. The kinetics of oxygen evolution reaction on Ti/IrO2+ MnO2 electrodes were studied deeply with quasi-stationary polarization curve recorded by slow linear potential sweep voltammetry. The related kinetics parameters, reaction process and rate determining steps were obtained. Tafel linear regions wih double slopes were explained well by analyzing the ohmic voltage drop corrected Tafel curves. Kinetics equations based on the proposed oxygen evolution reaction mechanism were deduced mathematically, which were in good agreement with the experimental results. The reaction order of hydrogen ion close to 0, the one of apparent activation energy of 30.31kJ/mol in the low potential region and the other of 13.64kJ/mol in the high potential region, further proved the correctness of above mathematical model.

Abstract:Based on the Johnson-Cook model and Gruneisen equation of state, a finite element analysis model was established, and the LS-DYNA software was used to carry out numerical simulation research on the penetration process of tungsten wire reinforced copper-zinc composite materials and tungsten-nickel-iron alloys into steel targets. The deformation of each stage in the tungsten wire is discussed, and the influence of the anisotropy of the tungsten wire on the penetration performance is discussed. The results show that the tungsten wire reinforced copper-zinc composite exhibits obvious self-sharpening phenomenon, which is consistent with the experimental results. During the penetration process, the stress is mainly concentrated on the axial tungsten wire, the stress value reaches 2.5GPa, and the stress of the brass is less than 0.47GPa. The deformation mode is as follows: tungsten wire bends after contracting the target plate. the forced direction of the tungsten wire has changed to a certain angle with the axial direction. The strength and plasticity of the composite are significantly reduced at this direction. With the destroy of deformation areas, a sharp head of the composite penetrator is formed, which shows the characteristics of self-sharpening.

Abstract:In this study, carbon aerogel (CA) substrates were prepared by using bacterial cellulose as template, then flexible W-O-C/CA and WC/CA composite electrode materials were prepared by impregnation and high temperature treatment. The effects of preparation process on the phase, morphology and electrocatalytic performance of methanol were investigated. With the increase of heat treatment temperature and the extension of holding time, the phase change occur as tungsten precursor→tungsten oxide (WO3, WO3-x, WO2)→W→WCx→WC. For the flexible electrode prepared at 700 ℃ for 2 h, the phases of the supported particles are oxygen-deficient tungsten oxide (WO3-x) ,WO2 and tungsten carbide (WC). The electrode has good electrocatalytic performance for methanol oxidation (peak current density of 76.5 mA cm-2 at 0.8 V) and long-term cycling stability, the peak current density remains 88% of the initial value after 1000 cycles. This flexible electrode is expected to be used in the anode of portable or micro methanol fuel cell.

Abstract:Zirconium alloys used as fuel claddings in water-cooled nuclear reactors generally serve in a harsh environment of high-temperature high-pressure water and strong neutron irradiation. Nb is known to play an important role in improving the corrosion resistance of zirconium alloys. Therefore, studying the microstructural changes and its effect on the corrosion behavior of zirconium alloys with different Nb contents before and after irradiation can provide a basis for the design of advanced zirconium alloys. In this work, Zr-0.75Sn-0.35Fe-0.15Cr-xNb (x=0, 1.0, wt%) alloys were prepared and irradiated with 2 MeV He_⁺ at 300 ℃. The effects of irradiation on the microstructure and corrosion behavior of the alloys were investigated by using scanning electron microscope and transmission electron microscope. The corrosion environment was 360℃/18.6 MPa/0.01 M LiOH aqueous solution. The results revealed that the number, average size and crystal structure of the second phase particles in Zr-0.75Sn-0.35Fe-0.15Cr-xNb alloys changed with the increase of Nb content prior to irradiation. After He_⁺ irradiation to 1 dpa, however, a large number of He bubbles and -type dislocation loops were induced in the radiation damage peak region in the alloys. To some extent, addition of Nb can affect the number of He bubbles and dislocation loops and elemental diffusion from the second phase particles. The corrosion results showed that He_⁺ irradiation or addition of 1.0wt% Nb could accelerate the corrosion of Zr-0.75Sn-0.35Fe-0.15Cr alloy, but the irradiation could reduce the acceleration effect of Nb on the corrosion of Zr-0.75Sn-0.35Fe-0.15Cr alloy.

