Abstract:The composition controlled Ni-Co-P multi-component alloy coatings with the thickness of about 0.7 μm were prepared on the surface of carbon fibres (CFs) using the palladium-free electroless plating. Then the copper matrix composites reinforced by the Ni-Co-P coated CFs, namely the CF/Cu(Ni-Co-P) composites, with CF content of 10vol%, 20vol%, 30vol%, and 40vol%, the uncoated CFs reinforced copper matrix composites (CF/Cu) with 30vol% CFs, and the Ni-coated CFs reinforced composites, namely the CF/Cu(Ni) composites, with 30vol% CFs were prepared by the vacuum heat pressure sintering at 850 °C and 30 MPa. The distribution of reinforcement and interface phase elements and the fracture morphologies of the composites were observed by the scanning electron microscope and energy dispersive spectrometer. The tensile properties of different copper matrix composites were characterized by the electronic universal testing machine. Results show that the smooth Ni-Co-P coatings of uniform thickness can be obtained on CFs surface by electroless plating at 70 °C for 10 min. The tensile properties of CF/Cu(Ni-Co-P) composites are firstly increased and subsequently decreased with increasing the CFs content. The highest tensile and yield strengths are obtained for the 30vol% CF/Cu(Ni-Co-P) composite. The mechanical properties of CF/Cu(Ni-Co-P) composite are obviously better than those of the CF/Cu and CF/Cu(Ni) composites with the same content of reinforcement (30vol%). The fracture mechanism of CF/Cu(Ni-Co-P) composite is non-accumulative fracture.

Abstract:The Ti6Al4V alloy specimens were planished, polished, cleaned by ethyl-alcohol with ultrasonic, and dried. Then, the treated specimens were put into a special equipment for oxygen-carbon co-cementation. The X-ray diffractometer (XRD), scanning electron microscope (SEM), energy disperse spectroscope (EDS), HV hardness tester, and universal material testing machine were used to analyze the phase, microstructure, composition, hardness, frictional wear, and mechanical properties of the co-cemented layer. XRD results show that TiC and TiO_x phases appear in the co-cemented layer. The microstructure of the original Ti6Al4V alloy specimen is changed by the oxygen-carbon co-cementation. The microstructure of the co-cemented layer is obviously different from that of Ti6Al4V alloy specimens after carburization treatment, oxygen permeation treatment, and treatment under CO₂ atmosphere. EDS results show that the content of C and O elements changes gradually. The surface hardness of the co-cemented layer is 3.8 times higher than that of the substrate, and the hardness of the co-cemented layer also changes gradually. The oxygen-carbon co-cementation changes the adhesive wear and friction state of the original specimen. Only slight friction trace occurs on the surface of the co-cemented specimen and no wear appears. The wear amount of the co-cemented specimen is 3.5% of that of the original specimen, and the friction coefficient is about 30% of that of the original specimen. In the tensile fracture process, the outer surface of the co-cemented specimen peels off to a certain extent, and the surface is covered by cracks, resulting in the slightly decreased strength of the specimen. The elongation and the reduction of area are comparable to those of the original specimen. After oxygen-carbon co-cementation of Ti6Al4V alloy, the surface hardness of the specimen is improved, the wear rate and friction coefficient are reduced, and the mechanical properties of the specimens basically remain.

Abstract:The growth kinetics process and tribological properties of niobium carbide (NbC) coatings prepared by the pack cementation method on the 40Cr and 45 steel substrates were investigated with the main raw materials of iron niobium powder, ammonium chloride, and alumina under the conditions of different temperatures (1123~1273 K) and different treatment durations (1~4 h). Results show that the coating is compact and well bonded with the substrate interface, and it is mainly composed of NbC phase. The thickness of the coatings on 40Cr and 45 steel substrates is 1.703±0.285~8.457±0.240 and 1.987±0.355~9.247±0.275 μm, respectively. The growth kinetics study shows that the coating growth is controlled by the diffusion process, and the thickness has a parabolic relationship with the treatment duration. The activation energies of the NbC growth process on the 40Cr and 45 steel substrates are 113.80 and 102.76 kJ/mol, respectively. After treatment at 1273 K for 4 h, the hardness of NbC coating reaches more than 21 560 MPa, which is 5.49~8.06 times higher than that of the steel substrate. With GCr15 steel ball as the grinding material, the average coefficient of friction of NbC coating on the 40Cr and 45 steel substrates is 0.393 and 0.342, respectively; the average coefficient of friction of substrate is 1.3~1.6 times higher than that of the NbC coating. The volume wear rate of NbC coating is about 34.9%~37.5% of that of the steel matrix, indicating that the NbC coating has excellent wear resistance and wear reduction performance. The friction and wear mechanism of NbC coating is abrasive wear, adhesion wear, and oxidation wear.

Abstract:To improve the high-temperature thermal shock performance, the Si-Ti-Cr silicide coatings were prepared on Nb-Hf alloy by slurry sintering and high-temperature permeation methods. The high-temperature thermal shock performance of Si-Ti-Cr silicide-coated Nb-Hf alloys in atmosphere and vacuum was comparatively analyzed. The failure mechanism of Si-Ti-Cr coating in atmosphere and vacuum after thermal shock tests was determined by simulating the temperature and thermal stress distributions of the coating during thermal shock. Results show that the mass loss of the coating in vacuum is less than 0.8 mg/cm² after 100 thermal shock cycles at 1300 °C. The mass gain of the coating in atmosphere is less than 3 mg/cm² after 200 thermal shock cycles at 1600 °C. Therefore, the silicide coating exhibits excellent thermal shock resistance at 1300 °C in vacuum and at 1600 °C in atmosphere.

Abstract:To improve the deposit (the main components are CaO, MgO, Al₂O₃, and SiO₂, together referred to as CMAS) corrosion resistance of thermal barrier coatings (TBCs), the filtered cathodic vacuum arc (FCVA) technique was adopted to prepare a dense Al₂O₃ coating on the surface of TBCs. The wetting behavior and CMAS corrosion resistance of Al₂O₃-modified TBCs and as-deposited TBCs were compared and analyzed. Results show that the preparation of Al₂O₃ coating by FCVA technique has no obvious influence on the structure of 7wt% yttria-stabilized zirconia (7YSZ) phase. Besides, the Al₂O₃-modified TBCs have better comprehensive performance compared with the as-deposited TBCs. Under the CMAS corrosion at 1250 °C, the Al₂O₃ coating effectively restricts the spread of molten CMAS on TBC surface. In addition, the Al₂O₃ coating fills the gaps between 7YSZ columnar crystals and hinders the infiltration of molten CMAS. It is proved that FCVA method is appropriate to Al₂O₃ coating preparation in order to improve the CMAS corrosion resistance of TBCs, and the Al₂O₃ coating and its preparation do not have negative influence on the thermal shock performance of TBCs.

