Abstract:Diffusion couples for Co-rich fcc Co-Cr-V alloys were prepared, all of which were annealed at 1473 K for 259200 s. The interdiffusion coefficients in fcc Co-Cr-V ternary systems were investigated by means of Whittle and Green method with the help of electronic-probe microanalysis. On the basis of the thermodynamic parameters available in the literature, the interdiffusion data were critically assessed to develop the atomic mobilities for the fcc Co-Cr-V alloys via the DICTRA software. Comprehensive comparisons between calculated and experimental diffusion coefficients showed that the experimental data could be well reproduced by the atomic mobilities obtained in this work. And the validity of the diffusion mobilities was tested by simulating the concentration-distance profiles and diffusion paths in diffusion couples.

Abstract:In this paper, Al-La, Al-Ti and Al-La-Ti alloys were prepared to study the influence of Ti and La on the electrical conductivity and strength of alloys. The electrical properties, strength and microstructure evolution of alloys before and after homogenization treatment at 500 ℃ for 8 h were investigated. The results show that the electrical conductivity of Al-La can keep a high level as 60.35% IACS when the content of La does not exceed 0.3% due to the precipitation of the compounds containing La, Si and Fe. The tensile strength of Al-Ti alloy was enhanced rapidly with the increasing addition of Ti due to the increasing content of Ti atoms in Al matrix. When La and Ti were added simultaneously, the strength of alloys was higher than that of Al-La alloys, and the electrical conductivity was decreased compared with that of Al-La alloys but was higher than that of Al-Ti samples, which is mainly attributed to the formation of the new secondary phase Ti₂Al₂₀La. Homogenization treatment had little impact on microstructure of alloys but reduced the number of casting defects so that increased the electrical conductivity of all samples.

Abstract:A new improved test system was developed based on the non-contact inductance method, which can be used to characterize the piezomagnetic properties of Fe-based amorphous alloy ribbon properly. The studies show that when the test frequency is 1 kHz, the voltage is 0.3 V and the compressive stress σ is no more than 0.1 MPa, the amorphous magnetic material of Fe_73.5Cu₁Nb₃Si_13.5B₉ has excellent piezomagnetic properties, and its ribbons of different specifications have exhibited perfect stability and repeatability after many times experiments. It"s excited that the ribbons are extremely sensitive to tiny stress, and they show a rapidly large rising trend of the inductance once the initial pressure was applied on the ribbons. Moreover, the further amplifying experiment indicated that the sensitivity range is about 0-1.5 KPa; In addition, the size of Fe_73.5Cu₁Nb₃Si_13.5B₉ ribbons can make a big influence on its piezomagnetic property, the initial inductance and its corresponding SI (%) Max value of the ribbons increase substantially along with the sample size increasing; with the same width, the piezomagnetic property is superior to others while the thickness is 33-36 mm, the maximum value of SI (%) is 19.8%. Accordingly, with the same thickness, the ribbons with a width of 20 mm show a more excellent piezomagnetic property and the SI (%) Max has reached to 22.02%.

Abstract:The Al₃Zr-η′ core-shell particles were observed in the Al-12Zn-2.4Mg-1.1Cu-0.5Ni-0.2Zr alloy using high-resolution transmission electron microscopy and electron diffraction. Two types of Al₃Zr particles appeared in the Al matrix: one a standalone Al₃Zr particle coherent with the matrix and the other an as-core Al₃Zr particle acting as nucleation for η′ precipitates resulting in a core-shell particle which is semi-coherent with the matrix. The shell is composed of η′ precipitates with four variants. The strain in as-core Al₃Zr is lower than the standalone, and a considerable amount of strain exists across the interfacial regions between the η′ precipitates and the matrix.

Abstract:The effect of minimum temperature on the mechanical properties and reversed austenite of 9%Ni steel subjected to cryogenic treatment was experimentally investigated in the present work. Cryogenic treatments with different temperatures and soaking time were conducted by combining with the newly developed quenching, lamellarizing and tempering (QLT) heat treatment of 9% Ni steel. The results showed that the execution of cryogenic treatment at -80 and -110 °C had no obvious influence in the reversed austenite and mechanical properties of 9%Ni steel. However, the room temperature impact toughness was improved by cryogenic treatment at -140 °C soaking for 24 hours, which was attributed to the modification of reversed austenite morphology from bulks into strips. The volume fraction of reversed austenite was reduced slightly due to the isothermal martensitic transformation at -140 °C. The conduction of cryogenic treatment at -196 °C soaking for 24 hours increased the volume fraction of reversed austenite as well as refined the secondary martensite laths, as a result of improving both the room temperature impact toughness and cryogenic ductility. This observed results were explained through the precipitation of ultra-fine carbides and increase of internal stress during cryogenic treatment which provided more nucleation points for the reversed austenite in the process of tempering.

Abstract:In this present work, TiN/Cu nanocomposite films were deposited by axial magnetic field-enhanced arc ion plating (AMFE-AIP) on high-speed steel (HSS) substrates, and the effect of substrate bias voltage on the chemical composition, microstructure, mechanical and tribological properties of the films were investigated by X-ray photoelectrons spectroscopy (XPS), X-ray diffraction (XRD), nanoindentation and wear measurements, respectively. The results showed that Cu content firstly increases and then decreases with the increase of the pulse bias voltage, being a low value in the range of 1.3 to 2.1 at.%. The XRD results showed all the films only appear TiN phase and no Cu phase is observed. And the preferred orientation for the films changes significantly with increasing the pulse bias voltage. The maximum value of hardness, 36 GPa is obtained with pulse bias voltage of -200V corresponding to the film containing approximately 1.6 at.% Cu. Compared to pure TiN film, Cu addition to TiN films significantly improves the wear resistance.

