Abstract:Mg2Ni-type hydrogen storage alloys with nominal composition Mg20-xLaxNi10 (x = 0, 2, 4, 6) were prepared by melt spinning. The microstructures of the alloys were studied by XRD, SEM and HRTEM. It is found that no amorphous phase formed in the as-spun La-free alloy, but the as-spun alloys containing La mainly held a major amorphous phase. When La content x≤2, the major phase in the as-cast alloys is Mg2Ni phase, but with the further increase of La content, the major phase of the as-cast alloys changes into (La,Mg)Ni3+LaMg3 phases. The hydrogen absorption and desorption kinetics of the as-cast and spun alloys were measured using an automatically controlled Sieverts apparatus, indicating that the hydrogen absorption and desorption capacity and the kinetics of the x = 2 alloy clearly increase with rising of spinning rate, but a contrary result is obtained for x = 6 alloy. The electrochemical measurement shows that the discharge capacity of the x = 2 alloy grows with rising of spinning rate, but it is a completely contrary result for x = 6 alloy. The melt spinning significantly improves the cycle stability of the x = 2 and 6 alloys

Abstract:The effect of processing parameters, including deformation temperature, strain rate and deformation degree on the microstructure evolution and the microstructure variables (grain size and volume fraction of primary α phase) was investigated based on the microstructure observation and the quantitative metallography of the isothermally compressed Ti-6Al-4V alloy. The results show that the curves of grain size of primary α phase are oscillatory in the α+β two-phase region with increasing of the deformation temperature, and meanwhile the volume fraction of primary α phase decreases. The effect of the strain rate on the morphology of primary α phase is significant, while its effect on the microstructure variables of isothermally compressed Ti-6Al-4V alloy is dependent on deformation temperature. The grain size of primary α phase decreases with increasing of strain rate above 1203 K, but below 1203 K it fluctuates. The curves of volume fraction of primary α phase are oscillatory with increasing of strain rate above 1223 K, but below 1223 K the volume fraction decreases. The grain size of primary α phase increases slightly after a drop with increasing of the deformation degree, and meanwhile the secondary α phase decreases gradually. The effect of deformation degree on the volume fraction of primary α phase is not significant

Abstract:SiCf/Ti-6Al-4V composites were used to study the effects of thermal exposure on the thermal expansion behavior of composites. The expansion behaviors of the matrix alloy, as-processed composite, and composites exposed at 900 oC for 10, 25 and 75 h were investigated by coefficients of thermal expansion (CTE) test. The results indicate both in longitudinal and transverse direction, the CTE of the exposed composite is higher than that of the as-processed composite. The CTEs of the specimens exposed at 900 oC for 10 and 75 h are higher than that of the specimen exposed at 900 oC for 25 h, no matter in longitudinal or transverse direction. It can be attributed to that there is an appropriate interfacial reaction for the composite exposed at 900 oC for 25 h. Because the prediction of Schapery’s model for CTE of composite includes the influence of thermal tensile residual stress in matrix at the whole heating process, the CTE results predicted by Schapery’s model are lower than the real CTE obtained from experiments at the high temperature stage of the CTE curve

Abstract:The effect of Hf content on the microstructures after heat treatment and stress rupture properties of DD6 single crystal superalloy was investigated. The results show that with increasing of Hf content in the range of current research, the residual γ/γ′ eutectic increases apparently, the size of γ′ particles in dendritic cores has no obvious change and that in interdendritic decreases after heat treatment. With the increase of Hf content, the stress rupture life increases at first and decreases afterwards, and the elongation displays fast increasing first, and slow rising afterwards at 1100 oC, 140 MPa. At last the relationship between the microstructures and stress rupture properties of DD6 alloy with different Hf contents was discussed

Abstract:The interface combinations between Ag(110), (211) and Ni(110), (211) were studied by the first-principle based on the density functional theory calculations. The interface bonding energy, charge population and electronic structure were investigated. It is found that among all the combinations the interface bonding energy and electron hybridization reach the maximum values at Ag(100)-Ni(211) interface, and this interface combination is the most stable

