Abstract:Microstructures of different state Mg-5Sr-10Y master alloys (as cast, as solutionized and as extruded) and their effects on the grain refinement of AZ31 magnesium alloy were investigated by OM, SEM and XRD. The results indicate that all the master alloys are composed of α-Mg, Mg17Sr2 and Mg24Y5 intermetallic compounds, but the morphology of the α phase and the form, the quantity and the size of the second phase are different, which lead to the different grain refinement efficiencies in AZ31 magnesium alloy. It is found that the extruded Mg-5Sr-10Y master alloy has the best grain refinement efficiency, then the as cast and solutionized in turn. The different grain refinement efficiencies of various master alloys are related to the heterogeneous nucleation and the constitutional undercooling

Abstract:An electroless Ni-P-ZrO2 composite plating was prepared on the porous surface of the Ti6Al4V alloy pretreated by micro-arc oxidation (MAO) for 15, 30, 60 and 90 min, respectively. The effects of the microstructures of the MAO coatings on the adhesion properties of the electroless Ni-P-ZrO2 plating and their tribological behavior were examined by SEM/EDS, scratch and thermal shocking tests, a microhardness tester and a ball-on-disc wear testing machine. The results indicate that the adhesion property of the Ni-P-ZrO2 composite plating of the MAO coatings is distinctively improved with the increase of MAO processing time. The reason is attributed to the larger porosity and the enhanced mechanical interlocking effect. Compared with the Ti6Al4V alloy, the microhardness and the wear resistance under drying sliding condition of the Ti6Al4V alloy are greatly improved by the duplex treatments. The wear mechanism of the Ti6Al4V alloy is severe adhesion and abrasion wear, while the electroless Ni-P-ZrO2 composite plating shows microabrasion wear.

Abstract:Two kinds of stainless steel powders, having spherical shape and irregular one with the particle sizes from 38 μm to 150 μm were used to produce porous metal materials, the specimens were sintered at 1250 °C for 2 h in vacuum. Their porosities and compressive strength were tested using Archimedes’ principle and a computer controlled universal testing machine, respectively. Furthermore, the microstructures were observed by an optical microscope. In addition, the fractal theory was used to investigate the fractal dimension of the pore structure and analyze the relation ship between the compressive strength, the porosity and the fractal dimension. The results show that the fractal dimension increases gradually with increasing of the porosity. The relation ship between the fractal dimension and the porosity can be expressed using the Boltzmann model. The compressive strength and the fractal dimension can be presented by the exponential model

Abstract:High power pulsed magnetron sputtering (HPPMS) is a novel tool to fabricate films with high quality. In this paper, vanadium films on concave object have been deposited by HPPMS and conventional direct current magnetron sputtering (DCMS) under the condition of the same average power. The plasma composition, crystalline structure, surface morphology and film thickness have been investigated. The results show that the plasma produced by HPPMS is composed of Ar(1+), V(0) and a certain amount of V(1+). In contrast, the plasma produced by DCMS is composed of Ar(1+), V(0) and a very small amount of V(1+). Both films fabricated by HPPMS and DCMS demonstrate the similar microstructures. The HPPMS vanadium films are dense and flat on the top surface while the surface of DCMS vanadium films presents very sharp peak with larger height. The DCMS vanadium films exhibit a porous columnar grain structure. In contrast, the HPPMS vanadium films have slightly columnar and denser structure. The thickness of the HPPMS vanadium films is less than that of DCMS vanadium films. Compared with the surface on the top, the thickness of the DCMS vanadium films is decreased to about 32% at the side wall and to about 55% at the bottom. However, the HPPMS vanadium films can reach a thickness of about 35% at the side wall and 69% at the bottom relative to that on the top surface. HPPMS shows a better uniformity in the film thickness on concave object

Abstract:The novel Al-Si-Zn filler metals containing Ti and Sr were used for brazing of 6061 aluminum alloy. The results indicate that the addition of Zn into the Al–Si filler metal lowers the solidus temperature from 583 °C to around 520 °C. The minor addition of modification element Sr and refine element Ti into Al-Si-Zn alloy WILL cause the remarkable modification of Al-Si eutectic and the α-Al phase is also refined. The main phases in the filler metals as well as the brazed seams are α-Al, η-Zn, and Si phases. The large clusters of Al-Si eutectic in the Al-Si-Zn-Sr-0.04Ti brazed seam are refined by further adding 0.08 wt% Ti, the refined Al-Si eutectic is homogeneously distributed among α-Al phase. Diffusion layers can be found in the brazed interface, the Mn-Fe phase is also found in the brazed seam due to the diffusion of 6061 base metal into the brazing alloy which is helpful for reduce the formation of acicular β-Fe

Abstract:The evolution rules of transitional phases β1' and β2' during single and double aging and the heterogeneous nucleation of β1' rods on α-Mn particles in a Mg-6 wt%Zn-1wt%Mn (ZM61) alloy were studied by TEM technique. Age-hardening curves (130, 160, 180, 200 and 230 °C) show that double aging can more greatly enhance hardening level and rate than single aging. The rapid nucleation and the elongation of β1' rods occupies the stage before peak aging; the volume fraction increase of β1' rods results in hardness rise and also a huge accumulation of strain energy; in the over-aging stage the growth of β2' discs at the cost of β1' rods can effectively relieve such a strain energy accumulation. G. P. zones of about 10 nm in diameter are densely distributed in matrix after the pre-aging (90 °C/24 h), which can act as the heterogeneous nuclei for β1' rods and thus considerably raise their number density. Moreover, β1' rods frequently heterogeneously nucleate on α-Mn particles, because such heterogeneous nucleation can result in a coherent β1'/α-Mn interface and thus reduce the interfacial energy

