Abstract:Mg-based foam biomaterials were prepared by a melt foaming process, wherein a Mg-Ca alloy was used as the matrix material, hydroxyapatite (HA) as the tackifier, MgCO3 as the foaming agent. The Mg-based foam biomaterials with uniform structure were tested to investigate their biodegradable behaviors. The biodegradable property of the Mg-based foam was mainly characterized by microstructure observation, immersion tests and electrochemical measurements. The results show that the weight loss rate increases with the increasing porosity of the specimen over a fixed period of time. The weight loss rate of the specimen without HA particles is much higher than that of the specimen with HA particles. Meanwhile, the open porosity of the Mg-based foam biomaterial increases with immersion time. Both the total porosity and added HA content have an important impact on the open porosity of the Mg-based foam biomaterial. Over a fixed period of time, the open porosity of the Mg-based foam biomaterial increases with the increase of the total porosity. Mg-based foam biomaterials with added HA exhibit higher corrosion resistance than Mg-based foam biomaterials without HA in simulated body fluid (SBF) media.

Abstract:The composite technique of templating and dealloying is proposed for synthesizing the low-density and hierarchical nanoporous gold (NPG). In this technique, the silica (SiO2) microspheres with an average diameter of ~700 nm are prepared as the sacrificial templates, the Ag@SiO2 and Au@Ag@SiO2 core-shell microspheres are prepared successively via the electroless plating approach, and the Au@Ag@SiO2 alloy bulks are formed through the cold-pressing and sintering method. By continually changing corrosion solutions, the templates and the Ag element can be completely eliminated from the Au@Ag@SiO2 alloy. The SiO2 templates are completely removed from Au@Ag@SiO2 microspheres so as to form the large-sized hollow spherical shells (with the diameter of ~675 nm), and the Ag element are eliminated by dealloying so as to generate a lot of small-sized pore (with the diameter of ~75 nm) structures on the shells. TEM images illustrate that the ligaments in NPG consist of the nano-grains with polycrystalline characteristic. The hierarchical NPG foam with low-density of 1.1 g/cm3 (the relative density of ~5.7 %) and high surface area of 4.24 m2/g shows the excellent catalytic activity and the rapid mass transfer rate for methanol electro-oxidation in alkali solution, which implies a promising application in catalysis.

Abstract:In this study, a biomedical β-Ti alloy Ti?25Nb?3Zr?3Mo?2Sn (wt. %) was fabricated via spark plasma sintering (SPS) its prealloyed powder. The prealloyed powder was produced by a plasma rotating electrode process. The majority of the powder particles had a microstructure composed of β-phase predominant dendrites, while a small fraction of the powder particles had a single crystal microstructure. SPS with a condition of 1000℃/5min/50MPa could just completely densify this β-Ti alloy powder and remove its prior dendritic segregation. After solution treatment, the consolidated alloy had a microstructure consisting of α″ + β phases, and exhibited a good tensile strength of 815 MPa and an optimal elongation of 14%, as well as a low elastic modulus of only 62 GPa. Aging at 500 ℃ brought about high number density of pure nanosized α needles, which renders this alloy a superior tensile strength up to 1015 MPa along with elongation and elastic modulus both acceptable. However, excessively low aging temperature should be avoided, due to the sharp embrittlement induced by nanoscale ω-phase precipitates.

Abstract:Aluminum matrix Boron carbide (Al/B4C) composites is an important thermal neutron shielding material. In order to prepare B4C/6061Al composite with higher density, Al/B4C composites reinforced by 30wt.% B4C particle were fabricated via hot isostatic pressing in the semi-solid temperature range of 6061Al. Microstructures, mechanical properties and densification mechanism of the composites were investigated. The results indicate that the density of Al/B4C composite is very close to the theoretical density with the usage of semisolid hot isostatic pressing. Although the tensile strength can reach up to 300 MPa, the ductility of the semisolid HIP Al/B4C composite is not good mainly because of the high content of 30wt%B4C. Aluminum liquid phase is observed indirectly which mainly formed during semisolid temperature range of 6061Al, it is helpful to improve the combination between the B4C particles and the 6061Al matrix. The increasing of density and Strength property mainly also due to the effect of aluminum liquid flows into the internal gaps under the hot isostatic pressing condition with high temperature and high pressure.

Abstract:Microwave absorption materials with high-effective, broad band and thin thickness have attracted a lot of attention of researchers. In this work, the flaky NdxCe2-xCo17 alloy powders were prepared by vacuum arc melting and high energy ball milling method. The influences of Nd content and matching thickness on phase composition, morphology, electromagnetic parameters and microwave absorbing property are studied by relevant equipments. The microwave absorption of Nd0.3Ce1.7Co17 powders were efficiently optimized generating a maximum RL of -32.36 dB and 4 times extension of effective bandwidth. Moreover, adjusting of Nd content successfully realize the optimization absorption of Ce2Co17 alloy powder. The absorption peak shifts to lower frequency region with the increasing Nd content and the maximum RL of Nd0.3Ce1.7Co17 powder can reach about -30.53 dB at 7.28 GHz at a given thickness of 1.8 mm with the effective bandwidth of 2.24 GHz, indicating that the Nd-Ce-Co alloy can be used as an ideal absorbing material in C-band with low thickness, broad band and high-effective.

Abstract:A simple and efficient synthesis of face-centered cubic (FCC) copper nanocrystal particles (Cu NPs) was presented by the gaseous detonation method which used the hydrogen-oxygen gases mixture as the explosion source and the copper (II) acetylacetonate as the precursor. The morphology, phase constitution and microstructure of the as-obtained products were analyzed by XRD, TEM, SAED and EDX. Meanwhile, to predict the growth characteristics of the Cu NPs, the Kruis model was tentatively integrated in reaction condition of gaseous detonation. The results showed that the as-synthesized FCC structural nanocrystalline copper with good dispersibility was coated with thinner graphite layer and the average size of particles was 24 nm. In addition, the growth characteristic of spherical Cu NPs was in consistent with the obtained experimental data based on Kruis model, which provided reliable theoretical guidance for the controllable synthesis of Cu NPs.