Abstract:Dynamic compression and in-situ tensile tests were carried out for two kinds of W-Ni-Fe alloys with 93wt% and 97wt% tungsten contents fabricated by P/M technique; their microstructures and damage model were examined and discussed. The damage mechanisms for 93wt% W alloy belongs to ductile separation of W-W interface, and that for 97wt% W alloy belongs to initiation and propagation of microcracks inside tungsten grains. On the base of Ostwald ripening theory for the sintering process, the microstructures of the two kinds of alloys with different tungsten volume fractions under various sintering conditions were predicted, and the results agreed with the tests very well. With the help of Ostwald ripening and micromechanical theory, we set up a relationship for sintering condition, volume fraction of tungsten and mechanical properties to help material design, production and mechanical property prediction

Abstract:Crystal structure, electronic structure and bonding characteristics of LaNi5-xCox(x=0, 0.5) and its hydride were investigated by the density functional theory based on general gradient approximation (GGA) and the ultra-soft plane-wave pseudopotential method. The total energy, energy band structure, density of states and Mulliken population were obtained. The results show that the interaction between Ni2c and La atoms is larger than that between Ni3g and La atoms in LaNi5 alloy. There is obvious covalent interaction between Ni2c―Ni2c and Ni3g―Ni3g. However, the covalent interaction is reduced after introduction of Co and H atoms. The interaction between H and Ni3g atoms is larger than that between H and Ni2c atoms. The expansion along a axis is larger than that along c axis because the lattice expansion results in outward moving of Ni2c atoms after hydrogen atom enters the tetrahedron

Abstract:Ti6Al4V alloy samples were modified by implanting silver ion at the dose of 5×1016, 1×1017, 5×1017 and 9×1017 ions/cm2 under an acceleration voltage of 30 kV. The potentiodynamic polarization curve was used to investigate the corrosion resistance of un-implanted and Ag+-ion-implanted Ti6Al4V alloy in Hank’s solution. The glancing angle X-ray diffraction and X-ray photoelectron spectroscopy were used to investigate the phase composition and chemical states of elements on Ti6Al4V alloy surface. The results show that silver ion implantation can improve the corrosion resistance of Ti6Al4V alloy in Hank’s solution. The corrosion current density of Ag+-ion-implanted Ti6Al4V alloy changed slightly with the Ag ion dose increasing. The corrosion resistance improvement of Ag+-ion-implanted Ti6Al4V alloy samples in Hank’s solution is attributed to all kinds of corrosion-resistant oxide layer, surface alloy layer produced during ion implantation and Ag and TiAg existing in the outermost surface of the Ag+-ion-implanted Ti6Al4V alloy

Abstract:A damping measurement system was developed for high temperature materials using double-reed cantilever specimens by means of resonant-dwell under base excitation in a high-temperature and vacuum environment. Some methods were proposed to improve the accuracy of damping measurement. The effect of air damping on damping tested results was analyzed. The damping of Ti-6-4 alloy was tested by the system and the relationships of material damping to temperature, strain amplitude and vibration frequency were studied. Results show that air damping has a significant effect on the damping of materials. The damping of Ti-6-4 alloy keeps constant and the vibration frequency has little effect on it below 400 oC. However, it increases rapidly with temperature elevation above 400 oC and the vibration frequency has a complicated effect on it. The effect of strain amplitude on the damping of Ti-6-4 alloy can be neglected in the temperature range from 25 to 600 oC

Abstract:Through the common-used acidic electroless nickel deposition system with hypophosphite, the electrochemical essence of catalytic activity of the substrate for electroless deposition was investigated. It is found that oxidation of hypophosphite is dominative for the electroless nickel deposition of the substrate by stable potential measurement, and there exists a typical reaction potential for the anodic oxidation of hypophosphite. On the basis of previously proposed oxidation model of hypophosphite, the necessary condition of the metal substrate with catalytic activity for electroless nickel deposition is put forward that the potential of the metal is not only higher than the redox potential of hypophosphite, but also lower than the metal’s potential of zero charge in the particular electrolyte. By examining the experimental results of five kinds of typical metal, the above hypothesis was proved.