Abstract:The space holder technique was widely used to fabricate metal foams specially for titanium foam. However, how to obtain the desired porosities has been a big challenge for this technique, because they are always not equal to the expected ones. The results of the previous study (i.e., P=ax+b. where a=1/(1+δ), b=δ/(1+δ)) resulted in a very interesting conclusion, that is the rate change of pore volume (δ) is an indefinite mathematical constant. On the basis of research works, this paper found a new results by establishing mathematical model which can be shown as equation δ=φ-1. Here, φ is the length index product stands for the ratio between actual value of length and designed length for a sintered metal foam. It reveals that the length index product (φ) is also an indefinite mathematical constant which we can measure its value. Therefore, δ was solved, means both a and b are solved, so the porosity (P) of titanium foam can be predicted by the equation P=ax+b dependent on the spacer content (x). It indicates that in the absence of measurement of porosity, the macroscopic dimensions of the sintered metal foam can be measured to obtain the control equation of porosity. The research of this paper provides new ideas and methods for the structural control of metal foams prepared by space holder technique based on powder technology.

Abstract:Interface fracture often occurs in systems of soft substrate and hard coatings during the service process. That fracture is related to the weak interface strength and also the unstable expansion of cracks along the interface induced by the residual thermal stress. The residual thermal stress mainly comes from the mismatch of thermal physical properties between matrix and hard coatings. In this study, a gradient carburized layer was formed on TC4 substrate before the deposition of TiN(TiN) coatings using double glow plasma carburization. And then the mono- and multilayer TiN(Ti) coatings are synthesized on the carburized layer, forming composite hard coatings. The effect of substrate carburizing on properties of coatings is studied. The results showed that the composite coatings’ hardness could be increased nearly 2 times and the bonding strength was enhanced to over 80N, comparing with mono- and multilayer TiN(Ti) coatings. Also the interface brittle fracture tendency was restrained obviously by the harden substrate, and the coordinative deformation ability of coating at extra load was optimized. The composite coating composed of pre-carburized layer and TiN hard coating showed a higher strength and toughness.

Abstract:Effects of Sr and Ca combined additions (Sr+Ca=0.05wt.%) on the microstructure of A390 aluminum alloy were evaluated by investigating the variation of quantity, size and shape of primary silicon, eutectic silicon, primary α phase and intermetallic phase. The results showed that the variation of microstructures resulted from the synergistic effect of Sr-Ca additions. The burned value and Sr loss rate were reduced with a small amount of Ca, meanwhile, coarse effect of primary silicon phase arising from Sr addition was also suppressed. The effect of Sr in A390 aluminum alloy was mainly modifying eutectic silicon phase and refining θ phase. Furthermore, the effect of Ca was principally modifying primary silicon phase and primary α phase. The optimal microstructure was obtained when combined addition of 0.05%Sr-Ca was applied and the atomic ratio of Sr and Ca was 5 to 1, in which primary silicon phase and eutectic silicon phase as well as primary α phase were all modified significantly compared with those with only 0.05% Sr addition.

Abstract:In order to better understand the temperature and load effect on recrystallization behavior of DD5 single-crystal hollow blade tenon. Samples with different load were heat treated by different solution temperature in a furnace. Optical microscope and scanning electron microscope were used to study the microstructure of recrystallization and size distribution of γ’ phase after solution treatment. Results show that there were no new grains found after solution treatment at 1230°C/4h, ac. However, the depth of affected area was increasing with the increase of bearing load and the size and depth of recrystallized cellular structure with newly-formed γ" phase particles increased with the load increases below the solution temperature. Besides, the recrystallized nuclei begin from the dendrite when the solution treatment at 1315°C/4h, ac. The dendrite arms was passivated and the boundary between dendrite arm and interdendritic space disappeared and γ/γ" phase eutectic structure existed between dendrites in the recrystallization area. Moreover, the recrystallization area and the primary dendritic size gradually increased with the increase of load above the solution temperature.

Abstract:The growth of well-aligned Au/TiO2 nanorods arrays by magnetron sputtering is presented for the first time. The feasibility of preparing Au/TiO2 nanorods was demonstrate via a dc reactive magnetron sputtering at room temperature and heat-treatment at 500 oC in air for 2 h. The heat treatment leads to the formation of Au/TiO2 nanorods with Au nanoparticles embedded in the TiO2 nanorods of anatase phase.These Au/TiO2 nanorods showed lower photoluminescence emission intensity and higher absorption and intensive response to the visible light, compared with traditional TiO2 nanofilms fabricated by similar method. The Au nanoparticles in the TiO2 nanorods suppress the charge recombination.

Abstract:A mathematic model has been built to describe the cladding casting process and the casting parametric influence on the cladding billet. The effect of casting speed, casting temperature and internal cooling water rate on the casting process performance was discussed. Based on the numerical simulation results, the cladding billet was prepared successfully. Moreover, the model has been verified against the temperature measurements during the cladding casting process. The interfacial characteristics were investigated using metallographic examination, Energy Dispersive Spectrometer and universal testing machine. The results show that there is a good agreement between the measured and calculated results. The comprehensively considered casting process is: casting speed is 100mm/min, internal cooling water rate is 35L/min, casting temperature are 1020K (AA4045) and 1000K (AA3003). Based on the simulation results, the AA4045/AA3003 cladding billet with no defects in size of φ140/φ110mm was fabricated successfully. A diffusion layer in width of 15 μm formed around the bonding interface. The interfacial bonding strength is 107.3MPa, higher than that of AA3003, indicating that the two alloys have bonded metallurgically.

Abstract:The hot deformation behavior of a typical nickel-based superalloy was investigated by means of isothermal compression tests in the temperature range of 1010-1160oC and strain rate range of 0.001-1s_-1. The results indicated that the work hardening, dynamic recovery (DRV) and dynamic recrystallization (DRX) occurred in the alloy during hot deformation. Considering the coupled effects of deformation parameters on the flow behaviors of the alloy, the constitutive models were established to describe the flow stresses during the work hardening-DRV period and DRX period. In the DRX period, the modified DRX kinetic equation was used to develop the constitutive models, and the strain for maximum softening rate was used in this equation. Additionally, the material constants in the constitutive models were expressed as the functions of Zener-Hollomon parameter by using linear fitting method. Meanwhile, comparisons between the measured and the predicted flow stresses were carried out, while the correlation coefficient (R) and average absolute relative error (AARE) between the measured and predicted values were also calculated. The results confirmed that the developed models could give an accurate estimation of the flow stresses.