Abstract:Porous Cu/Ni composites with uniform pore distribution were prepared by electrodeposion method and its coating layer number is from 2 to 5. The effects of processing parameters on both microstructure and mechanical properties were studied. The microstructure morphology and characteristic parameters of porous Cu/Ni composites were strongly dependent on coating layer number. As the coating layer number increased, the pore diameter and porosity decreased while the specific surface area and apparent density increased. The solid solution formed at the Cu and Ni layer interface due to the atomic diffusion. The mechanical properties of the composites were remarkably enhanced with the increase of coating layer number. The compressive strength reached 17.36 MPa and Young"s modulus increased by 7.9 times. Moreover, the energy absorption of per unit volume rose up by 13.9 times as the coating layer number increased to 5.

Abstract:An experimental investgation on the plasma temperature after the precursor powder injection can provide a reference for the process optimization in plasma spheroidization. The effect of tungsten powder injection on the intensity of emission spectrum and plasma temperature were investigated at different position and RF power with a single factor method, and the tungsten powder with the particle size of D50=20±5μm was spheroidization treatment. The results show that the emission intensity and temperature of plasma jets was both decreased after tungsten powder injection. The effect of plasma temperature was weakened with the increase of RF power, and the spheroidization and satellite ratio were about 95% and 21% when P=56kW, respectively. The flow ability and density of powder were significantly improved after plasma spheroidization.

Abstract:The Ti-43Al-9V-0.3Y alloy was manufactured by electrode induction melting gas atomization (EIGA) and hot isostatic pressing (HIPing). Effect of HIPing temperature and powders particle size on microstructure and properties of this alloy were investigated. The TiAl powders and HIPed samples were characterized by field emission scanning electron microscopy (FESEM), energy dispertive spectrum (EDS), X-ray diffraction (XRD), quantitative metallugraphy ( QM) and mass spectrometer (MS). The results indicate that the TiAl alloy powders mainly consist of β/B2 phase. After hot isostatic pressing, the alloy mainly consists of γ and β/B2 phases. In addition, the powder and HIPed state alloys both contain a small amount of YAl2 and Y2O3 phases. After 1000-1260℃/150MPa/3h HIPing, the TiAl alloy microstructure is near γ, which is mainly comprised of γ phase and β/B2 phase. With the HIPing temperature increasing, the size of γ phase as well as the tensile elongation increased, but the tensile strength decreased. The Ar content and hollow powder quantity reduced accompanied by the powder particle size decreased. The TiAl alloy powders were sieved into three particle size range (<53μm, 53-105μm, 105-250μm), and then consolidated by HIPing at 1200°C for 3hrs under 150MPa argon pressure followed by furnace cooling. The microstructure and tensile strength of the alloy did not change significantly with the particle size, but the high temperature tensile elongation of the alloy increased obviously with the decrease of the particle size.

Abstract:The effects of physical properties of powders on the quality of selective laser melted(SLM) components, deposition state and microstructure after heat treatment were studied using different particle size distribution of titanium alloy powder obtained by powder screening and mixing. The results show that the increase in the proportion of fine powder, powder median size decreased, fluidity decreases and the bulk density did not change significantly; the density of parts manufactured by three kinds of powder particle size was more than 99%, the surface roughness increases with the increase of fine powder; quantity of fine powder in 23%, the minimum porosity formed after deposition; the microstructure of cross section of primary grain, internal acicular martensite, the longitudinal section of the visible columnar crystal; heat treatment results show that the decomposition of martensite at 600-800℃, and alpha + beta layer thicker at 800℃, heat treatment should be strictly controlled the annealing temperature and time to avoid layers coarse and impact performance.

Abstract:Two kinds of paving method of the stainless steel fiber porous materials are designed in this paper, parallel paving and erect paving. The materials with different pore structure are obtained by controlling the paving method, the ratio of length to diameter and the sintering process. The sound absorption properties of the stainless steel fiber porous materials with different pore structure were analyzed. Results show that the cost performance of the stainless steel fiber porous material is the highest, the length and diameter ratio is 5000. When the thickness of the material is ≤15mm, the sound absorption properties of the fiber porous materials which prepared by the parallel way are better than the erect. When the thickness of the material is ＞15mm, the influence of paving method is not significant. The number of sintering nodes has little contribution to the sound absorption properties of the stainless steel fiber porous materials.

Abstract:In this paper, super-fine high-speed steel powders with low oxygen content were prepared by electroslag remelting and atomizing technology, and high-performance PM high-speed steels were fabricated by non-capsule hot isostatic pressing technique. The effects of different particle size and oxygen content of high-speed steel powders on sintering characteristics, microstructure and performance were studied. The results showed that due to the high-speed steel powder with the particle size of less than 12 μm and lower than 100 ppm oxygen, the as-sintered microstructure was uniform and carbides were fine. After heat treatment, the bend strength, impact toughness and hardness reached 4200 MPa, 22 J, and 65 HRC, respectively.

Abstract:Nanoporous silver owning to large specific surface area and high densities of active sites, has a great potential for superior formaldehyde detection. Both chemical dealloying and electrochemical dealloying of Ag30Zn70 precursor alloy in 0.1 mol?L-1 hydrochloric acid solution were employed to fabricate NPS. The effects of duration time of chemical dealloying and applied potential of electrochemical dealloying on the formation of nanoporous structure and the current response of formaldehyde have been investigated. The results show that slow selective dissolution of Zn elements in intermetallic ε phase takes place during chemical dealloying of 24 h, which leads to the formation of nanoporous structure consisting of Ag and residual ε phase. Through electrochemical dealloying with applied potential of 0.1 V for 6000 s, 3D bi-continuous NPS with characteristic pore size of 80 nm was achieved. The results of cyclic voltammetry show that the oxidation current density of formaldehyde was enhanced with the increasing of formaldehyde concentration in 0.1 mol?L-1 KOH solution. The response oxidation current densities linearly depended on formaldehyde concentrations between 10~100 mmol/L, and the sensitivity of formaldehyde detection was 0.10. The present reagents of nanoporous silver had superior formaldehyde detection abilities in high concentrations of 50~100 mmol?L-1.