Abstract:High temperature hot corrosion is one of main failure modes for the hot components. The Na₂SO₄ and NaCl molten salts can accelerate the hot corrosion at high temperatures and even lead to the catastrophic accidents. Thus, this research discussed the molten salts (Na₂SO₄ or/and NaCl) induced hot corrosion with Na₂SO₄ as the main corrosion reactant. The corrosion behavior and performance characteristics of two typical types of hot corrosion were introduced. Several hot corrosion models and mechanisms were introduced, as well as the reaction formulas and corrosion mechanisms of Na₂SO₄, NaCl, and Na₂SO₄+NaCl molten salts. According to the current research status, the protective coating is an optimal approach in the hot corrosion reduction. The advanced progress of the MCrAlY coatings, NiAl coatings, thermal barrier coatings, and novel coatings was summarized. In addition, the methods to further improve the corrosion resistance of coatings were investigated. Finally, the development direction of protective coatings was predicted.

Abstract:In order to improve the wear and corrosion resistance of micro arc oxidation (MAO) coating on Ti-5Al-1V-1Sn-1Zr-0.8Mo alloy, 0-1.00g/l graphene oxide (GO) was added to the electrolyte to prepare micro arc oxidation coating. The thickness, roughness, micro morphology and composition of MAO coating were characterized, and the wear and corrosion resistance of the coating were tested and analyzed. The results show that with the increase of GO content, the thickness of coating increased from 102.3 μm to 115.3 μm. The roughness reduced from 56.7 μm to 32.9 μm. The diameter of micropore on the surface of the coating were about 10-60 μm without GO in electrolyte, and it decreased with GO. With 0.75 g/L and 1.00 g/L content, the diameter of micropore were stable at 10-20 μm. XRD results show that the content of rutile TiO₂ in the coating increases slightly with GO in eletrolyte, and the mass loss of the coating during wearing is significantly lower than that without GO. With 0.75 g/L GO, the binding force between coating and substrate alloy is the largest, reached to 53.3 N, which is 6.2 N higher than that without GO. After salt spray corrosion for 480 h, the coating with GO content of 0.75 g/L and 1.00 g/L have better corrosion resistance.

Abstract:A new dual-stage high power pulsed magnetron sputtering technology is proposed. The TiN coating was prepared by reasonably adjusting the parameters of the two-stage pulsed electric field under different N2 flow conditions, and its microstructure and performance were analyzed. The results showed that as the N2 flow rate gradually increased from 10 to 40 sccm, the preferred orientation of the TiN coating gradually changed from (111) to (220) crystal plane. The surface morphology of the coating changed from a multi-directional angular cone structure to a tightly combined round-cell structure. The coatings all present the growth mode of columnar crystals and the average crystal grain size is nanometers. When the N2 flow rate is 20sccm, the N/Ti atomic ratio of the coating is closest to the standard value of 1, and the coating structure is the densest and has the best mechanical properties and film-base bonding properties. At the same time, the use of new dual-stage high-power pulsed magnetron sputtering process can effectively improve the technical shortcomings of traditional high-power pulsed magnetron sputtering with a low average deposition rate. When the N2 flow rate is 20sccm, it can reach 46.35nm/min.

Abstract:The Bi₂Sr₂CaCu₂O_x (Bi-2212) precursor powder was prepared by spray pyrolysis. The phase evolution during the heat treatment process and the superconductivity of wires were analyzed. Results show that the powder prepared by spray pyrolysis is spherical with the average particle size of 3.03 μm and the dispersion distribution. The phase evolution during the heat treatment process of powder includes four main reaction processes. The decomposition of nitrate and the pre-reaction process between components occur firstly at 527 °C. Then the Bi₂Sr₂CuO_x (Bi-2201) phase is formed at 588 °C due to the high reactivity of spray powder. The Bi-2212 phase is generated at 780 °C, and the powder is completely melted at 834.2 °C. The heat treatment temperature window of the Bi-2212/Ag wire is very narrow. The critical current (I_c) is reduced by 31 A when the maximum heat treatment temperature (T_max) is changed by ±2 °C. When the optimal T_max of Bi-2212/Ag wire is 885 °C, the maximum I_c (4.2 K, 0 T) is 486 A. The critical current is increased to 712 A in the oxygen atmosphere during heat treatment.

Abstract:SiC_P/Mg₉₄Zn₅Y₁ composites with 0.5wt%~2.0wt% SiC_p were prepared by the casting method. The mechanical properties and damping capacities of the composites were investigated. The microstructure and phase components of the composites were analyzed via the scanning electron microscopy and X-ray diffraction. Results show that after the addition of SiC_p into the matrix, the SiC_p is evenly distributed in the matrix, which refines the microstructure of the composite. The SiC_p/Mg₉₄Zn₅Y₁ composites contain the α-Mg, I-phase (quasicrystal phase), and SiC_p phase. The damping capacities and mechanical properties of the SiC_p/Mg₉₄Zn₅Y₁ composites were evaluated by the dynamic mechanical analyzer and an AG-X testing machine, respectively. The mechanical properties of the composites are better than those of the original Mg₉₄Zn₅Y₁ alloy. The 1.0wt% SiC_p/Mg₉₄Zn₅Y₁ composite exhibits the compressive strength of 350 MPa. The damping properties of all the composites are much higher than those of the parent alloy. The optimal damping capacity is achieved when the composite contains 0.5wt% SiC_p. Moreover, according to the efficiency coefficient method, the 1.0wt% SiC_p/Mg₉₄Zn₅Y₁ composite has the optimal comprehensive properties.

Abstract:The Al-0.59Mg-0.54Si-X (X=0, 0.253Ca, 0.253Mn) alloys were prepared to investigate the effect of minor addition of Ca and Mn on the microstructure, mechanical properties, and electrical conductivity of the Al-0.59Mg-0.54Si-X alloys after casting, solid-solution, and aging treatments. Results show that the Ca and Mn addition can significantly refine the grains of α-Al matrix. Moreover, Ca can induce the precipitation of Mg₂Si and Al₂Ca particles with high contents in the as-cast α-Al grains, which contributes to the optimum mechanical properties of alloys. The solid-solution and aging treatments cause the coarsening of particles and the particle segregation at the grain boundaries, leading to the rapid decline in mechanical properties but an extraordinary increase in electrical conductivity (52.44%IACS) for the alloys. Mn addition can transform the coarse β-Al₅FeSi impurity phase at the grain boundaries into the α-Al(FeMn)Si particles and also induce the precipitation of Mg₂Si and AlMn particles in the as-cast alloys. Consequently, the Al-0.59Mg-0.54Si-0.253Mn alloy after solid-solution and aging treatment exhibits the optimal mechanical properties and acceptable electrical conductivity.

Abstract:A novel machining method based on the graphene nanoparticles dispersed in canola oil as the cutting fluid to provide lubrication/cooling effect for the processing area was proposed. The effects of the nanofluid on the chip adhesion layer of the cutter were determined. Compared with the dry cutting method, the thicknesses of chip adhesion layers on the flank face and rake face of cutter decrease by 38.8% and 28.8% with the canola oil+graphene nanofluid, respectively. In addition, the cutting force and workpiece surface roughness decrease by 51.4% and 50.1%, respectively. The relatively high thermal conductivity of graphene can reduce the temperature of the cutting zone. In addition, the graphene can penetrate the contact zone between the chip adhesion layer of cutter and the workpiece, which effectively protects the coating of cutting tool and decreases the chip adhering to the workpiece surface. Besides, the graphene can fill the pits on the workpiece surface, thus improving the cutter surface quality.

