Abstract. RP/M is an advance technology based on build-up and discrete idea, and Laser direct deposition by coaxially feeding the powders to laser melting pool is a RM technology in general use. During depositing metallic components the variation and control of temperature field have been priority research problem in the research works all along, and major research object for this problem is simulating real temperature field during the deposition by finite element method. Finite-element model to simulate the temperature field in depositing process of vertical thin wall samples is created, and Solid-liquid coupling thermal conduction problem and heat content within Solid-liquid dilution zone are treated by use of equivalent thermal conductivity and enthalpy potential method in the paper. The simulating results objectively exposure the characteristics on the temperature field during depositing the vertical thin wall samples of 316Lstainless steel. By means of analyzing the simulation results, it is obtained that mean cooling velocity of the melting pool is at 103℃/S order of magnitude in the temperature upward 700℃，and the cooling velocity merely is at 101℃/S order in the temperature upward 240℃. Fluctuating temperature of the substrate undergoes three stages: elevation, stable, descends, and the thermal conduction in the substrate has little influence on the cooling velocity of the melting pool at the descending period. The conformity of the simulating result data with the experimental findings in public literatures is very well.

Abstract. RP/M is an advance technology based on build-up and discrete idea, and Laser direct deposition by coaxially feeding the powders to laser melting pool is a RM technology in general use. It is a major attention problem in the researches on this technology that the distortion occurring in the depositing process, particularly in the substrate. The characteristics on the substrate distortion and “Christmas tree step” occurring in the depositing process of vertical thin wall samples of 316L stainless steel are analyzed by use of results simulating the thermal stress field in this paper. The analysis results have explained that varied temperature field and dissimilar temperature of melted pool at the position of the start point and end point of laser scanning paths cause the “Christmas tree step”. The distortion of the substrate only occur in the region on which 316L stainless steel have been deposited, and there is the rigidity displacement at the left end and right end. It has demonstrated the finite element models simulating the temperature field and the thermal stress field that the test results to measure the rigidity displacement are agreement with simulating results of finite element.

In the present paper, mechanical behavior of HSLA-65, DH-36, AL-6XN and Nitronic-50 is systematically studied. Strains over about 40% are achieved in these tests over a temperature range of 77-1,000K and strain rates of 0.001 to 8,000/s. The results show that, 1) Plastic flow stress of the four newer steelsis is sensitive to the temperature and strain rate, flow stress decreases with decreasing temperatures and increasing strain rates; 2) With increasing or changing plastic strain, the temperature history remarkably affects the microstructure; 3) Dynamic strain aging occurs at lower strain rates and higher temperatures. With increasing strain rates, the stress peak of dynamic strain aging will shift to higher temperature region, or even disappear in the present strain rate range. Taking into account all these phenomena, based on the mechanism of dislocation motion, including the effect of viscous drag on the motion of dislocations, the physically-based model is shown, but excluding the dynamic strain aging effects, The parameters of this model contain the physical concept. Finally, the results of model is discussed. The model predictions are compared with the results of the experiments in a wide range of temperatures and strain rates, but excluding plastic flow stresses in dynamic strain aging region.

Positron annihilation lifetime and SEM were used to study the change of internal defects before and after hydrogen charging in a Fe-Ni based precipitation strengthened austenitic stainless steel which was heat-treated under different conditions. Positron annihilation lifetime spectrum was fitted in terms of two lifetime components. Both positron annihilation lifetime and tensile tests at room temperature indicate that solution treated alloy has a very little grain-boundary carbide and hydrogen charging will increase its strength while decrease its plasticity. Peak aging will produce more grain-boundary carbide and the  phase is in the size below 20nm，but is coherent with the matrix. After hydrogen charging, hydrogen will not enter the - interface，but the grain boundary and inter-grain vacancy clusters resulting in a obvious drop of plasticity, over-aging will induce much more interconnected grain-boundary carbide and  will coarse in a size of more than 70nm. As a result, hydrogen will enter the grain boundary and - interface with dislocation, which leads to the dramatic drop of plasticity.