Abstract:Nickel based alloy has good corrosion resistance in chloride medium, but its wears resistance is insufficient.In this paper, WC-CoCr coatings were prepared on Inconel617 alloy surface by HVOF (high velocity oxygen fuel). Electron beam remelting process is explored to modify the morphology and the phase composition of the coated layer. Some structural defects of as-sprayed coating have been improved after electron beam treatment. Tribological tests concerning the sliding wear behaviour of the tested materials revealed a significant decrease of the wear rate for the alloyed surface in comparison with the base material. After high energy electron beam treatment, the micro-hardness of the surface is 1100 HV0.3 which is about 2 times as much as the matrix (550HV0.3) due to the formation of new phase (especially the Co₆W₆C phase) with high hardness, the amount of porosity of the coatings are reduced, and the grain is finer. EDS spectrum analysis found that the process of electron beam cladding elements occurred in the proliferation of cladding layer and the substrate to achieve a good metallurgical bonding. Moreover, the corrosion resistance of the cladding layer in salt water is higher than that of the matrix.

Abstract:The effects of the different heat treatment parameters on the microstructure and mechanical property of as-extruded Mg-4.8Zn-1.2Y-0.4Zr magnesium alloy were described based on the experimental results and analysis. The results indicate that the microstructure of alloy changed obviously during heat treatment process. After T4 solution treatment, although the alloy grain has grown obviously, the plastic of alloy has been greatly enhanced. This mainly dues to the massive fish-bone W-phase decomposed into fine granular W phase, which reduces the pinning effect of the grain boundary. After T5 heat treatment, except W-phase, there is a small amount of Mg-Zn phase precipitated in the alloy, which can improve the performance of alloy. After T6 heat treatment, the W-phase has been almost complely decomposed into Mg-Zn and Mg-Y phase. The dispersively distributed phase greatly improves the strength and plasticity, which increases the ultimate tensile strength and elongation from 311MPa and 16.89% in as-extruded alloy to 374MPa and 21.97%. At last the most suitable scheme for heat treatment of Mg-4.8Zn-1.2Y-0.4Zr magnesium alloy is( 500℃×2h 200℃×48h).

Abstract:Ti-5A1-5Mo-5V-3Cr-1Zr near β titanium alloy containing the initial acicular α was hot compressed at 750~775 ℃ and 10-3~10_-1 s_-1, in which the fragmentation behavior of acicular α was investigated. With the increasing of strain, the acicular α undergoes the rotation displacement, partial fragmentation up to transform to the equiaxial morphology completely. During the fragmentation of acicular α, when the Burgers orientation relationship exists between neighbor α and β phases, the dislocations in β matrix are easy to enter into the neighbor acicular α through slip transmission at α/β interface, followed by the formation of high-density dislocations and then transforming to the sub-microstructures in acicular α. In case of no Burgers orientation relationship between neighbor α and β phases, the dislocations pile up at some α/β interface with the large orientation discrepancy. The as-resulted local stress concentration causes the formation of sub-microstructures composing of local shear bands in acicular α. Sequentially, β matrix hedges into the acicular α along the interfaces among sub-microstructures, leading to the fragmentation of acicular α. The increasing of temperature promotes the dynamic β recovery and then decreases the dislocation density, which doesn’t benefit the formation of sub-microstructures in acicular α. The increasing of strain rate decreases the deformation time, which suggests that the formation of high-density dislocations and then transformation to the sub-microstructures may not perform sufficiently in acicular α. As a result, the increasing of temperature and strain rate both delay the fragmentation of acicular α.

Abstract:Notched fatigue samples were designed to approximate a typical leading edge of the blade with foreign object damage (FOD) in order to study the anti-fatigue performance of FOD-blades with laser shock processing (LSP). The surface at the crack tip of the notches of TC17 fatigue samples was LSPed with double sides. A YAG laser system was used with laser energy of 30 J, pulse width of 15 ns and square spot of 4 mm×4 mm. The residual stress, microstructure, fatigue performance and fatigue fracture of samples with and without LSP were measured and analyzed by X-ray diffractometer, Transmission Electron Microscope (TEM), high-frequency fatigue tester and Scanning Electron Microscope (SEM). Compared with the notched fatigue samples without LSP, the surface residual stresses of LSP-TC17 alloy increased to -445MPa. High density dislocation, twin and nanocrystallite were formed in the surface. The fatigue strength of LSP-TC17 notched fatigue samples increased by 55.6%. Fatigue strengthening mechanism of TC17 notched fatigue samples was high amplitude compressive residual stress and surface nanocrystallite. The experiment results lay the theoretical foundation and provide the technological reference for LSP-FOD blades.

Abstract:In this study, the welding joint of vanandium alloy (V5Cr5Ti) and HR-2 steel was investigated based on the microstructural analysis and mechanical property by optical microscope (OM),X-ray diffraction(XRD),transmission electron microscope(TEM).Results show that using both focus point migration and inclided groove, a defect-free joint can be achieved when the fusion ratio of vanandium alloy was controlled to be less than 15%. The tensile strength is approximately 400 MPa, and the fracture surface exhibits typical mixed fracture mode. The formation of phases in the weld boundaries is affected by the fusion ratio of vanadium alloy and the directional diffusion of vanandium atoms to the low temperature zone during initial stage of solidification. When the degree of vanandium enrichment is low, Fe-Cr substitutional solid solution with bcc structure is formed. When the V/Fe ratio was higher than 4 ot 2, intermetallics such as Fe_0.1Ti_0.18V_0.72, V₂Cr₂Fe appear. The occurrence of hot cracking and cold cracking is due to the formation of vanadium-rich intermetallics, thermal stress (approximately 400 MPa) during welding cycle and residual stress (approximately 300 MPa).