Abstract:The DC volume resistivity and high field conductivity of nano-Ag/epoxy resin polymer composite were researched. The results show after trace addition of Ag nanoparticles with small sizes, the composite has obviously higher volume resistivity than pure epoxy resin. The increase of resistivity is relative with Ag particle size, adding content and characteristics of base polymer. High field conductivity tests show that the coulomb blockade effect appears when Ag particles of small size disperse evenly in the polymer, i.e. the transmission of electron charge can be restricted by nanoparticles. When the adding content of Ag nanoparticles is too much or their size is too big, the composite shows space charge limited current property. TSC results show that more deep traps exist at the interface between nano Ag and polymer, which causes space charge limited current for charge captured and escaped from the traps

Abstract:Joint addition of Y and Ce results in excellent ignition-proof effect and realizes no-protection melting in air for magnesium alloys. AES and XRD surface analyses show that an oxidation film mainly composed of Y2O3 was formed on the surface when the Mg-Y-Ce ignition-proof alloys were exposed in air at high temperature. When the Mg-Y-Ce alloys were oxidized at 773, 873 and 973 K in dry air, the oxidation dynamics curves followed the cubic law. Base on the oxidation thermodynamics, the selective oxidation mechanism for Mg-Y-Ce alloys at high temperature was analyzed. The semiconductor characteristics of Y2O3 film and its proof effect on magnesium alloy oxidation were discussed electrochemically

Abstract:Ag supported ZnS (ZnS/Ag) composite nanowires were prepared by a hydrothermal method. The phase structure, morphology and optical properties of the prepared nanowires were characterized by XRD, TEM and UV-Vis spectrophotometer. With methyl orange as degradation target, photocatalytic performances of the prepared composite nanowires under ultraviolet radiation were evaluated. Results show that the photocatalytic activity of ZnS nanowires prepared by the hydrothermal method was superior to that of commercial ZnS. Meanwhile, the Ag supported ZnS nanowires exhibit higher photocatalytic activity than that of non-supported ZnS nanowires, which is attributed to that Ag particles promote the separation of the pairs of excited electrons and holes, and increase the activity points of ZnS nanowires

Abstract:The liquid phase of the Mg-Si binary system was re-assessed by the Calphad approach. Combined the thermodynamic data of Mg-Zn and Zn-Si binary systems, the thermodynamic parameters of Mg-Zn-Si ternary system were obtained by extrapolation. Based on the phase diagram of Mg2Si-MgZn2 pseudo-binary system, the liquid ternary interaction parameters of Mg-Zn-Si system were assessed. The results show that the calculated phase diagram agrees basically with the experimental data. The solidification process of the Mg-2.33Zn-0.9Si (at%) alloy was simulated by Scheil model, and the phase evolution of Mg alloy during cooling casting was predicted. The results agree with the previous experiment results

Abstract:he dynamic mechanical properties of fine-grained tungsten heavy alloy 93W-4.9Ni-2.1Fe with trace yttria addition were investigated under dynamic compression using Split Hopkinson Pressure Bar. The microstructure of the alloy sample after dynamic compression was analyzed. The results reveal that two obvious adiabatic shear bands were observed at the strain rate of 1900 s-1, indicating that the susceptibility of the fine-grained alloy to local adiabatic shear is significantly enhanced and the fine-grained alloy can form the shear bands at a lower strain rate. The adiabatic shear bands initiate in the crack tip region of the surface area of the specimen, propagating deeply along orientations at 45o to the impact direction. The bands have much narrower width of about 10-25 mm than that of traditional tungsten heavy alloy. Within the center of the bands, the tungsten grains are severely elongated to be fibrous along the propagation directions of the adiabatic shear bands, exhibiting plastic flow localized instability