Abstract:Carbon loaded PtNi alloy nanocatalysts (Pt2.7Ni/C) were prepared by liquid phase synthesis using platinum acetylacetonate (Pt(acac)₂) and nickel acetylacetonate (Ni(acac)2) as precursors, tri-n-octylphosphine oxide (TOPO) as surface modifier, oleylamine (OAm) as reducing agent, N,N-dimethylformamide (DMF) as auxiliary, and superconducting carbon kochen black ECP as carrier. The morphology of Pt2.7Ni/C was characterized by TEM, the qualitative and quantitative analysis by ICP-AES, the structural characterization by XRD, and the electrochemical cathodic oxygen reduction catalytic performance was further investigated. It was shown that the particle size of the prepared Pt2.7Ni/C nanocatalysts were in range of 3-11 nm with an average size of ~6.25 nm. The mass activity of Pt2.7Ni/C nanocatalysts was 796.08 mA.mg-1Pt (4.0 times as effective as the commercial Pt/C(JM) catalysts) and the specific activity was 3.60 mA.cm2(11.3 times as effective as the commercial Pt/C(JM) catalysts) under acidic conditions when the potential was at 0.9 V (vs. RHE). The catalytic activity of the Pt2.7Ni/C nanocatalysts remained higher than that of the commercial Pt/C(JM) catalysts after 5000 and 10000 turns of accelerated endurance experiments, showing excellent oxygen reduction catalytic performance of the Pt2.7Ni/C nanocatalysts.

Abstract:The laser manufactured high-performance GH4169 Ni-based alloys were generally prepared in a closed environment, resulting in limited component dimension and increased fabrication cost. In order to broaden the application of laser additive manufacturing and remanufacturing GH4169 alloy, this work was attempted under different atmospheres (Ar, N2) in atmospheric environment. The results indicat that the laser-repaired layer under Ar atmosphere is mainly composed of γ phase and long-chain shaped Laves phase, with a typical columnar crystal structure. The tensile strength, yield strength and elongation is 874 MPa, 621 MPa and 23.1 %, respectively. In contrast, due to its higher thermal conductivity and faster molten pool cooling rate under N2 atmosphere, the laser-repaired layer is mainly composed of γ phase, granular Laves phase with smaller size and volume fraction, and granular (Ti,Nb)N phase. The dendritic structure is refined, with tensile strength, yield strength and elongation of 935 MPa, 649 MPa and 24.9 %, respectively. Under the combined effects of fine grain strengthening and second-phase precipitation strengthening, the laser repairing of GH4169 alloy can be achieved successfully under N2 atmosphere at low cost and high efficiency.

Abstract:Laminar gas atomization technology based on Laval nozzle can efficiently prepare high-performance metal powders, but there is no systematic research on the process parameters and powder properties of this technology. In this paper, AlSi10Mg alloy powders were prepared by laminar gas atomization equipment based on Laval nozzle. At the same time, the effects of atomization gas pressure and tube inner diameter on the overall morphology, three-dimensional morphology, sphericity, particle size distribution, physical properties and internal defects of the powders were studied by traditional analysis methods and X-ray computed tomography technology. Combined with the numerical simulation of single-phase gas flow field and gas-liquid two-phase flow, the influence of process parameters on powder properties is explained. The results show that the performance of AlSi10Mg powders prepared by laminar gas atomization technology based on Laval nozzle is better than traditional gas atomization methods. Due to the higher gas pressure and narrow tube inner diameter, the gas-to-melt mass flow rate is higher, and the metal melt is more likely to be broken. Therefore, the powders have better sphericity, narrow particle size distribution, high fine powder yield of nearly 50%, and less irregular powders and hollow powders, The overall performance of AlSi10Mg alloy powders prepared by laminar gas atomization can meet the requirements of additive manufacturing.

Abstract:The effects of Er and Sc addition on the microstructure and properties of Al-7Si-0.6Mg fabricated alloy by wire arc additive manufacturing (WAAM) were studied by metallographic microscope, scanning electron microscope, room temperature and high temperature tensile tests. The results show that the addition of Er leads to the shortening of the dendrites and the thinning of the dendrites in the as-deposited alloy, and the addition of Sc leads to the shortening of the size of the α-Al dendrites of the as-deposited alloy, which tends to be equiaxed. After T6 heat treatment , the microstructure differences were eliminated. The addition of Er , Sc can improve the high temperature performance stability of WAAM Al-7Si-0.6Mg alloys at 200℃ and 250℃, and the effect of Sc is better than that of Er.

