Abstract:The grain refinement of Ni-Cr-W based superalloy was obtained by near liquidus casting. The melt was heated to the predetermined temperature near liquidus by induction heating and solidified directly in the crucible by furnace cooling. A fine-grained microstructure was obtained under a certain crucible nucleation undercooling and the related mechanisms are discussed. The solidification process of the undercooled melt is divided into two parts, a nonequilibrium process and a near-equilibrium process. The critical radius Rc for disturbance developing of spherical grains decreases greatly in the nonequilibrium process compared with the near-equilibrium process. Grains grow in dentritic manner in the nonequilibrium process and a crystal multiplication occurs in this process by remelting dentrite. Grain density is determined in the nonequilibrium process. In a near-equilibrium process, the disturbance of the spherical grains will develop with a larger Rc. In situation of high nuclei density, decided by the nonequilibrium process, the larger Rc and the solidification terminates before disturbance developing. Thus, granular grains are obtained.

Abstract:The HfO2 thin films with resistive switching behaviors were grown on indium tin oxide (ITO) /Glass substrates by radio-frequency (RF) magnetron sputtering method. The results of electrical tests indicate that HfO2 thin films show a bipolar resistive switching behavior. Using Ti as a buffer layer on the cathodal side of the memory cell, relatively reliable endurance (>2×102 cycles at 20 oC) and long data retention time (>104s at 20 oC) have been demonstrated, and the high-resistance to low-resistance ratio can reach 104. Based on the electrical property test results, the phenomena can be correlated with oxygen-vacancy-related traps. Space charge limited current (SCLC) mechanism is believed to be the reason for the resistive switching from the OFF state to the ON state

Abstract:In this study, high Nb containing TiAl alloy (TAN) was welded by reaction-diffusion bonding using Al foil as interlayer at 1200 °C for 2 h. The desired full lamellar microstructure (γ+α2) was obtained across the bonding seam when the joint was heat-treated according to the heat treatment process of TAN alloy. The present paper also investigated microstructure and bonding mechanism in details. The results show that liquid Al can react with TAN to form TiAl3 intermetallic layer, and then the TiAl3 layer will transform to γ-TiAl by solid-state diffusion at high temperature, finally a full lamellar structure is formed after heat treatment. Furthermore, sound joints with full lamellar structure can be also obtained when TAN alloy is directly bonded in accordance with the heat treatment cycle of TAN alloy

Abstract:The corrosion resistances of bulk metallic glasses (BMGs) Cu55-xZr37Ti8Inx (x=0~5, at%) and Cu61-xZr34Ti5Inx (x=0~3, at%) were investigated in 3.5 wt% NaCl aqueous solution. The electrochemical potentiodynamic polarization curves demonstrate that the addition of indium to copper-based BMGs can significantly enhance the corrosion potential and reduce the corrosion current density, i.e. greatly improves the corrosion resistance. And the value of Icorr for copper-based BMGs added with indium is lower than those without indium addition, by roughly one order of magnitude. The moderate replacement of copper by indium improves the corrosion resistance further. While the excessive addition of indium reduces the corrosion resistance, resulting from the lack of Zr-rich protective surface film

Abstract:The Deform-3D software was employed to describe the microstructure evolution of a high Nb containing TiAl billet (Ti-42Al-8Nb-0.2W-0.1Y) during its hot pack-forging. To obtain the simulation parameters, hot compression tests were performed at temperatures of 1100~1250 °C and strain rates of 0.001~0.5 s-1. Dynamic recrystallization model was developed by using an undirected method, and the recrystallized volume fraction was described by an Avrami-type equation. The constitutive model of the flow stress of the alloy was established based on Cingara hardening equation and the dynamic recrystallization model. The simulated results indicate an inhomogeneous distribution of grain structure occurs due to friction, heat loss and single direction upsetting operation in forging process. The microstructure evolution of the present alloy during pack-forging is validated by comparing the simulated results with that of the experimental data. The result indicates that the implemented microstructure module can be effectively used to predict the microstructure evolution of the high Nb containing TiAl alloy during pack-forging

