Abstract:Thermal stability and thermo-mechanical properties of Pd₂₀Pt₂₀Cu₂₀Ni₂₀P₂₀ high entropy metallic glass (HEMG) were investigated by differential scanning calorimetry, X-ray diffraction, and thermomechanical analysis. Results show that compared with other classical precious metal-based metallic glasses, Pd₂₀Pt₂₀Cu₂₀Ni₂₀P₂₀ HEMG presents comparable performance with distinct characteristics.

Abstract:In order to improve the thermal stability and to obtain a large supercooled liquid region of metal glasses, the Zr_65-x(Al_0.21Ni_0.29Cu_0.04Ag_0.46)_35+x (x=0, 7.5, 15.0, 22.5) metallic glasses were investigated. The effects of component concentrations on the thermal stability, heat-induced precipitate phases, and mechanical properties were analyzed. Results show that with increasing the component concentrations, the peak position of the broad diffraction pattern shifts towards higher angles, indicating the occurrence of glass transition phenomenon. With increasing the glass transition temperature (T_g) and crystallization temperature (T_x), the liquidus temperature (T_l) is decreased, leading to decrease in the temperature difference (namely supercooled liquid region, ΔT_x) between T_x and T_g and resulting in the increase in reduced glass transition range (T_rg). Additionally, the nucleation activation energy (E_x) and the growth activation energy (E_p1) are increased with increasing the solute concentration. The primary crystal changes from the combination of tetragonal Zr₂Ni, Zr₂(Cu, Ag), ZrAg, and hexagonal Zr₅Al₃ phases into the single tetragonal ZrAg phase. The Vickers hardness is also increased with increasing the solute concentration. In this research, a novel metallic glass, Zr_65-x(Al_0.21Ni_0.29-Cu_0.04Ag_0.46)_35+x (x=7.5), is developed, which presents a large ΔT_x of 141 K, high thermal stability, and strong crystallization resistance. This research adopting the multicomponent replacement strategy is of great significance to improve the thermal stability of metallic glasses.

Abstract:Tribological properties of Al₁₉Fe_20-xCo_20-xNi₄₁Mo_2x (x=0, 1, 2, 3, 4, 5) eutectic high-entropy alloys (EHEAs) were investigated in this research. Results show that EHEAs with trace Mo addition can form the face-centered cubic (fcc)+B2 eutectic microstructure, whereas EHEAs with relatively higher Mo content can form fcc+B2+μ dendritic microstructure. Mo element is beneficial to the strength enhancement of L1₂ phase and the ductility improvement of B2 phase. However, with increasing the Mo content to x>2, the resultant Mo-rich μ phase degrades the strength and plasticity of EHEAs. Al₁₉Fe₁₈Co₁₈Ni₄₁Mo₄ EHEA has the optimal combination of high strength and high ductility. Increasing Mo content can improve the oxidation resistance of EHEAs. With increasing the Mo content, EHEA forms a tribo-oxide layer with improved oxidation resistance during sliding process, and the friction coefficient is monotonically decreased. This research provides guidance for the investigation of tribological properties of Al₁₉Fe_20-xCo_20-xNi₄₁Mo_2x EHEAs.

Abstract:To understand the dynamic mechanical properties and thermodynamic stability of β-Ti phase-embedded Zr/Ti-based bulk metallic glass composites (BMGCs), (Ti_0.474Zr_0.34Cu_0.06Be_0.126)_100-xFe_x (x=0, 2) BMGCs were prepared and investigated. Results show that by introducing Fe element, the stability of β-Ti phase is improved. An abnormal internal friction peak can be observed due to the precipitation of ω-Ti in the metastable β-Ti phase. Below the glass transition temperature T_g, both BMGCs show abnormal overshoot on storage modulus due to the coupling effect of phase transition and partial crystallization of amorphous matrix. This research provides information about the complex dynamic mechanical relaxation behavior of the in-situ metastable β-Ti BMGCs.