Abstract:The high-temperature oxidation/reduction cycle of Pd/PdO was investigated by high-temperature X-ray diffraction and thermogravimetric technique. Moreover, effects of minor Mn addition on the thermal stability of Pd/PdO were also studied. The results show that PdO will decompose to metal Pd sharply at a certain temperature, and the decomposition temperature is independent of powder granularity. The dispersion state of Pd powder decides the hysteresis characteristics of the phase transition Pd/PdO. Proper Mn addition can change the high temperature thermal stability and hysteresis curve of Pd/PdO system

Abstract:The liquid lithium tin alloy is a promising breeder material for the tritium blanket of the fusion fission hybrid reactor (FFHR). For an effective design of the deuterium-tritium fuel circulation of FFHR, a mathematical model of kinetics of tritium desorption behavior from liquid Li25Sn75 alloy was built based on the action theory of metals and hydrogen. The calculation data of tritium desorption behavior under different operating conditions of temperature, tritium partial pressures, helium gas flow and mass transfer coefficients were obtained. The results show that the overall desorption process, even though including five sub-processes (transport of the tritium by diffusion and convection, transport of the tritium by diffusion through a layer of eutectic adjacent to the gas-eutectic interface, heterogeneous reaction at the interface of the tritium atoms recombination, diffusion of the tritium through the gas-phase boundary layer and transport of the gaseous tritium by diffusion and convection from the gas phase boundary layer), is governed by the diffusion of tritium atoms in the Li25Sn75 and by the heterogeneous reaction at the gas-eutectic interface of the tritium atoms recombination in the desorption temperature range from 673 to 873 K

Abstract:Titanium matrix composite coatings were prepared on TA15 titanium alloy surface through laser melting depositing pre-mixed TA15+30%TiC powders (volume fraction). The microstructure, the hardness and the interface bonding strength of the coating were investigated. The results show that during the laser melting deposition process, original TiC particulates dissolved and re-precipitated fine TiC in the solidification process. The precipitated TiC presented two different morphologies, i.e. equiaxed and dendrite. There were some unmelted TiC particulates in the coating. The hardness of the coating was up to HRC 60. The coating was metallurgical bonded with the substrate. The interface bonding strength was higher than 310 MPa and the shearing strength of the coating were 330 MPa. There was no debonding after bending and thermal shock tests, indicating the good compatibility of the coating with the titanium alloy substrate

Abstract:The isothermal oxidation behaviors of two kinds of single-crystal nickel-base superalloys DD10 with different cobalt contents were investigated at 900, 1000 and 1100 oC in air by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy disperse X-ray analysis (EDX). It is found that increasing the cobalt content can decrease the diffusion activity energy of the alloy and thus increase the oxidation rate slightly. For the oxidation at 900 oC and 1000 oC, the mass gain basically obeys the parabola law. The oxide scales consist of three layers: an outer layer of Cr2O3 and TiO2, a thin intermediate layer of CrTaO4 and Ta2O5, and a continuous inner layer of Al2O3. For the oxidation at 1100 oC, because of the severe spalling of the scale and the volatilization of the CrO3, the kinetics curves deviate from the parabolic law a little. Some spinels such as NiCr2O4, CoAl2O4, CoNiO2 and Co2TiO4 form and inner nitridation phenomenon happens

Abstract:Biphase intermetallic compound wear-resistant alloy was prepared by laser melting deposition technique with bulk silicide Ti-5Si3 as primary phase and with Ti5Si3/NiTi eutectic as substrate. The wear resistance of Ti5Si3/NiTi alloy was tested under dry sliding wearing condition at room temperature and the worn mechanism was discussed. Results show that the Ti5Si3/NiTi alloy has excellent wear resistance and extremely low load-sensitivity under dry sliding wearing conditions, which is attributed to the good match between the toughness and the strength as well as the protection for the alloy from the formation of microstructurally featureless layer with high hardness on the worn surface of the alloy

Abstract:The microstructure and grain orientation of the high-purity tungsten prepared by a CVD method (CVD-W) were analyzed by optical microscope (OM), X-ray diffraction (XRD) and electron backscatter ring diffraction (EBSD) in a scanning electron microscopy (SEM). The dynamic and static mechanical performances were tested by Hopkinson split-bar and electron testing machinery. Results show that the CVD-W is of columnar-grain microstructure and has (100) texture. The dynamic yield strength of the CVD-W is above 2000 MPa, and the static yield strength is about 1350 MPa. CVD-W has strain-rate sensitivity