Abstract:Differential scanning calorimetry (DSC) and thermal simulation continuous cooling experiments were used to systematically study the behavior and microstructure of γ′ multi generations precipitation during the continuous cooling process in the third generation high performance PM superalloy. The results show that the alloy can obtain a multimodal size distribution of γ′ precipitates at cooling rates less than 1.4 ℃/s-1. The multi generations precipitation is closely related to the cooling rates. The slow cooling is the dominant factor causing the multimodal size distribution of γ′ precipitates. The linear regression method is used to get the quantitative relationship between the average sizes of secondary γ′ and cooling rates, and the formation kinetics and mechanism of multimodal size distribution of γ′ precipitates on the γ matrix are analyzed and discussed. Results of long-term aging of alloy with γ′ multimodal size distribution show that reverse coarsening phenomenon occurs due to the unstable morphology of the large-size secondary γ′, i.e., the average size of γ′ precipitates decreases with the increase of aging time. This reverse coarsening effect increases the strength of the alloy, and increases the long-term stability of the microstructure of the alloy. The conditions and reasons for the reverse coarsening of γ′ are also discussed. This work will provide a theoretical basis for the further research and development of new high performance PM superalloys.

Abstract:According to the purposes of high properties of graphite/copper composites, resin carbon-coated graphite/copper composites were fabricated by using phenolic resin-coated graphite, electrolytic copper, silica as raw materials via traditional powder metallurgy method. The difference of the microstructures and properties compared with natural graphite/copper composites and copper-coated graphite/copper composites was researched. The results indicated that the structure of graphite can be protected through phenolic resin. Phenolic resin can break up the oxide layer on the Cu powder surfaces. The reduced Cu can accelerate the elements’ diffusion and sintering between the Cu particles and increase the sintering densification of the Cu matrix. Compare to the natural graphite/copper composites, the physical, mechanical and tribological properties of resin carbon-coated graphite/copper composites improved. The electrical conductivity, flexural strength, hardness are 9.87 MS·m-1, 81 MPa, 22 HV, respectively. These property values are equivalent to copper-coated graphite/copper composites, and tribological properties is a litter better than copper-coated graphite/copper composites.

Abstract:NaCl beads were prepared using starch, distilled water and NaCl powders as raw materials.The raw constituents were mixed to form a colloidal salt paste and then thermal treated in 70°C oil under vigorous stirring, high spherical NaCl beads were obtained under the cutting action of the blender. Afterwards, the “fried” NaCl beads with a particle size distribution of 0.4-2.4mm were calcined and sintered at 740°C, and thus the high purity NaCl beads with small amount of micro-pore (pores size about 10-20μm) on the surface were obtained. The 0.6-1.0mm salt beads were selected to form a “salts bed” in a steel die and the aluminum powder was filled into “salt bed” gap via a tapping method by the Autotap instrument.The tapped mixture was cold pressed under 200MPa to obtain the green compact parts. Then the salts were dissolved and removed in distilled water and three-dimensional open-cell green Al foam with controllable structure and highly reproducibility was derived. After sintering at 460 °C for 2 h, the final Al foam was obtained and its relative density and porosity were 0.217 and 78.3%. The number of connectivity windows between cellular aluminum cells is 4-6 on average, and the window size is about 120-200 μm. The compressive load-displacement curve shows that the aluminum foam undergoes an elastic deformation stage - the plateau stress area - the stress steep increase stage, The curvemanifest typical foam metal compression mechanical properties, and its compressive strength and Young''s modulus are 2.42 MPa and 0.38 GPa.

Abstract:Abstract: The effect of prior particle boundary (PPB) on the crack growth behavior of a powder metallurgy Nickel- based superalloy formed by direct hot isostatic pressing (As-HIP) was investigated. The results show that the precipitated carbon and oxide on the boundary of prior particles in the powder metallurgy superalloy will decrease the fracture toughness (KIC) and initiate cracks from the interface easily. In the course of crack propagation, fractures occur along the inter-particles, which changes the direction of extended edges, aggravates the propagation of cracks along the grain boundaries, and increase the crack growth rate. The fracture toughness of the crack tip extending along the boundary of prior particle is closely linked to the physical properties, number and size of the precipitates on the PPB. The denser the precipitates, the smaller the KIC, and the crack propagation accelerated in these weak areas.

Abstract:The content of Nb in GH4169 alloy powder was adjusted by ball milling alloying combining with laser additive manufacturing(LAM) technology. The effect of the composition adjustment on microstructure evolution of GH4169 superalloy by LAM was studied. The results showed that the typical microstructure of as-deposited GH4169 superalloy consisted of γ columnar dendrites growing epitaxially along the deposition direction. According to the theoretical results, the mixing enthalpy of alloy powder during LAM increased with the increase of Nb content, which made the growth direction of columnar crystal gradually changed from the deviation of the laser beam to the inward of the laser beam. The increase of solute concentration and the mixing enthalpy of alloy powder during LAM promoted the precipitation of γ+Laves interdendritic eutectics, and the morphology γ+Laves interdendritic eutectics was gradually like net. With the increase of Nb addition, the initial melting point of Laves phase increased, and the initial melting point of dendrite core γ phase decreased by DSC. The LAM alloying GH4169 changed the composition of the primary gamma phase, increasing the content of Nb element in the dendrite core. The highest concentration of Nb can reach 7.5wt.%. Therefore, the solid solution strengthening function of the Nb was enhanced.

Abstract:Ti-Al-Fe-Mo alloy was prepared by powder metallurgy method with titanium, aluminum, molybdenum and iron powders used as raw materials, and the alloy was used to fabricate valves for motorcycle engines. The microstructure as well as performance evolution of the alloy during the preparing process was investigated. The performances of motorcycle engines assembled with Ti valves were also tested. The results show that Ti-Al-Fe-Mo alloy prepared by powder metallurgy has excellent comprehensive performances with ultimate tensile strength 1232 MPa, yield strength 1186 MPa, elongation 6.5% and hardness 49 HRC. The fabricated valves after coating TiN can meet the requirement of on board tests of the motorcycle engine. Compared with assembling steel valves, power and torque of the motorcycle engines assembled with Ti valves are improved by about 12%, fuel consumption rate is reduced by 1% and the noise is also significantly lowered.

