Abstract:Although there are many studies on the hydrides in Zirconium alloys, the microstructure and crystallographic orientation of hydrides with higher hydrogen content has received little attention. The Zr-Sn-Nb alloy charged with 147, 340 and 1480 ppm of hydrogen by gaseous hydriding procedure at 400 ℃ with different holding time. The microstructure and crystallographic orientation of hydrides is investigated by a combination of optical microscopy (OM), scanning electron microscope (SEM), transmission electron microscopy (TEM) and electron backscatter diffraction (EBSD) techniques. The results indicate that the orientation is affected by the hydrogen content. The interphase boundary components are used to evaluate the crystallographic orientation of hydrides along with pole figure analyses. We found that there are two orientation relationships between the α-Zr and the hydrides, i.e. (0001)α∥{111}δ and {10-17}α∥{111}δ. EBSD analyses also revealed changes in the orientation of hydrides when hydrides grew from one matrix grain to another to accommodate the matrix modification. Besides, there are many Zr grains with both inter-granular and intra-granular hydrides, and only the intra-granular hydrides exhibit habit relationships with the Zr grains.

Abstract:Compared with zero dimensional, two dimensional and three dimensional nano-materials, one dimensional nano-materials have superior gas sensing properties. In this paper, one dimensional ZnFe2O4 nano-fibers were prepared via electrospinning method using Zn (NO3)2? 6H2O and Fe (NO3)3? 9H2O as raw materials. The precursor was analyzed by TG-DSC, and the as-prepared samples were characterized by XRD, SEM, TEM, FTIR, nitrogen adsorption and XPS, respectively. The gas sensing properties of the as-prepared samples were investigated. The results showed that ZnFe2O4 prepared at 500oC exhibited nano-fiber morphology; it was revealed that the sensor device based on ZnFe2O4 nanofibers prepared at 500?C exhibited excellent selectivity toward acetone at the operating temperature of 190oC, the ratio of S1000 ppm acetone to S1000 ppm ethanol reached 8; when the concentration of acetone was as low as 1 ppm, the response was still able to reach 1.1.

Abstract:Single crystal iridium exhibits anomalous deformation behaviors in contrast to other fcc-metals and its intrinsic deformation mechanism remains controversial. To investigate the deformation behaviors and underlying deformation mechanisms with respect to crystallographic orientations in single crystal iridium, molecular dynamics simulations were performed at 1 K. Bulk single crystal iridium with different loading axis orientations of [100], [110] and [111] has been considered in current study. Atomic simulation results showed that the on the stress–strain curves differed significantly between crystallographic orientations. And the mechanical properties including elastic modulus, yield stress, ultimate tensile stress and elongation more or less differed between crystallographic orientations owing to different deformation mechanisms. Under tensile loading, [100] oriented single crystal iridium deformed predominantly by dislocations glide with partial vacancies coalescence involved, while plastic deformation in [110] oriented single crystal iridium was initiated by stacking faults. Nevertheless, [111] oriented single crystal iridium underwent little plastic deformation before breaking.

Abstract:Selective laser melting (SLM) is a laser cladding/deposition based technology, which can fabricate and repair near-net-shape high-performance components directly from metal powders. Characterizing mechanical properties of the SLM components is prerequisite to the applications of SLM in aircraft engine industrial productions. Nickel-based superalloys such as IN718 are the most commonly used metal materials in aircraft engine high-performance components. In the present study pre-alloyed, rapidly solidified IN718 powder served as a precursor for the production of additive manufactured components using SLM. The laser deposition process is optimized through a set of designed experiments to reduce the porosity. Material microstructure and mechanical properties of laser-deposited IN718 are studied and compared under heat treatment conditions of as deposited, direct aged, solution treatment and aging (STA), and full homogenization followed by STA. Tensile test results showed that the direct age treatment produces the highest tensile strength to the wrought material, while the homogenization treatment followed by STA exhibits good ductility. Failure modes of the tensile samples were analyzed by fractography. Considering the room and high temperature tensile test results of three heat treatment, homogenized STA samples not only have higher strength than the AMS wrought specifications, but also have good plastic. Therefore, homogenized STA is suitable heat treatment method for LSM IN718 alloy. Then, stress rupture properties at 650 _oC/700 and 725 MPa, low cycle fatigue properties at 455 _oC of the homogenized STA samples were investigated, fracture mode was analyzed and compared to wrought IN718 alloy.

Abstract:Abstract: A series of Ni50-xCoxMn39Sn11 (x = 0-8) alloy ribbons were prepared by a single-roll melt spinning method and its crystal structure, phase transition, and magnetocaloric effect are investigated. The martensitic transformation temperatures decrease rapidly and the Curie temperature of austenitic phase increases monotonously with the substitution of Ni by Co. The structural transformation can be induced not only by the temperature, but also by the magnetic field. Under field change of 30 kOe, we get large magnetic entropy change and refrigerant capacity in the heating process and cooling process with much lower hysteresis loss.

Abstract:A large-diameter thin-walled high temperature alloy tube with serrated groove is produced by inner spinning whose blank is welded up, and the micro-hardness and microstructure characteristics of the serrated groove in the tube are investigated. The welding results in coarse and uneven dendrites in the as-welded joint, which leads to larger the micro-hardness difference between the as-welded joint and the out of -welded joint zone. Both the original grains from the outer of the welded joint zone and the dendrites of the as-welded joint are refined by the inner spinning on the serrated groove. The micro-mechanical property unevenness of the serrated groove is significantly improved by severe plastic deformation.

Abstract:γ-TiAl alloys with low density and high stiffness are preferred structural materials for weight saving of aircraft engines. The present paper deeply reviews flow behavior and constitutive equations of γ-TiAl alloys compressed at elevated temperature. Deformation processing parameters, deformation history and adjusted preheating treatment, chemical compositions and initial microstructures are main factors that determine flow behavior of γ-TiAl alloys compressed at elevated temperature. The constitutive models describing flow stress-strain curves are segmented into genres, such as empirical models, model coupled with different softening mechanisms and models about deformation mechanisms. Arrhenius model and H-S model are deeply discussed. Also, constitutive model including softening mechanism and models involving deformation mechanisms are summarized and analyzed. It predicts that emphasis on further research in γ-TiAl alloys is to establish constitutive models involving multiphase coordinating deformation mechanisms.