Abstract:The effects of different contents of Y on microstructures and corrosion resistances of Mg-5Al-1Sr-2Ca alloys were investigated. Mg-5Al-1Sr-2Ca-XY(X=0,0.5,0.7,1.0; wt%) alloys were prepared using mixture method and were analyzed by optical microscopy (OM), scanning electron microscopy(SEM) and X-ray diffraction (XRD). The results indicate that the grain size can be obviously reduced when the content of Y is 0.7 wt%. With the addition of Y, Al2Y phase is formed and acts as the heterogeneous nucleus of α-Mg to enhance the nucleation rate. Simultaneously, Al2Y is aggregated in the front of α-Mg and hinders the growth of α-Mg grains. The corrosion resistance of Mg-5Al-1Sr-2Ca-XY(X=0,0.5,0.7,1.0; wt%) alloys in 3.5% NaCl aqueous solution was investigated through static weight-loss test and polarization curve measurement. It is found that due to the addition of Y, the corrosion resistance is improved substantially. Mg-5Al-1Sr-2Ca-0.7Y alloy has a low corrosion current and the best corrosion resistance among the investigated alloys

Abstract:Grain growth behaviors of Ag-Cu-Zn alloys with different contents of Zn were studied at various heat treatment temperatures and for different holding time. The experimental results show that the grain grows along with the increase of the holding time. The higher the content of Zn is，the larger the grain size will be under the same holding time. The grain growth exponent n increases and the grain growth active energy Q decreases with the increase of the content of Zn

Abstract:This study mainly analyzed the effect of NaF and LiF on the hydrogen release properties of NaAlH4 and LiAlH4 by PCT (pressure-composition-temperature) apparatus. The results show that doping with NaF causes an obvious increase of the hydrogen release amount of NaAlH4 except for the doping with 0.5 mol%, 4 mol% NaF. In addition, the doping with NaF induces an increase of the hydrogen release rate in the first stage. Among all the samples doped with NaF, the sample doped with 1mol% NaF presents the optimal hydrogen release properties with the largest hydrogen release amount and the fastest hydrogen release rate. Comparatively, the results from the study on the LiAlH4 doped with LiF show that doping with LiF decreases obviously the hydrogen release amount of LiAlH4

Abstract:The hot compression deformation of U720Li superalloy was investigated systematically. Through by the analysis and the calculation of the mechanical behavior and the microstructure evolution during hot compression deformation, the variation of strain rate sensitivity exponent m, activation energy Q and grain size exponent P values at different strain rates and different temperatures were obtained. The hot processing map based on dynamic materials modeling was drawn while high-temperature deformation mechanism maps incorporating dislocations inside grains were obtained. The processing map was used to analyze the hot deformation behavior and to determine processing instability regime and appropriate processing regimes. Within appropriate processing regime, based on the elevated temperature deformation mechanism maps, the Burgers vector compensated grain size, the modulus compensated stress and the dislocation quantities of U720Li superalloy at different temperatures, the hot deformation mechanisms were elucidated.

Abstract:The adsorption, the diffusion and the dissociation of H2O molecule on α-U(001) surface have been studied using density functional theory (DFT) within generalized gradient approximation (GGA). The calculation results indicate that H2O molecule is preferentially adsorbed on the top site in a flat-lying configuration with the adsorption energy of 0.58 eV. The adsorption interaction is mainly contributed by the overlapping between the 1b1 orbital of H2O and the 6d orbital of the top-layer U atom, along with some weak H2O 3a1-U 6d mixing. The activation energy for H2O diffusion between two adjacent top sites is 0.20~0.23 eV, indicating that the on-surface diffusion is easy for H2O molecule. The OH+H dissociative adsorption is about 1.24~1.39 eV higher in energy than molecular adsorption, together with the dissociation barrier of 0.56~0.62 eV, suggesting that the dissociation of adsorbed H2O into OH and H can occur under the certain heat activation condition