Abstract:Tin whisker growth on the surface of ErSn3 phase was investigated during air and vacuum aging of ErSn3, respectively. The results indicate that tin whisker growth occurs on the surface of the oxidized ErSn3 phase during air aging. Moreover, the growth rate is slow and the distribution is uneven during room temperature aging; on the contrary, the growth rate of tin whiskers is fast and the distribution is even during 150 oC aging; however, no tin whisker is found on the surface of ErSn3 phase during vacuum aging. The volume expansion which is caused by diffusion of oxygen atoms into ErSn3 lattice during oxidization in air produces compressive stress that provides the driving force for tin whisker growth; thus tin whisker growth happens during air aging and no whisker is found during vacuum aging

Abstract:To evaluate the effect of hydrogen attack on mechanical properties of U-2.5Nb alloy, hydrogen consumable amount of hydrogen attack was precisely controlled by temperature and gas pressure, and the mechanical properties were measured on a tensile test machine. The morphologies of hydrogen corrosion and fracture surface were observed by SEM and OM. The results show that, ductility parameters such as elongation and reduction decrease distinctly due to hydrogen attack, and ultimate tensile strength decreases slightly with increasing of hydrogen corrosion. According to morphologies of hydrogen corrosion and fracture surface, it is concluded that the micro-cracks and pits induced by hydrogen attack result in the loss of ductility of U-2.5% Nb alloy

Abstract:With Nb and Si powders as starting material, the dense Nb/Nb5Si3 composites were in situ synthesized by spark plasma sintering (SPS) technology. The microstructures of the composites were analyzed through SEM, XRD and EPMA, and the forming mechanism was studied. The results show that the synthesized composites consist of nearly-spherical Nb particles and Nb-Nb5Si3 eutectic. Si powders and surface of Nb particles were melted due to the action of spark plasma during SPS, and the Nb-Nb5Si3 eutectic was formed by eutectic reaction of melted Si and Nb during cooling process. The residual particles of Nb were distributed homogeneously in the eutectic microstructure

Abstract:Laser melt injection (LMI) was used to prepare single crystal particle reinforced WCp/Ti-6Al-4V functionally graded materials (FGMs) layer on Ti-6Al-4V. In situ tensile test in scanning electron microscope (SEM) was employed to study the crack formation and propagation of the FGMs layer. The micro fracture behavior was also studied. The results show that there are mainly two failure mechanisms: WC particle cracking and WCp/Ti interface decohesion. WC particle cracking forms the majority of the crack nucleation. In contrast, WCp/Ti interface decohesion is a rarely observed phenomenon, which usually occurs at higher strains. In addition, the regular cellular reaction layer formed in LMI plays a positive role in the load transfer from the matrix to the particle. During the tensile test, the stress state of WCp gradually changes from initial compressive stress to tensile stress. Furthermore, the maximum tensile stress inside the WC particle is about 2000 MPa, which is much higher than the critical fracture strength of single crystal WCp

Abstract:A prediction model for microstructure evolution and ageing strengthening was developed for Al-Cu-Mg-Ag alloys with high Cu/Mg ratio before peak ageing stage. Firstly, the expression of critical parameters was built for the quantitative relationship of Mg and Mg-Ag atom clusters to consumed Cu atoms during Ω phase precipitation, i.e. the interface energy model of Ω precipitates and the substrate. Provided the alloy is pseudo-binary approximation, quantitative distribution model of Cu solute atom in the two strengthened phases for the Al-Cu-Mg-Ag alloy was set up based on the thermodynamic model and the classical nucleation and growth theories. The model can predict the evolution of the radius and precipitation density of two strengthened particles and the solute concentration with temperature and time. Finally, the strengthening model based on Orowan equation was solved. The microstructure evolution and strength prediction of the model were generally in good agreement with the experimental data, which verified the reliability of the models.