Abstract:The influence of the δ phase on the toughness of GH4169 alloy was investigated by means of the fracture toughness J0.2BLand instrumented impact experiment. Experimental results indicate that with the increase of solution temperature, δ phase content reduced from 1.54% to 0.045%, and grain size grew up from 12.59 to 35.21 μm. δ phase content has no obvious effect on the strength of the material, but the fracture toughnessJ0.2BL increased from 112 KJ/m to 355 KJ/m, the impact toughness increased from 35 J to 75 J. δ phase is mainly distributed along the grain boundary, there is no strengthening phase precipitation around it. The zone with no strengthening phase near the grain boundary will be formed, it promote the crack propagation along the grain boundary. Moreover, the δ phase itself is the intermetallic compound. Under certain plastic deformation conditions, it is easy to separate from micro plastic zone and form a cavity. In the micro plastic zone, the cavities are rapidly interlinked to form a crack, and the crack grows along the grain boundary with the cavity, which reduces the crack propagation resistance and accelerates the crack propagation. Therefore, the presence of δ phase provides an extended channel for the crack and reduces the toughness of the material.

Abstract:NbCr₂/Nb-XMo (X=0, 2.5, 5.0, 7.5, 10at.%) alloys have been prepared by mechanical alloying and hot pressing. The effects of Mo on microstructures and properties of the NbCr₂/Nb alloy have been studied. The results show that the additions of Mo element do not change the phase components of the NbCr₂/Nb alloy, which are composed of Nb solid solution and NbCr₂. Adding alloying element Mo can increase the stress at the NbCr₂ / Nb phase interfaces, which promotes the increase of stacking fault /twinning in the NbCr₂ particles and the movement of dislocations in the Nb matrix. The NbCr₂ / Nb alloy adding with appropriate amount of alloying element Mo can maintain good plasticity and toughness as well as higher strength.

Abstract:Through the research of hot deformation behavior of Nb-16Si-22Ti-2Cr-2Al-2Hf-xFe(x=0、1、2、3、5) alloys, this paper made the hot working diagrams of these alloys which would provides a theoretical basis for subsequent Nb-Si alloys′design and hot working study. The maximum dissipative efficiency factor η appears in the region of low strain rate and high temperature; the minimum appears in low temperature and high strain rate region. There are unstable regions in the thermal processing map of the alloys with different Fe content, mainly distributed in the regions with high strain rate and low temperature, coinciding with the low dissipative efficiency factor regions. The grains in the unstable regions are obviously elongated and the grain boundaries are curved. The grain size is uneven and local plastic flow occurs. The dynamic recrystallization structure exists in the stable deformation zone as well as the fine recrystallized grain is distributed along the grain boundary. With the increase of the deformation temperature and the decrease of the strain rate, the size of the dynamic recrystallization grain increases.

Abstract:At this stage, the aircraft engine material K4169 alloy is difficult to perform at high temperature. Therefore, a new nickel base K4750 is researched by IMR and Jiangsu ToLand Alloy Co. Ltd, which can serve at 750 oC. In order to get excellent properties, the solidification microstructures and elemental microsegregation behavior are researched to provide reliable data of the new alloy. The solidification microstructures and elemental microsegregation behavior of a new Ni-base superalloy K4750 was comparatively investigated by differential thermal analysis (DTA), Thermo-Calc calculation and isothermal solidification quenching (ISQ) experiment. The results of ISQ indicate that the temperature of liquidus and solidus of K4750 alloy was 1350 oC and 1270 oC respectively, and the precipitated temperature of MC carbide was 1320 oC. The temperature of liquidus obtained by DTA and Thermal-Calc was in close agreement with the the result of ISQ, but the temperature of solidus obtained by DTA and Thermal-Calc was 1306 oC and 1296 oC respectively. In the initial stage of the solidification process, the volume fraction of residual liquid decreased sharply. In solidification process within the temperature range of 1310 oC～1290 oC, the residual liquid in the interdendritic region transformed from connected channels to isolated micro-liquid pools. In the last stage of solidification, these isolated micro-liquid pools were quite sluggish and resulted in the formation of porosity. The microsegregation coefficients of W, Fe and Cr were larger than 1, so they were considered to be negative segregation elements and segregate in solid. In contrast, the microsegregation coefficients of Ti, Nb, C and Mo were less than 1, thus they were positive segregation elements and segregated in the liquid.

Abstract:In order to modify the wear resistance of Inconel 718 superalloy, TiC reinforced Inconel 718 superalloy based composites were in-situ synthesized by co-axial powder feeding plasma melting deposition technique. Microstructure and in-situ synthesized process of the composites was analysed. The effect of volume fraction of the TiC reinforcing phase on microhardness and high temperature dry sliding wear properties of composites was discussed. The high temperature wear mechanism of the composites was studied. Results show that the microstructure of composites is refined and dense, microhardness values are remarkably influenced by the volume fraction of the TiC primary phase. The higher the volume fraction of the TiC primary phase, the higher the microhardness values of the composites. The composites showed excellent wear resistance under high temperature dry sliding wear test conditions.

Abstract:K4169 alloy is a widely used superalloy due to its excellent performance below 650℃. However, the residual impurities in the alloy will dramatically deteriorate the mechanical properties. In this research, the influence of nitrogen content on the microstructure and mechanical properties of superalloy K4169 has been systematically investigated through Thermo-Calc calculation, DSC analysis and quenching experiments with optical microscopy (OM), scanning electronic microscopy (SEM), electron-probe micro-analyzer (EPMA) and transmission electron microscope (TEM). The results indicate that when the content of nitrogen in the alloy increased from 17 ppm to 100 ppm, the precipitation temperature and the quantities of carbides and nitrides are also increased. Moreover it has been proved that the morphologies of carbides can be greatly affected by the content of the nitrogen. A number of large bar-like carbides can be identified when the N content is less than 17ppm and this number is decreased significantly when the content of N is increased to 70 and 100ppm. With the increasing content of N, the morphologies of MC carbides are changed from bar-like to block-like. The elevated temperature performance of this alloy can be greatly affected by the N content while the room temperature performance is rarely changed. When the content of N is increased from 17ppm to 100ppm, the creep-rupture life and elongation are both decreased obviously. Base on this research, as an overall consideration, it is rational to control the N content below 30ppm in K4169 alloy.