Abstract:Ti-6Al-4V alloy powders were prepared by a self-developed electrode induction melting gas atomization (EIGA) equipment. Two kinds of gas atomizing nozzles, ring-hole type and ring-slit type, were used in the experiment. Different atomization pressure and power input were used. Four sets of processing parameters were designed and their effect on the powder properties was studied. The powder were sieved by 270 standard mesh (powder particle size ≤53μm) and analyst the size distribution by using MASTERSIZE 2000 Laser Particle Size Analyzer. The powder particle shape was quantified with Occhio 500NanoXY+HR Particle Size and Shape Analyzer. Results showed that optimal results were achieved with good sphericity by the combination of ring-slit nozzle with atomization pressure of 5 MPa and smelting power of 25 kW. A normal distribution of powder size was attained and the D10, D50 and D90 were 19.4μm, 31.9μm and 51.5μm, respectively. The mean Circularity and Occhio bluntness were 90.6% and 92.7%, respectively. It was found that more than 80% of powders have Occhio outgrow of 0. Further analysis of the powder by XRD, SEM, EDS and oxygen and nitrogen analyzer were carried out. The microstructure of the powder was acicular α′ martensite with random orientations. The amount of hollow powder is extremely small. The powder composition is practically same as the ingot with a low oxygen content, which satisfies the requirements of the SLM process. The Ti-6Al-4V powder achieved by optimal process was used for Selective Laser Melting and the relative density, surface roughness and microhardness are 99.02% and 4.89 μm, and 352.5 HV0.5 respectively.

Abstract:P-type with nanostructured CoSb₃ was successfully synthesized by solid-state reaction method. The phase composition and crystallographic structure were characterized by X-ray diffraction and scanning electron microscopy. The electrical properties of the samples prepared at different temperatures and holding time were tested at room temperature. The samples with better power factor at room temperature were selected to study the thermoelectric properties at different temperatures. The results show that the single phase Skutterudite thermoelectric materials can be prepared by ball milling combined with solid-state reaction. The samples have many micron-size pores uniformly and the grain was in the nanometer range. The maximum Seebeck coefficient was 222.64 μV/k obtained at the prepared temperature of 863 K. The maximum power factor of 132.17 μW/ (mK^₂) at 570 K was obtained and the maximum figure of merit, ZT~0.053 at 600 K was obtained by the sample which prepared temperature of 903 K. This study provides a new technology for the rapid preparation of Skutterudite thermoelectric materials.

Abstract:The first-principles calculations were performed to investigate the structural, elastic and electronic properties of typical face-centered cubic precipitate of Mg3Zn3Y2 under high pressure based on density functional theory (DFT). The optimized lattice constants at 0 GPa were similar to the other calculated and experimental results. The elastic constants of Mg3Zn3Y2 were calculated and analyzed. The bulk modulus （B）, shear modulus (G), Young''s modulus (E), Poisson''s ratio (ν), anisotropy index (A), melting points and hardness were further calculated based on the elastic constants. The calculation results showed that the mechanical properties of Mg3Zn3Y2 changed positively with the increase of pressure. In addition, the anisotropy index (A) of Mg3Zn3Y2 increased as the pressure increasing. The electronic density of states (DOS) of Mg3Zn3Y2 phase was analyzed, and it revealed that the structural stability of the phase was decreased as the increasing of pressure.

Abstract:: With the continuous development of spacecraft, nuclear powered ships, nuclear fusion power generation and other fields, the material not only requires excellent performance, but also requires the material to meet the normal work under extreme conditions (irradiation, high temperature, etc.). How to ensure the service life of materials under long time irradiation? The design and preparation of metal composite with strong radiation resistance has become a hot issue in the field of national defense and nuclear fusion. In addition, the structure evolution, performance changes and internal mechanism of metal and its composite materials under irradiation are also the key to the design and preparation of radiation resistant materials. Graphene has excellent anti radiation ability. What new changes will happen in adding graphene to metals? This review summarized the sequential advancements made in research involving graphene/metal composites and irradiated graphene, including cutting, modified modification structural design and industrial functionalization. The mechanism of graphene / metal composites after irradiation is further understood, which provides a theoretical basis for the application of graphene / metal composites in nuclear industry.

Abstract:The intermittent vacuum gas nitriding (IVGN) process was introduced to improve the surface properties of TB8 titanium alloys. The phase constitution and microstructure of the surface-modified layer were measured by XRD and SEM, and the surface hardness and wear resistance of the treated samples were analyzed. The results indicated that a surface-modified layer composed of TiN, TiN_0.3, and Ti₂AlN was formed after IVPN treatment at 800 ℃ for 4 h. The microstructure of modified layer was dense and had a good bonding with its substrate. The surface hardness of treated samples was up to 850-900 HV, which was three times as much as that of the untreated samples. The thickness of hardened layer was about 80-100μm. The wear resistance was greatly improved due to the formation of a gradient hardened layer.

Abstract:Stress relaxation tests at different combinations of temperatures (775℃、800℃、825℃), initial stresses (150MPa、200MPa) and pre-strains (7.85%、15.7%) were performed for the titanium alloy TA32 to study the influences of the process parameters on its stress relaxation behavior. The microstructures of the specimen after the experiments at different temperatures were observed to investigate the temperature effects on the microstructure evolution. The stress relaxation curves were fitted with the quadratic delay function. And the creep constitutive equation at the high temperature was established and applied to define the stress relaxation behavior of TA32 titanium alloy in the finite element analysis. The experimental results show that the stress drops rapidly with high stress relaxation rate in the first 200 s of the stress relaxation. The stress tends to be stable and finally reaches the limit of stress relaxation after 3600s. The stress relaxation rate increases with the increasing temperature while the stress relaxation limit decreases. And the initial stress and pre-strain have little effect on the stress relaxation behavior. The equiaxed and grown grains can enhance the plasticity with the increase of temperature. The simulation results and experimental stress relaxation curves are in good correlation which validated the reliability of the creep constitutive equation.