Abstract:The novel AgZrB₂ electrical contact materials with different ZrB₂ contents were prepared by the combination method of ultrasonication, ball milling, and spark plasma sintering, and the arc erosion and material transfer behavior were investigated by the electrical contact tests. The results show that the ZrB₂ content significantly affects the arc erosion resistance of AgZrB₂ electrical contact materials. The Ag-3wt% ZrB₂ contact material presents the stable make/break-arc energy and duration, indicating the excellent arc erosion resistance. However, the increased ZrB₂ content results in higher make-arc energy and longer make-arc duration with large fluctuations of break arc energy and duration, leading to the severe arc erosion. This result suggests that the excessive ZrB₂ is not beneficial to the enhancement of arc erosion resistance. Moreover, it is found that the Ag-3wt% ZrB₂ and Ag-5wt% ZrB₂ contact materials have the same material transfer mode from anode to cathode, whereas the Ag-7wt% ZrB₂ contact material has the opposite transfer mode from cathode to anode.

Abstract:The AlCrCoFeNi_2.1 high-entropy alloy (HEA) was prepared by the spark plasma sintering method at different temperatures. The microstructure, corrosion resistance, and mechanical properties of this HEA were investigated. Results show that the maximum relative density of the AlCrCoFeNi_2.1 HEA can reach 99.18% after sintering, and the HEA is mainly composed of body-centered cubic (bcc) and face-centered cubic (fcc) phases with the phase fraction of 20.6% and 79.4%, respectively. Compared with that in fcc phase, the fraction of recrystallized and deformed microstructures in bcc phase of AlCrCoFeNi_2.1 HEA is higher. In addition, the bcc phase can be easily corroded in 3.5wt% NaCl solution. The pressure recovery rate of bcc and fcc phases is decreased and the hardening effect is enhanced with increasing the strain rate. The higher ultimate tensile strength of AlCrCoFeNi_2.1 HEA after sintering at 1050 °C can be achieved due to the grain size strengthening, solid solution strengthening, and good interface bonding between HEA particles. The failure mode of AlCrCoFeNi_2.1 HEA includes the brittle fracture of bcc phase and the ductile fracture of fcc phase.

Abstract:The hot deformation behavior of the equiatomic FeCrNiMn high entropy alloy was studied through the isothermal compression at 900~1050 °C with strain rate of 0.001~1 s^-1. Results show that the initial microstructure is mainly composed of equiaxed grains with face-centered cubic structure and fine body-centered cubic phase particles. The flow curves exhibit the typical single stress peak type. The peak stress is decreased significantly with increasing the temperature and decreasing the strain rate. The constitutive model was developed based on the hyperbolic-sine law to predict the flow stress. The stress exponent and the apparent activation energy were calculated as 3.13 and 405 kJ/mol, respectively. The processing maps were obtained based on the dynamic material model at different strains. It is found that no instability zone appears in the processing maps at different strains, suggesting the excellent hot deformability of the alloy. The deformation microstructure is closely related to the power dissipation efficiency η. The recrystallization fraction is 17.6vol% when η is 28%, and it is increased to 37.5vol% when η is 38%. Two optimal hot working condition ranges can be identified according to the processing maps: 900~940 °C/strain rate of 10^-3~10^-1.3 s^-1 and 960~1050 °C/10^-3~10^-0.3 s^-1.

Abstract:Based on the advantages of digital image correlation method in the characterization of local mechanical property for welding joint, the differences in mechanical property, hardness, and microstructure of as-received, tempered, and solution treatment and aging (STA)-treated welding joints of 15CrMoR base metal with Ni-based welding material were compared. The tempering treatment transforms the dendritic structure into the dispersed tempered sorbite in the welding fusion zone (WFZ). The uniformity of mechanical properties is improved, and the matching degree of mechanical property between base metal zone (BMZ) and WFZ is improved. STA treatment transforms the dendritic structure into the uniform columnar dendrite structure in WFZ, which causes the disappearance of pearlite and the grain coarsening in BMZ, resulting in the degradation of strength and the increase of mismatching degree between WFZ and BMZ. Therefore, the suitable heat treatment needs to balance the requirements of BMZ and WFZ to obtain the excellent comprehensive mechanical property for welding joints.

Abstract:Deuterium retention behavior in W-Fe-Ni alloy was investigated by the gas-phase driven permeation system and thermal desorption tests. The deuterium permeability, diffusion coefficient, solubility, and diffusion activation energy of deuterium in the W-Fe-Ni alloys were investigated. The thermal deuterium charging and thermal deuterium desorption experiments were conducted. Combined with the microstructure characteristics and numerical simulation, the deuterium retention behavior in W-Fe-Ni alloys was studied and the diffusion model of hydrogen isotope in W-Fe-Ni alloy was established to predict the deuterium retention in W-Fe-Ni alloys with different shapes. Compared with the results of thermal desorption tests, the amount of hydrogen isotope retention in W-Fe-Ni alloy can be accurately estimated by the multi-physics field numerical simulation.

Abstract:A multicomponent two-phase model was established to describe the macro/micro-transportation and the freckle formation during solidification, and the dynamic mesh algorithm was applied to perform the filling process during the vacuum arc remelting (VAR). Firstly, the thermodynamic calculation approach was used to evaluate the liquid composition with the variation of solid fraction during solidification, and the interdendritic liquid density of multicomponent alloys was obtained. Then, the freckle formed during the horizontal directional solidification was simulated and compared with the experiment one to study the freckle formation mechanism and influence factor. Finally, the developed model was used to investigate the influence of process parameters on the freckle formation in the industrial-scale VAR casting. Results show that the element composition has a significant effect on the density change of liquid phase during the solidification. The freckle forms with a high thermosolutal convection strength. The growth direction of freckles is determined by the liquid density difference and the angle between solidified interface and gravity direction. It is also found that the molten pool profile is affected by the electrode melting rate and cooling rate during VAR.

Abstract:To improve the accuracy of the straightening process of S304/Q235 composites, the elastic-plastic deformation and straightening process of the bimetal composite plates were investigated by the Abaqus finite element software. In addition, the neutral layer offset of the bimetal composite plates with different thickness ratios was also analyzed. Results show that the neutral layer offset is dependent on the yield strength and thickness ratio of composite plates. The theoretical calculations, numerical simulations, and experiment results are compared. Then the fitting formula for neutral layer offset is obtained and verified. Additionally, the dynamic change of the neutral layer offset state was analyzed. This research provides the theoretical basis for the establishment of high precision straightening force model.