Based on the distribution of stored energy in hot deformed austenite simulated by a crystal plasticity finite element method (CPFEM), the static recrystallization of a low carbon steel was investigated by a 2D cellular automaton (CA) model on mesoscale. The effect of the inhomogeneous distribution of the stored energy on the static recrystallization was simulated, which was difficult for the traditional recrystallization CA models. The simulated results revealed that the density of recrystallization nucleation varied in different sites due to the inhomogeneous distribution of stored energy, and the nuclei concentrated both at the grain boundary and in the heavily deformed grain interiors. The number of recrystallized nuclei increased and the distribution of the nucleation inclined to homogeneity with the decreased critical stored energy for nucleation. In addition, the recrystallization kinetics under various nucleation criteria was discussed in the present paper.

The effect of long-term aging on the γ’ characteristics and the mechanical properties have been investigated in a corrosion resistant nickel-base superalloy K44 aged isothermally in the temperature range of 800-900℃ up to 10000 h. SEM observation reveals that the coarsening kinetics of γ’ follows Lifshitz-Slyozof-Wagner (LSW) theory at different temperatures, with the activation energy of 255 kJ/mol for growth. Morphological instability occurs in relatively small γ’ precipitates during aging process. At room temperature (RT) and 900℃, yield strength decreases with aging temperature and aging time increasing, while fluctuation of elongation is observed. The dependence of the yield stress on particle size is explained by Labusch-Schwarz hardening theory rather than classical strengthening theory on coherency and mismatch strengthening. Shearing of strong-coupled dislocations is dominant strengthening mechanism.

The heat resistance of Mg alloys can be improved by adding rare earth and alkaline earth elements into Mg-Al alloys. Based on the binary phase diagrams of Al-Sr and Al-Nd、Miedema model and Toop model, the thermodynamic calculation model for predicting the precipitation behavior of the Al-Sr and Al-Nd intermetallic compounds in a ternary alloy system was deduced. The temperature of precipitating Al-Sr intermetalic compound in the Mg-8Al-3.5Sr ternary system was calculated by using this model. The calculated results are in good agreement with the references, indicating this calculated model is feasible. The lowest content of X (X=Nd、Sr), making the Al-X intermetallic compounds precipitate prior to α-Mg in the Mg-9Al-X and Mg-6Al-X (X=Nd、Sr), was calculated based on this model. According to the calculated results, the precipitation behaviors of the Al2Sr and Al11Nd3 intermetallic compounds were analyzed and the effects of these compounds to the properties of Mg alloys were discussed. A new method to prepare the heat resistance of Mg alloys by adding Nd and Sr was proposed.

Cr-Al(Cr)2O3 cermets with relative density of about 90% have been successfully produced by thermo-explosive combustion synthesis and pressure on the melt. Cr particles are well-distributed in ceramic plates or boundary between ceramic plates. The size of Cr particles is as small as 200nm. The tribological properties of the cermets were investigated. The results show that the cermets have good wear resistance property under dry sliding. The wear volume of samples is related to addition amount of diluents Al2O3 and excessive Cr2O3. Through rational balance of them, the wear volume of Cr-Al(Cr)2O3 is lower than that of powder sintered alumina ceramic. The main wear mechanism of the cermets is the peeling off under dry sliding. After oil lubrication, there is little wear volume loss in the sample under loading of 147N and 6000m sliding distance. The wear volume of the cermet is increased with loading, but is smaller a order of magnitude than that of Cr12MoV steel.

Co0.2Zn0.2Mn0.6Fe2O4 nanoparticles were prepared through the pyrolysis of polyacrylate salt precursors prepared via in situ polymerization of the metal salts and acrylate acid. The pyrolysis behavior of the polymeric precursors was studied by use of thermal analysis. The structural characteristics of the as-calcined products was analyzed by powder X-ray diffraction (XRD), transmission electron microscope (TEM) and electron diffraction (ED) pattern. The results revealed that the spinel ferrites had nanosized morphology and good crystallinity. Magnetic properties of the samples at room temperature were measured using a vibrating sample magnetometer (VSM), showing that the sample exhibited characteristics of weak ferromagnetism.