Abstract:Noval Zn-Al-Ti filler metals have been designed and used to braze Cu and Al dissimilar metals. The phase constitutions and morphologies of intermetallic compounds at the Zn-22Al-xTi/Cu interfaces were studied in this paper. The results indicate that, with Ti addition from 0.01 wt% to 0.05 wt%, the microstructure of the Zn-22Al alloy are refined significantly. The spreading area of Zn-22Al-0.03Ti on Cu substrates increases by 60.4% compared with that of ZA. However, the melting range and melting point of the Zn-22Al-xTi alloys also increase with the addition of Ti. In particular, the addition of trace Ti into the Zn-22Al filler metal can refine the microstructures and decrease the thickness of the intermetallic compounds layer produced in the Cu/Al brazing. The shear strength of Cu/Al joint brazed with Zn-22Al-0.03Ti is 13.4% higher than that of the Zn-22Al filler metal, and the fracture position changes from the interface layer to the matrix of the filler metals. The X-ray diffraction result indicates that the CuAl2, CuZn, and Cu9Al4 phases are produced at the filler metal/Cu substrate interface

Abstract:Al1-xMgx (x=0.1, 0.2, 0.3, 0.4, 0.5) alloys (designated here after as AlMg alloys) were prepared by mechanical ball milling. The thermites were prepared by sonication dispersion method. AlMg/KMnO4 thermites with different Al/Mg ratios were investigated by differential scanning calorimetry (DSC), ignition and combustion measurements. The results show that the reaction temperatures of AlMg/KMnO4 thermites decrease obviously with the increase of Mg contents, indicating that the thermal reactivity of AlMg/KMnO4 thermites is superior to that of Al/KMnO4. Furthermore, it is found that both the reaction temperatures and the burning velocities of AlMg/KMnO4 thermites decrease from 723 to 493 K, and from 254 to 204 mg/s, respectively, as the content of Mg increases from 0.1 to 0.5, among which the Al0.5Mg0.5/KMnO4 thermite displays the largest flame splash range. It is expected that AlMg/KMnO4 will be the most promising energetic material in ordnance applications

Abstract:A new mathematic model for the nucleation and the dendrite growth of twin-roll-continuously cast pure aluminum thin strip during solidification process was developed based on cellular automaton(CA)-finite element(FE) method and the classical transfer equations during dendrite growth. The model coupled the temperature field calculation and microstructure simulation. The solute diffusion, the curvature undercooling and the latent?heat?releasing were also considered in the model, all of which have significant influence on the dendrite evolution. So the dendrite growth morphology can be modeled. The applications of the model in equiaxed dendrite growth, multiple equiaxed dendrite growth, columnar grain growth, and columnar dendrite transformation to equiaxed dendrite in twin-roll-continuously cast aluminum thin strip solidification were presented. The microstructure simulation results were compared with the experimental results and they were in good agreement in dendrite morphology

Abstract:The hydrogen storage property of the porous/hollow TiO2 using yeast as template was investigated. It is demonstrated that crystalline TiO2 forms until the temperature reaches 620 °C. The product is composed of TiO2 and minor amount of H2Ti3O7 after heat treatment. The porous/hollow TiO2 with a specific surface area of 252.6 m2/g is obtained due to the removal of yeast. Pressure-composition isothermal (P-C-I) curve of TiO2 shows that a reversible hydriding/dehydridng process occurs at 30 °C, suggesting an obvious physisorption. The change of the chemical bond in Fourier-transform infrared (FT-IR) spectrum in hydriding/dehydridng indicates that hydrogen reacts with OH group on TiO2 surface even at 30 °C. The porous/hollow TiO2 collapses as cycles increase and the corresponding specific surface area decreases dramatically. Contrary, the hydrogen uptake increases with increasing of temperature, which is caused by chemisorption.

Abstract:The microstructure of aging Mg-8Zn-1Cu magnesium alloy with Cr, Ce and Sb compound addition was studied by HRTEM. The results show that the hardening rate of the aging Mg-8Zn-1Cu-0.2Cr-0.5Ce-0.5Sb alloy is relatively high in the initial stage of the aging. For the alloy aged at 160 ℃ for 8 h, a number of stacking faults, dislocations and moiré fringe come into existence, and the short rod-shaped pre-precipitates in the grains and the precipitates in the trigeminal grain boundaries are simultaneously formed. For the alloy aged at 160 ℃ for 20 h, its peak hardness reaches 945 MPa and the alloy consists of a large number of short rod-shaped -MgZn2 precipitates, blocky -MgZn2 precipitates and granular precipitates. When the alloy is aged at 160 ℃ for 48 h, it consists of a large number of elongated precipitates and granular precipitates. The elongated precipitates are formed perpendicularly to the basal plane of magnesium. Compared to the Mg-8Zn-1Cu alloy, the sizes of elongated precipitates become much smaller