Abstract:The effects of high strain rate on hot deformation behavior and extrusion feasibility were investigated by Gleeble thermal-simulation experiment and finite element method (FEM). The results show that the flow stress of 690 alloy is sensitive to the strain rate. The temperature rise in the alloy deformed with high strain rate (above 10 s_-1) is significant. The recrystallization grain size decreases with the increase of strain rate under low strain rate, however, that increase with the increase of strain rate under high strain rate. The maximum extrusion force presented earlier decrease and later increase trend with the increase of extrusion rate. The 690 pipe were succeesfully extruded according to the experiment and FEM results.

Abstract:A series of axial force controlled fatigue tests at 1070℃ had been performed to elucidate the influence of stress ratio (-1/-0.33/0.1/0.5/0.8) on high cycle fatigue behavior of DD6 single crystal superalloy. In order to analyze the fracture micro-mechanism under different stress ratio, fracture morphology and microstructure of these samples were characterized by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Experimental results indicate that the high cycle fatigue life of DD6 alloy with different stress ratio decreases with the increase of stress amplitude and mean stress. When the stress amplitude is constant, the fatigue life of DD6 alloy decreases with the increase stress ratio. The fatigue life of DD6 alloy increases with the increase stress ratio when the mean stress is constant and the stress ratio is less than 0.5. However, when the mean stress increases to a certain extent, the stress ratio has no significant effect on the fatigue of the alloy. Analysis on fracture surfaces of DD6 alloy at 1070℃ demonstrates that that quasi-cleavage mode is observed under the condition of low stress ratio, but is dimple mode at high stress ratio. The fatigue fracture mode under medium stress ratio has the mixing characteristics of the above mentioned mode. High temperature oxidation under low stress ratio is helpful to the initiation and propagate of cracks.

Abstract:An adherent Si-Mo coating on Mo-based alloy was produced by fused slurry method. The thermal shock resistance of the coating was evaluated by cycle test from room temperature to 1600°C in air. Besides, the microstructures of the coating were analyzed by SEM, EPMA, WDS and XRD. The results showed that the coating could bear thermal shock for 400 cycles from room temperature to 1600℃. During the oxidating process, the coating evolved from the original MoSi₂-Mo₅Si₃ bilayer structure to SiO₂-MoSi₂-Mo₅Si₃ multilayer structure. At the initial stage of the thermal shock, the longitudinal cracks were formed and gradually extended to the substrate, the longitudinal cracks run through the coating at the later thermal shock stage. In the meantime, the volatilization MoO₃ leads to the increase stress in the interface of coating/substrate and produce transverse cracks.

Abstract:The effect of artificial ageing on the intergranular corrosion behavior of 7055 aluminum alloy were investigated by accelerated corrosion test, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and elemental mapping of X-ray energy dispersive spectra (EDS). The results show that when the alloy is aged at 120 ℃, the grain boundary precipitates (GBPs) are the preferential corrosion sites; however, when the alloy is aged at 400 ℃, the Al-matrix near the GBPs is the preferential corrosion site compared rather than the GBPs. According to the TEM and EDS results, when the alloy is aged at 120 ℃, extended ageing leads to the coarsening and discontinuous distribution of GBPs as well as increased Cu content in the GBPs. These factors result in the evolution of corrosion morphology from a typical intergranular corrosion morphology to pitting morphology. When the alloy is aged at 400 ℃, Cu element atoms will concentrate in the precipitates, especially in the GBPs, and the Al-matrix deplete Cu element. As such, the corrosion potential of GBPs becomes higher than the Al-matrix nearby, causing intergranular corrosion guided by the Al-matrix dissolution along the grain boundary.

Abstract:During the operation of material removal, the release and re-distribution of residual stresses is crucial to machining deformations of aircraft structural parts. Hence, the non-uniform plastic deformations, which caused by the high temperature gradient field in the quenching process, will give rise to residual stresses. Therefore, the finite element model is established for the quenching process according to the convective heat transfer coefficient. Whether the amplitude or distribution, the simulated residual stresses are in good agreement with the experimental data. On this basis, the proposed method is further used to analyze the formation mechanism of residual stress in the quenching of 7075 aluminum alloy thick plate. It is concluded that the final residual stresses are already determined when the plastic deformations in the central layer is over at the end slip time. The residual stresses remain unchanged even if the temperature will continue to drop. Finally, the performance-controlled and deformation-controlled method is suggested for residual stresses. It is known that the deformation-controlled region can strongly impact the final residual stresses whereas the performance-controlled region has a few changes of the final residual stresses. Consequently, the decrease of the convective heat transfer coefficient in the deformation-controlled region and the increase in the performance-controlled region, can fast the cooling velocity and reduce the final residual stress.

Abstract:AZ91 magnesium alloys with different Ce content were prepared, and the distribution of alloy elements and compounds structure were studied on the basis of analyzing the microstructure of the alloy, in order to investigate the reason of the change of the structure of the alloy. The results show that The solid solution of Ce in a -Mg is only a few dozen ppm, and the amount of solid solution of Al in a -Mg is less than the average content in the alloy, while Zn mainly exists in the β-Mg17Al12. The grain size decreases with increasing the Ce content, and the Ce is gather in front of solid/liquid interface lead to form composition under-cooling which cause the grain refinement. Ce can reduce the amount of Al participated in the eutectic reaction which make β-Mg17Al12 decrease and its distribution from continuous to discrete. Zn ion replacement Al ion results in lattice distortion of β-Mg17Al12 and the lattice constant increase.

Abstract:Stir casting process are well suited for large scale and complex composite components,but the flow behavior becomes complex due to the addition of SiC particles, therefore the mould filling process becomes the key factors of preparing high quality composite castings. In this study, the flow model of SiCp/A357 composites was built through numerical method, and the fluidity and SiC particle distribution were tested with fluidity test. The results showed that numerical simulation was roughly accord with fluidity test. The fluidity of SiCp/A357 composites increased with pouring temperature, which was more obvious in semi-solid state. The volume fraction of SiC particles at the flow-front was lower than the end, the whole homogeneity of SiC particles decreased, this tendency intensified with pouring temperature increasing. The fluidity of SiCp/A357 composites decreased with volume fraction. With volume fraction increasing, the tendency of SiCp reduce at flow front slowed, the homogeneity of SiCp inproved.