Abstract:Based on the glass-forming ability (GFA) during cooling process and the glass stability (GS) of heating process, a triangle to evaluate GFA and GS, namely Tri-FAS, with the combination of pseudo-four characteristic parameters as vertices was established. Accordingly, a GFA&GA criterion (G-FAS) was deduced as G-FAS=T_g/T_l+T_x/T_l+T_x/T_g (T_x is onset crystallization temperature; T_l is liquid temperature; T_g is glass transition temperature). Additionally, the criterion was modified based on the competitive relationship between amorphous phase and crystal phase during cooling process and the contribution of each component to the criterion: G-FAS_m=T_g/(1.5T_x)+T_x/T_l+T_x/T_g and G-FAS_m′=T_g/T_l+T_x/T_l+(T_x/T_g)^a (a≈1.5±0.2). The correlation between G-FAS and critical cooling rate R_c and that between G-FAS and T_xg (T_xg reflects the supercooled liquid region of glass, T_xg=T_x/T_g) were discussed, which could reflect GFA and GS, respectively. Through the determination results of GFA and GS of abundant metallic glasses and other glass formers, the validity of the proposed G-FAS criterion was evaluated. Results show that with respect to both GFA and GS, the G-FAS criterion is reliable in various glass former systems, showing wide applications. The proposed Tri-FAS and G-FAS criterion can provide guidance during the fabrication and application of metallic glasses.

Abstract:The single-pass thermal compression experiments were conducted on NiCoFeCrAl high entropy alloy by Gleeble-3800 thermal simulation tester. The Arrhenius constitutive model was established based on the peak stresses. With four instability criteria (Prasad, Murty, Gegel, and Malas), different heat processing maps of dynamic material model were established. The applicable ranges of the instability criteria for the alloys in the heat deformation process were analyzed and compared. Results show that the optimal heat processing ranges of the alloys are the temperature range of 980–1010 °C+strain rate of 0.01–0.001 s^-1 and the temperature range of 1050–1100 °C+strain rate of 0.01–0.1 s^-1. The average power dissipation rate is greater than 36%. Through EBSD microstructure analysis, the softening mechanism of thermal deformation is changed from dynamic recovery to dynamic recrystallization with increasing the deformation amount.

Abstract:Due to the disordered structure of amorphous alloys, the complex structural dynamics involves the particle rearrangements with a large span in time and size scales. The characterization and mechanism of structural dynamics of amorphous alloys are crucial and fundamental for the further research of relaxation behavior and physical aging kinetics of glasses. Abundant researches show that the relaxation spectra of rare-earth-based amorphous alloys, which are represented by lanthanum- and cerium-based alloys, show obvious secondary relaxation process, and the system becomes an ideal carrier to investigate the relationship between structural dynamics and mechanical properties of amorphous alloys. In this review, the anelasticity of metallic glasses was discussed. The anelastic deformation, as the main component of deformation, can totally recovery after unloading in creep experiments, and its mechanism is important to form deep understanding about the structural dynamics of metallic glasses. Additionally, the main characteristics of anelastic deformation during creep and creep recovery were summarized, and some theoretical models for quantitative and qualitative description were introduced.

Abstract:In recent years, high-entropy alloys (HEAs) have become the research hotspot in the field of metal structural materials because of their novel design concepts and excellent physicochemical properties. With the continuous popularization of lightweight alloy design concepts, the conception of “entropy regulation” has been widely used to develop new lightweight alloys. Lightweight HEAs (LHEAs) are a new type of low density HEAs based on lightweight alloy designs. Their development and design mainly combine the empirical parameter criteria, phase diagram calculations, and first-principles calculations. Al-Ti-V-based LHEAs attract much attention among various LHEAs due to their excellent mechanical properties, good high temperature oxidation resistance, and fine corrosion resistance. This paper summarized the research progress of Al-Ti-V-based LHEAs from the perspective of composition design, preparation methods, microstructures, and physicochemical properties. Meanwhile, the problems and challenges for Al-Ti-V-based LHEAs were also prospected.

Abstract:The relaxation dynamics of metallic glasses, as one of the most challenging issues, is complex. The relaxation, including α relaxation, slow β relaxation, and fast β relaxation, occurs at different temperatures. Taking advantage of the microscopic atomic information of simulation, the characteristics and mechanisms of these three typical relaxations were summarized to discuss their influence on mechanical properties of metallic glasses. Recent progresses on dynamical, structural, and physical mechanisms by simulation method were discussed. This review is beneficial to understand the nature of glass and to establish the dynamics-structure-property relationship of glassy materials.