Abstract:Low pressure turbine guide serves in extreme conditions. Repeated heating/cooling cycles have a significant impact on microstructure and properties of alloy used in turbine guide vane. In this paper, the microstructure, mechanical properties and thermal fatigue behaviors of the serviced K417G guide vane were systematically investigated. The results show that coarsening of γ′ phase for the serviced K417G alloy has significantly degraded the microstructure. The strengthening effect of γ′ phase in the serviced K417G alloy has significantly weakened. Due to low bonding strength of precipitate interfaces and grain boundaries at high temperature, the tensile strength and yield strength of the K417G guide vane have decreased with the increase of temperature. The thermal fatigue crack forming process of K417G alloy under thermal stress has been observed with time. With increase of thermal cycles, the thermal barrier on surface of the vane has fallen off due to thermal fatigue stress, which leads to oxidation of surface of the alloy. The thermal fatigue crack sources can be initiated in the place where the oxide particles fractured and fell off. The a~N and da/dN~N curves obtained from thermal fatigue tests indicate that the crack growth rate decreases with the increase of thermal cycles, which is resulted from the release of thermal stress due to presence of secondary cracks.

Abstract:SNi-30.5Al-39V (at%) alloy is prepared by vacuum non-consumable arc meltingSin this paper.The phase composition and morphology of the alloy at different solidification positions were analyzed by optical microscopy (OM), X-ray diffraction (XRD) and scanning electron microscopy (SEM).And the results show that the solidification structure of Ni-30.5Al-39V(at%) is composed of NiAl+V sheet eutectic.Through the test of fracture toughness and high temperature compression, the results show that the fracture toughness of NiAl-39V alloy is three times that of NiAl alloy, and crack deflection and crack bonding are the main toughening mechanisms.Finally, based on the Arrhenius model, the constitutive relation of NiAl-39V alloy was constructed as ε = 5.398×[sinh(0.037128σ)]_2.3exp(-109.95×10₃/RT) and the activation energy was 109.95 kJ?mol_-1. Keywords: Eutectics; Room temperature fracture toughness; High temperature strength; Constitutive equation

Abstract:By using molecular dynamics method with the second nearest neighbor modified embedded-atom method (2NN MEAM) interatomic potential, we studied the γ/θ-DO₂₂ interfacial structure of Ni-Al-V superalloy at different compositions, and calculated the interfacial energy and the work of separation on the interfaces. The research shows that with the Al atom concentration increases, the interfacial energy can increase while the work of separation can reduce; with the concentration of V atoms increases, the interfacial energy increases first and then decreases; but the change of atomic concentration has little effect at the work of separation; and the interfacial energy and the work of separation are closely related to the interfacial migration. It has great guiding significance to the alloy design that the results can be used to further study the dynamic behavior of Ni-Al-V superalloys in the process of precipitation, such as the composition segregation and interfacial migration.

Abstract:Compression tests between 800 and 1200℃ and 10_-3 and 10_-1s_-1 and conventional transmission electron microscopy have been employed to investigate the high temperature mechanical behavior and the deformation mechanisms of the NbCr₂/Nb alloy with the composition Nb-22.5 at.% Cr, prepared by mechanical alloying and hot pressing process. The results show that the peak strength of NbCr₂/Nb alloy decreases with the increase of deformation temperature and the decrease of strain rate. The main deformation mechanism of Nb matrix is the slip of dislocation. While, the deformation mechanism of the Laves phase NbCr₂ is through by stack fault/ twins and partial dislocation.

Abstract:The tensile deformation and fracture behavior of the Ti555211 alloy with dual structure were investigated using in-situ SEM technology. Results showed that It was found that slip bands were given priority within the primary α phase along with angle of 45o with the tensile loading direction for the Ti555211 alloy with initial dual structure. As the crack propagated, the slip bands appeared dense. Moreover, the crack growth was dominant by interconnected microcavities for the alloy with initial dual structure. The Ti555211 alloy with initial dual structure and lamellar structure show different fracture morphologies. For the alloy with initial dual structure, there displayed a small flat surface causing by shear slip, but no obvious shear lip showed in fracture. The deformation and fracture behavior of the near-β titanium alloy of Ti555211 can be tracked by the SEM in-situ tensile test method in real time. The research results of this method have great theoretical value and engineering significance.

Abstract:Differential scanning calorimeter (DSC) experiments were performed on a solid-solution strengthening Ni-base superalloy 625, considering the effects of the powder particle size (<37μm, 45-53μm, 75-105μm, 105-150μm, 150-355μm) and microstructure on the phase transformation temperature. The alloy powders were characterized by FESEM, EPMA and synchrotron XRD. The results indicate that the dendritic structure is evident in powders with different particle size and the dendritic arm spacing is in the 2-10μm range. Elements Ni and Cr are rich in dendritic core whereas the Mo and Nb tend to distribute in the interdendritic region. Only the matrix γ phase exists in the PM625 powders with different particle size range. The PM625 powders with weak segregation tendency exhibit a sharp inflection point in DSC heating curves in the region near solidus temperature, there is only a 2-5°C gap between the incipient melting temperature of the alloy (deviation from the baseline inflection point) and the nominal solidus temperature (tangent-onset intersection) for different particle size. However, the gaps between the norminal solidus and the end of the solidification temperatures are relative large, which is in 53-65℃ range, in DSC cooling curves, because the low segregation characteristic of original powders has been removed during the full remelting and re-solidified process. The differences in solidus, liquidus and incipient melting temperatures in DSC heating curves are maximum 3℃, 2℃ and 2℃ among different particle size powders, whereas they are 6℃ and 2℃ for the solidus and liquidus temperatures of the alloys in the cooling curves. Therefore, the particle size has minor effect on phase transformation temperature of solid-solution strengthening PM625 alloy powder.