Abstract:As a new type of neutron absorbing material, Al-Sm alloy has the advantages of low cost, high plasticity and high neutron absorption. After preparing the alloy into a foil, it can be used for neutron devices such as neutron collimator and Fermi chopper. The neutron transmittance of Al-Sm alloy was simulated by Monte Carlo simulation (MCNP), The results showed that when the Sm content increased above 20 wt.%, the neutron transmittance of the material in the range of 1-6 mm are less than 20%, Al-20Sm alloy satisfies the neutron absorption rate and has a certain plasticity. Al-20Sm alloy was prepared by vacuum induction melting, the microstructures and phases of the as-cast and heat-treated alloys were investigated by XRD, EDS and SEM. The results show that the as-cast microstructures are α-Al and β-Al4Sm. After heat treatment at 550 °C for 2 h, allotropic transformation occurs, and all β-Al4Sm in the alloy is transformed into γ-Al4Sm. After heat treatment at 550 °C for 300 h, and part of γ-Al4Sm undergoes crystalline transformation to form Al3Sm. The micromechanical properties of the Al-Sm intermediate compounds were tested by nanoindentation technique, in which the hardness of β-Al4Sm, γ-Al4Sm and Al3Sm were 8.97 GPa, 8.91 GPa and 9.89 GPa.

Abstract:In order to study the effect of fused corundum content on properties of silicon-based ceramic cores, the ceramic cores with different amount of fused corundum(0%~30%) were prepared by the hot injection method, where quartz glass powder was used as raw materials, fused corundum as mineralizer, and the ceramic casting wax as the plasticizer. The results showed that with the increase of fused corundum, the shrinkage of the samples increased gradually, the porosity decreased at first and then increased, resulting in the higher degree of densification, while the flexural strength and high temperature creep resistance were falling after firstly climbing. When 10% fused corundum was added, the sample showed excellent comprehensive properties, with a shrinkage of 1.02%, a porosity of 20.91%, a bulk density of 1.7083 g·cm3, a bending strength of 14.83MPa and 20.96 MPa at room temperature and high temperature, and a high temperature deflection of 0.39 mm.

Abstract:GH720Li alloy is the preferred material for aero-engine turbine disk. The morphology, microstructure and micro-area composition of three kinds of γ′ in GH720Li dual-aged alloy were investigated via combination of scanning electron microscope (SEM), transmission electron microscope (TEM) and energy dispersive spectroscope (EDS). γ phases and primary γ′ phases were analyzed by EBSD-EDS method based on the focused ion beam/ electron microscopic system. 3D reconstruction of primary γ′ phases was done by Avizo software. The shapes, morphometric parameters and volume fraction of primary γ′ phases were given by the software and compared with the analysis results of 2D slice. The results show that there are a large number of Σ3 twin boundaries in both γ phases and primary γ′ phases. The primary γ′ phases have multiple shapes from a three-dimensional perspective. The larger continuous primary γ′ phases in three-dimensional space present discontinuous distribution in 2D slice sometimes. The real morphology of primary γ′ phases can be represented comprehensively by 3D EBSD method instead of 2D method. 3D information of primary γ′ provides the basis for heat treatment’s improvement of GH720Li alloy.

Abstract:Using powder metallurgy sintered billet as raw material, 0.02 mm molybdenum foil with tensile strength exceeding 795 MPa and elongation exceeding 1% was prepared by multi-pass rolling and intermediate annealing. The microstructure, texture and mechanical properties of the foil were analyzed by means of field emission scanning electron microscopy, electron backscatter diffraction and room temperature tensile test, and were compared with the 0.06 mm one under the same process. The results show that the microstructure characterization of 0.02 mm foil is granular or slender fibrous grain shape, more uniform and finer, and the aspect ratio is larger than 0.06 mm foil. The distribution frequency of low-angle grain boundaries is lower, especially the difference of sub-grain boundaries is more obvious. The texture composition in 0.02 mm molybdenum foil is more concentrated in α-line texture, and its grains account for 99.7%. Although the main texture of two molybdenum foils is {001}<110>, the proportion of {001}<110> component of 0.02 mm foil with larger deformation is much lower than that of 0.06 mm one, while the proportion of {112}<110> is significantly higher. The disparity in mechanical properties of 0.02 mm foil in different directions is more prominent, and the IPA value, which is used to characterize the degree of anisotropy, has been improved to different degrees on three mechanical properties. As the foil is thinned, two different trends which shows in tensile strength, yield strength, elongation and yield ratio of molybdenum foil in different directions reveal work hardening in the RD and TD directions, and deformation toughening in the 45°-RD direction.