Abstract:The control of atomic-scale structure of metallic glasses (MGs) to improve their physical, chemical, and mechanical properties is an essential issue. Over past decades, large efforts have been devoted into the development of effective MG control approaches, such as the cryogenic treatment (CT) technique. This research reviewed the effects of cryogenic treatment on the properties and their dependence on the initial structural energy state of MGs. Then, it focused on the atomic-scale structure evolution in MGs during CT, which is of fundamental importance to understand CT effects.

Abstract:This study employs vacuum arc melting technology to fabricate FeCrMnAlCux (x=0, 0.5, 1.0, 1.5, 2.0) high-entropy alloys. The phase structure and microstructure of the alloys before and after corrosion were characterized using XRD, SEM, and EDS. The corrosion behavior of the alloys in 0.5M H2SO4 solution was analyzed through potentiodynamic polarization curves, EIS, XPS, and immersion tests. The results indicate that the addition of Cu promotes the formation of the FCC phase in the alloy, transforming it from a single BCC structure to a mixed BCC+FCC dual-phase structure. The high-entropy alloys with five different compositions exhibit a typical dendritic morphology. As the Cu content increases, the grains gradually refine, and the microstructure becomes more uniform. The FeCrMnAlCu1.5 high-entropy alloy has the highest corrosion potential (-0.363 V) and the lowest corrosion current density (2.148×10-5 A/cm2). The alloy"s corrosion resistance initially improves and then deteriorates with increasing Cu content. At x=2.0, the corrosion potential decreases to -0.394 V, and the current density increases to 2.865×10-4 A/cm2, yet its corrosion resistance is still superior to that of the alloy without added Cu. After corrosion, a composite oxide protective film forms on the cross-section of the alloy, effectively reducing its corrosion rate in 0.5M H2SO4 solution.

Abstract:: The first density functional theory and virtual crystal approximation (VCA) method were used to establish the crystal structure model, and the structural properties, elastic properties and heat of energy of high entropy alloy Al0.4Co0.5VxFeNi were calculated. According to the minimum energy principle, the optimal K-point value of Al0.4Co0.5VxFeNi high entropy alloy is 12×12×12, and the cutoff energy is 1000eV. The results show that FCC+BCC structure can be formed by Al0.4Co0.5VxFeNi alloy, and the mechanical stability of FCC is obviously better than that of BCC. When V content increases from 0.2 to 0.8, BCC lattice constant decreases by 4% and FCC lattice constant decreases by 6%. The bulk modulus and shear modulus of Al0.4Co0.5VxFeNi alloy decrease with the increase of V element. When the content of element V is 0.8, the Poisson"s ratio of BCC structure increases abnormally, which further indicates that with the increase of element V content, the plastic deformation capacity of materials decreases and the brittleness of materials increases. The experimental results show that Al0.4Co0.5VxFeNi alloy is composed of FCC and BCC, and its microstructure is two-phase. When the content of element V decreases from 0.2 to 0.8, the elongation decreases by ~85%. The experimental result is the same as that calculated by the first principles.

Abstract:At present, the traditional design concept of alloying materials based on enthalpy change is approaching its limit, while new metal materials based on entropy change design have a large degree of freedom in the design of medium and high entropy alloys, which make up for the shortcomings of room temperature brittleness and metastable crystallization of metastable materials and continuously make breakthroughs in performance. Laser additive manufacturing technology differs from traditional processing design and manufacturing concepts, providing new possibilities for promoting the development of advanced alloy materials and has become a key technology for linking materials and products. In this paper, based on laser additive manufacturing technology, the research status of high-entropy alloy coating prepared by laser cladding technology, high-entropy alloy prepared by 3D printing technology and high-entropy high-temperature shape memory alloy prepared by 4D printing technology are described from three dimensions of 2D, 3D and 4D, respectively. The key technical problems and solutions in the current research are discussed. Finally, the preparation of advanced alloy materials by laser additive manufacturing technology is summarized and prospected.