Abstract:The mathematical models on the needling processing parameters and the multiple mechanical performances of needling C/C composites were established based on Response Surface Methodology by the design-expert system. The response surface models of tensile strength, shear strength,tensile strength and shear strength ratio,compression strength and preform density have high fitting degree, P of which is less than 0.05 and R-Squared of which is higher than 0.82. These response surface models are able to design and predict the needling processing parameters and the mechanical performances of needling C/C composites with reasonable accuracy. The comprehensive optimization results of multiple response targets of needling C/C composites show that: when the needling density is 12.18Pin/cm₂, the needling depth is 11.68mm and the Non-woven density is 90.55g/m₂, the comprehensive mechanical performances of needling C/C composites are the best. At this point, the tensile strength is 116.49MPa, the bending strength is 121.48MPa, the shear strength is 19.41MPa, the compression strength is 160.88MPa and the preform density is 0.42g/cm₃.

Abstract:Ultrasonic soldering technology, which commenced in the late 30s of last century, has been used to successfully join aluminum alloy, aluminum matrix composites, titanium alloy, ceramics and other hard to wetting materials without the assistance of flux. It is widely regarded as the most promising alternative to the flux-assisted soldering. Removing the oxide film at the interface of solder/base material is one of the most important problems for the ultrasonic soldering process. In the light of the presence of residual oxide film at the frontier of acoustic-induced solder spreading on the aluminum alloy, combined experimental and simulation analysis work was conducted to discover the characteristics and formation of the residual oxide film. Meanwhile, the elimination measure for the oxide residues was put forward. The results are of great significance to improve the quality of the ultrasonic-assisted coating, surface metallization and ultrasonic soldering.

Abstract:The titanium and tungsten were used as the transition layer respectively, the mirco-crystalline diamond films on a silicon substrate were prepared by PE-HFCVD method. The field emission characteristics of the films were studied in this paper. The results show that, the metal transition layers can significantly enhance the field emission properties of the diamond films. When the transition layer is tungsten, the opening field intensity of the diamond film is 5.4 V/μm, which reduces by 44% compared with non-transition layer ; while the field emission current density can reach 1.48 mA/cm₂ when the electric field intensity is 8.9 V/μm. The structure characterization of the films show that, The enhancement of the field emission properties is mainly attributed to the decrease of the electron transport barrier at the interface and the increase of the sp₂ C content in the film. The formation of good conductive channels at the interface and the diamond film make the electron more easy to transport to the film surface. Hence, the diamond films which use metal transition layers show excellent field emission properties.

Abstract:Vaporizing Foil Actuator Welding (VFAW) has the promising potential to be widely used to join steel with non-ferrous metals, such as titanium, magnesium, and aluminum alloys, which is difficult with fusion welding techniques. The aluminum foil acts as the medium of energy transmission from electric energy to dynamic energy during VFAW process. Its working efficiency is of vital importance for the welding technique. In this article, the influence of the working efficiency of the aluminum foil on impact velocity between the flyer and target was explored via Photon Doppler Velocimetry (PDV) experiments. The experiments were carried out with foils of three different thicknesses under varied input energies. When the distance between the fly and target was 2.5mm with the impact angle of 5°, the vaporization energy of the foil is the key factor contributing to the impact velocity. According to the analysis of impact velocities, the 0.051mm –thick aluminum foil has the best efficiency with the input energy under 3 kJ, 0.076mm-thick aluminum foil works most efficiently with the input energy of 3kJ to 6kJ, and with the input energy of 6kJ to 12kJ, the 0.127mm-thick aluminum foil has the highest working efficiency.

Abstract:To solve the problems of Gantry therapy device met—huge magnet weight, expensive operation, this paper proposes a new type of coil structure based on tilted solenoids. We have completed a 2.5 T NbTi superconducting magnet prototype design for heavy ion Gantry. The design can reduce the gantry’s size and weight and make it more comparable with gantries used for proton therapy. The magnet consists of ten layers of tilted solenoids with operating current of 1000 A. The coil clear bore is 176 mm and the good field region can be up to 2/3 of the aperture. Because of the magnet’s special shape, it doesn’t require optimization and the higher order harmonics naturally integrating to zero through the ends. To ensure magnet safe and stable operation in the case of rotation, it uses the conduction cooling form. From the concept of tilted solenoid coil,Sthe magnetic field design is reported in detail. Based on ANSYS thermal FEM software, we simulate the temperature profiles inside the magnet and the thermal shield and obtain the thermal distribution of magnet cryogenic system. Finally, we give a brief introduction about the magnet processing.

Abstract:Dry friction hysteresis characteristics of metal rubber was studied based on numerical model established absolutely with actual material and process parameters. The numerical model was verified in the four respects: forming force, tissue structure, size and loading-unloading curve. Elastic micro element and its local coordinates were built. Quantity of contact pairs, ratio of sliding contact pairs and status of contact pairs were researched. The number of contact pairs increases with loading and decrease with unloading. Sliding contact pairs account for nearly 80 percent of all contact pairs. The contact pairs were divided in two kinds: typical contact pairs and untypical pairs. And the typical contact pairs are the main components. According to the meso-characteristics of contact pairs, contact pair mechanical model and mathematic model of metal rubber hysteresis were set up. The mathematic model is accurate and reliable, and its parameters have clear physical meaning. The hysteresis of metal rubber can be described well with the mathematic model and metal rubber products can be designed with the formulas.