Abstract:In order to further understand the electronic structure and the optical properties of MoS2, using the first-principle and based on density functional theory, the electronic structure and the optical properties of single-layer MoS2 were calculated and analyzed by the plane wave pseudo-potential method. Band structure, density of states, and optical absorption, reflection, energy loss, optics constants and dielectric function spectra of monolayer MoS2 were obtained. The calculation results show that the single-layer MoS2 has a direct band structure, the band gap width is 1.726 eV. It is found that MoS2 monolayer has a strong absorption of photons from visible light to the ultraviolet region, the maximum absorption coefficient of 1.98′105 cm-1. The analysis indicates that the single-layer MoS2 is suitable for the fabrication of microelectronic and optoelectronic devices, especially in the ultraviolet (UV) detector applications

Abstract:The effects of Er on the microstructures and the lattice parameters of the as cast Mg-5Sn-xEr (x=0, 0.5, 1, 1.5, 2, 4, 6, 8，10) alloys were investigated by X-ray fluorescence(XRF), optical microscopy(OM), X-ray powder diffraction (XRD), Scanning Electron Microscopy (SEM)/Energy Dispersive Spectroscopy (EDS). The addition of Er will result in the grain refinement, inhibite the formation of the phase Mg2Sn, promote the formation of RE-phase with irregular polygon-like shape, so the Er-Adding has obvious effect on Mg-5Sn as cast alloy. The Rietvel whole pattern fitting methods were used to analyze the lattice parameters of α-Mg solid solution in different alloys, on base of it, the Er solubility was calculated with the Vegard’Law on the orientation of a, c axis in α-Mg, respectively, the results show that the calculation of a axis is more reasonable

Abstract:Lithium iron phosphate is a new kind of cathode materials for lithium ion battery. It has found wide applications in lithium ion battery industry. It has excellent comprehensive electrochemical performance. Unfortunately, its high rate performance is not satisfactory. In order to enhance its conductivity and improve the high rate performance of the cathode material, highly conductive Ti3SiC2 modification was adopted. Ti3SiC2 modified LiFePO4/C powders were prepared via a ball milling process followed by heat-treatment at 400 °C. The effects of addition amount of Ti3SiC2 on electrochemical performance of the cathode material were investigated. It is found that a Ti3SiC2-based conducting network characterized by a “plane-to-point” conducting mode is constituted in the LiFePO4/C cathode. Galvanostatic charge/discharge test indicates that Ti3SiC2 modification is effective to improve the discharge capacity at high rates. Cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and potential step chronoamperometry (PSCA) measurements prove that the Ti3SiC2-based conducting network enhances electrochemical reversibility, alleviates charge transfer impedance and facilitates lithium ion diffusion (from 8.5′10?11 cm2·s?1 to 8.2′10?10 cm2·s?1). The 4wt% Ti3SiC2-modified LiFePO4 sample exhibits the best electrochemical performance with capacities of 131.7, 119.6 and 97.4 mAh·g?1 at 1 C, 2 C and 5 C, respectively, much higher than those without Ti3SiC2 modification. They are only 120.8, 101.9 and 64.0 mAh·g?1 at the corresponding rates, respectively

Abstract:N-type, P-type modulation-doped Si80Ge20 solid solution alloy and equivalent stoichiometric ratio uniform-doped Si80Ge20 solid solution alloy were prepared by our mature technologies. We concentrated on the thermoelectric properties of both alloy materials. The results show that the power factors of N-type, P-type modulation-doped solid solution alloys are enhanced by 13.6% and 49.2% respectively, compared with that of uniform-doped Si80Ge20 solid solution alloy. And their ZT (thermoelectric figure of merit) are enhanced by 7.9% and 12.9%, respectively

Abstract:Thermal stability of carbides in a new corrosion-resistant Ni-Cr-Mo alloy with high strength was studied by means of OM, SEM, TEM and chemical phase analysis. Results show that the microstructure of the alloy on standard heat treatment condition consists of equiaxed grains of f.c.c γ with an average size of 50 μm. Second phase particles of various sizes ranging from 100 nm to 2 μm are not only presented at grain boundaries, but also randomly distributed in grain interiors and were identified as the Mo6C and μ phases, respectively. After exposure for 10~1000 h at 600 °C, almost no change in their morphologies, phase particle sizes and distribution can be seen, which implies that the Mo6C and μ phases are stable during aging at 600 °C. However, their morphologies change gradually from granular to plate-like during exposure of up to 500 h at 650 °C. Beyond 500 h the Mo6C and μ phases will dissolve gradually and meanwhile, the continuous precipitates Cr23C6 are formed at the grain boundaries, which indicates that the Mo6C and μ phases are not stable during aging at 650 °C and the service temperature of the new alloy should be lower than 650 °C