Abstract:The mechanical properties and deformation mechanism of a novel Ni-Co-based superalloys at room temperature (25 ℃) and medium temperature (650 ℃, 700 ℃ and 750 ℃) were studied using SEM, EBSD and TEM. The results show that the yield strength and elongation rate of the alloy were 1176 MPa and 22.5% respectively at room temperature, and the decreasing trend with temperature increase. At room temperature, the main deformation mechanism is that a large number of dislocations slip, and the partial dislocations shear the γ′ particles into isolated stacking faults. When the temperature reaches 650 ℃, it is observed that microtwins run through the secondary γ′ particles and γ matrix，but it is mainly deformed that continuous stacking faults shearing secondary γ′ particles and γ matrix. At 700℃-750℃, the secondary γ′ particles and the γ matrix are sheared simultaneously by continuous stacking faults and microtwins, and the length of stacking faults and thickness of microtwins increase with temperature. In the 650 ℃-750 ℃ range, the mechanism for shearing a γ′ particles once transitions from APB to isolated stacking faults. This study discusses the variation of deformation mechanism with temperature and the formation mechanism of microtwins and stacking fault under medium temperature conditions. An atom interchange diffusion model for SEFS formation of a/6 <112> partial dislocation shear γ′ particles is presented, which explains the formation process of microtwins and provides a reference for the further development of novel Ni-Co-based superalloys with high performance level.

Abstract:The preparation of micron-sized spherical particles by the Pulsed Orifice Ejection Method (POEM) is a typical unconstrained heat transfer and solidification process, and the prepared spherical particles have the characteristics of uniform particle size, high roundness and consistent thermal history. The heat transfer mechanism dominated by convection and radiation is crucial for the preparation technology, solidification process and microstructure control. According to the preparation process, heat transfer and solidification characteristics of micron-sized spherical metal particles by POEM, a numerical calculation model of heat transfer and solidification in a three-dimensional spherical coordinate system is established in this paper. The proposed model considers the behavior of the convection and radiation heat transfer of pure Cu particles in the unconstrained solidification process, and adopts the temperature recovery method to deal with the latent heat of pure metal solidification. The temperature variation and distribution of spherical particles at different solidification stages are calculated, and the temperature gradient, cooling rate, liquid-solid interface movement and solidification rate during the solidification process are also investigated. In addition, the convective and radiative heat transfer and their contribution are simulated and analyzed, and the effects of different preparation processes on the convective heat transfer of the particles are explored. The results provide references for the optimization of the preparation and the regulation of the solidification process of micron-sized spherical particles by POEM.

Abstract:GH4141 wrought superalloy is widely used in the manufacture of high-temperature load-bearing components for aerospace engines due to its high strength and good oxidation resistance at high temperatures. In this paper, based on chemical composition analysis and crystallographic method, the typical precipitates in the as-cast GH4141 alloy were identified and analyzed in detail. The dissolution behaviors of the precipitates during the homogenization process were analyzed through the high-temperature homogenization experiments. Under the medium and low temperature homogenization conditions of 1130~1160 oC, the needle-like σ phase, plate shape η phase, M3B2 boride and γ’ strengthening phases of the original as-cast structure are dissolved into the matrix, while the M6C carbide can still be existed. Under the condition of high temperature homogenization at 1190~1210 oC, most of the precipitates including M6C in the alloy have been dissolved into the γ matrix, and only a small part of MC carbides remain in the structure. Besides, it’s worth noting that the MC carbides are dissolved in the solid-liquid two-phase region, and the MC carbides are difficult to be completely dissolved and eliminated through homogenization heat treatment.

Abstract:Laser deposition manufacturing (LDM) technology has unique advantages in additive manufacturing of large aircraft frames and beams. However, stress and deformation have become bottlenecks that hinder the application of this technology. Therefore, the islands process is widely used to discrete the residual stress and alleviate the deformation of the parts. However, the traditional islands process does not take into account the geometric structural features of parts easily lead to irregular partition lap, which introduced pores, poor fusion and other defects. In order to solve this problem, a feature islands method is proposed. According to the geometric shape characteristics of the slicing layers of typical frame and beam structural parts, The features are classified into four types: “十”-shape, T-shape, L-shape and “一”-shape features, and all kinds of features are limited from three aspects :shape, pose and size to complete the definition of island features. A feature recognition algorithm based on region skeleton line detection is proposed, where the skeletonization is used to effectively simplify the features and retain the part characteristics. The vector cross-product and fixed-ratio point method are used to calculate the relevant parameters such as feature angle, plane attitude angle and number of feature branches. Feature type identification is achieved by comparing calculated values with defined values. The algorithm is verified by slice data of a typical aircraft frame model. The results show that the algorithm can quickly and accurately identify various features to realize automatic feature islands of parts, which lays a foundation for intelligent additive manufacturing technology.