ABSTRACT In this paper, the method using Solid Oxygen-Ion Membrane (SOM) to produce tantalum from tantalum oxide was investigated. Experiment was carried out at 1150℃ and 3.2V of DC electrolysis potential in the flux system of 55.5wt.%CaF2- 44.5wt.%MgF2. Sintered Ta2O5 solid and liquid copper saturated with carbon loaded in zirconia tube were used as the cathode and the anode, respectively. The results of scanning electron microscopy (SEM) with an energy dispersive X-ray spectrometer (EDX) indicated that the amount of oxygen in tantalum oxide decreased obviously even approached to the zero level and tantalum was produced.

Aluminium doped zinc oxide polycrystalline thin films (AZO) were prepared on microscope glass substrates by sol-gel dip-coating process. Zinc acetate solutions of 0.5 M in isopropanol stabilized by diethanolamine and doped with a concentrated solution of aluminium nitrate in ethanol were used. The quantity of aluminium in the sol was varied from 1 to 3 at. %, and the deposition times was varied from 5 to 15. Crystalline ZnO thin films were obtained following an annealing process at temperatures between 300℃ and 500℃ for 1 h. The coatings have been characterized by X-ray diffraction (XRD), optical spectroscopy (UV-Vis), scanning electron microscope (SEM), and electrical resistance measurement. With the annealing temperature increased from 300℃ to 500℃, the film was oriented more preferentially along the (0 0 2) direction, the grain size of the film increased, the transmittance also became higher and the electrical resistivity decreased. The X-ray diffraction analysis revealed single-phase ZnO hexagonal zincite structure. Optical transmittance over 90% in the near UV and VIS regions and electrical resistivity as low as 3.2×10-3 Ω·cm were obtained under such conditions, doping concentration 1 at. %, annealing temperature 500℃, deposition times 10.

Nano-crystalline Ce1-xNdxO2-x/2 (0≤x≤0.6) powders were prepared by low temperature combustion process with citrate acid-nitrate system. The influences of the Nd3+ doping constant on the powders phase structure, morphology and particle size were studied. TG/DSC curves and XRD patterns show that a slightly fuel-deficient ratio resulted in smaller particle size. XRD results indicate that the as-prepared powders were single fluorite structure with crystalline size ranging from 15 to 24 nm. The lattice constant increases with the increase of the doping constant x. TEM micrograph shows that the particles size ranges from 30 to 40nm. The broader Raman band at 580cm-1 is attributed to the presence of oxygen vacancies, which increase with the increase of the doping constant. The XRF shows that the actual doping density is close to the original chemical composition ratio

In order to investigate the effect of surface treatment on fatigue behavior of high strength steel in ultra long life regime, cantilever-type rotating-bending fatigue tests were performed in laboratory air at room temperature using hour-glass-shaped specimens of high carbon-chromium bearing steel, JIS SUJ2, with three kinds of surface treatment, which can induce residual stress and hardening in the specimen surface layer. Surface treatments included superoll processing, fine-particle and conventional particle shot-peening. The results obtained are summarized as follows: (1) After surface treatment, fatigue crack initiation site in high cycle region transfers from subsurface in a ground specimen to interior of the specimen, where compressive residual and hardened layer vanish. The largest transference is attributed to the superoll processing specimen, followed by the conventional particle shot-peening one and the smallest is fine-particle shot-peening one. (2) After sur-face treatment, stress gradient of bending fatigue and tensile residual stress exist at fatigue crack initiation site, and affect the fatigue strength of nominal stress amplitude. Fatigue strength of the superoll processing speci-men is improved due to the deeper stress gradient of bending fatigue as compared with the ground specimen. However, that of the shot-peening specimen is not improved. (3) Fatigue strength of high strength steel in ultra long life regime under rotating-bending can be improved by surface treatment which must induce smaller ten-sile residual stress and deeper compression residual stress distribution in surface layer of the material.