Abstract:In order to solve the low efficiency and high cost of electrode materials used in the process of electrolytic water hydrogen evolution, porous Ni-Cr-Mo-Cu phosphating electrode was prepared by powder metallurgy and low temperature phosphating method. The phase, morphologic structure and element distribution of the electrode were characterized by X-ray diffraction analysis (XRD), field emission electron microscope (SEM) and X-ray energy spectrum analysis (EDS). The electrocatalytic hydrogen evolution properties of phosphor electrode materials were tested by open-circuit potential, linear polarization and ac impedance. The results showed that the porous Ni-Cr-Mo-Cu phosphating electrode exhibited excellent hydrogen evolution performance and its catalytic activity can be improved to a great extent by adjusting the phosphating time. At room temperature, the porous Ni-Cr-Mo-Cu phosphating electrode with a phosphating time of 2 hours has a good hydrogen evolution performance in a solution of 6mol/L KOH, and its hydrogen evolution overpotential is only -0.19V (vs RHE). When the exchange current density is 10 mA/cm2, the corresponding polarization potential is -0.20V (vs RHE). After 18000s, the open-circuit potential (OCP) of the electrode material changed from +0.80 to 0.78V (vs RHE), which decreased only 0.02 V, indicating that the electrode material had good electro-catalytic stability.

Abstract:Based on the traditional high-pressure torsion process and the introduction of floating die technology, a high pressure torsion (HPT) process for tungsten and copper alloys with high performance differences was developed. High performance tungsten copper composite materials with good interface bonding were obtained at 300 ℃ and 1.5GPa. The effects of grain refinement and dislocation accumulation on interfacial element diffusion and microhardness during large shear deformation were analyzed by X-ray diffraction (XRD)、optical microscope (OM) and scanning electron microscope (SEM). The results show that with the increase of HPT turns and torsion radius, the equiaxed coarse grains of tungsten are elongated and refined to streamline shape with the average size of 9.0±2 μm after 20 turns and the dislocation density increases to 3.4 × 1014 m-2, which is 2.9 times higher than the initial sample due to the shear deformation. The grain refinement of copper is almost saturated, and equiaxed ultrafine grains with the average size of about 0.3-1.5 μm were obtained within 20 turns of HPT processing. The dislocation density keeps dynamic equilibrium at about 2×1014 m-2 due to the dynamic recrystallization caused by large shear strain. The high-density grain boundaries and dislocations produced by large shear deformation promote the mutual diffusion of tungsten and copper at the interface. With the increase of HPT turns from 10 to 20, the diffusion depth of tungsten and copper increase from 1.2μm and 2.9μm to 1.6 μm and 6.2 μm respectively. Under the effect of grain refinement and dislocation accumulation, the microhardness of tungsten and copper is significantly enhanced to 548.3 ± 360 Hv and 125.0 ± 4 Hv respectively.

Abstract:Cu/Al bimetallic composite rod was successfully fabricated by 4 passes ECAP at room temperature and post-annealing. Scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and electron backscatter diffraction (EBSD) were used to investigate the microstructure of the bonding interface of Cu/Al bimetallic composite rod, and the interfacial bonding strength was also tested by shear test. The results show that under the severe shear deformation during ECAP process, mechanical bonding occurred firstly at the interface of the Cu/Al bimetallic composite rod through plastic deformation, and then the mutual diffusion between copper and aluminum atoms were promoted during the post-annealing. Under the combined effects of large pressure, high temperature and concentration gradient, a good metallurgical bonding at the interface of the Cu/Al bimetallic composite rod was formed. The thickness of Cu/Al interface layer was about 1.47 μm and a new phase of intermetallic compound CuAl2 was generated, consisting of ultrafine grained (UFG) microstructures with high angle grain boundaries and homogeneous distribution, and there was no obvious preferred grain orientation. The average shear strength of Cu/Al bimetallic composite rod was 28.94 MPa, showing the good interface bonding quality. Moreover, the main shear failure mode was brittle fracture.

Abstract:The dynamic recrystallization (DRX) behavior of fine-grain TC4 titanium alloy prepared by continuous variable cross-section recycled extrusion during hot working was investigated by combining experiment and finite element simulation. The critical strain and DRX dynamic models of fine-grain TC4 titanium alloy were established based on the true stress-strain curves obtained by the experiment. The material properties were defined based on the DRX models, and the thermal compression process was simulated by DEFORM-3D software. The results show that the DRX behavior of fine grain TC4 is significantly affected by thermal compression processing parameters; the volume fraction of dynamic recrystallization (XDRX) and the grain size are increased with increasing deformation temperature and decreasing strain rate; the equivalent strain and range of the deformation zone are increased simultaneously with increasing strain; the correlation between the experimental value and the simulated value of XDRX is 0.9762, which indicates the high accuracy of the established model.

Abstract:The Fe_63.3Mn₁₄Si_9.1Cr_9.8C_3.8 and (Fe_63.3Mn₁₄Si_9.1Cr_9.8C_3.8)₉₉X₁(x=Ag,Cu,Ce) medium entropy alloys were fabricated by magnetic levitation melting and negative pressure copper mold suction casting method. The effects of adding 1% Ag, Cu and Ce on the microstructure, mechanical properties and corrosion resistance of the alloy were studied. After adding 1% of Ag, Cu, Ce, the alloy entropy value is between 1R and 1.5R, which belongs to the category of medium entropy alloy. The mixed alloy is negative, and the atomic size difference, electronegativity difference and valence electron concentration value are small so it has the single FCC structure. (Fe_63.3Mn₁₄Si_9.1Cr_9.8C_3.8)₉₉Ce₁ alloy has the largest δ and large lattice distortion energy. Ce has the best comprehensive mechanical properties by purifying the melt and grain refinement. The fracture strength is 2815 MPa, and the yield strength is 854 MPa, the elongation rate is 22.89%, and the maximum hardness can reach 658.4 Hv. The alloy system has lower energy, finer grains, and enrichment of rare earth Ce on the surface, so a dense and uniform passivation film is formed after corrosion. In (Fe_63.3Mn₁₄Si_9.1Cr_9.8C_3.8) ₉₉Cu₁, the Cu-rich phase and Cr-rich phase form micro galvanic cells. The Cu-rich phase will corrode preferentially, and Cu deteriorates the corrosion resistance of the alloy.

Abstract:The inhomogeneity of the microstructure affects the comprehensive performance of the parts, and the characteristics of semi-solid forming can easily cause large differences in the microstructures of different parts of the parts. How to improve the uniformity of the semi-solid structure is the key to obtaining molded parts with excellent comprehensive performance. In this paper, the wall thickness of four kinds of parts are designed, and the influence of the wall thickness of the parts on the microstructure uniformity and performance of rheological extrusion parts is studied. Research indicates: The microstructures of CuSn10P1 alloy semi-solid extrusion castings with different wall thicknesses are all composed of α-Cu phase, δ-Cu41Sn11 phase, β"-Cu13.7Sn phase and Cu3P phase. As the wall thickness decreases, the solid-liquid two-phase synergistic deformation ability of CuSn10P1 alloy semi-solid slurry becomes worse during filling. This resulted in the uneven distribution of the microstructure along the filling direction, and the intergranular structure (α+δ+Cu3P) gradually showed a large-area network or long strip with uneven distribution of clusters. The size of primary α-Cu grains decreases first and then increases, and the primary α-Cu grains of 10mm wall thickness castings are the smallest. As the wall thickness decreases, the room temperature tensile strength and elongation of CuSn10P1 alloy semi-solid extrusion castings both increase first and then decrease. When the wall thickness is 10 mm, the performance is the best, 445.7 MPa and 37.78%, respectively. This is mainly due to the homogenization of the structure, the solid solution strengthening effect and the fine grain strengthening effect.