Abstract:Effect of poly acrylic acid (PAA) addition on the thermal stability and electrochemical performance of the V(V) positive electrolyte for all-vanadium redox flow battery (VRFB) were investigated in this paper by ex-situ stability tests, UV–Vis spectrometry, Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), Cyclic voltammetry (CV) and charge-discharge test. The results indicate that PAA additives can improve the thermal stability of V(V) electrolyte. A small amount of PAA additives can slightly improve electrochemical performance of the positive electrolyte and the energy efficiency of the VRFB at room temperature. Besides, the cell employing the positive electrolyte solution with 3% PAA shows good cycling performance at 50 ℃, the charge capacity retention of which is higher than that of the cell without PAA during the cycling.

Abstract:The phase equilibria in the Ni-Al-Sn ternary system were investigated by means of electron probe microanalysis and X-ray diffraction. The experimental results showed that: (1) No ternary compound was found at 800°C and 1000°C. (2) The Ni-Al side presented four binary compounds included NiAl, Ni3Al, Al3Ni and Al3Ni2 phases. The solubilities of Sn in the binary NiAl and Ni3Al phases were determined as 3.1 at.% (Atomic ratio) and 14.7 at.% at 800°C, and 3.0 at.% and 8.0 at.% at 1000°C, respectively. As for the binary Al3Ni and Al3Ni2 phases, the solubilities of Sn were almost negligible. (3) The Ni-Sn side displayed three binary compounds included Ni3Sn(r), Ni3Sn(h) and Ni3Sn2(h). The Ni3Sn(r) phase was stable at 800°C dissolving 4.2 at.% Al but it was replaced by the Ni3Sn(h) phase with a 5.5 at.% Al solubility at 1000°C. The solid solubility of Al in Ni3Sn2(h) was 8.4 at.% and 12.1 at.% at 800°C and 1000°C respectively. (4) The Al-Sn side was occupied by an interconnected liquid region having only ~1 at.% Ni solubility.

Abstract:In this investigation, the plates of AA2024-T351 and AA7075-T651 with 5 mm thickness were butt joined by friction stir welding. The microstructural evolution in the nugget zone (NZ) of the dissimilar AA2024-7075 joints along the weld thickness direction was studied. The results indicated that the grain size of the NZ decreases from the top to the root of the joint. The fraction of dynamic recrystallization in the shoulder affected zone (SAZ) and the weld bottom is lower than that in the center of the NZ. Simple shear texture can be developed in the NZ and the texture distributions are heterogeneous. The SAZ consists of B and?B components, while A or?A components are the major textures at the bottom position. C component is found in the middle of the NZ. The texture intensity in the middle of the NZ is lower than that of at the top and bottom. This is mainly due to the presence of the onion ring, in which materials mixing occurs, resulting in a more random grain orientation.

Abstract:The corrosive behavior of the nickel-based alloy G3 at room temperature (25℃) and high temperature (90℃) in a complex medium environment containing H2S, CO2, Cl- with various states of elemental sulfur was studied by using electrochemical microscope (SECM), scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS) in this paper, and the influence of elemental sulfur was analyzed. The results show that the corrosion becomes more serious with increasing temperature and slight pitting occurs on the surface of the nickel-based alloy G3. The anode polarization curve has a passivation region at room temperature, but the active dissolution appears and passivation disappears at a temperature of 90℃. The phases were analyzed that the passivation film formed on the surface of the nickel-based alloy G3 is mainly composed of oxides of Ni, Cr and Fe. The passivation film is dissolved due to the intrusion of S2-, and the corrosion products were composed of NiS and FeS2. The corrosion resistance of G3 alloy is weakened in the sulfur-contained environment, and the suspended sulfur has the most dense passivation film and the least corrosion rate compared with the deposition of sulfur and the precipitation of sulfur. Studies have shown that sulfur is a strong catalyst, and its existence leads to severe local corrosion. The state of elemental sulfur is a key factor affecting the compactness and growth rate of corrosion product membranes and the corrosion rate of alloys.

Abstract:Aiming at the problem of very-high-cycle-fatigue(VHCF) of aeroengine compressor blades under complex loading, three-point bending ultrasonic fatigue tests of TC4 titanium alloy under stress ratio R of 0.3 and 0.5 were performed, and failure mechanisms of VHCF under three-point bending was also investigated. Test results show that S-N curves present a bilinear characteristic. SEM analysis indicates, the crack initiation sites are transferred from the surface to the sub-surface with the decrease of the maximum stress. Fatigue crack initiations are results of competition between surface slip and internal cleavage fracture. Then a model based on fatigue life is proposed to describe the competition between the two mechanisms, which is in agreement with the experimental results. The temperature of the specimen surface is monitored by infrared camera. It can be divided into four stages in high-cycle-fatigue (HCF) regime: steady rising, steady decreasing, fast rising and fast decreasing stage. While it can be divided into three stages in VHVF regime: steady rising, fast rising and decreasing stage. Finally, The characteristics of heat production and transfer are described, and the correlation between temperature and stress distribution is analyzed.

Abstract:The solidification process and the segregation behavior of the elements of GH4282 superalloy were investigated by a combination of differential scanning calorimeter (DSC), microstructure observation and thermodynamic calculation. The solidification sequence and the characteristics of elements segregation were obtained. The results show that the solidification sequence of GH4282 is as follows: γ matrix, MC carbide and a small amount of boride. The solidus-liquidus temperature range determined by DSC is 1316~1367 ℃. The measured solvus temperature of MC carbide, M6C carbide and γ′ phase is 1338 ℃, 1092 ℃and 1003 ℃, respectively. Thermodynamic calculations show that C, B, Ti and Mo segregate to the interdendritic regions, while Al segregates to the dendrite cores. Cr, Fe and Co do not exhibit any significant tendency to segregate to either the interdendritic region or the dendrite core during the solidification process of GH4282 superalloy. These results about segregation behavior of the elements agree well with those observed by as-cast microstructure observation.