Abstract:The new muti-compositional Ti2AlNb alloy Ti-22Al-25Nb-1Mo-1V-1Zr-0.2Si was treated by the process of near beta forging and heat treatment. The effect of heat treatment on the microstructure and mechanical properties were analyzed by means of the scanning electron microscopy (SEM), transmission electron microscopy (TEM) and tensile test machine. The results show that the initial microstructure contains the primary α2 phase, the needle like O phase and the matrix B2 phase. On the one hand, with the increasing of solid solution temperature, the alloy strength is enhanced at room and high temperature, but the alloy ductility is reduced. On the other hand, with the increasing of aging temperature, the variation of strength and ductility is completely opposite, compared to the increasing of solid solution temperature. It is analyzed that the primary alpha phase volume fraction α2/O was mainly influenced by the solid solution treatment for the alloy. With the increasing of the solution temperature, the α2 /O primary alpha phase volume fraction is reduced, leading to the strengthening effect of needle like O phases enhanced. At the same time, the grain boundary pinning effect of the α2 phase to B2 is weaken, then the B2 grain growth cause the plasticity decrease. The morphology of precipitated phase is mainly affected by aging treatment. With the decreasing of aging temperature, the thickness of precipitated fine strip phase decrease, which makes the strengthening effect of fine strip increase, the volume fraction of B2 phase decrease, and the ductility of the alloy reduce.

Abstract:Ti-TiN-Zr-ZrN multilayer films were deposited on TC11 titanium alloy and Si wafer by vacuum cathodic arc ion plating technology. The Ti-TiN-Zr-ZrN multilayer films with different modulation periods, different R_Ti/TiN:R_Zr/ZrNmodulation ratio and different thickness. The structure and performance of the multilayer films, especially residual stress were investigated by various analytical methods including scanning electron microscopy (SEM), X-ray diffraction(XRD), micro-hardness tester, scratch adhesion tester and stress gauge. The results show that increasing the modulation period, residual stress decreased, adhesive strength and hardness were increased. Reduce the modulation of RTi/TiN:RZr/ZrN modulation ratio, is residual stress and hardness increases, the adhesive strength decreased. Increasing the thickness of multilayer films, residual stress increased slightly, adhesion and hardness are improved. the film’s hardness around at 30Gpa when it’s thickness up to 7.54μm.

Abstract:High-temperature tensile test at a deformation temperature of 895-935℃ and a strain rate of 8.3×10_-4-1.32×10_-2 s_-1 is conducted for TA32 high-temperature titanium alloy developed independently by our country, and electron back-scattered diffraction (EBSD) technique is used to characterize grain morphology, orientation, and grain distribution. The results show that TA32 alloy provides superior superplastic deformation capability, with a maximum fracture elongation up to 1141.8%. In high temperature and low strain rate conditions, growth of grains tends to result in the rise of true stress in late deformation stages. Both the true stress and fracture elongation are sensitive to deformation temperature, deformation degree, and strain rate. Dynamic recrystallization is more likely to occur in high temperature or low strain rate conditions. The degree of dynamic recrystallization increases with the increasing deformation temperature, the decrease of strain rate, or the increase of deformation degree. After deformation, the textures nearly exhibit random orientations, and the original grains get equiaxed with better dimensional uniformity. During the process of deformation, discontinuous dynamic recrystallization serves as the dominant dynamic recrystallization mechanism. With the increase of deformation temperature, decrease of strain rate, or increase of deformation degree, discontinuous dynamic recrystallization plays a more important role, while continuous dynamic recrystallization weakens.

Abstract:Optimization of the process parameters of arc ion plating so as to improve the structure and properties of TiAlN coatings has important practical value in the application of TiAlN coatings. In the work, TiAlN coatings were deposited by pulsed bias arc ion plating, and the influence of duty ratio of pulsed bias on the structure and properites of TiAlN coatings was studied. It was found that the density of surface defects and surface roughness of TiAlN coatings are first decreased and then increased with the increase of the duty ratio; and the density of surface defects and surface roughness is the lowest when the duty ratio is 70%. The micro-hardness and wear resistance of TiAlN coated samples is first improved with the increase of the duty ratio, while the further increase of the duty ratio above 50% has an adverse effect on the micro-hardness and wear resistance. The key wear mechanism of TiAlN coatings includes adhesive wear and oxidation wear when Si₃N₄ ball is used as the friction pair.

Abstract:Abstract: The effects of the co-addition of B and Y on the microstructure and mechanical properties of a novel near α high temperature titanium alloy were studied. The solidification paths and the refinement mechanism of the titanium alloys with different B and Y additions were analyzed and studied. The results show that the addition of B and Y has a significant effect on the refinement of grain size of the Titanium alloys. The ultimate compressive strength and yield strength increase with the addition of B and Y, mainly due to the grain refinement caused by the addition of B and Y. The compressive plasticity and fracture toughness of the alloys decrease gradually with the addition of B and Y, which is attributed to the fractured TiB together with Y2O3 pulled out the matrix, accelerating the expansion of the crack.

Abstract:Nickel aluminum bronze coating was deposited by cold spray technology on the nickel aluminum bronze 9442# substrate. Microstructure, electrochemical behavior and tribocorrosion behavior were observed and tested by SEM, OM, XRD, XPS, electrochemical working station and abrasion machine. The results showed that intergranular corrosion and optional corrosion took place in electrochemical corrosion process, microspore and cracks appeared on coating after electrochemical corrosion; tribocorrosion process consisted of competition between friction and passivation and promotion of anodic dissolution by friction; compared with static state, E_corrof coating and substrate under tribocorrosion condition drastically decreased, I_corrof coating and substrate increased an order of magnitude, corrosion resistance of coating and substrate became worse; compared with dry friction, friction coefficient of coating and substrate increased drastically, wear resistance of coating and substrate became worse.

Abstract:The effects of ultrasonic vibration and heat treatment on the microstructure and tensile properties of laser direct forming IN718 superalloy were investigated. The results show that microstructural grain size became finer due to the actions and influences of ultrasonic vibration. In addition, the microhardness and tensile strength of the parts fabricated by LDF with ultrasonic vibration were higher compared with that of the ones fabricated by LDF without ultrasonic vibration. With the heat treatment of homogenization, solution and double aging, the columnar dendrites changed to equiaxed grains due to recrystallization. Laves phase dissolved, and there were grainy and acicular δ phase distributing in and along boundaries of the grains. Besides, a large number of strengthening phase γ″ and γ′ separated out on the matrixes. The room-temperature tensile properties of heat treatment samples reached the wrought standard of Q/3B 548-1996.