Abstract:Corrosion behavior of two Ti(C,N)-based cermets with 38 wt.% Ni or Ni–20Cr binder was investigated in 0.2 M H₂SO₄ and 0.2 M NaOH solutions at room temperature. In 0.2 M H₂SO₄ solution, there were significant differences in corrosion behavior and resistance between both cermets. For cermet with Ni–20Cr binder, binder phase was very slowly dissolved during immersion, mainly due to that the spontaneous formations of NiO, Ni(OH)_x(SO₄)_y, Cr₂O₃ and Cr(OH)₃, and no passivation occurred and current density steeply increased beyond the pseudo-passive region during potentiodynamic polarization, differing from cermet with Ni binder. By contrast, in 0.2 M NaOH solution, there were no significant differences in corrosion behavior and resistance between both cermets. For both cermets, ceramic grains were very slowly dissolved during immersion, accompanied by the formations of NiOOH and Cr^₆₊ compound, and no passivation but pseudo-passivation occurred during potentiodynamic polarization.

Abstract:During the loss-of-water accident in the nuclear reactor, the high-temperature steam can react with the Zr alloy cladding tube and lead to oxidation of the Zr alloys, which lead to the embrittlement and fracture of the cladding tube. The process is closely related to the microstructural evolution of the Zr alloys. In order to reveal the embirttlement mechanisms of the Zr-Sn-Nb cladding tube, the steam oxidation experiments of Zr-Sn-Nb alloy at 1000~1250 ℃ were performed. The microstructure was investigated by an optical microscope, a scanning electron microscope and a transmission electron microscope. The hydrogen content was identified by a oxygen, nitrogen and hydrogen analyzer. The results show that the Zr-Sn-Nb alloy can be oxidized into three layers, including ZrO2, α-Zr(O) and Prior-β. The thickness of ZrO2 layer and α-Zr(O) layer increase with increasing oxidation time, meanwhile, the number of cracks increase in α-Zr(O) layer. The lath β-Zr phase of the Prior-β layer is transformed into sheet-like α-Zr phase and grain width of α-Zr phase become larger when the alloy is exposed to longer steam oxidation time. Loose ZrO2 layer with a large number of transverse cracks can be formed in 1000℃ steam, while dense ZrO2 layer can be observed at higher temperatures. H content of the Zr-Sn-Nb alloy matrix increases with the oxidation time. The hydrogen pickup of the Zr-Sn-Nb alloy matrix is much higher at 1000°C steam than those at other temperatures. The orientation relationship between the α-Zr matrix and the hydride is (0002)α-Zr//(-20-2)δ-ZrH1.66 and [2-1-10]α-Zr//[011]δ-ZrH1.66 in 1000℃ steam, and (-2110)α-Zr//(20-2)δ-ZrH1.66 and [01-10]α-Zr//[111]δ-ZrH1.66 in 1200℃ steam.

Abstract:Quasicrystal is a new material, there are great research value and application potential in its special structure and property. The Al63Cu25Fe12 quasi-crystal-alloy was produced by vacuum non-consumable arc smelting copper mold casting technology, and then the Al63Cu25Fe12 melt-spinning with different cooling rates was prepared by vacuum single roll spin quenching technology. The effect of different cooling rates on the phase structure and micro-structure of the alloy was researched through using various analytical ways, such as X-ray Diffraction (XRD), Differential Scanning Calorimeter (DSC), Optical Microscope (OM), Scanning Electron Microscope (SEM), Energy Dispersive Spectrometer (EDS), Transmission Electron Microscope (TEM) and others. The result shows that the cooling rate of copper mold-casting was about 1×102Ks, and the corresponding cold speed of the ribbon strip prepared under different speeds (500/2000/4000) r/min is 6.37×105K/s, 1.77×106K/s, 3.98 ×106K/s. Copper-mold-casting samples contained λ phase (AL13Fe), quasi-crystal I phase (Al63Cu25Fe12), β phase (ALFe(Cu)) and τ phase (AlCu(Fe)). The quasicrystal I phase was mainly distributed around λ phase. When the cooling rate of melt-spinning reaches (105-106)K/s, the phase structure consists of quasicrystalline I phase with icosahedron structure and β phase with a little Cscl simple cubic structure.

Abstract:Based on the principle of sub-rapid solidification, AA6022 aluminum alloy sheets for automotive were successfully prepared by electromagnetic oscillation twin roll casting technology. In order to improve the comprehensive mechanical properties of the end products, the heat treatment process of the sheet was studied. Combined with OM, SEM, EBSD, macro hardness and tensile test, the effects of different heat treatment parameters on the microstructure and mechanical properties of sub-rapid solidification sheet were studied. The results show that the composite application of Al-Ti-B grain refiner and electromagnetic field can significantly improve the proportion of fine equiaxed grains. Solution + pre-aging treatment can significantly inhibit the natural aging hardening effect, enhance the natural aging stability of alloy sheet, and improve the stamping formability and paint hardening increment of alloy sheet. Under the optimized conditions (560 ℃ × 5 min + 150 ℃ × 5 min + 30 d at room temperature + 175 ℃ × 30 min), the yield strength, tensile strength, elongation, macro hardness and r value of the alloy sheet increased from 258.98 MPa, 295.7 MPa, 10.65%, 47.6 HV and 0.663 of 1# sample to 295.71 MPa, 322.01 MPa, 16.09%, 61.2 HV and 0.753 of 4# sample, respectively.

Abstract:The rapid development of entire-process-vacuum high pressure die casting (HPDC) technology provides the possibility for the industrial application of bulk metallic glasses (BMGs), which has received widespread attention. However, the room-temperature brittleness of BMG is still one of the biggest stumbling blocks limiting the application of BMG parts in some key fields. To overcome this problem, in this paper, 304 stainless steel skeletons were introduced into Vit1 BMGs by HPDC technique under high pressure and with large filling rate to create BMG/stainless steel composites. Furthermore, the effects of stainless-steel volume fraction on the microstructure and mechanical properties were studied systematically. The results showed that the stainless steel skeleton in the HPDCed composites was uniformly distributed in the metallic glassy matrix and displayed metallurgical interface with the Vit 1 BMG. The mechanical properties test indicated that the plasticity of the brittle Vit1 BMG was significantly improved with the introduction of stainless steel skeleton. As the mesh number of stainless steel increased (corresponding to the increase of the volume fraction of crystalline phase), the plasticity of composites displayed an increasing trend. However, when the mesh number exceeded 200, there were some deteriorations in mechanical properties due to the unfilled porosity defects in the composites. When the volume fraction of crystalline phase is about 53.7%, the fracture strain of composites reaches the maximum value of about 10%, which is much higher than that of Zr-based BMG composites toughened by traditional stainless steel fibers. The analysis of the toughening mechanism showed that the brittle-ductility transition of the HPDCed Vit1 BMGs mainly resulted from high efficiency suppression of shear band propagation by metal skeleton, which promotes the proliferation and initiation of shear bands and reduce the localization of macroscopic plastic deformation, as well as the reduced stress concentration due to decrease of mesh number. This study provides new insights for the design and preparation of BMGs composites with excellent mechanical properties, and has important engineering value for application of BMGs.