Abstract:Based on the KKS model which couples the temperature field, concentration field, flow field and orientation field, the phase-field model for the magnesium alloys with hcp structure was established to simulate both of the single and the multi-grain dendritic growths of magnesium alloys during solidification under forced flow. The results show that the growths of three directions on the upstream side are much faster than those on the downstream side when the forced flow velocity is 0.02 m/s. At the same time, the primary dendrite on the upstream side is the longest, the two dendrites with level direction of 60o angle on the upstream side are second, the two dendrites with level direction of 60o angle on the downstream side are more shorter, and the primary dendrite on the downstream side is the shortest. Under the case of the multi-grain, the grains grown face to face influence mutually and grow competitively. The dendrite arms of different dendrite collide each other and are mutually inhibited, ultimately an unsymmetric dendrite morphology is formed. Based on the continuous nucleation model of the multi-grain dendritic growths of magnesium alloys, the simulation results show that there is a high consistency of the dendritic morphologies between simulation and experiment, verifying the validity of the KKS phase-field model

Abstract:The changing rules of flow stress at high temperatures for TC18 titanium alloy were studied by thermal simulation experiment, in temperature ranging from 750 to 950 ℃, at strain rate from 0.01 to 10 s-1 and the deformation degree of 60%. The constitutive equation of TC18 Ti alloy was derived through Arrhenius hyperbolic sine function. According to the experimental results, the processing maps of TC18 Ti alloy were developed for strain of 0.3 and 0.5. The results show that flow stress of TC18 titanium alloy decreases with the increase of deformation temperature and the decrease of strain rate. Under the experimental conditions, TC18 titanium alloy shows two kinds of softening mechanism of dynamic recovery and recrystallization. Arrhenius hyperbolic sine function can well describe the constitutive equation of the TC18 titanium alloy. The result of processing map shows that three unsteady zones of high temperature deformation appear on the process map at strain of 0.3. The two unsteady zones of high temperature deformation appear on the process map at strain of 0.5. From the processing maps, better thermal processing interval is in a temperature of 830 ~ 920 ℃ and at strain rate of 0.01~0.32 s-1 region

Abstract:W-30Cu composite powder fabricated by sol-spray drying and subsequent hydrogen reduction was pressed and directly liquid phase sintered at 1340~1420 ℃ for 15~120 min, the densification and grain growth mechanism were studied. The results show that the significant densification occurs in the early sintering stage of the liquid phase. When sintered at 1340 ℃ for 15 min, the relative density reaches above 90%. With the sintering time increases, the relative density increases. When sintered at 1380 ℃ for 90 min, the maximum relative density of 99.1% is obtained. During liquid sintering, W grains grow up as spherical shape, and the grain size G and sintering time t matches the relationship G3∝ kt, which means that the grain growth of W is subjected to the dissolution-precipitation mechanism. When sintered in the range of 1340~1420 ℃, the grain growth kinetic coefficients increase from 1.61×10?2 to 4.65×10?2μm3/min. The results suggest the formation of liquid, particle rearrangement, dissolution-precipitation and grain growth cause nano-sized W-30Cu composites to reach nearly full density

Abstract:The magnetic behaviors of the magnetic-field cooled Ni50Mn37In13 film at low temperature was investigated. The results show that below the characteristic temperature Tf, the alloy presents a super spin glass (SSG) state when cooled in the absence of a magnetic field; however, it will transform to the super ferromagnetic (SFM) structure after magnetic field cooling. The SFM clusters in the SFM structure are coupled with the antiferromagnetic matrix, resulting in the exchange bias

Abstract:Aiming to improving the bonding strength, wear resistance and room temperature toughness of the Fe-Al intermetallic coating, the FeAlCr cored wire was designed. The coatings were prepared on the 45# steel substrate by high velocity arc spraying technology. Microstructures, phase composition and wear resistance of the composite coating were investigated by SEM, XRD and CETR wear tester. The mechanical properties were tested on a tensile testing machine and a hardness tester. The results show that the composite coating is characterized by compact microstructure, low oxygen content and well bonding with the substrate. The phases of the coating are composed of α-Fe, Cr3C2, Fe-Al, Ni3Al intermetallic compound and little oxide. The adhesive strength and average hardness of the coating are 47.2 MPa and 5.5 GPa which is about 2 times of the substrate. The wear resistance of the composite coating under load of 100 N and the oil lubricating abrasion condition is higher than that of the substrate. Furthermore, while the friction time is processing, the wear rate of FeAlCr coating is being decrease