Abstract:The hot corrosion behavior of plasma-sprayed NiCoCrAl-Y2O3 coating on TiAl alloy surface in the mixed melted salt of 75%Na2SO4+25%NaCl at 850 oC for 100 h and the influence of the coating on the anti-corrosion properties of TiAl intermetallics were investigated. The results show that the plasma-sprayed NiCoCrAl-Y2O3 coating could remarkably improve the hot corrosion resistance of TiAl matrix by generating a compound oxide layer of Cr2O3, NiO and NiCr2O4. In the course of hot corrosion, S, carried by Ni, gradually infiltrated into the composite coating and generated a transition product of Ni3S2. Then the partial pressure of the oxygen increased, followed by oxidation which produced oxides including Cr2O3 and NiO. As the amount of the both oxides increasing, the solid-state reaction took place and generated the NiCr2O4 compounds of spinel structure. The transition product of Ni3S2 and the chloridion contained in corrosion media jointly constituted micro-cell, thus accelerating hot corrosion

Abstract:Adding cerium complex to the silicate alkalinity electrolyte, the ceramic coating on the surface of Zircalloy-4 was prepared by constant voltage micro-arc oxidation. The existing form of the rare-earth element Ce in the ceramic coating and the influence of Ce on the coating thickness, phase composition, wear resistance and corrosion resistance were analyzed. The results show that Ce can enter the ceramic coating and exists in the form of solid solution, so that the relative proportion of t-ZrO2 and m-ZrO2 phases changes, the pores and granules are obviously reduced, the surface becomes smoother and more compact, the thickness of the coating increases, and the corrosion resistance and wear resistance are remarkably improved. The optimal addition amount of cerium complex in the electrolyte is 0.001-0.003 mol/L

Abstract:Quartz/ZnO/TiNi and quartz/TiNi/ZnO multilayer films were prepared by RF magnetron sputtering process on the quartz substrate. The phase composition, microstructure and mechanical properties of the multilayer films were investigated by XRD, SEM and scratch test methods, respectively. The change rule of the damping capability with the frequency and amplitude was investigated by DMA for quartz/TiNi and quartz/ZnO/TiNi multilayer films. Results show that the frequency response of quartz/TiNi is within 10 Hz, while that of quartz/ZnO/TiNi almost reaches to 20 Hz. The damping amplitude of quartz/ZnO/TiNi is 1.0 V, while that of quartz/TiNi is only 0.6 V. The damping capability of quartz/ZnO/TiNi is superior to that of quartz/TiNi. The critical adhesion forces between the multilayer thin film and quartz substrate for quartz/ZnO/TiNi and quartz/TiNi are 45.75 N and 40.15 N, respectively

Abstract:The TC4 alloy fastener hole structure parts were researched experimentally and theoretically. Based on the mathematical model of structure detail initial fatigue quality, the corresponding crack size distribution in certain time was determined by the crack growth equation of structure detail under loading spectra. By selecting appropriate referred crack size, the life of fastener hole structure detail in which 5% crack happened was provided and the resulted life was suggested as the economical life of aircraft structure. All the work is helpful to the economic repair of the modern aircraft structure

Abstract:Electroless copper deposition was performed by activation of Ta/SiO2/Si substrates using PdCl2/BOE/HNO3 displacement solution. Field emission scanning electron microscope (FESEM) and X-ray diffraction (XRD) were employed to investigate the effects of activation time and ultrasonic on surface morphology and structure of electrolessly deposited copper films. The results show that the coverage of copper films decreased gradually with the activation time increasing from 30 s to 150 s when the plating progressed without ultrasonic, while the high coverage of copper films was held with the activation time increasing when the ultrasonic was involved. The analysis of XRD indicates that the diffraction intensity of Cu (111) and (200) orientation increased obviously after the ultrasonic was introduced. When the activation time was 60 s, the diffraction intensity ratio of Cu (111) orientation to (200) orientation (I(111)/I(200)) was 4.53. The results of electroless Cu deposition on Ta/SiO2/Si substrates with trench patterns show that the presence of ultrasonic in electroless Cu plating can remarkably improve the effect of filling in trenches