Abstract:The process parameters and microstructure of the laser forming repaired (LFR) samples of Inconel 625 alloy are investigated. The results show that a wide range of process parameters are suitable for the laser forming repairing of Inconel 625 alloy. The laser power mainly affects the width of single track LFR samples. The scanning velocity has significant effect on the size of single track LFR samples. The powder feeding rate has less effect on the size of single track LFR samples. The interface between the substrate and laser repaired zone (LRZ) shows a metallurgical bonding. The phases in substrate mainly consist of the γ(Ni-Cr) matrix, MC (NbC, TiC) carbids with bimodal sizes of about 10μm and 0.5μm, and laves phase. In the LRZ, columnar dendrites grow epitaxially from the substrate, approx following the deposition direction. The phases in LRZ mainly consist of γ matrix, laves phase and a small amount of MC carbids. Due to the increase of nucleation sites, a large ammount of laves phase are precipitated in the layer interface and track interface.

Abstract:The influence of different aging time at 750 ℃ on microstructure and mechanical properties of GH3625 alloy tube were investigated by means of OM, SEM, EDS, Universal Testing Machine and other means in this work. The results show that the MC, M6C, M23C6, ?? and ? phase are mainly precipitated in the GH3625 alloy at 750 ℃ for 1000 h. The grain growth in the aging process of GH3625 alloy is closely related to the phase transition behavior at the grain boundary and the solute drag of Nb atoms. Due to the transformation of different types of the phase at the grain boundaries, the grain boundaries width of the GH3625 alloy with increases initially and then decreases during the long-term heat preservation at 750 ℃. Before and after aging, the change of tensile strength of the alloy is not obvious, and the yield strength of alloy shows a trend of increasing continuously. However, the elongation of the alloy has lost by 62.55%, and the fracture mode changes from ductile fracture to brittle fracture.

Abstract:The DD98M nickel-based superalloy tube is fabricated by using laser additive manufacturing (LAM). The microstructural variations of the as-deposited, solution-aged and long-term aging are studied. The precipitates distribution of deposited and solution-aged alloy were analyzed combining with the study of γ‘ precipitates evolution at 1000 ℃ long-term aging. The results show that the as-deposited microstructure of the alloy mainly consists of epitaxial finer columnar grains with an optimum amount of cubical γ‘ precipitates with around 70 vol. %. No γ-γ‘ eutectic is observed at interdendritic. Rapid solidification during LAM process largely eliminates the segregation of metal elements with an increase of γ‘ precipitates sizes from 210 nm at dendritic arms to 560 nm at interdendritic regions. After solution-aged treatments, γ‘ precipitates (about 370 nm) are uniformly distributed in γ matrix with the sizes distribution fitting the LSW model. During the long-term aging of 500 h at 1000 ℃, no TCP (Topologically Close-Packed) phase exists and the sizes of cubical precipitates have a slight increase. In addition, the micro-hardness of the as-deposited is 442 HV and it will obviously increase to 487 HV after solution-aged heat treatment. Long-term aging reduces around 5.9 % of the maximum micro-hardness.

Abstract:Fatigue crack growth behavior at 650℃ of a P/M superalloy FGH97, which was made by Argon Atomization (AA) + Hot Isostatic Pressing (HIP)process, was investigated. Comparison tests were conducted using a Russian EP741NP disk made of Plasma Rotating Electrode Process (PREP) + HIP process. The effects of different powder making methods, oxygen content, grain size and gamma prime size on the fatigue crack growth rate were evaluated. The results revealed that the fatigue crack growth behavior of AA + HIP processed FGH97 test disk has a lower crack growth rate compared with EP741NP disk, and disks with larger grain size, larger gamma prime size have lower crack growth rates, the oxygen content between 100~150 ppm range has no significant effect on the crack growth rate.

Abstract:Titanium and its alloys are wildly used in aerospace, chemical and biomaterials industries since its high strengths, good corrosion resistance and excellent biocompatibility. For titanium, which has been used as one of the most important biomaterials, the casting method is the most important way to produce implantable products such as spinal cage and knee implants before. While, this method is outdated to fit new biomaterials requirement such as personalized implants and precision medicine cure. With the development of the 3D printing technology, producing titanium implants by using 3D printer is becoming more and more popular and important. This paper will mainly discuss the development of 3D printing technology on bio-used titanium and its alloy, and especially focus on porous titanium implants printing. Suggestions for further development on biomaterials 3D printing industry will also be given at the end of the paper.

Abstract:As electronic devices develop toward the direction of miniaturization and portable type, film electronic devices fabricated on the flexible substrate have attracted more and more attention. As one of the necessary components of electronic devices the flexible transparent conductive films have become an important research area. Indium tin oxide is the traditional materials used in transparent conducting, but they are not used in flexible devices due to their poor flexibility. Silver nanowires films are considered to be very promising candidates of indium tin oxide for their excellent electrical and mechanical properties, acceptable price and conductivity of oxide. In this paper, we introduce the related theories and preparation and the research progress at home and abroad of the flexible transparent conductive silver nanowires films Further, we look forward to the future development of the flexible transparent conductive silver nanowires films.

Abstract:In the present work, compressive properties and deformation modes of binary Ti-16V alloy have been investigated during dynamic compressive tests performed on split Hopkinson pressure bar. For metastable Ti-16V alloy, the flow stress and strain hardening rate were both independent of the loading strain rate within the strain rate range (1000~3700 s-1) in our experiments. According to the optical microstructure evolution, the critical instability strain rate was confirmed to be about 3000 s-1. Multiple deformation modes including {332}<113> type mechanical twinning and stress induced ω phase transformation were identified by electron backscatter diffraction and transmission electron microscopy. With the help of Schmid factor values calculated in a spherical coordinate system, the dynamic twinning behavior of Ti-16V alloy was analyzed and the critical Schmid factor was proved to be a key parameter determining the activation of twinning behavior. Combining the critical Schmid factor value and true stress, the critical resolved shear stress range of {332}<113> type twinning was calculated to be 334~338 MPa.