Abstract:Titanium-stabilized 15Cr-15Ni austenitic stainless steel in 20% cold-worked condition has been considered as a promising candidate high temperature structural material for core components in liquid metal-cooled fast reactors (LMFR). Microstructure and high temperature mechanical properties of as cold-worked and different aging treatments alloys were investigated by using metallographic microscope, scanning and transmission electron microscope, and tensile testing machine. The results demonstrate that the recovery took place when the alloys were aged at 550℃ for 336h. The emergence abundant of twins was attributed to dislocations movement. When aging temperature increasing to 650℃ and 750℃, the amount of twins reduced because of alloy′s further recover. Sigma phase precipitated from austenitic matrix along grain boundaries when alloys were aged at 650-750℃ for 336h. The amount and size of sigma phase increased with the aging temperature and time increasing. Because of the grain boundary strengthening, alloys aged at 550℃ had slightly higher yield strength and ultimate tensile strength than those of as-cold worked alloy. The high temperature yield strength and ultimate tensile strength decreased significantly, while plasticity increased observably when aging temperature increasing to 650℃ and 750℃.

Abstract:In this paper, a Zn-Mg-Ti master alloy was prepared by mould casting, and the effect of Zn-Mg-Ti master alloy on the microstructure and mechanical properties of pure magnesium were studied. The results showed that the master alloy was mainly composed of matrix and flower-like Zn-Mg-Ti ternary phase, and that the Zn-Mg-Ti master alloy had a significant influence on the microstructure and mechanical properties of pure magnesium. The grain size of magnesium alloy decreased first and then increased with the increase of master alloy addition; when the addition amount of the master alloy was 8%, the finest grain size could be obtained. The grain refinement of the magnesium alloy is mainly attributed to the Ti atoms that agglomerate at the front of the solid-liquid interface and thus restrict the crystal to grow. Compared with the microstructure of the Mg-6.4wt.% Zn alloy and M-8 alloy, it was found that Ti element could not only significantly refine grain size of Mg-Zn alloy, but also promote the dissolution of the second phase into the matrix. The mechanical properties of as-extruded alloys showed that the strength and elongation of magnesium alloy increased first and then decreased with the increase of addition amount of the master alloy; when the content of the master alloy was 8%, the ultimate tensile strength and elongation of the magnesium alloy were 308 MPa and 21.5%, respectively.

Abstract:A new gas blow forming-cold contraction bonding process for forming Mg/Al composite tube was presented .The circumferential flow stress and elongation of AZ31 magnesium alloy and 7475 aluminum alloy were obtained by the unidirectional hot tensile tests at 420℃, 440℃and 460℃. On the basis of these datas, the initial gas pressure and maximum gas pressure required to deform the Al tube and Mg tube was calculated and the AZ31/7475 composite tube was successfully manufactured at 460℃. The as-formed AZ31/7475 composite tube is closely combined with no metallurgical bonding. Due to the existence of eccentricity between the AZ31/7475 tubes and the die cavity, the wall thickness distribution of the cross section is not uniform; The residual contact stress between outer tube and inner tube was deduced, which includes the residual contact stress caused by the elastic recovery and the residual contact stress caused by the cold shrinkage of the two alloys. The residual contact stress of the composite tube was measured by the compression tests and the calculated value agrees well with the measured value, with a difference of about 19.2%.

Abstract:Optimization of ultrahigh frequency pulsed VP-GTAW (HPVP-GTAW) welding parameters on microhardness for 5A06 aluminum alloy was carried out. Taguchi method was employed to design the experiment. The microhardness of the fusion zone and heat affected zone (HAZ) was taken as indicator, and the characteristic welding current parameters of HPVP-GTAW were taken as factors. The experimental results were analyzed by both the range analysis method and regression analysis method. Results show that the optimal parameters of variable polarity current frequency fL, pulse frequency fH and pulsed current proportional coefficient ψ are 1kHz, 20kHz and 0.6 (high-frequency background current 75A, high-frequency peak current 180A, duty cycle of high-frequency pulse 0.2), respectively. Meanwhile, fL influences on microhardness the most significantly, followed by fH, and the impact extent of ψ on microhardness is the least. The confirmatory experiment shows that the microhardness, tensile strength, percent elongation and ratio of reduction with the obtained optimal parameters are 84.7%、94.3%、80% and 93.4% of those of the base matel, respectively.

Abstract:The ternary alloy of Ni-34Al-32V(at%) and Ni-28.5Al-43V were prepared with success by vacuum non-consumable arc melting.The various locations of alloy solidified microstructure and compression behavior were investigated by using optical microscope(OM), X-ray diffraction(XRD) as well as scanning electron microscope (SEM).The results show that the solidified microstructure of the ternary alloy NiAl-32V was mainlly composed of the NiAl primary phases and NiAl+V eutectic.Meanswhile, the NiAl-43V was mainlly composed of the V primary phases and NiAl+V eutectic.At the same time, the mechanical properties of these two alloys were tested.From the fact, the compressive properties at room and elevated temperatures of the two composites are much higher than those of NiAl alloy.According the fact that V additions can remarkably improve the room-temperature fracture toughness and the elevated temperature strength of the NiAl-V alloy.

Abstract:Refractory metals 93W and Mo1 were bonded with Ni interlayer by plasma activated sintering. Investigations were mainly focused on the influence of bonding temperatures on the microstructures, elemental distributions across the interfaces and mechanical properties of 93W and Mo1 joints. And fracture mechnism of joints was also analyzed. Reliable bonded joints 93W/Ni/Mo1 were obtained when bonding temperature was above 800℃. Shear strength of 93W/Ni/Mo1 joints firstly increased (650~850℃) and then decreased (800~1000℃) with the rising of bonding temperature, and the maximum strength (100.2 MPa) of joint was obtained at 800℃. Soild solutions were formed at the 93W/Ni and Ni/Mo1 interfaces when bonding temperature was below 800℃, while MoNi brittle phase was emerged at Ni/Mo1 interface which debased the strength of joints. Fracture failure mainly occurs at Ni/Mo diffusion interfaces.