Abstract:Electro-stream machining is mainly a process of electrochemical anode dissolution, which causes corrosion damage to the single-crystal material and affects the performance of the film holes under service conditions. Based on the microscopic analysis and in-situ fatigue test, the damage behavior of electro-stream machining on the film holes of DD6 single crystal superalloy were investigated. The results show that the corrosion zones of the film hole are all characteristics of electrolytic corrosion of DD6 single crystal superalloy, which a part of the γ phase is eroded and the γ′ phase is prominent. In addition, there are two ways of fatigue crack initiation of the DD6 single crystal superalloy specimen with a single hole: one is originate from the porous defect at the edge of the hole and the other is that from the electrolytic corrosion damage layer at the edge of the hole.

Abstract:It is of great significance to predict the grain evolution of magnesium alloy pipe in the process of pilger rolling deformation in real time for controling the final performance of the magnesium alloy pipe. In this paper, the cellular automata model based on dynamic recrystallization, static recrystallization, static recovery, grain coarsening and grain topological deformation was established by rolling experiments on AZ31 magnesium alloy pipes on a Pilger mill.Finally, the results of each pass obtained by the finite element calculation are combined with the cellular automata to obtain the grain evolution of the magnesium alloy pipe in the rolling process in real time. It is found that the grains are continuously generated during the rolling process. and was finally verified by experiments.

Abstract:The dynamic softening behavior of coarse-grained Ti40 alloy during superplastic deformation was studied by means of tensile tests as well as TEM observation and EBSD analysis. The results show that coarse-grained Ti40 alloy exhibits good superplasticity in most test condition and the maximum elongation 436% was obtained at the condition of 840oC, 1×10-3s-1. The deformation conditions can be divided into three areas: none superplasticity area, dynamic recovery area and dynamic recrystallization area based on the Zener-Hollomon factor and elongation combined with the microstructure analysis. The critical strain model and dislocation density evolution model of dynamic recrystallization were established based on Sellars model and KM equation respectively. The dynamic recovery mechanism is dominated by dislocation motion—dislocation cells—polygonization—subgrain formation, while the recrystallization mechanism is mainly the continous dynamic recrystallization resulting from the subgrains rotation leading to the formation of high-angle grain boundaries.

Abstract:An inverse temperature gradient is generally adopted in order to avoid second nucleation at the initial homoepitaxial growth due to O, C and H impurities. In this paper, we investigated the temperature distribution and mass transfer at the initial homoepitaxial AlN growth stage in a proprietary and fully automatic physical vapor transport sublimation reactor by FEMAG and an in-house finite element multi-phase mass transfer code, respectively. Homoepitaxial growth experiment was also conducted successfully based on numerical simulation results. The simulation and experiment results showed the deposition of O, C and H impurities at the initial homoepitaxial growth stage could be efficient avoided by an inverse temperature distribution. The crucible position played a key role on the temperature distribution and mass transfer during the subsequent AlN crystal growth stage. The numerical simulation results and successful homoepitaxial growth experiment placed a solid foundation for our future size enlargement growth experiments.

Abstract:Titanium and mild steel sheets were welded by resistance spot welding with insert of 100 μm thick niobium foil. The interfacial microstructure characteristics were analyzed; the effects of welding on the nugget diameter and tensile shear load of joint were studied. The results reveal that the niobium foil disconnect during spot welding when the welding current is greater than 8 kA, the nugget is mainly composed of Fe-Ti intermetallic compounds in the case; and that the nugget is mainly composed of Fe-Nb compounds and some solid solution when the niobium foil do not disconnect during spot welding. The tensile shear load of joint increased and then decreased with the increase of welding current. A tensile shear load of a maximum of 4.7 kN was obtained at a welding current of 7 kA.

Abstract:Aiming at the high material cost of K418 cast super alloy impeller, the complex manufacturing process and the currently volume damage, the laser remanufacture for edge volume damage of this type was taken for target, the composition approached and process matched alloy was designed, the shape and performance was recovered by using the waveform modulated pulse laser. The results of experiments show that, there were no surface and internal cracks existed，there was metallurgical bonding between the forming layer and the substrate, the forming precision was within 1mm, the deformation precision is within 0.03mm, the surface hardness of the forming zone was 900~1400 HV0.1 , which is 20% higher than the substrate. Under the high temperature dynamic balance test, the maximum rotation of the impeller is 13500 r/min, the maximum amplitude is 0.4mm, there is no exception, no deflection and surge existed, which meet the dynamic balance performance requirements.

Abstract:For improving the mechanical properties and avoiding the filament fractures or wire breaks in multi filament MgB₂ wire, the traditional in-situ powder in tube (PIT) method was introduced to the MgB₂ wires fabrication process using the Monel alloys with higher strenth as the outer sheath materials. MgB₂ wire with the conducting structure of 19 filaments was fabricated by the PIT method. Multi-filament compound billet is processed from Φ25 mm to Φ1.4 mm in diameter with drawing, rolling and annelling process. Superconducting filament is uniformly distributed and the thickness of Nb diffusion barrier is also smooth without breaking points through the microstructure analysis of the wires at each fabrication stages. The mean diameter in MgB₂ supercongducting cores is aroung 100 μm in final wires with the diameter of Φ1.0 mm. The tensile strength and yield strength of the wire heat-treated at 670℃/2h is around 396 MPa and 200 MPa respectively. The critical current density (Jc) is arrived 1.23×10₅ A.cm_-2 at 4.2 K、4 T.

Abstract:The expansion behavior and partitioning behavior of alloying elements in α+β→β phase transformation of TC21 titanium alloy during continuous heating were carried out by combining dilatometric method, optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results show that the change in the length of the TC21 alloy during the continuous heating process results from the transformation of α phase with hexagonal close-packed to β phase with body-centered cubic and macro volume variation which originates from redistribution of α-stabilizers and β-stabilizers in the alloy during the continuous dissolution of α phase when the temperature is over β transformation temperature. It is found that the content of Al element increases in the α phase with the dissolution of α phase, but it decreases in the β phase. Additionally, the increasing content of Al element leads to decrease in volume of β phase, which is also main reason for shrinking of the alloy during α+β→β phase transformation. However, Mo, Cr and Nb element diffuse to the α phase during α→α+β phase transformation, so that the composition imbalance was found at the α/β interface.