Abstract:Feasibility of electrodepositing aluminum coatings on the rare earth alloy in the acidic AlCl3-EMIC (2:1) room temperature molten salts was discussed, and the effects of pretreatment process of the rare earth alloy on aluminum coatings was studied. The microscopic analysis for the surface and interface of the samples was performed by SEM, EDS and XRD and the adhesion was determined by score-tearing test. The results show that the aluminum coatings can be electrodeposited on rare earth alloys in the room temperature molten salts. The pretreatment in kerosene for the rare earth alloy surface can prevent the emergence of rare earth oxide film; thus, uniform and dense aluminum coatings with good adhesion can be achieved. Under the condition of current density 2 A/dm2 and deposition time 2500 s, aluminum coatings with the particle size of 10 μm and the thickness of 17 μm can be obtained and the current efficiency is close to 100%. The mechanism of electrodeposition of aluminum on rare earth alloy surface was also discussed

Abstract:AZ61A magnesium alloy tube with large diameter and thin wall was fabricated by centrifugal casting technique. The microstructures and tensile properties of the tube were studied and it was compared with the conventional sand casting. The results show that the grains of the tube by centrifugal casting are significantly refined. The eutectic transformation L→ α-Mg+β-Mg17Al12 are suppressed to a great extent under the balanced solidification condition. As a consequence, the alloying elements Al and Zn show much higher solid solubility and the microstructure of the tube dominantly consists of supersaturated primary α-Mg solid solution. The tensile properties of the centrifugal casting tube are remarkably increased. In addition, the fracture surfaces exhibit amounts of dimples, indicating quasi-cleavage ductile fracture characteristics, and the ductility is improved obviously

Abstract:The microstructures and phase composition of as-cast AZ91 magnesium alloys with addition of 2.5wt% RE (RE=La, La and Nd or Nd) in total were investigated by SEM/EDS and XRD. The mechanical properties of the alloys were analyzed at room temperature. The results show that the β-Mg17Al12 amount of AZ91 alloy is decreased evidently with the 2.5wt% addition of RE. The Al-RE phases of Mg-9Al-1Zn-2.5La and Mg-9Al-1Zn-2.5Nd are acicular Al11La3 and particle-like Al2Nd, respectively. Both Al11La3 and Al2Nd are formed with co-addition of La and Nd, whose sizes are smaller than those of single addition. The relative content of the two Al-RE phases is proportional to the addition content of La and Nd. Part of La in Al11La3 or Nd in Al2Nd is substituted by Nd or La respectively when La and Nd are co-added into AZ91 alloy. Compared with single addition of La or Nd, co-addition can improve the mechanical properties of as-cast AZ91 alloy more significantly. In all magnesium alloys investigated, the Mg-9Al-1Zn-1.0La-1.5Nd alloy exhibits the best mechanical properties, whose UTS is 235 MPa and d is 10% at room temperature

Abstract:The samples cut from the arc-melted Nb-14Si-22Ti-2Hf-2Al-4Cr alloy were directionally solidified in an optical imaging floating zone furnace under argon atmosphere with different growth rates. The effects of directional solidification (DS) technique on phase composition, microstructure characteristics and the mechanical properties at room and high temperatures were investigated with those of arc-melted alloys for comparison. Results show that compared with the arc-melted alloys, the DS samples are still composed of NbSS (Nb solid solution) and Nb5Si3, without any change. Nbss of DS alloys is dendritic, and the lath-like Nb5Si3 distributes along growth direction. The compressive strength of the samples at the DS speeds of 15 and 10 mm/h increase to 442 and 493 MPa at 1250 oC respectively, from 290 MPa of arc-melted alloys. After DS at 15 mm/h, the fracture toughness of the samples increases to 15 MPa·m1/2 from 12 MPa·m1/2 of the arc-melted alloys. The alloys prepared by the optical floating DS method possess good mechanical properties at room and high temperature