Abstract:The laser surface melting of an antiferromagnetic Fe32Mn3Al7Cr precision resistance alloy has been performed using a continuous CO2 laser, in order to improve the corrosion resistance. The microstructure, the phase structure, the microhardness and the corrosion property of the laser surface melted Fe32Mn3Al7Cr alloy were investigated. The laser surface melting layer was constructed by a fine equiaxed cellular crystal, a columnar dendritic crystal, and heat-effected matrix. A single austenite phase of the laser surface melting layer was obtained in the depth of about 650 mm. The microhardness of the laser surface melting layer was increased up to HV0.5 N 32 GPa from HV0.5 N 16 GPa of the austenite matrix. The anodic polarization behavior of the laser surface melting layers at the 100 μm and 350 μm depths, respectively, was evaluated in 1 mol/l Na2SO4 solution. Their self-passivation was observed instead of an active-passivation of the original alloy, with higher corrosion potentials of –420 mV(SCE) and –478 mV(CSE) and lower passive current densities of 1.3 μA/cm2 and 1.0 μA/cm2 than that of –658 mV(SCE) and 2.9 μA/cm2 for the austenite matrix. In 0.1 mol/l NaCl solution at pH=14, the laser surface melting layer exhibited an apparent improvement of the pitting corrosion resistance with no pitting corrosion. The electrochemical impedance spectroscopy (EIS) of the laser surface melting layer has the larger diameter of capacitive arc, the higher impedance modulus |Z|, the wider phase degree range, compared to that of the original alloy. The polarization resistant Rt of the melting layer fitted by using an equivalent electric circuit of Rs-(Rt//CPE) increased to 38.7 kΩ·cm2 from 13.8 kΩ·cm2 and the calculated effective capacitance CB decreased to 19.7 μF/cm2 from 32.5 μF/cm2. The laser surface melting led to a significant improvement of corrosion resistance of Fe32Mn3Al7Cr alloy

Abstract:The Dy-Fe-Co and Dy-Fe-Co-Al alloy powders were prepared by the arc melting method and high energy ball milling. The phase structures and the microstructures of the alloys powders were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM), then their microwave absorbing properties were analyzed by Vector network analyzer. The results show that the absorption peaks of DyxFe90-xCo10 (x=6, 9, 12, mole fraction, %) shift towards higher frequency region from lower frequency region. At low frequency, the microwave absorbing properties of Dy6Fe84Co10 alloy is better than those of the others, when the material thickness is 1.8 mm, the absorption peak of Dy6Fe84Co10 alloy reaches –6.7 dB at 3.6 GHz. The addition of Al can improve the low frequency characteristics of Fe-Co alloys. When the thickness is 1.8 mm, the absorption peak of Dy12Fe70Co10Al8 alloy reaches –9.2 dB at 5.4 GHz. The microwave absorbing properties of Dy12Fe70Co10Al8 alloy is better than those of Dy12Fe78Co10 alloy on the band of 3~6 GHz

Abstract:The bonded magnets of (Nd,Pr)10.5-xDyxFe83.5B6 (x=0，1，2) alloys were prepared by melt-spun method. The glass transition temperatures of as-spun ribbons were measured by DSC. The effects of Dy addition on the transition temperature were investigated. It is shown from DSC curves that the glass transition onset temperature, peak temperature and end temperature increase with the Dy addition. The transition temperature range between the onset point and the end point enlarges. The ribbons are crystallized under higher annealing temperature due to their higher thermal stability. The optimum annealing temperature for (Nd,Pr)8.5Dy2Fe83.5B6 alloy with 2at% Dy is 15 °C and 30 °C higher than those for (Nd,Pr)9.5Dy1Fe83.5B6 and (Nd,Pr)10.5Fe83.5B6, respectively. With the Dy addition, the intrinsic coercivity Hcj enhances, but the remanence Br reduces. The magnetic property is: Br=0.638 T, Hcj=611 kA/m, and (BH)m=71.6 kJ/m3

Abstract:Mg17Al12 alloys were prepared by mechanical ball milling for systematical studying the influence of milling time on the information of Mg17Al12. In order to modify the surface performances of the alloys, 5% (mass fraction) or 10% of simple substances (Ni and Cu) were added into Mg17Al12 alloys mechanically milled for 12 h. The storage properties of the alloys were determined by P-C-T apparatus. The effects of different mass fraction simple substances on the hydrogen storage properties of the alloys were investigated. The results show that the Mg17Al12 has a slow rate of absorbing hydrogen and a long-term absorption process, the maximum reversible storage capacity reaches 4.1wt% after 1400 min which is closed to the theoretical one (4.4wt%). Cu can modify the surface performance and enhance the kinetics markedly. The alloy with 5%Cu has a hydrogen absorption of 4.07wt% at 623 K in 180 min as the alloy with 10%Cu the hydrogen absorption of 3.9wt%. Mg17Al12 modified by adding Cu and Ni has a better absorption performance, as the alloy with 5% Cu can desorb 3wt% hydrogen at 553 K. Ni can modify the surface performance and enhance the properties, too. But its effect is not obvious compared to that of Cu