Abstract:The asynchronous rollability of as-cast and heat treated multiphase V₆₀Ti₂₀Ni₂₀ alloys for hydrogen separation and the effects of different speed ratio on the microstructure, hardness and texture coefficient of the alloys were studied. The results show that the effect of asynchronous rolling process on improving the rollability of the alloys is higher than that of heat treatment process. Heat treatment plus asynchronous rolling can effectively improve the rollability of the alloys. The asynchronous rollability of the alloys increases with the increase of different speed ratio, and the hardness of the alloys hardly changes with the change of different speed ratio. The alloys show obvious rheological characteristics at high rolling reduction. V-based solid solution (Vss) and NiTi phase have large deformation and elongation along the rolling direction and form layered structure. With the increase of different speed ratio, the microstructure of the alloys gradually shows uneven deformation at a low degree along the thickness direction, and the deformation degree at the center is higher than that in synchronous rolling. The shear deformation introduced by asynchronous rolling along the thickness direction can weaken the rolling texture of the alloys to a certain extent.

Abstract:_{: The 6063Al-xAl2O3 (X= 0,2,4,6) composite was prepared by the method of near liquid line casting using CuO-Al as the reaction system to form Al2O3 particles in the in-situ reaction of 6063 aluminum alloy. The influence mechanism of the shape, size, quantity, distribution and interface characteristics of in-situ reaction particle Al2O3 and in-situ crystallization particle Mg2Si of 6063 aluminum alloy on the microstructure and wear resistance of the alloy was studied. The results show that near spherical θ-Al2O3 particles with sub-micron size are formed in the in-situ reaction of 6063 aluminum alloy. The (311) crystal plane has a coherent interface with the (111) crystal plane of 6063 aluminum alloy matrix. The size of Mg2Si in 6063 aluminum alloy is about 100nm, which is banded, and its (02-2) crystal faces with Al matrix (111) belong to coherent interface. With the increase of the content of Al2O3 particles, the grain morphology of 6063 Al matrix composites changes from rose-like to equiaxed grain gradually, and the grain size decreases gradually. When the mass fraction of Al2O3 is 6%, the microstructure of the composite is composed of equiaxed grains and fine columnar grains. When the load is 50N, the wear of 6063 aluminum alloy is 6.72mg, and the wear of 6063-6Al2O3 composite is 1.63mg, which is 75.7% lower than that of 6063 aluminum alloy. The in-situ particles (Al2O3+Mg2Si) form a coherent interface with the aluminum matrix. There is no pollution between the interfaces and the interface bonding strength is high. In the wear process, it is not easy to fall off from the matrix and bear most of the load in the wear process. The synergistic effect of in-situ formation of high hardness Al2O3 particles and in-situ crystalline particles Mg2Si can improve the wear resistance of composites. When the applied load is 40N, the wear mechanism of the composites changes from adhesion wear to abrasive wear with the increase of the mass fraction of reinforcement phase. The wear mechanism of 6063 aluminum alloy is mainly serious adhesion wear. The wear mechanism of 6063-2Al2O3 composites is mainly adhesive wear, and the wear of 6063-4Al2O3 and 6063-6Al2O3 composites is mainly abrasive wear.}

Abstract:The phase precipitation behavior of a new low-cobalt casting nickel-based superalloy was studied by thermodynamic calculation software JMatPro and differential scanning calorimetry (DSC), and compared with the microstructure and composition of the actual ingot. The results show that the as-cast microstructure of low-cobalt alloy mainly includes γ (matrix), γ′, carbides (MC, M6C) and γ+γ′ eutectic structure (volume fraction about 13.9%). Positive segregation of Ta and Hf occurrs during solidification. The DSC test shows that the initial melting point, final melting point and γ′ phase remelting temperature of the alloy are 1349.6℃, 1300.1℃ and 1272.1℃, respectively. Theoretical calculations are basically consistent with the experimental results. Thermodynamic calculation shows the increase of Al and W content can increase the precipitation amount and re-solubilization temperature of γ′ and M6C carbides, respectively. Hf and Ta elements may increase the liquid-precipitation tendency of MC carbides. The expected stress rupture property of the new low-cobalt alloys is better than that of existing commercial nickel-based polycrystalline casting superalloys.

Abstract:The stress-strain curves of forged GH4742 superalloy at deformation temperature of 1020~1150 ℃ and the strain rate of 0.001~1 s-1 under the true strain of 0.65 were obtained by single-pass isothermal compression experiments, the hot deformation constitutive equation and hot working diagram of GH4742 superalloy were constructed, and the evolution of the micro-substructure and γ′ phase during the thermal deformation process were studied by SEM, EBSD, and eventually the correlation of the deformation process conditions-the microstructure difference-the mechanical property variety was established. The results show that the evolution mechanism of the alloy"s microstructure and mechanical properties were closely related to the Z parameter. When the strain rate increased from 0.001 to 1 s-1 at low temperature deformation of 1080 ℃, the lnZ value increased from 75.6 to 82.6, the thermal effect was strengthened, which resulted in the proportion increment of dynamic recrystallization, and the proportion of low-angle grain boundary decreased, the hardness of the matrix increased due to the refinement of the microstructure; With increasing strain rate at high temperature deformation of 1110 ℃, the lnZ value increased from 74 to 78.5, the dislocation slip and grain boundary migration were suppressed, which decreased the proportion of dynamic recrystallization, and the proportion of the high-angle grain boundary was improved, and the hardness of the matrix increased due to the work hardening. The critical lnZ value of GH4742 superalloy without grain coarsening of dynamic recrystallization was 73. The optimum hot working parameters for forged GH4742 superalloy was 1110～1150 ℃ and 0.001～0.01s-1 by the analysis of thermal processing map and the hot deformation microstructure.

Abstract:The first-principles calculation method is used to study the alloy atom vacancy formation energies of O phase, B2 phase and α2 phase in TD3 alloy, and the energy stability and diffusion behavior of oxygen atoms in the three phases. The calculation results show that the vacancy formation energies of Al atoms in the three phases are all lower than those of Ti and Nb, which is beneficial to the formation of α-Al2O3 dominated oxide film on the surface of TD3 alloy. The interstitial energy of oxygen atoms in the octahedral interstitial positions of O phase, B2 phase and α2 phase is lower than that of tetrahedral interstitial positions, and the interstitial energy of titanium-rich octahedral interstitial positions is the lowest, the lowest oxygen atom interstitial energy is -5.0815eV respectively , -4.9425eV and -5.9315eV. The barriers to be crossed for oxygen atoms to diffuse along the best diffusion path in O phase, B2 phase and α2 phase are 0.812 eV, 1.913 eV and 1.164 eV, respectively.