Abstract:GH4151 alloy is a new type of casting and deformation superalloy of turbine disk with the temperature bearing capacity up to 800 ℃. The alloy has severe elemental segregation during solidification, main segregation elements including Nb, Ti and Mo element. Meanwhile, the alloy contains a large amount of C element. In the late stages of solidification, due to the enrichment of elements in the residual liquid phase, a large number of harmful phases, including (γ-γ′) eutectic, Laves phase, η phase and MC carbides, precipitate between the dendrites. By studying the influence of C content on the segregation elements, it is found that increasing C content can reduce the segregation of Nb elements between dendrites. In addition, with the increase of C content, the dendrites become more developed and the inter-dendrite area decreases. The melting points were determined by studying the effects of homogenization heat treatment at different temperatures from 1160 ℃ to 1210 ℃ that (γ-γ") eutectic and Laves phases are about 1180 ℃, η phase is about 1200 ℃ and MC carbide is more than 1300 ℃. At the same time, it is found that the 1170 ℃/16 h-1200 ℃/8 h double step homogenization heat treatment can not only eliminate the segregation in the ingot, but also avoid the holes caused by the overburning of the low melting point phases, which makes the billet more conducive to the subsequent billet deformation.

Abstract:In order to explore the principle of metal composite assisted by high frequency pluse current, the test of rolling-welding magnesium composite plates prefabricated notch assisted by high frequency pulse current is designed.The microstructure evolution and mechanical properties of bonding interface and areas near interface of the composite plates were compared under different loading frequencies (25 kHz, 50 kHz, 75 kHz).The morphological characteristics of microstructures near interface of magnesium alloy composite plates was observed by metallographic microscope;Nanoindentation test and Vickers hardness test were used to characterize the characteristic of the interface micro-region and cross section hardness distribution respectively;The tensile properties and fracture morphology of magnesium alloy composite plates were analyzed by tensile testing machine and electron microscope.The results show that with the increase of the frequency, the composite effect of the interface increases first and then decreases;when the high frequency current parameter is 50 kHz, the tensile strength and elongation of magnesium alloy composite plates are the best, reaching 292.52 MPa and 25.7%, respectively.This can be contributed to the comprehensive role of skin effect、proximity effect、Joule heat effect of current and contact resistance of interface micro-region.

Abstract:The quasi-β forging of TC21 titanium alloy was carried out,and then embarked on the solution aging heat treatment experiment,and the effects of different solution aging heat treatment systems on the microstructure and mechanical properties of the alloy.The results showed that after TC21 titanium alloy was forged by quasi-β and treated by solution aging heat treatment process,the microstructure of the alloy presents a typical basket-weave structure.With the increase of solution temperature,the content and length of the lamellar α phase decrease significantly,and the strength of the alloy increase,while the plasticity change showed the opposite trend.With the increase of aging temperature,the effect on the lamellar α phase was slightly smaller,but the thickness of the secondary α phase increases significantly,and the strength of the alloy decreases and the plasticity increases.The morphology of the fracture becomes flatter with the increase of the solution temperature,and the fracture surface and crack growth path become flatter.The fracture toughness value presented a downward trend,but it increased with the increase of aging temperature.The maximum fracture toughness value of the alloy can reach 66MPa·m1/2.Considering the good match between the strength,plasticity and fracture toughness of the alloy,after comprehensive analysis,it can be obtained that the best heat treatment system of TC21 titanium alloy after quasi-β fracture is:870°C/2 h,AC+590°C/4 h,AC.