Abstract:Using first-principles pseudo-potential plane wave method, the formation enthalpy ΔH, the binding energy ΔE and the electronic structure of the NiTiNb shape memory alloy doped with Co, Pd elements have been systematically calculated and analyzed carefully. The results show that the ΔE and ΔH of NiTi(Co→Ni) and NiTi(Nb, Co→Ni) models are smaller than those of NiTi(Co→Ti) and NiTi(Nb, Co→Ti), which means the alloying element Co will replace Ni atom in NiTiNb alloy. However, the Mulliken population and electronic density calculations show that the Co will cohere the nearest neighbor Ti atoms to be confined by strong bonds after solid solution, resulting in the Ni/Ti ratio increasing instead of decreasing by Co→Ni reaction process, then the Ms of NiTiNb(Co) is decreased. To Pd element addition, although the ΔH of NiTi(Pd→Ti) and NiTi(Nb, Pd→Ti) crystals are bit smaller than that of NiTi(Pd→Ni) and NiTi(Nb, Pd→Ni), the ΔE of the Pd replacing Ni models are much smaller than those of Pd replacing Ti. And the Mulliken population results show that some strong metallic bonds appear between Pd and Ti atoms in Pd→Ni solid solution reaction. So the Ms of NiTiNb(Pd) alloy will increase by the addition of Ni/Ti ratio for Pd taking the place of Ni. Then it can be seen, the bond strength between alloying elements and Ni or Ti atoms is the other micro-factor influencing on the ratio of Ni/Ti to the Ms.

Abstract:A LaNi4.25Al0.75/SiO2 composite was prepared by fumed silica encapsulation method. Microstructure and hydrogen absorption kinetics during hydriding-dehydriding cycling in H2 with 50 mg/L CO were investigated. The results show that apart from large amount of absorbed CO, the surface of LaNi4.25Al0.75 was covered by NiO, La(OH)3, La2O3 and Al(OH)3. Although the capacity and kinetics of both the LaNi4.25Al0.75 and LaNi4.25Al0.75/SiO2 composite were deteriorated after absorption/desorption cycling in the mixed gas, the latter has better poisoning resistance performance

Abstract:The influences of Sc contents on the microstructures of Al-5.5Mg-0.5Mn-XSc-0.1Zr (0.05≤X≤0.50) as cast alloy and the morphologies of the second Al3(Sc,Zr) precipitates as well as their strengthening effect after aging treatment were investigated by optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and micro-hardness tester. The results show that when X≤0.09, no precipitates containing Sc are found in as cast alloy. On this case, the alloy possesses the typical columnar dendritic microstructure, and the strengthening effect after the aging treatment is weak. While for the alloy with 0.16%~0.23% Sc, primary and eutectic Al3(Sc,Zr) particles precipitate during solidification, which not only refine grains, but also not impair the thermal stability of the second Al3(Sc,Zr) precipitates, and the strengthening effect is strong. When X≥0.23, a large volume of primary and eutectic Al3(Sc,Zr) particles precipitate. Though this can refine the grains strongly, but a side effect is that the Zr content in the alloys after solidification would be severely decreased, resulting in the second Al3(Sc,Zr) precipitates becoming less thermal stable. After aging at 450 ℃ for 24 h, the second Al3(Sc,Zr) precipitates coarse a lot, and its strengthening effect becomes very weak

Abstract:Effects of Cu/Al compound addition on the anti-corrosive and magnetic properties of (Pr, Nd)12.8Dy1.0FebalNb0.1B6.0 (at%) sintered magnets were investigated. It is found that the corrosion current density decreases from 46.90 μA·cm-2 for the magnet without Cu/Al to 11.14 μA·cm-2 for the magnet with additions of 0.6 at% Al and 0.2 at% Cu in 0.001 mol/L HCl solutions, the mass loss reduces from 13.2 mg·cm-2 to 0.4 mg·cm-2 in hot/humidity atmosphere for 100 h. The 0.6 at% Al- and 0.2 at% Cu-added magnet has the maximum corrosion resistance. The improvement of the corrosion resistance can be ascribed to the enhanced chemical stability and the optimized distribution of (Pr, Nd)-rich grain boundary phase. Additionally, the optical grain boundary microstructure is benefit for the magnetic properties

Abstract:Hot compressive deformation tests of as-cast burn resistant titanium alloy (Ti-35V-15Cr-Si-C) were performed on the Gleeble-1500 simulator in the temperature range of 900~1200 °C, over the range of strain rate from 10-3 s-1 to 1 s-1. The compressive true stress vs. true strain curves were measured. The discontinuous yielding phenomenon was explained. The hot processing maps developed on the basis of dynamic material model (DMM) exhibits the following three domains. The alloy dynamic recovery and continuous recrystallization in the temperature range from 900 °C to 1030 °C and at lower strain rate (＜0.1 s-1). A peak power dissipation efficiency area of 50%~65% occurring at higher temperature (≥1030 °C) and lower strain rate. In addition to dynamic recovery and continuous recrystallization, the carbide solution phenomenon is observed. The alloy exhibits a wide region of flow instability manifested by flow localization and carbide solution at higher strain rate. The ‘Necklace’ dynamic recrystallization occurs at the strain rate of 1 s-1

Abstract:The microstructure, the segregation and the evolution of g/g ′ eutectic during the solidi?cation of Ni-base superalloy DD6 prepared by dual heating zone melting and liquid-metal cooling (LMC) direction solidification technique were investigated over a range of cooling rates. The microsegregation behavior during solidi?cation was also quantitatively examined by EPMA to clarify the in?uence of elemental segregation on the evolution of g/g ′ eutectic. The effect of dendrite arm spacing was also taken into consideration. The results demonstrate that the g/g ′ eutectic fraction first increases and then decreases with the increasing of cooling rate. The back-diffusion in solid phase would reduce the microsegregation during dendrite growth. Back-diffusion occurs during the solidi?cation of Ni-based single crystal superalloy DD6, but its influence on decreasing of the volume fraction of g/g ′ eutectic would be negligible depending on the diffusivity of each solute element when the cooling rate is up to a certain limit. As the cooling rate increases, the dilution effect of microsegregation owing to dendrite arm spacing decrease plays a leading role during solidi?cation