Abstract:Microstructure evolution and fracture modes of Be/CuCrZr joints with 50μm Ti interlayer by hot isostatics pressing bonding at high temperature (780 ℃ ~ 850 ℃) and different time (0.5 h ~2 h) were studied by mean of EPMA. The results show that forming process of intermetallic compounds at Be/Ti and Ti/CuCrZr interfaces conformed to Flux-Energy law. The diffusion rate of Be in Ti is greater than that of Cu in Ti. But the Ti-Cu-Be ternary intermetallic compound with high Be content formed in the Be/Ti interface reaction zone is very brittleness, which caused the property deterioration of the Be/CuCrZr joint. By contrast, the Ti-Cu-Be ternary intermetallic compounds with low Be content formed in the Ti/CuCrZr interface reaction zone have relatively little influence on Be/CuCrZr joint properties. HIP conditions affected significantly on Be/CuCrZr joint properties. The Be/CuCrZr joint bonded by HIP under 800 ℃, 2 h and130 MPa provided with optimum properties, and tensile strength is up to 122.8 MPa. The joint exhibited the good bonding interface without hot cracks, and the fracture of the joint is caused by cleavage fracture of Be12Ti+Be10Ti mixed intermetallic compound layer.

Abstract:TA15 alloy samples with different forging passes and deformation temperature were prepared by multidirectional forging process. Using metallographic observation, EBSD, grain size statistics and qusai-static tensile test, the microstructure morphology, grain size, phase content, misorientation angles and mechanical properties during deformation process were analyzed. The experimental results show that a significant equiaxed structure of TA15 alloy is obatained after multidirectional forging at mediun temperature of 700 ℃, and the ratio of high angle boundary increased. Moreover, after 3 pass deformation the average grain size of primary α phase can be refined to 6.0 μm. Besides the deformation microstructure is (α+β) phase, the content of β phase increases compared with initial microstructure. With the increasing of deformation temperature, the grain size increases at 800 ℃ and 900 ℃, but is still smaller than the intial sample. The tensile strength has been improved significantly after multidirectional forging, correspondingly after 3 pass MDF at 700 ℃, the tensile strength of the samples is increased to 1443 MPa and the elongation is 13.6%, which have been slightly lower than the as-received sample. Deformation sample at 900℃,tensile strength is 1178 MPa, the elongation is increased to 15.8%. Finally, comprehensive properties of materials are significantly improved

Abstract:With the development of deep space exploration, miniaturization has become the trend of satellites, which heightens the reliability demand of satellite electronic systems. Solder plays an important role in integrated circuit, providing electronical and mechanical interconnection of electronic devices. To understand the microstructure and performance evolution of solder joints under cosmic irradiation environment and meet the reliability demand of solder joints used on satellites, the effect of γ-ray irradiation on the mechanical performance and microstructure of eutectic SnPb solder joints were investigated. The results show that after γ-ray irradiation, the generation of micro-voids and micro-cracks in Pb-based solid solution are observed due to the accumulation of irradiation damages. Energetic electrons induced by γ photon through Compton Effect, could knock Pb atom out and form point defect, which is the cause of mico-voids and micro-cracks. After 964 kGy irradiation, the tensile force of eutectic SnPb solder joints decreases by 14.12%. Moreover, the analysis of fracture morphology shows that the fracture kinds of eutectic SnPb solder joints before/after γ-ray irradiation are all plastic fractures, but the ductility of eutectic SnPb solder joints is reduced with unobvious dimples.

Abstract:Finemet-type Fe73Si15Nb3B8Cu1 ribbon cores were prepared through adding pre-annealed treatment before crystallization annealing at 540 oC. It is found that, with an increase of pre-annealing temperature, the toughness of the pre-annealed and final crystallization annealed ribbons gradually decreased; and the second crystallization peak temperature shifted toward the higher temperature, although the difference among the first crystallization temperatures of the amorphous ribbons by pre-annealing treatment at different temperatures was not obvious. Namely, the pre-annealing expanded the crystallization annealing temperature range for the amorphous ribbon, which was beneficial to obtaining more stable and high performance amorphous nanocrystalline ribbons. The grain size of the additional pre-annealed ribbons was more uniform than that of the direct crystallization annealing ribbons, which was in the range of 8~15 nm for the ribbons by additional pre-annealing at 450 °C. The amplitude permeability and iron loss of iron cores with pre-annealing treatment had significantly improved compared with direct annealing samples, particularly, the cores pre-annealed at 450 oC had the largest amplitude magnetic permeability (μa=8.6×104, f=10 kHz) and the smallest AC core loss (P0.5/10k=8.7 W/kg), which were increased 16.0% and decreased 17.1% compared with directly annealing cores, respectively.

Abstract:_: _{The effect of different ultrasonic time on the morphology, structure and electrochemical}_{performance of}_{Li-rich materials}_Li[Li_0.144_Ni_0.136_Co_0.136_Mn_0.544_]O₂_was_{studied by ultrasonic assisted co-precipitation method.}_Our_{study found that}_ultrasonic_{can make the materials more uniform, and therefore the structure became more reasonable, which is beneficial to improve the electrochemical performance. The}_sample_{with 8h ultrasonic}_time_{shows the best capacity, and the initial discharge specific capacity of 0.1C rate is 327.8 mAh g}_-1_{(higher than 265.2 mAh g}_-1_{of the sample without}_ultrasonic_{). The discharge capacity is 181.6 mAh g}_-1_{at 1C rate after 50 cycles, with the capacity retention of 84.8%. After the cyclic voltammetry test and the EIS test, it was found that the composite oxide had higher current and reduced charge transfer impedance, and better rate performance.}

Abstract:The key to solving pulverization and stripping from collector caused by volume expansion of high performance electrode lies in flexible electrode was prepared, which has excellent interface structure and electron/ion mass transfer capacity. A unique process has been used to prepare high performance transition metal oxide (nickel oxide) coupled carbon fiber mat flexible electrode. When directly applied such a flexible negative electrode for lithium-ion battery, due to the high theoretical specific capacitance of nickel oxide, unique low dimensional characteristics and huge draw ratios for internal stress dispersion of carbon fiber mat, NiO carbon nanofiber (NiO-CNF) deliver excellent cyclic characteristic and better rate electrochemical performance simultaneously much higher than NiO nanofiber (NiO NF) without carbon. NiO-CNF and NiO NF have reversible capacities of 418 mAh.g_-1 and 242 mAh.g_-1 after 200 cycles at 0.5C, respectively. These electrochemical properties can be attribute to the cross-linked structures provide diffusion kinetics and external stress buffering.