Abstract:A new kind TiBN powder material was synthesized by boronizing sintering method. TiBN was both ceramic and metallic, with a resistivity of 2.6 × 10-3 Ω·cm. Cu/TiBN and Cu/TiN electrical contact materials were prepared by powder metallurgy using TiBN and TiN as reinforced phases. These microstructure and physical properties of electrical contact materials with different contents of TiBN and TiN were systematically investigated. The results demonstrated that, when compared to TiN, the TiBN reinforced phase can significantly improve the electrical conductivity, oxidation resistance, hardness, and arc erosion resistance of Cu-based electrical contact materials. When the content of TiBN was 5wt.%, the arc erosion resistance of Cu/TiBN was the best, and the weight loss was only 1.5mg. During arc erosion, products such as TixOy, B2O3 and N2 were formed on the surface of Cu/TiBN. These products can significantly improve the arc erosion resistance of Cu/TiBN electrical contact materials. The newly developed Cu/TiBN electrical contact materials had excellent mechanical properties and resistance to arc erosion, and had a broad application prospect in the electrical contact industry.

Abstract:Longitudinal wave rolling + flat roll rolling ( LFR ) is a new rolling process to reduce edge cracks and basal texture of magnesium alloy. This process can prepare magnesium alloy sheets with light edge cracks through one-pass longitudinal wave rolling + two-pass flat rolling. However, the LFR process deformation law is not clear. In this paper, the thermo-mechanical coupling finite element virtual rolling comparison and physical experiments of AZ31 plate longitudinal wave rolling + flat rolling ( LFR ) and flat rolling + flat rolling ( FFR ) were compared, the metal deformation law in the longitudinal wave rolling deformation zone and its influence on the edge damage of the plate were analyzed. The results show that a special-shaped rolling area has formed in the longitudinal wave rolling, which caused shear strain in different parts of the sheet. Furthermore, the temperature drop at the edge of the plate was avoided due to the plastic deformation heat generated by rapid metal flow, which is beneficial to improve the plasticity. The influence of shear strain and temperature promotes the formation of mixed microstructure of LFR sheet, reduces the damage of trough, and effectively inhibits the generation and development of edge crack of magnesium alloy sheet.

Abstract:The corrosion behavior of four typical Ni-based corrosion-resistant alloys in supercritical aqueous solution of Na3PO4, Na2SO4 and NaCl at 450 ℃/23 MPa was studied by using XRD, SEM, etc. After corrosion for 50 h, the surface of the alloys was covered with short rod-shaped and needle-shaped products mainly consisting of NiCr2O4，Cr2O3，NiO，Ni3(PO4)2，CrPO4 and Na3PO4. With the prolong of time, the thickness of the corrosion layers increased and the corrosion resistance was ranked as X-1#>X-2#>625>C-276

Abstract:Ni/WC composite coating with high wear resistance, corrosion resistance and high hardness characteristics, it is widely used in shield components, raerospace and other fields. In order to improve the service life of hydraulic machinery overflow components, the paper simulated the material of hydraulic turbine blades, WC particles and Ni-based powder brazing filler metals were used to prepare Ni/WC composite brazing coating on the surface of 201 stainless steel by vacuum brazing process. The interface microstructure and mechanical behavior of the brazing coating were resolved with scanning electron microscope, metallographic microscope and rockwell hardness tester. The results show that the diffusion behavior of elements between the coating and substrate are main dissolution of elements Fe, Cr and Mn from the stainless steel into the coating microstructure, and the interface appears segregation precipitation phenomenon. 25wt.% WC coating occurs a uniform hardness distribution, 4.6 times more than steel substrate. The wear resistance of coating increased with the increase of WC content. 15~35 wt.% WC addition can significantly improve the wear resistance of the steel surface. The wear resistance of the coating is 8.4~15.7times that of the steel, the surface of the coating don’t change significantly, and the crack opening is flat and brittle fracture.