Abstract:The Zr-0.4Fe-1.0Cr-xMo alloys were prepared by vacuum arc melting method, and its tensile properties at room temperature and 350 °C were measured. Results show that the tensile strengths of Zr-0.4Fe-1.0Cr-xMo alloys are higher than that of Zr-1.0Sn-0.3Nb-0.3Fe-0.1Cr alloy. With the increase of Mo content, the tensile strength decreases at room temperature whereas increases at 350 ℃, which indicates the strengthening effect of Mo on Zr-0.4Fe-Cr alloy at high temperature. The variation of the strain hardening exponent n-value with Mo content is opposite to that of the yield strength. The effect of Mo on tensile properties is related to the change of second phase particles characteristics due to Mo addition.

Abstract:Grain texture evolution during the directional solidification of Ni-base single crystal superalloy DD3 in spiral selector has been simulated by ProCAST&CAFE model. The results indicate that the main function of starter block is to optimize the grain orientations. The favorably <001> oriented grains would overgrow the unfavorable grains with increasing of the distance from the base of starter block, and when the distance is up to 26 mm, the average deviation of the grain orientations is controlled within 10?. Only one grain is allowed to grow into the cast by grain selecting in the spiral part, and no optimization occurs during grain orientation selection in the spiral. The grains near the outer wall of the spiral passage are always geometrically blocked by the spiral passage, and the grain near the inner wall of the spiral passage is usually selected as the final single crystal. It obviously depends on the location of the grains and has no apparent connection to the orientation of the grains whether the grains are selected or blocked in the spiral passage

Abstract:LiFe1-xNixPO4/C (x=0.0, 0.1, 0.3, 0.5) cathode materials were synthesized by a carbothermal reduction technique and the effect of Ni2+ substitution on the electrochemical performances were systematically investigated. The results reveal that the cycle performance and electrochemical reversibility of LiFePO4 are remarkably improved with the substitution of Fe2+ ions by Ni2+ ions and LiFe0.9Ni0.1PO4/C demonstrates good electrochemical performances with discharge capacity of 160 mAh·g-1 at a discharge rate of 0.2 C (1 C=170.0 mA·g-1). The improvement of the reversible capacity and the high C-rate performance of LiFePO4 could be attributed to the enhancement of the electronic conductivity and the decrease of the charge transfer resistance. The first-principle calculations were employed to investigate the electronic structures of the LiFe1-xNixPO4/C composites. The Lattice parameters, total energies, density of states have were also studies in details. The results show that the electronic conductivity of the Ni2+-doped materials can be improved to certain extent. LiFe0.875Ni0.125PO4 has the most stable structure, the smallest band gap and the best conductivity

Abstract:The ordering behavior of the L12 type Co3Ti-based intermetallics were studied by using the sublattice model supported with first-principles calculations. The results show that the stoichiometric intermetallics Co3Ti is fully ordered intermetallics, where Co atoms always occupy the 3c sublattice and Ti atoms always occupy the 1a sublattice. For ternary alloy Co72Ti24M4, where xCo/xTi=3:1 and M represents the ternary alloying element, when M represents Si, Ta or Ti atom, M occupies 1a sublattice, while when M represents Cu, Ni, Pd, Rh, V or W atom, M occupies 3c sublattice, and when M represents Al, Cr, Ge, Mn, Sc or Y atom, M occupies both 1a and 3c sublattices. The site preferences of these alloying elements are independent of the heat treatment temperature. While the site occupancy of ternary alloying element Fe, Hf, Mo, Nb, Ru or Zr in ternary alloy Co72Ti24M4 varies with the heat treatment temperature. With the increase of extranuclear electrons, the site preference of the transition metal tends to change from 1a sublattice to 3c sublattice gradually. The sublattice occupancy fractions varying with alloy compositions and temperature were also calculated in some other Co3Ti-based alloys where xCo/xT offsets 3:1. The predicted results are consistent with most of the literatures, and some disagreements in literatures were clarified

Abstract:In order to investigate the effect of 7075 aluminum alloy on the microstructure and mechanical properties of AZ91 magnesium alloy, the optical microscope, scanning electron microscope, X-ray diffraction method and universal material testing machine were used to analysis the microstructure and the mechanical properties of AZ91 magnesium alloy. The results indicate that the addition of 7075 aluminum alloy can refine the as-cast microstructure of AZ91 alloy obviously. The volume fraction of Mg17Al12 phase is decreased, and Al6Mn phase is formed when the addition content of 7075 aluminum alloy exceeds 4%. The tensile strength and elongation of AZ91 magnesium alloy increase with increasing of the addition amount of 7075 aluminum alloy. When the addition of 7075 aluminum alloy is 4%, the tensile strength and elongation of AZ91 alloy are at the maximum value, which are 186 MPa and 8.2%, respectively