Abstract:The deformation behavior and interfacial bonding properties of Cu/Al clad plates with different Cu/Al thickness-ratio by corrugated roll bonding (CRB) were investigated by shear strength test, microstructure observation of shear section and finite element simulation. The results show that increasing the Cu/Al thickness-ratio is beneficial to reduce the warpage of the Cu/Al clad plates and improve the overall bonding properties of the interface. When the Cu/Al thickness-ratio is 2:4, the Cu/Al clad plate hardly warps, and the shear strength reaches 47.24 MPa. As the Cu/Al thickness-ratio decreases, the rolling deformation zone expands and the rolling force is dispersed. Thus, the peak value of normal stress and average shear strength at the interface both decrease gradually. The shear stress generated by multiple "cross-shear" zones and the local strong normal stress formed at the interfaces during the CRB process significantly promote the plastic deformation and interface bonding of the clad plates.

Abstract:Selective Laser Melting (SLM) was used to fabricate Ti-Ni shape memory alloys. The effect of scanning speeds on alloys was studied using OM, SEM, XRD, and room-temperature compression. The results show that with increased laser scanning speed, the internal defect morphology changes from a nearly regular spherical shape to an irregular one. For instance, the width and continuity of the molten pool morphology decrease with the increase in laser scanning speed. Besides, the increasing laser scanning speed initiates B19" martensite content decreases, B2 austenite content increases, and the phase transition peak is reached during the transformation process. At 900 mm/s of the scanning speed, the relative density of the alloy reaches 98.5%, yielding the minimum internal defects. Simultaneously, the sample has a maximum compressive strength of 3120 MPa and a compressive strain of 41%, which is the best printing parameter to produce exceptional properties.

Abstract:Aiming at the poor ductility, toughness and formability of Al-li alloy, the effect of per-pass reduction on microstructure and mechanical properties of 2197 Al-Li alloy were studied by OM/SEM microstructure analysis, tensile properties and hardness/conductivity test, with a constant total reduction of 75%. The result show that the grain structure, the amount and distribution of precipitates are significantly affected by per-pass reduction. The strength of as-rolled alloy increases significantly with the increase of per-pass reduction, while the ductility and toughness decrease obviously. After T8 aging treatment, a large amount of precipitates are produced and the PLC (Portevin-Le Chatelier phenomenon) effect in the rolled alloy is eliminated. The mechanical properties of the alloy rolled by light and heavy reduction are improved significantly. After aging treatment, alloy exhibits the optimal comprehensive mechanical properties with tensile strength of 384.94MPa and the elongation to fracture of 12.45%, which are 2%, 21% and 29%, 31% higher than those of the light and middle reduction alloys, respectively.

Abstract:A novel nickel-based single crystal superalloys containing 0.4% Mo - 6.4% Re, 2.8% Mo - 6.4% Re and 0.4% Mo - 6.8% Re, respectively, in nominal composition was prepared. The element concentrations of alloys after SHT were measured, γ′ phase evolution and topological close-packed phase (TCP) precipitation of the alloys thermal exposed at 1100℃ up to 1 000 h were analyzed. The slight increment of Re and the increase of Mo content obviously facilitated the segregation of elements between dendrite and interdendrite, and between γ and γ′ phase. The coarsening rate of the γ′ phase during thermal exposure was reduced due to the segregation of low-diffusion elements such as Re in the dendrite core and the γ phase. The slight increase of Re promoted the precipitation of P phase but inhibited the growth rate of P phase, because the nucleation of the P phase was promoted by the segregation of the P phase forming elements Re, W and Ru in the dendrite core. However, the growth rate was inhibited because of contaction and intersection of precipitated P in large amount. The large increase of Mo content made both μ phase and P phase exist during the long-term thermal exposure at 1100 ℃. The μ phase was preferentially precipitated with a large number and a large size, while the precipitation of the P phase was delayed with smaller number and size. Mo promotes the segregation of the main constituent elements of μ phase, Re, W, and Mo in the dendrite core, especially the increase of Mo content, which promotes the preferential precipitation of μ phase. With the consumption of μ phase forming elements, and the presence of P phase is more stable at 1100 °C, P phase precipitates subsequently.