Abstract:Through a series of hot compression tests on a novel powder metallurgy superalloy FGH4113A (WZ-A3), the effects of deformation temperature, strain rate and strain on the microstructure evolution were investigated. The results demonstrate that when the temperature is 1100 ℃, the strain rate is 0.1 s-1 and the true strain is 0.1~0.7, the increase of strain is beneficial to promote dynamic recrystallization and grain refinement. With the increase of strain, the volume fraction of γ" phase first decreases, then increases, and eventually remains stable. The morphology of γ" phase gradually becomes spherical during the thermal deformation process. Under the conditions of temperature 1100 ℃, deformation 50% and strain rate of 0.01~1 s-1, the increase of strain rate can improve the degree of dynamic recrystallization and refine the grains. With the increase of strain rate from 0.01~0.1 s-1 to 1 s-1, adiabatic temperature rise and dislocation slip intensify, resulting in the volume fraction of γ" phase reduces by about 2%. When the strain rate is 0.1 s-1 and the deformation is 50%, the increase of deformation temperature can promote dynamic recrystallization and grain growth in the temperature range of 1070~1160 ℃. With the deformation temperature rising to 1130 ℃, a large quantity of γ" phase has dissolved, the ability to pin the grain boundary has been significantly weakened, and the average grain size has increased to 12.1 μm. At the deformation temperature of 1100 ℃, strain rate of 1 s-1 and deformation of 50%, fine and uniform “γ+γ′ dual-phase structure " and the grain size above ASTM 12 can be obtained.

Abstract:This work is aimed to investigate time-spatial distribution rules and the effect of process parameters and geometric parameters to the forming quality of CLA16 F/M steel manufactured by electromagnetic incremental forming. Based on LS-Dyna R8.0 platform, an electromagnetic field-structure field sequential coupled finite element-boundary element model of electromagnetic incremental forming process of dummy fuel element was established. With the aid of the numerical simulation model, the electromagnetic forming process of dummy fuel element under different discharging voltages, flyer tube-base tube clearances and wall thickness of flyer tube were simulated and analyzed, and the sample fuel element was manufactured, for the sake of studying the local plastic flow rules, defects generation rules and characterizing the forming quality. Results show that oversized discharging voltage brings about the concentration of deformation zones to both ends of the tube. Also, the collision between the flyer tube and the base tube is aggravated and section distortion is introduced. Undersized discharging voltage can not generate the collision, deformation and sticking and thus leads to disconnection. Appropriate adjusting the clearance between base tube and flyer tube can effectively avoid wrinkling and nonuniformity of wall thickness. By comprehensive optimization of process parameters, through-process high quality precise forming of defects control of dummy fuel element was realized and the sticking precision between base tube and flyer tube reaches 10μm.

Abstract:To acquire the boundary of the heat treatment parameters satisfying property boundary is significant for property optimization of powder metallurgy FGH96 turbine disks, especially the boundary of the minimum cooling rate required for FGH96 alloy with a certain grain size under the premise of satisfying the performance requirements. Tensile behavior at 25 ℃, 650 ℃ and 750 ℃ of FGH96 specimens was investigated with different grain size under various cooling rates from solution temperature. The microstructures were observed. The results show that a multi-mechanistic strengthening model including the effect of chemical composition, γ′ size and fraction and grain size agree well with the experimental measurements. The strengthening model was applied to study the minimum cooling rate and grain size. The minimum cooling rate and grain size were obtained as: grain size should be smaller than 14 mm if cooling rates is 55 ℃/min, grain size should be smaller than 16.8 mm if cooling rates is 72 ℃/min, and grain size should be smaller than 20 mm if cooling rates is 81℃/min. The minimum cooling rate and grain size can be used as a guideline to design heat treatment process through simulation.

Abstract:In this paper, Al-30Zn-3Cu-2.5Si high Zn Al-based alloy is taken as the research object, the effect of Er and Zr on the microstructure and mechanical properties of as-cast and heat-treated alloys is investigated, and the action mechanism is analyzed and discussed. The results show that the grain size of the alloy can be obviously refined by adding 0.10 wt% Er and 0.10 wt% Zr, the average grain size is reduced from 74.28 μm to 60.01 μm, and the grain size of α-Al is changed into fine equiaxed grains. The addition of rare earth elements Er and Zr can form fine particles of Al3(Er, Zr) in the alloy and pin dislocations to improve the mechanical properties of the alloy. After adding Er and Zr, the tensile strength of as-cast alloy increased from 323.01 MPa of alloys without addition of Er and Zr to 358.29 MPa, and the tensile strength increased by 10.93%; and the yield strength increased from 309.33 MPa to 315.00 MPa, and the yield strength increased by 1.83%; the elongation has not changed basically. The tensile strength and yield strength of the alloy strengthened by solution-aging heat treatment are 449.48 MPa and 408.51 MPa respectively, which are 25.45% and 29.68% higher than those of the as-cast alloy. The coarse second phase exists at the grain boundary, which results in the poor elongation of the alloy.