Abstract:The effect of different aging processes on the mechanical and intergranular corrosion properties of 7A85 high strength aluminum alloy were investigated using the methods of tensile test, conductivity test, intergranular corrosion test and metallographic microscope observation etc.. The results indicate that when the aging temperature is in the range of 110~140 ℃, the conductivity of the 7A85 aluminum alloy increases with increasing aging temperature, intergranular corrosion depth decreases gradually and the intergranular corrosion resistance of the alloy is improved. The alloy shows first peak hardness at aging time of 30 h and aging temperature of 120 ℃. At the aging temperature of 120 ℃, the conductivity increases and the intergranular corrosion depth of the alloy decreases with aging time extending, that is to say, the intergranular corrosion susceptibility of the alloy decreases with increasing aging time. After the alloy is treated with the aging process of 470 ℃/2 h +120 ℃/30 h, the tensile strength of 710.3 MPa, yield strength of 655.46 MPa, elongation rate of 11.25%, conductivity of 30.7% IACS, and average intergranular corrosion depth of 0.100 mm can be reached. The heat treatment system can make the alloy maintaining good mechanical properties as well as high intergranular corrosion resistance

Abstract:The hydroxyapatite(HA)/Chitosan (CS) coating was prepared by a microarc oxidation process on the surface of the biomedical used titanium. The morphology and the phase composition of the coating were analyzed by using scanning electron microscope (SEM), X-ray diffractometer (XRD) and infrared spectrometer (FTIR). The toxicity of the coating material to the osteoblasts and its bioactivity in vivo were evaluated. The characteristics of the HA/CS coating by the microarc oxidation method, and its possibility of application in the bone regeneration were analyzed. The results show that the HA/CS coating on the surface of titanium with a thickness of 40±2 μm, a roughness of 3.3±0.1 μm, a porosity of (30±2)%, approximately circle pores and their diameter in the range of a few microns to 20 μm, and a bond strength of 20.5±1.1 MPa, can be prepared by using the microarc oxidation method. The HA and CS in the coating do not form chemical bonds. HA crystals occupy 10% of the total particles with an average particle size 37 nm. The other 90% are amorphous HA particles. Titanium base HA/CS coating can promote the proliferation of osteoblasts and it is not toxic. In addition, it can induce the formation of bone trabecula and shows a high bioactivity. In general, the HA/CS coating material with a high bioactivity will have a good application prospect in the aspect of bone regeneration

Abstract:A Ni-5at%W ingot was prepared by medium frequency induction melting. The ingot was forged, hot-rolled and cold-rolled into trips with 60 μm thickness and 50 m length. Recrystallization annealing for the substrate trip was carried out at different temperatures (800~1200 °C) for different time. Taking account of high cube texture and shallow boundary, the recrystallization annealing of 1100 °C/0.5 h is regarded as the best. According to X-ray diffraction and EBSD analyses, the cube grain content of the tape annealed at 1100 °C for 0.5 h reaches as high as 98.9% (tolerance angle of less than 10°), and grain size is uniform. The FWHM values of the in-plane and the content of crystal twin are slightly different from that of the commercial Ni5W tape supplied by Germany Dresden

Abstract:HfB2 powders were prepared successfully by combining sol-gel with carbonthermal reduction. The phase components and micro-structure were analyzed by XRD and SEM, respectively. The oxidation behavior of the powders at high temperature was measured by TGA. The results show that reduction temperature and content of boric acid have obvious effects on the purity, the average size and the oxidation behavior of HfB2. As the temperature is 1800 ℃ and the content of boric acid is higher than its stoichiometric ratio of the synthesizing of HfB2, the obtained HfB2 with high purity and uniform particle size has the better oxidation behavior. Moreover, the reactive mechanism of preparing HfB2 powders was also discussed

Abstract:The TC4 alloy was brazed to SiO2 composite using AgCu-4.5Ti filler alloy. The interfacial microstructure of joint was analysed and its formation mechanism was discussed. The influence of brazing temperature on the interfacial microstructure and the shear strength of joints was studied. The typical interfacial microstructure was SiO2 composite/TiSi2/Cu4Ti3+Cu3Ti3O/Ag(s, s)+Cu(s, s)/TiCu/Ti2Cu/α, β-Ti/TC4 alloy at brazing temperature 850 ℃, for 10 min. The increase of brazing temperature would increase the thickness of interfacial reaction layers near SiO2 composite and TC4 alloy, and the AgCu eutectic microstructure would disappear at 870 °C. The shear strength of joint also changes with the increase of temperature. The shear strength of the joints reaches a maximum of 7.8 MPa when the temperature is 850 °C and the holding time 10 min

Abstract:The lap joint of commercial purity titanium (TA2) and copper (T2) plates was made via friction stir welding technique. Based on the optimization experiments, the suitable process parameters have been obtained as follows: rotation speed of 800rpm, travel speed of 20 mm/min and rotation speed of 900 r/min, travel speed of 30 mm/min. Under this process conditions, the defect-free lap welds with well formed surface and the interface of joint can be obtained. Using OM and SEM the investigation on the weld characteristics was conducted. Results show that the phenomenon of the flow in the macro scale of Cu and Ti between the joint-interface is exhibited obviously, and the flow amount of Ti to Cu is more than that of Cu to Ti greatly, furthermore, some parts of joint-interface present the typical bounded texture microstructure of Cu and Ti. About 4.8 μm thickness of diffused intermediate layer is formed in the interface of lap joint, the diffusion velocity of Cu is faster than that of Ti, and the lap joint of Cu and Ti has formed the metallurgical bonding