Abstract:The effects of SiC and Al₂O₃ abrasive particles on micro-abrasion behavior of a biomaterial Ti-25Nb-3Mo-3Zr-2Sn alloy in Hank’s solution was investigated. The effects of particle size and type were considered. The specific wear rate, friction coefficient, wear mechanism and the synergistic effect between the micro-abrasion and corrosion were studied. The results showed that the specific wear rates increased with an increase in the particle size. Due to the hardness and machinability of SiC particle is higher, the material loss caused by the SiC particle is greater than the Al₂O₃ particle under the same size. The average friction coefficients obtained in Hank’s solution are larger than those in distilled water for the SiC particle; however, the Al₂O₃ particle is just the opposite. For the same particle size, the average friction coefficients acquired by the Al₂O₃ particle is larger than the SiC particle. Due to the corrosivity of Hank’s solution, the stability of the friction coefficient in Hank’s solution is poor compared to that of distilled water. With a decrease of the particle size, the wear mechanism changed from a three-body rolling abrasion to a mixed mode and finally to a two-body grooving abrasion. The mechanistic map of the AC-PA against the PA illustrated that the contribution of corrosion to the total material loss cannot be ignored, and the main regime is abrasion-corrosion.

Abstract:The kinetics of crystallization of Zn38Mg12Ca32Yb18 bulk metallic glass was studied by differential scanning calorimetry (DSC) in both non-isothermal and isothermal (at different heating rates) modes. Under isochronal process, theoretical models were adopted to analyze the apparent activation energies for characteristic temperatures. The results indicated that the apparent activation energies for characteristic temperatures in the Zn38Mg12Ca32Yb18 bulk metallic glass by Kissinger model, Flynn-Wall-Ozawa (FWO) model and Augis-Bennett (AB) model were in good agreement with each other. Furthermore, crystallization transformation kinetics during isothermal process was analyzed by the Johnson-Mehl-Avrami (JMA) model. The Avrami exponent n ranges from 3.25 to 4.12 in the isothermal mode. It is noted that the activation energy corresponding to isothermal conditions calculated using Arrhenius equation is larger than the value calculated by the Kissinger method in isochronal conditions, because the energy barrier in isothermal annealing mode is higher than that of isochronal conditions.

Abstract:Typical fracture morphology of Mg-3Al-1Zn alloy after cyclic deformation was investigated using optical microscope (OM), scanning electron microscopy (SEM), transmission Kikuchi diffraction (TKD) and transmission electron microscopy (TEM). Cross-section samples were extracted from secondary twin regions for TEM/TKD observation. The results showed that a large amount of {10-12}-{10-12} secondary twins were observed in the region near the fractured edge. Two-beam bright field (TBBF) technique was performed to study the types of dislocations along secondary twin boundaries. It was found that pyramidal dislocations were highly active within {10-12}-{10-12} secondary twins, which is considered to make pyramidal dislocations have the relationship with {10-12}-{10-12} secondary twins. Localized stress concentration within the secondary twins may lead to the formation of pyramidal dislocations.

Abstract:Two approaches to testing corrosion in autoclave with different time intervals for heating and cooling were carried out to investigate the corrosion resistance of Zr-1Nb alloy in the 0.01 mol/L LiOH aqueous solution at 360 °C/18.6 MPa, the stress, and defect density in the oxide film. The stress and defect density in oxide film were measured by a curl method and the Ion Migration Method (IMM), respectively. Results showed that the stress level and defect density in the oxide film in the shorter interval corrosion tests were lower than that in the longer interval corrosion tests at the initial stage of corrosion with the weight gain less than 34.37 mg/dm2. The corrosion resistance in the subsequent stages of corrosion was better in the shorter interval corrosion tests. It indicates that at the initial stage of corrosion the weight gain shows no obvious difference between the two approaches of corrosion tests in autoclave under different time intervals for heating and cooling. However, the stress level and defect density in the oxide film exhibit noticeable differences, which leads to two distinct microstructural evolution rates of the oxide film. The distinct microstructural evolution rates cause different corrosion resistance in the subsequent corrosion stages.

Abstract:In this paper, TiN and TiC films were prepared on Ti6Al4V substrates by plasma based ion implantation. The effect of N+C and Ti+N hybrid ion implantation at 50 kV, and Ti+C ion implantation at 20 kV, 35 kV and 50 kV on mechanical properties was studied. The implantation was up to 2×1017 ions/cm2 fluence. XPS and XRD were used to characterize the modified surface of the implanted samples. It was found that the modified layer of Ti+C implanted at 50 kV was TiC and Ti-O bond and the layer of Ti+N implanted at 50 kV was TiN and Ti-O bond. The nano-hardness and the friction coefficient were measured by nano-indentation measurements and pin-on-disc-test. Hardness tests have shown that the hardness increased with N+C, Ti+N and Ti+C ion implantation. For Ti+C implanted samples, the hardness was increased with increasing negative voltage. The sample of implanted with Ti+C at 50 kV exhibited the highest hardness of 11.2 GPa. The results of wear tests showed that both Ti+C and Ti+N ion implanted samples had much better wear resistance compared un-implanted sample. The wear rate of Ti+C implanted at 50 kV sample was 6.7×10-5mm3/N.m, which was decreased over one order than un-implanted sample.

Abstract:In order to investigate the effect of rare earth elements on the properties of Mg-Zn magnesium alloys, the structural stability, electronic structure, elastic and optical properties of Mg₂Y, Mg₂La and Mg₃La are calculated and analyzed by using the plane wave pseudo-potential method based on the first principles calculation. The calculated heats of formation and cohesive energies show that Mg₃La has the strongest forming ability and Mg₂La has the most stable structure. The stabilization mechanism of the structure is analyzed based on the calculation of electron densities of states (DOS), electron occupation number and electron density difference. The bulk modulus B, shear modulus G, Young"s modulus E, and Poisson"s ratio ν are further calculated by the elastic constants. The calculated results show that Mg₂Y has the strongest ability of resisting deformation, Mg₃La has the strongest stiffness and resistance to shear deformation, Mg₂La has the strongest plasticity, Mg₂Y and Mg₂La are ductile phases while Mg₃La is brittle phase. Furthermore, the calculated results of hardness and melting temperature shown that Mg₃La has the best abrasive resistance and Mg₂Y has the best heat resistance among the three intermetallic compounds. Finally, the refractive index, reflectivity, absorption coefficient and loss function of the three crystal structures were calculated and analyzed..