Abstract:Zr48－xCu45Al7Gdx(x=0~7) bulk metallic glasses (BMGs) were prepared by injection in copper mould with arc melting. The effect of Gd content on the glass-forming ability (GFA), microstructures, fractured surfaces and mechanical properties of the alloys were investigated by X-ray diffraction (XRD), differential scanning calorimetry (DSC), scanning electron microscope (SEM), hardness tests and compression tests. Results show that Gd content has evident effect on the GFA and mechanical properties, the rod-shaped BMGs with 4mm diameter can be obtained at Gd content of (2~5) at%. The BMGs possess a larger supercooled liquid region ΔTx with value of 73~79 K and a better reduced glass transition temperature Trg with value of 0.694~0.698, which consists of only amorphous phases with compression strength σb of 1768~1794 MPa and Vickers hardness of 5.08~5.32 GPa. In compression test of the BMGs a brittle fracture happens in pure elastic deformation way, and all fractured surfaces are flat and smooth with typical vein-like morphologies

Abstract:A dense ceramic oxide coating with approximate 40 μm thickness was prepared on 2A06 aluminum alloy by means of microarc oxidation in an alkali-silicate electrolytic solution. The morphology and the microstructure were analyzed by scanning electron microscope (SEM) and X-ray diffraction (XRD). Coating thickness and surface roughness (Ra) were measured after the coating was synthesized. The tribological performance of the coatings was evaluated using a dry sand abrasion test and a solid particle erosion test. The results show that microarc oxidation coatings consist of the loose superficial layer and the inner dense layer. Both the inner layer and the outer layer are composed of α-Al2O3 and γ-Al2O3, While the Al6Si2O3 phase is observed only in the outer loose layer, and the inner layer has a higher content of α-Al2O3 than that of the outer layer. The average of the microhardness of the ceramic coatings is 20.96 GPa. Moreover, under the same experimental condition, the specific wear rate of ceramic coating is smaller than that of 2A06 aluminum alloy which indicates the friction and the wear properties of the 2A06 aluminum alloy are improved and the lifetime of 2A06 aluminum alloy employed in harsh environments is extended with the increase of coating thickness and quality improvement

Abstract:Quenching and tempering heat treatment were carried out to the as-cast Ti-46Al-0.5W-0.5Si alloy, near lamellar and duplex microstructures were obtained. Tensile properties of the heat treated alloy were tested at room temperature. The fracture surface and the cracks adjacent to the fracture zone of the specimens were investigated to analyze the tensile fracture behavior. Results show that the ductility and tensile strength of duplex structure are better than that of near lamellar structure. The cracks in duplex structure can bypass the small γ phase particles, and propagate along the interface of γ phase particles and α2/γ lamellar. The cracks also can propagate in a trans-lamellar mode. The cracks in near lamellar structure propagate in a mixed mode of inter-lamellar and trans-lamellar.

Abstract:Microstructures and hydrogen absorption and desorption properties of (V60Ti22.4Cr5.6Fe12)100-xMnx (0≤x≤3) alloys made from FeV80 master alloy were investigated systematically. XRD and PCT testing results show that lattice parameter decreases, and plateau pressure increases first and then decreases with the increasing of Mn content. Meanwhile, as the Mn content increases , the hydrogen absorption capacity decreases, but the desorption capacity varies a little .When the Mn content reaches 2.5at%, the plateau pressure of hydrogen desorption reaches a maximum of 0.14 MPa at room temperature, while the hydrogen absorption capacity is 3.64wt% and the hydrogen desorption capacity is 2.00wt%. SEM and EDS analysis show that all of the alloys consist of bcc main phase, Ti-rich phase and rare earth oxide phase. Mn is mainly distributed in the bcc main phase, and only a small amount of Mn exists in the Ti-rich secondary phase.

Abstract:The effect of mixed powder ultrasonic vibration on the surface structure and the mechanical properties of Ti-6Al-4V in Electro-Discharge Machining (EDM) were studied. The surface roughness, the residual stress and the micro hardness of Ti-6Al-4V simples machined by conventional EDM, powder mixed EDM (PMEDM) and combination process of powder mixed EDM with ultrasonic machining (PMEDM+USM) were measured, respectively. The recast layers and the surface cracks of samples machined by EDM, PMEDM and PMEDM+USM were observed by SEM, the quantitative analysis of each element of samples machined by PMEDM and PMEDM+USM was performed by energy spectrum analyzer. The effect mechanism of added Al and SiC powder in kerosene and ultrasonic vibration of electrode on the surface structure and the mechanical properties of Ti-6Al-4V machined by PMEDM+USM were also discussed. The results show that the surface structure and the mechanical properties of Ti-6Al-4V are improved by PMEDM+USM. With under the effects of the electrode ultrasonic vibration and SiC added in kerosene, the surface roughness decreases by Ra 0.5 μm, the recast layer reduces by 40 μm, the surface residual stress decreases by 50 MPa, and the surface hardness increases from 7650 to 9870 MPa than PMEDM