Abstract:The medical Ti-Mo alloys were fabricated by powder metallurgy. The effects of different process parameters on the phase, the morphology and the mechanical properties of Ti-Mo alloys were investigated through X-ray diffraction (XRD), scanning electron microscopy (SEM) and mechanical properties test methods. The results show that after sintering at 1050 °C, the microstructure of Ti-Mo alloys mainly consists of β phase. By adjusting the pressure, sintering time and Mo contents to regulate the porosity of Ti-Mo alloy and α→β phase transition, thus the flexural strength and the elastic modulus of Ti-Mo alloys can be controlled

Abstract:The Rn-Ir-Sn metal oxide anodes coated on titanium were prepared by thermal decomposition. The anodes were studied by SEM, EDX, cyclic voltammetry, electrochemical impedance spectroscopy and accelerated life test, which characterized the deactivation behavior of metal oxide anode electrolyzing at different temperatures of seawater. The results indicate that the center of the deactivated anodes electrolysed at 5~20 °C has traces of the coating with remained dried-mud cracks while the bare Ti substrate is exposed in the surrounding area at the edge, which os caused by the dissolution of the active components, and the peeling of the coating. When the electrolysis temperature of seawater is 40 °C, the service life of the anode is longer, the uniform electrochemical dissolution of the anode coating takes place. In addition, the electrochemically active surface area and the stability of the anode increase with the rising of the temperature. The deactivation of the anode at 5~20 °C is attributed to the selective dissolution of Ru and the partial detachment of the coating, and the deactivation of the anode at 40 °C is ascribed to the formation of TiO2 between Ti base and the active coating

Abstract:The effects of Thermo-Mechanical Processing(TMP) on microstructure, hardness, electricity, intergranular and exfoliation corrosion resistance of extruded 2099 Al-Li alloy were investigated by microstructure observation, XRD analysis, hardness and electric conductivity testing. The results show that compared with the extruded 2099 Al-Li alloy after T83 heat treatment (540 °C/2 h solid solution, 3% pre-compression, 121 °C/14 h + 181 °C/48 h aging), the samples after TMP (540 °C/2 h solid solution, 400 °C/48 h overaging, about 50% large strain deformation, 540 °C/2 h solid solution)+(121 °C/14 h + 181 °C/48 h aging) recrystallize obviously. The HV hardness is a little lower(2006.2 MPa vs 1865.3 MPa) and so is dislocations strengthening. The electric conductivity and the intergranular corrosion resistance are improved significantly and the exfoliation corrosion resistance is also enhanced. This study shows that TMP is an effective method to improve the intergranular resistance with the hardness not greatly reduced

Abstract:NiCuZn ferrite powder with fine particles size distribution and high activity was synthesized by chemical co-precipitation. The effects of synthetic conditions, such as reaction temperature, stirring speed and flow rate of salt solution, on the precursor particle size of NiCuZn ferrite were investigated. The samples prepared at the optimal condition were characterized by XRD, TEM, laser particle size analyzer (LPS), precision impedance analyzer and vibrating sample magnetometer (VSM). The results show that the powder is possessed of pure spinel, the particle size of about 30 nm, the average grain size of 11 nm, while the synthetic conditions are the reaction temperature for 70 °C, the flow velocity of the salt solution for 0.5 mL/min, stirring speed for 300 r/min. NiCuZn ferrites, presintered at 500 °C and sintered at 900 °C, have achieved excellent magnetics. The relative density of sample is 98%, the initial magnetic permeability is 200, quality factor is 150 and the cut-off frequency is 70 MHz

Abstract:Hot stretch-creep process is a novel compound forming approach for thin-wall titanium alloy components. In this process, a thin-wall stock of metal sheet or profile is stretched and bended after heating to the hot forming temperature via the heating methods such as resistance heating. When the finial configuration is formed, the temperature remains and the material creeps along stretch direction based on the mold surface. This leads to the internal stress decrease in the formed workpiece and a stress relaxation on-line. Then the springback of the component is reduced due to the decrease of the residual stress and the forming precision is improved. The research status, process principle, key equipment, processing technology, and the merits/demerits of the new process and technology were introduced. Finally, the applications of hot stretch-creep compound forming technology in future are proposed

Abstract:This paper presents a comprehensive review about the effect of cooling rates and impurities on the microstructure of zirconium alloys during β→α transformation with the expectation to facilitate the development of high-performance zirconium-based cladding materials. For zirconium alloys, the diffusionless Martensitic transformation does not produce a surface rumpling after quenching the pre-polished specimens. The Ms temperature keeps independent of β quenching rates. When alloy composition is fixed, increasing of cooling rate causes microstructural change in the following sequence: lenticular α→Parallel plate α→Basketweave α→Martensitic α'. The impurities which can form insoluble second phase particles in β phase will promote the formation of Basketweave Widmanstatten structures. However, the impurities that might increase β phase transformation temperature will lead to more Parallel-plate Widmanstatten structures