Abstract:This study aims at producing sphere Ti6Al4V powders with tailed physical characteristics for additive manufacturing application. Ti6Al4V powders were prepared by a novel electrode induction guiding gas atomization (EIGA) equipment designed independently. The yielding rate of fine powders could be improved by reasonably increasing feed rate and atomization gas pressure. Interestingly, the yield (35%) of powder particles below 45μm by EIGA is significantly higher than the yield (~ 10%) by conventional plasma rotating electrode technology. The powder properties and microstructure were characterized by scanning electron microscope (SEM), X ray diffraction (XRD) and optical microscope (OM). The powders exhibited satisfactory flowability and high apparent density for good sphericity and smooth surface. The powders with tailed size ranges could be used for various additive manufacturing methods and injection moulding etc. The β phase of Ti6Al4V translates to needle-like α′ phase during atomization process because of fast cooling rate calculated to be 104-108 K/s.

Abstract:The one-dimensional NiFe1.98RE0.02O4 (RE=Pr, Nd, Sm) nanowires have been fabricated by using sol-gel method, electrospinning technique and heat treatment technology. The structure, morphology and magnetic properties of NiFe1.98RE0.02O4 (RE=Pr, Nd, Sm) nanowires are characterized by X ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and vibrating sample magnetometer (VSM). The result shows that the nanowires surface is smooth and the diameter of the nanowires is about 60 nm which is continuous and symmetrical. All samples present a pure phase spinel structure. Doping Pr3+, Nd3+ and Sm3+ respectively lower the crystallinity of NiFe2O4, and the grain size D decreases from 44.8 nm to 33.8 nm. NiFe1.98RE0.02O4 (RE=Pr, Nd, Sm) nanowires exhibit soft ferrimagnetic behavior. The saturation magnetization (Ms) of NiFe1.98RE0.02O4 (RE=Pr, Nd, Sm) nanowires are 39.58 emu·g-1, 41.10 emu·g-1, 34.23 emu·g-1; and the coercivity (Hc) of the nanowires are 176.49 Oe, 170.98 Oe, 199.22 Oe, respectively. Among them, the soft magnetic properties with the largest Ms (41.10 emu·g-1) and the smallest Hc (170.98 Oe) of NiFe1.98Nd0.02O4 nanowires is the best.

Abstract:Casting WC particles (WCp) were used as reinforced particle, 4Cr5MoSiV1 steel particles were used as metal matrixs, and Laser Melt Injection (LMI) was employed to produce WCp/4Cr5MoSiV1 metal matrix composite on Q235 steel. Microstructure of MMC layer was analyzed by X-ray diffraction (XRD), Optical microscopy (OM) and scanning electron microscopy (SEM), microhardness was tested along the depth direction of the coatings, pin-on-disk wear test was conducted at room temperature, and morphologies of worn surfaces was analyzed by SEM. Results show that the compound layer mainly comprises γ-Fe, WC, M2C, M6C, M23C7, (Fe,W)3C (M=(Fe, Cr, W, Mo), carbides exhibit different forms in the composite layer. The hardness of the compound layer is 723.74HV0.2, which is 4.6 times of the substrate and 50% higher than traditional hardened 4Cr5MoSiV1 steel. The average friction coefficient of MMC layer is 0.283, which is only 87.1% of the cemented carbide and 61.1% of the 4Cr5MoSiV1 steel. The relative wear rate is 43.45, which is 1.7 times of the cemented carbide and 43 times of the 4Cr5MoSiV1 steel.

Abstract:The high-pressure die castings of AZ91 Mg and ADC12 Al alloys of 3 mm were welded by frciton stir welding. OM、SEM/EDS、XRD and universal tensile testing machine were used to analyze the microstructure and tensile property of the joint. The main conclusins are: 1). Defect-free welded joints were obtained when ADC12 die-casting aluminum alloy was placed in advancing side with a welding speed of 40mm/min and the rotational speeds of 900-1300r/min. 2). Mg and Al alloys are mixed with each other in the nugget zone, and mechanical interlocking occurs. In the parent material, the thick and large casting dendrites are obviously refined, and the non-Mg/Al matrix phases mainly include Si, Mg2Al3, Mg17Al12 and Mg2Si. 3) The average tensile strength of the joints increased first and then decreased with the increase of rotating speed. Fracture occurred at the interface of the thermal affceted zone and the nugget zone in advancing side.

Abstract:In this study, molecular dynamics simulations are employed to study the nanometric machining process of single crystal γ - TiAl alloy. The influences of different cutting speeds and depths on nanometric cutting process of single crystal γ - TiAl alloy are?studied by?molecular dynamics modeling, calculation and analysis.?The results show that the accumulated volume of chips increases with the cutting depth increases in nano-cutting process, at the same time the atoms in the chip stack are tighter and the dislocation density is increased; however the dislocation density decreased with the cutting speeds increases. In a certain cutting depth and speeds range, in front of the tool will produce "V"-type dislocation ring of the cutting process, temperature and potential energy of the workpiece will increased correspondingly. In particular, when the cutting speed is 400m/s, there is no atomic misalignment on the cutting surface in front of the tool.

Abstract:The Sm (CoFeCuZr)_z permanent magnets with different z values (z=7.5~8.5) were prepared by powder metallurgy. The properties, constituent phase, precipitated-phase content, microstructure and element distribution of the magnet were characterized by magnetic measurement system, X ray diffraction analysis, electron probe and transmission electron microscope. Magnetic properties change with z value, and the inherent mechanism is explained in this essay. The results show that the increase of z value leads to the increase in the size of cell structure and the 2:17R phase with high saturation magnetization, which finally results in the improvement of remanence B_r. The precipitated Zr-riched phase increases with the z value increases, which has a weakening effect on the squareness H_k/H_cj. The z value changes the enrichment of Cu element at the edge of 2: 17R phase, which has a significant effect to the coercivity H_cj. Within the certain range (z <8.2), the higher the content of Cu at that edge, the larger the coercivity is.