Abstract:Additive Manufacturing (AM) is an advanced digitalized technology that has been extensively applied in the fabrication of high temperature alloys. This paper reviews the microstructure of high temperature alloys prepared by AM, summarizes the type and features of pores, and categorizes the development of models interpreting the formation of cracks. The application of computational science in the research of preparation of high temperature alloys was also reviewed. Finally, the prospect of AM in the research and development of high temperature alloys was discussed.

Abstract:Due to its low coefficient of thermal expansion, high temperature strength, high elastic modulus and other characteristics, molybdenum metal is widely used in aerospace, military, petrochemical and nuclear industries and other cutting-edge industries, is an indispensable material to promote the development of high-tech fields. Molybdenum powder as the basic material of molybdenum products, its physicochemical properties are closely related to the properties of molybdenum products. Compared with ordinary molybdenum powder, superfine molybdenum powder has larger specific surface area, higher activity and lower sintering temperature. At present, the main methods for preparing ultrafine molybdenum powder are thermal reduction method and thermal decomposition method. Thermal reduction method can prevent grain growth by adjusting the reduction process. The development of thermal decomposition method mainly involves the upgrading of equipment and the optimization of process. In this paper, focusing on the preparation process, reaction mechanism and product state of superfine molybdenum powder, the development process and technical characteristics of the typical process were analyzed, the research status and progress of the preparation technology of superfine molybdenum powder were summarized, and the problems faced by the current technology and the future research direction were put forward, in order to provide ideas for the development and industrial application of the preparation technology of superfine molybdenum powder.

Abstract:Heterojunction solar cells have the advantage of high cell efficiency and show great potential in the field of solar photovoltaics. Low-temperature metallization is an important process in the manufacturing of heterojunction solar cells, which is used to form metal grids on the cell surface. Currently, low-temperature-cured silver paste combined with screen printing is widely used to achieve this. However, the high consumption of expensive low-temperature silver paste is one of the reasons for the high cost of the cells. The photovoltaic industry is working hard to improve and optimize metallization process to reduce silver consumption. This paper reviews the recent progress on metallization technologies for heterojunction solar cells, and summarizes in detail how the components of low-temperature silver paste as well as the curing process affect the overall performance. In addition, the main metallization approaches used to increase cell effectiveness are introduced and compared, including silver paste reduction strategies such as multi-busbar and pattern transfer printing technologies, and non-silver metallization strategies such as silver-coated copper and copper plating technologies. Finally, the current challenges of different metallization process for heterojunction solar cells are analyzed and their future development are also prospected.

Abstract:With the rapid development of the third-generation semiconductors SiC and GaN, traditional packaging materials such as Si-based lead-free solder cannot satisfied the requirements of high-power density and high-temperature loadings in power electronic devices any more. Nowadays, the joints packaged by Cu nanoparticle sintering technology could not only be bonded at low-temperature and serving at high-temperature, but also exhibit excellent thermal conductivity, electrical conductivity and relatively lower cost comparing to Ag nanoparticles. Thus, more and more attentions has been attracted in the field of Cu nanoparticle sintering technology using in power electronic packaging, which makes Cu nanoparticles become one of the most potential high-temperature-resistant packaging and interconnection materials. In this work, the current research progress of Cu nanoparticle sintered technology was summarized, including the fabrication of Cu nanoparticle pastes, the factors affecting the performance of sintered joints and the reliability of joints. Meanwhile, the oxidation behaviors as well as the anti-oxidation methods of Cu nanoparticle were introduced. Also, the high-temperature working reliability and failure mechanism of Cu nanoparticle sintered joints were discussed. This review was aimed at promoting the application of low-cost Cu nanoparticle sintering technology for high-performance and high-reliability power electronic packaging.