Abstract:Microstructure evolution of recycled nickel-base superalloy K417 after melt superheat treatment at different temperatures of 1530, 1650, 1700 and 1800 oC for 5 min were investigated using optical microscope (OM) and scanning electronic microscope (SEM). The size, distribution and morphology of carbides were studied. The effect of microstructure change after melt superheat treatment on tensile properties at room and elevated temperatures was analyzed. Results show that the propagation of cracks is prevented effectively due to the morphology changes of carbides from block to script during the melt high temperature treatment, which results in higher strength and ductility of K417 alloy at room and elevated temperatures

Abstract:The Sm-Fe alloy powders were prepared by cryomilling in liquid nitrogen. By means of XRD, HRTEM and Inert Gas Pulse-Infrared-Thermal Conductivity method, the microstructure evolution of the Sm2Fe17 alloy powders during the cryomilling process was studied. The results show that the grain sizes of Sm-Fe alloy powders were rapidly reduced by cryomilling in liquid nitrogen. The grain sizes of the alloy powders were about 10 nm and 5 nm after cryomilling for 5 h and 9 h, respectively. The nitrogen content in the Sm-Fe alloy powders increased with longer cryomilling time. After cryomilling at 150 r/min for 9 h, the content of nitrogen reached 1.62wt%. With increasing of the cryomilling time, the Sm2Fel7 phase changed to amorphous phase. Low cryomilling speed can slow down the formation of amorphous phases

Abstract:The effects of the additional resistance in a circuit under constant voltage on characteristics of microarc oxidation (MAO) coatings of pure titanium substrates in Na2SiO3-Na3PO4 solution were studied. The results show that the coatings’ growth characteristics, phase component, surface morphology and the samples’ corrosion resistance after treatment are strongly influenced by the additional resistance in the MAO process. The phase component and surface morphology of the coatings prepared without the resistance are closely relative to the treating voltages; when the voltage is lower than 450 V, the coatings consist of anatase phase; when the voltage is greater than or equal to 450 V, the coatings consist of anatase and rutile phases. While the phase component and surface morphology of the coatings prepared with the resistance have little relation with the treating voltage; the coatings only consist of anatase phase, and the micropore size is smaller whose distribution is more uniform. The corrosion resistance test in sulfuric acid solution (30%) shows that the corrosion resistance of the samples prepared with the resistance is 40% higher than that prepared without the resistance averagely

Abstract:The nanoparticles dispersed in the liquid are influenced by the factors of surface wetting, inter-particle energy, double-layer electrostatic energy, space resistance function, etc. According to this theory, the best dispersion conditions for Ag nanoparticles in aqueous media were obtained through a method of high-speed shearing and ultrasound action by use of ABS, Tween 80 and sodium silicate compound, i.e. the concentration of sodium silicate, ABS and Tween 80 is 0.5%, 0.5% and 2% (mass fraction), respectively, and the ultrasonic time is 1.5 h. TEM observation reveals that nano-silver disperser was homogeneous and stable. Through the agar dilution method, the minimum inhibitory concentration (MIC) of nano-silver dispersion for the E. coli8099 and Staphylococcus aureus ATCC6538 are both 50 μg/g

Abstract:NZ2 zirconium alloy plate samples of 1.4 mm thickness were prepared at different hot rolling temperatures of 800, 700, 650 and 610 °C but under the same rolling reduction. The distribution and types of the secondary phases in the alloy were observed by OM, SEM and TEM. Furthermore, their sizes were calculated and the distribution rule was obtained by software. Results show that most secondary phases are in the grains while a few in the grain boundary. They are mainly spherical or claviform. Homogeneous and fine secondary phases distributing dispersively can be obtained at a lower rolling temperature (650 °C)

Abstract:Microalloying is an important method to excavate the potential and to improve the properties of alloys for advanced materials research and development. Now microalloying of aluminum alloys is becoming the research hot spot at home and abroad. The present paper analyzed the recent process and major problems of microalloying research for aluminum alloys and proposed its developing direction in the future