Abstract:In this paper, Zn-0.75Cu-0.15Ti-0.3Mg alloy sheet was prepared by extrusion and rolling method, and its microstructure evolution process, mechanical properties and corrosion resistance were discussed. The results show that the Zn-0.75Cu-0.15Ti-0.3Mg alloy exhibits a fine equiaxed crystal morphology after extrusion deformation. Micro-scale TiZn3 and MgCuZn phases and nano-scale CuZn5 phase exist in Zn matrix. Rolling deformation promotes the grain growth of Zn matrix and the grain size is relatively non-uniform. With the increase of rolling deformation, the matrix deformation induces the precipitation of more MgCuZn in the Zn grains. After rolling deformation, both the strength and elongation of the alloy show a decreasing trend, and the tensile strength decreases from 142.7 MPa to less than 110 MPa, which was mainly attributed to the growth of grains and the increase of brittle second phases. However, the rolling deformation contributes to the improvement of the corrosion resistance of the alloy. The as-rolled alloy exhibits a lower corrosion current density (25.47×10-5Amp/cm2) and a higher corrosion product layer resistance (166.7Ω/cm2) compared to extruded alloy.

Abstract:A series of WO3-Nb2O5 electrospun heterojunction nanofibers (WN NFs) with different W/Nb molar ratios were fabricated based on an electrospinning technology combined with calcination treatment. The structure and properties as well as the effect of WO3 content on the photocatalytic activity of WN NFs were investigated. The results confirmed that the coupling of WO3 with Nb2O5 resulted a remarkable red shift in the optical response of the heterojunction samples and inhibited the recombination of photoinduced carriers. In the photocatalytic degradation experiment towards methyl orange as the target pollutant, the as-prepared WN NFs exhibited remarkably enhanced photocatalytic activity. Particularly, the WN NFs with W/Nb molar ratio of 15% demonstrated the largest degradation rate, exhibiting a prominent value of 96.4% in 150 min under visible light irradiation. And the kinetic constant was 0.0222 min-1, approximately 13.1-fold and 5.8-fold higher than that of pure Nb2O5 and WO3 nanofibers, respectively.

Abstract:The Ni/Al micro-laminated composite sheet was prepared by the vacuum hot pressing method. The mechanical properties and crack initiation and propagation laws of Ni/Al micro-laminated composite sheet were studied through uniaxial tensile experiments under different temperatures and different deformations degree. The results show that the Ni/Al micro-laminated composite sheet has poor plasticity from room temperature to 400°C, and when the deformation is only 5%, the NiAl3 and Ni2Al3 intermetallic compound layer has produced more cracks perpendicular to the tensile direction. The Ni/Al micro-laminated composite sheet exhibits good plastic deformation ability at 600℃, with the elongation at break as high as 56%, and when the deformation reaches 20%, the NiAl3 layer begins to appear microcracks, and the crack does not propagate to Ni2Al3 layer and Al layer when the deformation reaches 50%. The pressure free bulging experiment was used to study the forming performance of the Ni/Al micro-laminated composite sheet at 600℃, and the microstructure distribution of the bulging part was characterized. The results show that the limit bulging rate (limit bulging height/die diameter) of Ni/Al micro-laminated composite sheet at 600℃/5.5MPa/8min can reach 36.7%. The wall thickness of the gas bulged spherical shell gradually decreases from the bottom to the top, the top Ni and Al layers were severely necked, and cracks occurred in the NiAl3 layer, but they did not extend to the Ni2Al3 layer and the Al layer.

Abstract:In this paper, the as-cast alloys (Fe₈₁Ga₁₉)_1-xB_x (x=0,0.06,0.1,0.15,0.20) were prepared by vacuum melting method. The microstructure, morphology and composition of the alloys were characterized by X-ray diffraction, scanning electron microscopy, energy dispersion spectrum and metallography. The magnetostrictive properties of the alloys were measured by resistance strain gauge method.The results show that due to the addition of trace element B, the magnetostrictive properties of the alloy are improved, and the maximum saturation magnetostrictive value λs=138ppm is reached at x=0.10.The results show that the structure of (Fe₈₁Ga₁₉)_1-xB_x alloy is mainly α-Fe body center cube.The addition of B element causes lattice distortion and improves the magnetostrictive properties of the alloy, and the other part is distributed in the form of B-rich precipitates inside the grain.After the addition of element B, the grains of the alloy change into large columnar crystals, which are favorable to the magnetostrictive properties of the alloy. Because of the small grain boundaries, the large columnar crystals reduce the factors hindering the magnetic domain movement, which is favorable to the magnetostrictive properties of the alloy.

Abstract:The melt superheating treatment is carried out for reverted GH742 superalloy. Under the same solidification conditions, the microstructure evolution and its influence on mechanical properties is systematically investigated by changing the melt superheating temperature. The results show that the grain and dendrite are refined, and the dendrite segregation and the contents of N, O and S are decreased with the melt superheating temperature increasing from 1450 ?C to 1550 ?C. However, the grain and dendrite becomes coarse, dendrite segregation becomes serious and the contents of N, O increase after the melt superheating treatment at 1600 ?C. The morphology of MC carbide is rod-shaped or blocky. The melt superheating treatment has no significant influence on the morphology of MC carbide, but slightly decrease its size and area fraction. With increasing melt superteating treatment temperature, γ′ morphology changes from near-sphere to cube, but γ′ size first reduces with the increase of melt superheating temperature between 1450 ?C and 1550 ?C, but increases when the superheating temperature is higher than 1550 ?C. Corresponding to this, the tensile strength at room temperature is significantly improved after melt superheating treatment at 1550 ℃, but the ductile has no obvious change.

Abstract:In this study, the BCC lattice structure (CAD-based and TPMS-based) of NiTi memory alloy with different volume fraction were fabricated by selective laser melting. The compression response before failure was analyzed. The effects of volume fraction, unit configuration and microstructure on energy absorption were studied. The results show that the NiTi BCC structure (volume fraction 5 %~25 %) has excellent specific energy absorption (0.45~1.89 J/g) before compressing to damage, and can recover to more than 92% of the initial height after heating. Volume fraction and unit configuration have an important influence on the compression response of NiTi alloy BCC lattice structure. When the volume fraction is less than 15 %, the traditional CAD sample has longer compressible strain and better specific energy absorption than the TPMS sample. When the volume fraction is greater than 15 %, the TPMS sample has higher compressive stress and better specific energy absorption than the CAD sample. The ladder effect in the SLM process leads to different material microstructures on the lower surface and inside of the lattice structure, the molten pool streaks at the lower surface is deeper and wider, and the grains are larger. The heterogeneity of the material leads to relatively poor mechanical properties, which is not conducive to energy absorption. Due to the different stress concentration locations and heterogeneous ratios, material heterogeneity has a greater adverse effect on low volume fraction TPMS samples.

Abstract:In this paper, a successful attempt is demonstrated to prepare graphene/aluminum composites by in situ exfoliation of graphite flakes(GFs) using rotational friction extrusion(RFE) method. It is found the GFs were broken on a large scale and uniformly dispersed into the aluminum matrix during PRE. EBSD analysis indicated the grain was significantly refined, high angle grain boundaries were increased. As revealed by HRTEM that a number of 5-12 layer graphene can be peeled off from the GFs owing to the severe plastic deformation of RFE, and there exited obvious transition at the graphene-aluminum interface due to the diffusion of carbon atom at the broken graphene edge, which provided an an efficient load transfer for the composites. The yield strength and tensile strength of the prepared composites are 76.4MPa and 163.2MPa with 0.82 wt% addition of GFs , which are 91% and 71.4% higher than the RFEed base metal (1060 Al), respectively. Meanwhile, the elongation of the composites is 25.3%, and a good strength-ductility balance is obtained. This work may opens new opportunities for the fabrication of high-performance graphene/metal composite toward industrial application.