Abstract:Heterointerface induced crystallographic transformation, as a very unique interface phenomenon, has been recently reported in several experiment studies, but its origin has not yet been clarified. In this study, taking the Ni(111)/Fe(110) interface as an exemplary case, we investigate the atomic structures, energetic, and the responsible phase transition mechanism of FCC/BCC heterogeneous interfaces from the first principles. The results predicted the most energy favored structure to be {111}fcc/{110}bcc (K-S). The crystallographic transition occurs only within the near-interface Ni layers. The responsible mechanism is mainly due to interfacial commensuration strains, without involving the change of atom magnetic moments at the interface.

Abstract:The interfacial heat transfer coefficient(IHTC)is one of the important boundary conditions for the simulation of the plastic forming of zirconium alloys. In this paper, the contact temperature-time curves between Zr-4 alloy and H13 die steel with glass lubrication and without glass lubrication were measured and the characteristics of the interface heat transfer were analyzed. The corresponding empirical formula between the interfacial heat transfer coefficient and the temperatures of both the Zr-4 alloy and die steel were established. The results show that glass lubricant can reduce the interfacial heat transfer between the Zr-4 alloy and the die steel effectively. When the initial temperatures of the Zr-4 alloy and the die steel are respectively 700℃ and 470℃, the temperature of the zirconium alloy surface tends to be stable at time of about 16.3s and the IHTC is increased from 226W/(m₂.℃) to 2166 W/(m₂.℃) during this time under the condition of glass lubrication, while the temperature of the zirconium alloy surface tends to be stable at time of about 7.7s and the IHTC is increased from 250 W/(m₂.℃) to 2700 W/(m₂.℃) during this time without glass lubrication. The empirical formula of IHTC obtained in this paper has high accuracy that the maximum error between the simulated and experimental results is about 4.7%.

Abstract:In view of the problem that TC4/304 are difficult to be directly bonded by hot-roll, a TC4/304 composite plate was prepared by hot-roll bonding in a vacuum using a DT4 interlayer. The effects of the DT4 interlayer and the bonding temperature on the mechanical properties and interfacial structure of the composite plate were investigated by scanning electron microscopy, energy spectrometry, X-ray diffractometer and tensile-shear testing. The results show that, when the intermediate layer of DT4 is added, at a 20% reduction ratio, when the bonding temperature is between 750 ℃ and 950 ℃, the shear strength of the bonding surface increases with the increase of the bonding temperature. At 950 ℃, the bonding effect is best, the shear strength of the bonding interface reaches 248 MPa. At 1 050 ℃, formation of intermetallic compounds at the interface between DT4 and TC4 decreases the bonding strength.

Abstract:Pure AlSi10Mg alloy and Carbon Nanotubes (CNTs)-AlSi10Mg composite with different CNTs addition were fabricated by selective laser melting (SLM). The CNTs-AlSi10Mg composite was strengthened when the CNTs content was lower than 0.05 wt.%. With the increasing CNTs content, however, the strength was decreased significantly because of the poor density. In order to understand the influence of CNTs on the defects in SLMed AlSi10Mg alloy, nano-CT technology was used to get the 3D information of the defects. The results indicated that the volume fraction of large defects(with diameter larger than 50 μm) in the total volume of defects was increased from 12% to 46% in CNTs(0.5wt.%)-AlSi10Mg composite. The number of gas pores in CNTs(0.5wt.%)-AlSi10Mg composite were significantly increased. The diameter of gas pores in CNTs(0.5wt.%)-AlSi10Mg composite were larger than that in pure AlSi10Mg alloy. The agglomeration of CNTs in the powder and gas adsorption are the fundamental reasons for the increase of the two types of defects.

Abstract:Pure tungsten powder of which the particle size distributed intensively is processed to different samples by selective laser melting(SLM). Then, the samples are preserved in temperature of 1000℃, 1400℃ and 1960℃ for 2h. The mechanical property and microstructure of the samples of different densities and different heat treatment temperatures are studied. The morphology and microstructure are characterized by SEM and XRD respectively. Result shows that the density ratios of the pure tungsten sample vary from 75% to 95%. Bending strength and microhardness increase with the raise of the density, but the microstructure difference between these samples is not obvious. After the heat treatment under different temperature, the mechanical property of the sample by 1400℃ treatment is better than other samples. Under 1960℃ heat treatment, the grain size of pure tungsten sample raises, leading to the decrease of mechanical property. The XRD result demonstrates that the grain structure of the pure tungsten sample does not change after 1960℃ heat treatment.

Abstract:Based on metastable beta titanium alloy Ti-55531, the structure of the sample was obtained by solution quenching above the β phase. Room temperature compression was performed using a Gleeble3800 thermal simulation test machine and a 6.3MN forging simulator. OM, XRD and TEM were used to observe the deformed structrures after different strains. The results show that the maximum compression of 30% room temperature compression true-stress and true-strain curve at the strain rate of 0.0005s-1 is mainly divided into two stages that are elastic deformation stage and plastic deformation stage with obvious strain hardening stage. However, the maximum compression of 30% room temperature compression true-stress and true-strain curve at the strain rate of 0.1s-1 is mainly divided into two stages that are elastic deformation stage and plastic deformation stage without obvious strain hardening stage. Both of them do not have double yield phenomenon. The deformation structures have little different at the different strain rates of the same reduction. The deformation mechanism is dominated by slip. With the strain increasing, the dislocation density increases gradually and the dislocation tangles and shears appear. Strain induced martensite transformation occurs at the compression of 30% and the strain rate of 0.0005s-1 and 0.1s-1. The compression of 50% and 60% also appears strain induced martensite transformation at the strain rate of 10s-1.