Abstract:The influences of two homogenization temperatures on the microstructure, Nb segregation and stress-rupture properties of a K4169 alloy have been investigated. The results reveal that the amount of Laves phase decreases with the increasing of the homogenization temperature. Nb still segregates strongly in the interdendritic region after homogenization heat treatment at 1120 ℃. As the temperature raises to 1160 ℃, the microsegregation of Nb is improved distinctly. Meanwhile, Widmanstaten structure and granule-like δ phase are observed after solid solution and aging treatment, and a larger volume fraction of γ′′ phase is observed in the specimen homogenized at 1160 ℃. The investigation of stress-rupture property under the condition of 650 ℃/620 MPa suggests that with the increase of the homogenization temperature, the rupture life is enhanced evidently, while the elongation decreases. Additionally, the type of fracture changes from trans-granular ductile fracture to a mixture of trans-granular and inter-granular brittle fractures.

Abstract:The paper presented a new idea for body magnesium supplementation by magnesium ion release of magnesium products in drinking waters, analysised the degradation mechanism of magnesium and its alloys in the carbonated drinks, the magnesium ion concentration of solution and pH variation, and explored the feasibility of a magnesium alloy products as human sources of magnesium supplementation. The results show that Mg degradation is the fastest, AZ31 is followed, AZ91 is lowest. Surface corrosion layer of (Ca, Mg)CO3 is formed to inhibit the degradation; aluminum elements can effectively reduce the release rate of magnesium and the increament of pH value in carbonated beverages; the Mg ions released from the three magnesium alloy soaked in 600 mL of carbonated drinks for 2 ~ 4 h basically satisfy daily requirements of magnesium supplementation content, the change in small pH has, no significant effect on the quality of the carbonated drinks.

Abstract:Superplastic behaviors of coarse-grained Ti-22Al-25Nb alloy were investigated at temperatures ranging of 1213~1263 K and initial strain rate raging of 3.3×10-4~3.3×10-2s-1. The constitutive equation has been established according to the flow stress of the alloy during the deformation process. The results show that the alloy exhibits a certain degree of superplasticity under above conditions. The maximum elongation exceeds 370% at 1238 K and 3.3×10-4s-1. The elongation of the alloy increases with decreasing of strain rate. The average apparent activation energy of the alloy was calculated to be 759.918 kJ/mol. The deformation mechanism of the alloy mainly is dynamic recrystallization and the new phase growth up

Abstract:Gr.12 titanium extrusion tube billets were obtained adopting same mould and different extrusion processes, the defect parts of the extrusion tube billet wall were analyzed by SEM, EDS. The tubes obtained with different rolling processes were comparatively analysised by ultrasonic test and straightening. Titanium copper eutectic phenomenon is found in the defective parts of the extrusion tube billet. The surface quality of the extrusion tube billet is not stable when mold hardness HRC is less than 35 and surface roughness Ra is greater than 1.6 mm. The hardness of extrusion needle decreases rapidly and the inside surface quality is poor when the sheath is the copper material. The hardness of extrusion needle decreases slowly and the inside surface quality is better when extrusion temperature is 760～790 ℃, extrusion ratio is less than 18 and the sheath is the steel/copper composite. The surface quality of the finished product tube is better adopting pre-rolling by Q≤0.1, e≤35% and deformation degree per pass is less than 52%. The rolling and straightening cracking rate is less than 1‰ and ultrasonic inspection qualification rate can achieve to 95% using the above process for the mass production.