Abstract:In order to study the influence of solution treatment on the mechanical properties of INCONEL 625 components manufactured by micro-arc plasma additive, the samples of Inconel 625 alloy thin-walled components manufactured by additive were solution treated at 950℃, 1050℃, 1150℃ and 1250℃. The results show that with the increase of solution temperature, the degree of grain remelting increases continuously, and the growth orientation becomes disordered. The dislocation density gradually decreases and its distribution is concentrated in the grain boundary area. The precipitates gradually decrease, and the process of dissolution occurs. With the increase of temperature, the solution strengthening inside the structure improves the tensile strength, but the weakening of strain strengthening leads to the decrease of yield strength. At the same time, the weakening of Laves" resistance to dislocation slip improves the elongation of thin-walled members. After testing, the yield strength, tensile strength and elongation reached the best after solution treatment at 1150℃, and the corrosion resistance of thin-walled structure was significantly improved after solution treatment. This provides support for the optimization of mechanical properties of INCONEL 625 thin-walled components manufactured by micro-arc plasma additive manufacturing.

Abstract:The aluminum alloy is one of the widely used high-performance metal structure materials in aerospace field. However, due to the low hardness and inferior wear resistance, the aluminum alloy parts can be easily worn or scratched during the application. This research reviewed the methods for the improvement of wear resistance of aluminum alloys in terms of surface coating and nano-particle reinforcement, which provides important practical significance and scientific value for the exploration of new preparation methods of wear-resistant aluminum alloys and for the enhancement of the mechanical properties of aluminum alloys.

Abstract:The preparation of sound-absorbing materials with high porosity is very important for noise control. Silica aerogel has attracted increasing attention in recent years with its high porosity and high acoustic impedance. Combining silica aerogel with traditional sound absorbing materials can significantly combine their sound absorption advantages, and it is quite significant for noise elimination. The concept of sound absorption properties, sound absorption structure, mechanism, methods for measurement and characterization were introduced, and then the effects of air flow resistance, density, thickness, porosity, pore diameter, Young"s modulus and particle size on the sound absorption properties of aerogels were deeply investigated. In addition, the research progress of sound absorption properties of silica aerogels and organic compounds, organic/ inorganic minerals and non-woven fabric composites were reviewed in detail. Finally, the challenges faced at present and the development direction in the future were prospected.

Abstract:Compared with different exchange coupling models of one-dimensional to three-dimensional nanocomposite permanent magnet materials, exchange coupling will inhibit the magnetization reversal of soft magnetic phase, and different exchange coupling models have different effects on coercivity. The higher δM peak of Henkel curve indicates the stronger exchange coupling between grains. The peak of the first order reversal curve ( FORC ) corresponds to the exchange coupling. The effective anisotropy K_effof nanocomposite permanent magnet decreases with the decrease of grain size. When the grain size is constant, the higher the volume fraction of soft magnetic phase is, the lower the K_eff is. In order to obtain nanocomposite permanent magnetic materials with high maximum energy product, the grain size of soft magnetic phase should be about 10 nm, and the volume of soft magnetic phase should not exceed 50 %.

Abstract:With the rapid development of national economy, the chromium resources usage is increasing day by day, and the discharge of wastewater containing Cr(VI) is also increasing greatly. Cr(VI) has the characteristics of carcinogenicity, teratogenicity and mutagenicity. If it is not well treated, Cr(VI) will seriously pollute the ecological environment and threaten human health. In this review, the research progress of low concentration Cr(VI) treatment in wastewater by emerging extraction technologies was systematically summarized, and the technical difficulties and the research trends in the future are respectively summarized and prospected. The analysis shows that the traditional extractants are easily emulsified, volatile and low selectivity, and it is extremely urgent to develop a new economical, efficient and green extractants. Compared with the traditional solvent extraction (mixed-settler extraction, centrifugal extraction and tower extraction), chemical precipitation, electrochemistry, membrane separation, ion exchange, photocatalysis, adsorption, etc., these emerging extraction technologies, such as liquid membrane extraction, solid phase extraction, magnetic extraction and microfluid extraction, not only can remove low concentration Cr(VI) from wastewater, but also can obtain high quality chromium products. They are consistent with the concept of sustainable development. However, the above emerging extraction technologies are still in the laboratory research stage, a major research breakthrough of green extraction agents and new extraction equipments must be made in the future for achieving industrial application.

Abstract:The influencing factors in various stages of the turbine disk manufacture have been considered by numerical simulation to tightly control performance of finished turbine disk. This paper reviewed the developing status of numerical simulation method of superalloy turbine disks manufacturing way, which including seven process stages of vacuum induction melting (VIM), electroslag remelting (ESR), vacuum arc remelting (VAR), homogenization treatment, cogging, forging and heat treatment, and summarized the modeling methods and research focus of each stages. Then the research progress of integrated modeling of superalloy products manufacture were introduced, and our simulation research for the whole manufacture process of turbine disk was illustrated. Finally, the difficulties of multi-process integrated modeling were analyzed, which may provide references for the whole process integrated simulation of turbine disks manufacture in the future.

Abstract:Effect of microstructure on the fatigue crack propagation rates for TC17 Titanium alloy is studied in this paper, and crack growth path is analyzed. The results show that the crack growth rates increase with the temperature rising in the equiaxed structure on the step I and the step III during the crack growth for the TC17 titanium alloy, and the microstructure has fewer influences on step II on crack growth rate; The anysis conclusions of the crack growth rates for two different lamellar microstructres show that microstructure under the solution anneal has lower crack growth rates during the whole crack grwoth, the initia fracture zone matches higher sress intensity factor, and the crack growth path is more zigzag in solution anneal microstructure than that solution aging state.

Abstract:The low cycle fatigue behaviors of single-crystal superalloy CMSX-4 were investigated at 760 °C and 950 °C. At 760 ℃, specimens have longer fatigue lives and higher strength under higher strain amplitude. The fracture sections of specimens at 760 ℃ have a large height difference with an angle of 45° to the stress axis direction, and the cracks expand along the {111} plane; while the fracture sections of specimens at 950 ℃ are perpendicular to the stress axis, and the cracks expand along the {001} plane. Scanning electron microscope was employed to analyze the fatigue fracture, and it is found that the micropore near the surface of specimens at 760 ℃ is the main fatigue source, while the fatigue cracks originated from the oxide layer near the surface of specimens at 950 ℃ and it shows multiple sources of cracking. Transmission electron microscope was employed to analyze the dislocation motion modes. The deformation mechanism of low cycle fatigue at 760 ℃ includes planar slip and wavy slip, which is the process of transition from planar slip to wavy slip. Whereas, the dislocation at 950 ℃ mainly moves by cross-slip and a process of gliding and climbing.