Abstract:Experimental investigations on the ultrasonic consolidation of different1 materials were performed using 1100 aluminium and TA1 titanium foils as matyix materials. The layer-metal composite laminate specimens were prepared using the ultrasonic consolidated Ti/Al foil, which were used to investigate effects of amplitude and static force on the interface bonding strength of Ti/Al foil by peel test. In addition, the microstructure morphology observation and energy spectrum analysis of the peeled interfaces were performed using SEM and EDS respectively. Microstructure of Ti/Al foil interface was observed using TEM. The results have shown that a good bonding interface of Ti/Al foil can be obtained using the ultrasonic consolidation technique. The interface bonding strength increased first then decreased with increasing the static force, while increasing monotonically with increasing the amplitude. The optimum ultrasonic consolidated interface with a peeling strength 11.325 N/mm can be obtained using an amplitude 35 um and static force 1.5kN. A uniform distribution of Al element can be found in the peeled interface of Ti foil accompanying with the obvious nest microstructure. Element transition zone existed at the Ti/Al interface. Recrystallisation was obvious at the interface resulting in fine grains. The oxidation layer on the Al foil was broken, and titanium element penetrate Al grains uniformly.

Abstract:In this paper, the effect of deformation temperature on the evolution of microstructure and properties of TC4 alloy has been studied by a constant-strain rate tensile test at high temperature. The results show that both the peak stress and required strain of peak stress decrease with increasing temperature in a α+β dual-phase field. The deformed microstructure exhibits a strong temperature-dependent evolution with temperature. Deformation leads to an accelarated recrystallization and refinement of primary α phase at a lower temperature of α+β phase field (below 900 °C), whereas results in a significant spheroidization of secondary α phase at a higher temperature (above 900 °C). Additionally, deformation also affects the nucleation and growth process of β→α transformation, resulting in a larger amount of secondary α phase. With increasing deformation temperature, the volume fraction of α phase firstly decreases and then increases, which shows a good consistence with hardness. However, the corrosion resistance displays a reverse evolution with the amount of α phase. TC4 alloy exhibits a lowest volume fraction of α phase of 57% at a deformation temperature of 900 °C, which corresponds to a lowest hardness and a best corrosion resistance in a NaCl solution.

Abstract:CAD/CAM technology has become more and more popular in dental clinic. In recent years, polymer infiltrated ceramic network (PICN) material have attracted the attention of many dental practitioners owe to its good machinability. The new material shows the interpenetrating morphology of resin and ceramic, and its properties are similar to those of ceramic and composite resin, at the same time, it has its own unique advantage. Compared with the all- ceramic materials (composite resin and all- ceramic materials), the flexural strength of PICN materials ranged from 145 MPa to 336 MPa, which is better than that of composite resin and Feldspar- based machined ceramic materials, but is lower than that of lithium disilicate glass ceramics. In the study of simulating the normal occlusal condition of human beings, PICN materials show excellent fatigue resistance, which is obviously better than the traditional all- ceramic materials including Lithium, Leucite- based and Feldspar- based machined ceramic materials. In addition, Elastic modulus of PICN materials ranged from 25GPa to 88GPa and Vickers hardness value is between 1.7GPa and 4.8GPa, which is close to that of natural dental tissue, indicating that it maybe become a future star of dental materials. It can adjust the mechanical properties by changing the content of components, which is rare in dental all-ceramic materials. At present, PICN is mostly used as single crown restoration in dental clinic, but its long-term effect (≥ 5 years) is rarely seen. A new dental material often takes more than 10 years to be understood and accepted by more dental practitioners. Therefore, the application of PICN is still in the exploratory stage. Based on the analysis of the microstructure, properties and application of PICN, some suggestions are proposed for future research and dental application of PICN materials.

Abstract:electronic paste is an excellent thermal interface material (TIM), which is widely used in ultra-high speed computer chips, power semiconductor devices and LED, and it can achieve mechanical connection, electric connection and thermal connection between chip and heat sink by low temperature curing process, which can satisfy the application requirements and service conditions under high temperature. This article reviews the recent development of nano silver and carbon nanotubes application in low temperature curing electronic paste, based on the influence in thermal conductivity structure of silver nanoparticles and carbon nanotubes, separately presented: 1) the influence of the size of nano silver, surface coated agent and twins growth mode on the thermal conductivity in electronic paste; 2) the vertically aligned carbon nanotubes are prepared and the joint interface are modified and decorated, TIM was prepared to form high thermal conduction path by connecting chip and heat sink, 3) the interface influence of silver nanoparticles decorated carbon nanotubes and silver powder to prepare three-dimensional composite thermal conductive structure by sintered bonding on enhancing the thermal conductivity of electronic paste. Finally, we express the expectation for nano silver and carbon nanotubes application in improving the thermal conductivity of the electronic paste in the future.

Abstract:Carbon dots (CDs) are one of the most popular carbon nanomaterials after the fullerenes, carbon nanotubes and graphene. The emergence of carbon dots has caused great interest among researchers, because CDs have excellent water solubility, good chemical inertness, hypotoxicity, good fluorescence properties, favorable biocompatibility, excellent environmental friendly, resistance to photobleaching. Moreover, CDs are easier for functional modification. In this review, we systematically describe the preparation of CDs, we hope to stimulate more researchers to research in this field, especially for their potential applications in biomarkers, biological sensing, biochemical analysis, optoelectronic devices, photocatalysis and drug carrier and so on.