Abstract:Effects of different heat treatment regimes on the precipitate behavior and grain growth of low expansion superalloy were studied. The experimental results show that the size of Laves phase increases gradually but the grain size does not grow when under the Laves phase precipitation peak temperature ranges from 980℃ to 990℃. After holding at 1000℃~1040℃ for 1h, Laves phase began to dissolve, and the grain size gradually grew to grade 4, 3.5, 3 and 2. Therefore, in the process of hot working, to avoid the growth of grain size, the thermal deformation temperature should not exceed 1010℃, or the deformation at 1000℃ and holding time should not exceed 1h. Laves phase content at grain boundary has little effect on the properties of the alloy, but the grain size has a great effect on it.

Abstract:Multi-principal alloys have exhibited broad structural applications due to their unique microstructure and excellent comprehensive properties, and also been the research focus of structural metallic materials in recent years. As a new type of complex concentrated alloys, there are essential differences between multi-principal alloys and traditional alloys in atomic structure, in which the local chemical short-range order (CSRO) is one special atomic microstructure. The interactions between CSRO and moving dislocations can make a significant influence on the deformation behavior and mechanical properties of multi-principal alloys. Therefore, this paper mainly summarized the progress in the local chemical order in multi-principal alloys, including the formation factors, characterization methods, and effects on deformation behavior and mechanical properties. Moreover, the existing problems and shortcomings in the directly quantitative characterization, quantitative manipulation, theoretical model development and the influence on service performance of chemical short-range order in current research were analyzed and prospected.

Abstract:The annealing process is a very effective way to improve the soft magnetic properties of nanocrystalline alloys. In this paper, the research status of annealing process of nanocrystalline alloys are summarized and the characteristics of different annealing process are compared. Conventional annealing and Joule annealing are the key to determine the final grain size and crystallization ratio of the alloy, which is the premise to obtain the best properties. Magnetic field annealing and stress annealing can change the shape of the hysteresis loop after annealing, obtain higher induced anisotropy and reduce the constant permeability of the material under a certain magnetic field strength. Up to now, furnace annealing and magnetic field annealing are already widely applied, while joule annealing and stress annealing are affected by process equipment and production efficiency respectively, resulting in the lag of their industrial application. However, the high efficiency of Joule annealing and the extremely high induced anisotropy of stress field annealing also have significant advantages, which means the potentiality of futher industrial application.

Abstract:Fe-Co-P-B amorphous alloys with high FeCo contents (up to 87 at%) were synthesized. The effects of the replacement of Fe by Co on glass formation ability (GFA), thermal stability, and magnetic properties were investigated in details. Fe87-xCoxP2B11 (x=5-7) amorphous alloys have high saturated magnetization (from 1.75 T to 1.84 T) and good bending ductility even after annealing. The Curie temperature (Tc) of the present Fe-Co-P-B alloys obviously increases with the substitution of Fe by Co, deteriorating the coercivity (Hc). The tensile stress applied to the Fe-based amorphous alloys can obviously reduce Hc from 12.8 A/m to 6.5 A/m with the tensile stress change from 0 to 12 MPa. The optimal adjustment of both the alloy composition and stress provides a important way to obtain Fe-based amorphous with both excellent soft-magnetic properties and good bending ductility, which can avoid annealing-induced embrittlement.

Abstract:In present work the 630℃ long-term aging stability of FB2 rotor steel are investigated by impact test, hardness test in combine with SEM, TEM and XRD analysis. The investigation shows that impact toughness and hardness decrease with proloning aging time. The impact ductility decreases apparently after 2000 h aging and then keeps stable. The hardness stays in a high level (253 HBW). The size and amount of M₂₃C₆ carbide increases slightly during aging without apparent coarsen. The size increase of Laves phase is more obvious and Laves phase tends to gather at grain boundary. While no chain of Laves phase is observed. The coarsen and gathering of Laves phase at grain boundary is the major reason for impact toughness degeneration. Bases on the research, it can be concluded that FB2 rotor steel keeps stable at 630℃ for up to 5000 h.