Abstract:Carbon-encapsulated Fe–Ni alloy nanoparticles were synthesized through detonation using safety composite explosive precursors doped with Fe (NO3)3? 9H2O and Ni(NO3)2?6H2O. The morphology, components, and structure of the synthesized carbon-encapsulated alloy nanoparticles were characterized through X-ray diffraction studies, Raman spectroscopy and Transmission electron microscopy attached with energy dispersive X-ray spectroscopy (EDS). Results showed that the carbon-encapsulated Fe–Ni nanoparticles with a core–shell structure. The grains exhibited sizes ranging from 40 nm to 60 nm and were uniformly distributed. The encapsulated metal core was mainly composed of different proportions of Fe and Ni. The outer shell was composed of graphite and amorphous carbon, also there were onion carbon formed by the graphitization of diamond clusters in the vicinity of the nanoparticles. The electromagnetic characteristics of Fe–Ni alloy nanoparticles composites were measured by Agilent microwave network analyzer in the band of 2～ 18 GHz. The experimental results show that, 2 mm in thickness reflection loss R(dB) of the nanoparticles which the atomic ratio of iron and nickel is 1: 4, the absorption layer has double absorption peak, peak values are -14.6dB (9.7GHz) and -7.7dB (14.3GHz), the absorption band ranges of -10dB is from 8.5 to 11.8GHz. The reflection loss R(dB)of the nanoparticles which the atomic ratio of iron and nickel is 1: 1, 2 mm in thickness reaches to 30 dB at 12.88 GHz, the absorption band of -10dB is 9.7 ~ 14.4GHz, which has wide absorption band and excellent absorbing property.

Abstract:A new technology combined with slightly electromagnetic stirring and melt isothermal holding technology was formed: Two-way slightly electromagnetic stirring and isothermal holding. The effects of the isothermal holding temperature from 580℃ to 610 ℃and the isothermal holding time from 3min to 15min on the evolution of solidification microstructure were researched. The results indicated that under different isothermal heat treatment parameters, as the temperature increased and time prolonged, the size of the primary grains was gradually refined and spheroidized. However, the threshold value of the isothermal holding temperature and time could be found, so the grains became coarsened. Above the threshold value, by comparing the microstructure of the grain, it was found that the proper parameters were the isothermal holding temperature of 600℃and the isothermal holding time under 7min, at this conditions, the average equal-area circle diameter and average shape factor of the primary phase were 29.4μm and 0.86, respectively. Therefore, the proper temperature and time was the semisolid A356 aluminum alloy in the composite process to match the reasonable melt isothermal holding process parameters. The qualified semisolid aluminum alloy slurry could be prepared by the new composite process.

Abstract:In order to recycle the ultrafine high titanium slag produced in TiCl₄ production process, the titanium slag was sintered and employed as the cathode in a Solid Oxide Membrane (SOM) electrolytic process in molten CaCl2 to prepare metal Ti. The deoxidization process of the cathode and the behavior of impurities removing were studied at an electrolytic temperature of 1150 ℃with an electrolytic voltage of 3.5 V. Results showed with the increasing of electrolytic time, the size and porosity of cathode was decreased while the particle size in cathode was increased, and after 6 hours electrolyzing metal titanium was obtained which indicated the SOM process offered a high current efficiency. The deoxidization process of this electrolysis process was carried out as: TiO₂→CaTiO₃ →Ca(Ti₂O₄) → TiO→ Ti. Results also indicated the impurities which included Al, Mn, Fe, and Si were mostly reduced to corresponding elementary substance, which were moved into melting CaCl₂. A small amount of residual impurities in cathode can be removed by washing with dilute hydrochloric acid.

Abstract:The High-pressure torsion(HPT)deformation of sintered pure tungsten was carried out under low temperature condition. Recrystallization microstructures and behavior of pure W during the subsequent heating was analyzed under different torsion turns, which using a variety of detection and calculation methods such as EBSD, XRD and DSC. The results show that the deformation storage energy of pure W increases and the activation energy decreases after HPT deformation, but the recrystallization temperature is still high. Relative to obvious grain growth of the original sintered structure, recrystallized microstructure produced by HPT deformation is still small after DSC testing. The average grain size is about 4-6 μm. With the tortsion turns increases, grain size did not change significantly and deformed tissue is relatively stable.

Abstract:Graphite coated metal (Fe@G, Co@G, Ni@G) nanoparticles were prepared by a detonation method using ethanol, urea, RDX and metal source of nitrate as the composite explosive. The composition, morphology and microstructure of detonation products were analyzed by means of X-ray diffraction (XRD), transmission electron microscopy (TEM)-energy dispersive spectro-scopy(EDX) and X-ray fluorescence (XRF). To clarify the tribological properties, the lubricating mixed oils (SN150 base oil) with five different content (0%, 0.2wt%, 0.4wt%, 0.6wt% and 0.8wt%) of graphite coated metal nanoparticles were prepared, and then the four-ball tests were carried out separately. The results indicated that the product of detonation is core-shell structure with a range of 10-50nm. The core is single metal and the shell is mainly composed of graphite about 3-8nm. From the four-ball tests, the friction coefficient and wear scar diameter decrease first and then increase with the addition of graphite coated metal nanoparticles and Ni@G show the best tribological properties as a lubricant additive of graphite coated metal.

Abstract:Aimed at the difficulty in producing high-quality machined surface due to the existence of brittle-phase SiC in SiC_p/Al composites, this paper used the molecular dynamics simulation and ultra-precision turning test to investigate the material removal process of SiC_p/Al composites at nanoscale, and focused on the machined surface formation mechanism, brittle-ductile transition and tool wear mechanism in single crystal diamond ultra-precision turning of SiC_p/Al composites. The results indicate that high-pressure phase transition is the main reason for the brittle-ductile transition of brittle-phase SiC in SiC_p/Al composites. With the increase of cutting depth, the removal of SiC particles in SiC_p/Al composites experienced from ductile cutting mode to hybrid brittle-ductile cutting mode and finally to purely brittle cutting mode. The SiC-Al interface and soft Al matrix in SiCp/Al composites considerably affected the brittle-ductile cutting mode transition mechanism when machining SiC particles in SiC_p/Al composites. The existence of tensile stress on the uncut chip could induce the peak of brittle SiC crack initiation in the cutting zone. The primary wear mechanisms of SCD tools were abrasive wear originated from hard SiC particles’ scrape and machining induced graphitization.