Abstract:The Pt and Hf modified γ-Ni+γ′-Ni3Al coatings were fabricated on the DZ417G superalloy substrates by combined aluminizing and hafnizing using a pack cementation. During the co-deposition process, the phase structure formed on the coating surface changes with the increasing of hafnium contents in packs. When the hafnium contents are 2 wt%, 6 wt% and 12 wt% the coatings consist of the γ-Ni+γ′-Ni3Al, b-NiAl+Al16Hf6Ni7, and Al16Hf6Ni7, respectively. During post heat treatment the β-NiAl+Al16Hf6Ni7 and Al16Hf6Ni7 coatings are transformed to γ-Ni+γ′-Ni3Al and γ-Ni+γ′-Ni3Al+Al3HfNi12. Isothermal oxidation tests at 1100 ℃ for 10 h show that there are a lot of spallation on the surface of the substrate without coating, while the Pt and Hf modified γ-Ni+γ′-Ni3Al coating formed in the packs with 2 wt% Hf remains to be integrated after being oxidized for 30 h. The addition of the reactive element hafnium makes a further improvement on the oxidation resistance of the Pt+γ-Ni+γ′-Ni3Al coatings

Abstract:By using metal nitrates, rare earth oxides as raw materials and citric acid as complexing agent, Y3Al5O12: Eu3+ red phosphors were prepared by a citrate-gel method. The purified crystalline phase of Y3Al5O12 was obtained at 1000 ℃, which is 450 ℃ lower than that of ordinary solid state reaction. The result of XRD indicates that the samples are indexed to cubic symmetry, and the cell parameter a of Y3-xEuxAl5O12 (0.025≤x≤0.15) increases with x value increasing. The photoluminescence of Y3-xEuxAl5O12 (0.025≤x≤0.15) was investigated under UV region, it is found that there is a broad band around 240 nm assigned to the charge transfer transition (CTS) between Eu3+ and O2- in the excitation spectrum. In the emission spectrum, the most intense emission is at the peak of 590 nm corresponding to Eu3+ 5D0→7F1 transition. Compared with the sample synthesized by solid state reaction, the phosphor obtained by citric-gel method shows lower emission intensity, but it has relatively higher red/orange ratio and better color purity

Abstract:The vacuum diffusion bonding was used to weld 93W to Ta using Ni as an interlayer. Universal testing machine was used to test the shear strength of the bonded joint. The microstructure of the bonded joints was investigated by XRD, SEM and EDS. The results show that the shear strength increases with the increasing of bonding temperature and holding time, and exhibits a maximum value of 244 MPa. The joint is composed of the Ni/Ta and Ni/93W interface. The phases of hcp-Ni3Ta，fcc-Ni3Ta，Ni2Ta and Ni4W are formed in the interfaces. The fracture of the joint takes place in the Ni/Ta interface rather than the Ni/93W interface. The reaction process of the welding joints can be divided into the following stages: effective physical contact, solid solution forming, intermetallic reaction layer forming, and intermetallic layer growing.

Abstract:The surface morphology, the film-substrate bonding force, the corrosion resistance and the fretting friction and wear properties of anodic oxidized surface of conventional Ti and ultrafine-grained Ti were investigated. The results show that compared to the anodic oxidized surface of conventional Ti, the anodic oxidized surface of ultrafine-grained titanium exhibits a more nano-scale cavities, a higher film-substrate bonding force (bonding force of the latter is 2 times of the former), a higher corrosion resistance (corrosion rate of the latter is 2/5 of the former), a lower friction coefficient (0.12 vs 0.34) and a higher wear resistance. It is believed that these above mentioned improvements are caused by the increasement of crystal defects (internal energy) due to microstructure ultrafinement.

Abstract:Hardness，tensile property and crystal orientation of 5052 Al alloy after rolling process and different subsequent heat treatments (200 ℃/1 h, 350 ℃/1 h, 500 ℃/1 h, respectively) were studied. The study indicates that the hardness and the yield strength of commercial purity aluminium can be effectively improved by rolling process. As the material recrystallization occurs at 244.8 ℃, the subsequent heat treatments of 350 ℃/1 h and 500 ℃/1 h will make the hardness and the tensile property of 5052 Al alloy continue to drop. The results of analysis based on XRD show that crystal orientation has little improvement by rolling process and its subsequent heat treatment. Quantitative calculation based Taylor's formula shows that the dislocation introduced by rolling deformation process is one of the factors of 5052 Al alloy strength enhancing