Abstract:The highly ordered TiO2 nanotube arrays (2-step TiO2 NTs) were prepared via a facile two-step anodization method. The micro morphology, crystal form, elemental composition and photoresponse were characterized by SEM, XRD and UV-vis DRS respectively. The images of SEM showed that the 2-step TiO2 NTs exhibited superior array effect. At the same time, the UV-vis DRS showed that the range of photoresponse shifted towards long wave obviously. Nitrobenzene was utilized to be a target organic pollutant to characterize the catalyst performance. The result showed that nitrobenzene could be degraded by the 2-step TiO2 NTs effectively, and the photocatalytic activity of 2-step TiO2 NTs was far better than the 1-step TiO2 NTs. The photocatalytic degradation efficiency of nitrobenzene was improved remarkably. The reason of the efficiency improvement was caused by the highly ordered structure of the 2-step TiO2 NTs which increased the specific surface area of the photocatalyst. Therefore, the optical channel was increased, photoabsorption region was broadened and the photo-quantum efficiency was improved.

Abstract:In this paper, the Finemet-type amorphous-nanocrystalline ribbons with original Fe73Si15Nb3B8Cu1 and optimized composition Fe73Si15.5Nb1.1V2.4B7Cu1 substituted partial Nb for V as well as appropriately adjusted Si and B were prepared by single-roller rapid quenching and isothermal annealing technology. The microstructure and magnetic properties of the ribbons were studied by X ray diffraction, transmission electron microscopy and magnetic performance testers. The results show that two types of as-spun ribbons are mainly composed of amorphous phase, meaning that two kinds of alloys have good amorphous forming ability; According to Luborsky principle, the fracture srain λt is 5.05×10-2, which indicates that the toughness is poor; The nanocrystalline grain size of two kinds of annealed ribbons are 14.8 nm and 13.2 nm, respectively; Compared with the original composition ribbons,Curie temperature Tc and first crystallization temperature Tx1 of V-containing ribbons are slightly decreased; While the saturation magnetization of the V-containing ribbon is slightly lower than that of the V-free ribbon, the coercivity is smaller, initial permeability and static loss of the ring-shaped V-containing magnetic core samples reach 1.269×105 and 1.748 J/m3 respectively, and their AC iron loss advantage is more and more obvious than that of V-free ones with increasing frequency.

Abstract:A Cu-Diamond composite layer was successfully fabricated on CuCr0.5 alloy substrate by electroplating a Cu-diamond composite ‘planting sands’ layer, mould pressing the diamond particles into CuCr0.5 substrate, filling the nano-copper grains suspending in water into the ‘V’ grooves and mould pressing the composite layer to fix the nano-copper powder on Cu-diamond layer and finally sintering the sample with 900℃+60min parameters at Ar+H₂(10vol.%) protecting atmosphere. The surface morphology at different fabricating stages was investigated in details by scanning electron microscopy (SEM) and the surface thermal expansion coefficient of Cu-diamond composite layer was tested by electric resistance strain gauge method. The results show that the ‘V’ grooves were formed at the vicinity of substrate/diamond interface after mould pressing Cu-diamond composite layer fabricated by using W40 diamond powder. The ‘V’ grooves can be perfectly filled by filling the nano-copper grains into the ‘V’ grooves and mould pressing the composite layer and finally sintering the sample with 900℃+60min parameters at Ar+H₂(10vol.%) protecting atmosphere. The surface thermal expansion coefficient of Cu-diamond composite layer was 11.7×10_-6/℃ when the volume percent of W40 diamond particles on Cu-diamond layer was 40~45%.

Abstract:In this work, Graphene/SnO2 composites were prepared by hydrothermal synthesis method to modificate the surface of grapheme, which were then used to prepare Graphene/SnO2/Cu through powder metallurgy. Many different methods were used to measure and analysis the composites’ microstructure and properties. The results reveal that SnO2 nano-particles absorbing on the surface of grapheme will not shed during the process of preparation. At the same time, SnO2 particles can inhibit aggregation of graphene, and improve the composites’ density, hardness and thermal conductivity. Graphene/SnO₂/Cu composites’ density is 91.0%, hardness is 166 HBW, and thermal conductivity is 139 W/ (m℃), which are more higher than Graphene/Cu composites. Graphene/SnO2/Cu composites’ bonding at the interface is well, with no crack or interfacial reaction. There are three main reasons that lead to the decrease of electrical conductivity of the composites, namely edge dislocation and deformation twin of copper matrix and SnO2 nano-particles on graphene’s surface.

Abstract:The Al₂O₃ ceramic was brazed to GH99 superalloy using AgCuTi filler alloy, The influence of the process parameters on the mechanical property of the joints was studied and the fracture location of joints under different process parameters was analysed. The results show that, With the increasing of brazing temperature, the shear strength of joints decreased after increasing to a maximum, The maximum was obtained at 900℃,Which is 127.24MPa. When the brazing temperature is lower, the fracture is mostly in Al₂O₃/filler side, With the increasing of brazing temperature, The TiNi₃ reaction layer is gradually thickening and then parts of the fracture is in the TiNi₃ reaction layer/filler interface; At 900℃, With the extension of the holding time, The shear strength of joint gradually decreased. The joints is mainly fractured in the Al₂O₃ ceramic/filler interface when the holding time is short. When the holding time is too long, the reaction layer extends into the middle of the solder and the thickness of TiNi₃ layer is greatly increased, and the micro crack is produced in the reaction layer, Which cause the strength of the joint greatly reduced, And then the joint is partly fractured in the filler metal and TiNi₃ reaction layer.

Abstract:The nanocrystalline materials exhibit the microstructure with an average grain size smaller than 100nm, which is responsible for their unique properties. A high thermal stability is the key for the application of nanocrystalline materials. Hence, the grain growth of nanocrystalline materials has been the focus of intense research efforts in recent years. This article reviews the current status of research in this field. The microstructural characteristics of nanocrystalline materials have been introduced. The effects of solute atom, the second particle and internal strain on the thermal stability of nanocrystalline materials are discussed. The basic theoretical models in thermodynamics stabilization and kinetics stabilization are summarized.