In this paper, the hydrogen induced cracking (HIC) of X70 pipeline steel was studied in different concentrations of H2SO4 solution by means of electrochemical charging. Larger current densities, longer charging time and lower pH values of solution would promote the entry of hydrogen into X70 steel. Non-metallic inclusions such as nitrides and oxides play different roles in HIC of X70 steel. Microscopic observation shows that there is no dependency relation between cracks induced by hydrogen and the inclusions of titanium nitrides. Otherwise, oxides of magnesium aluminum and calcium etc are more harmful as the sources of hydrogen induced cracks. According to the results of hydrogen permeation test, the effective diffusivity (Deff) of hydrogen at room temperature is 3.34×10-9cm2/s. Tensile specimens of X70 steel and welds shows severe plasticity loss after hydrogen charging. The plasticity of welds is not as good as X70 base metal.

The corrosion performance of LY12 aluminum alloys/passivation film/epoxy coatings was characterized by electrochemical impedance spectroscopy (EIS) in NaCl solution. The results showed that with the increasing of immersion time, the impedances of composite electrodes continuously increased. In the beginning of immersion, the diffusion impedance emerged in the impedance spectroscopy of composite electrode, which was considered to result from the mass transport behavior of solving products of passivation film prepared on metal substrates. The observation of scanning electron microscope (SEM) suggested that the chromate conversion film presented the obvious crack morphology on metal substrates, which was favour for solving chromate to penetrate through the film and passivate the metal substrate surface. This may be the possible reason of the continuous increasing of impedance of composite electrodes.

Electrochemical studies were performed in aerated brine solution by electrochemical polarization measures and electrochemical impedance spectroscopy(EIS) measures. Experimental results revealed that stearamide derivative inhibitor acted as a good inhibitor for mild steel in aerated brine solution. The recorded electrochemical data showed that the corrosion resistance was greatly enhanced in the presence of stearamide derivative inhibitor. Polarization curves revealed that the inhibitor tested was an anodic type inhibitor and the inhibition efficiency increased with increasing concentrations to reach maximum at 0.5gL-1. Equivalent circuit of the investigated system was suggested.

Gas-atomized Ni53Nb20Ti10Zr8Co6Cu3 (at.%) amorphous powders with particles sizes of below 25 μm were used for kinetic metallization (KM) to deposit coatings with thickness of ~500 μm. It was indicated that fully amorphous metallic coatings were successfully obtained. The porosities of the deposited coatings decreased with increasing spray temperature and deposition efficiency. The corrosion property of the coatings was evaluated by potentiodynamic polarization in 1 kmol/m3 HCl aqueous solution. The coating keeps the same good corrosion resistance as its amorphous alloy at a lower porosity.

A new model and a numerical method are developed to solve the electromagnetic force field produced by the rotating magnetic field in electromagnetic stirring of processing. The model equations are transformed using the characteristics of rotating magnetic field, and the boundary renewal method is applied to boundary conditions. Using the present model, the electromagnetic force fields in different size billets considering the effect of iron core are computed. The three – dimensional distribution of electromagnetic forces are obtained in detail under the condition of variable parameters. The numerical results agree well with the experimental measurement.

The solidification structures of cast Fe-B-C alloy containing more than 2.0%B and lower than 0.2%C and the structures and properties of alloy after heat treatment were researched by means of optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD), hardness measurements, impact tester and pin abrasion tester. The results show that the solidification structures of cast Fe-B-C alloy are made up of boride (Fe2B), pearlite and ferrite, and boride distributes along grain boundary in network form. After normalizing at 950oC, the part broken network of boride of cast Fe-B-C alloy appears, the matrix all transforms into lath martensite. The hardness of cast Fe-B-C alloy increases obviously and nears to60HRC, its impact toughness and dynamic fracture toughness excel 10J/cm2 and 30MPa.m1/2 respectively. In the condition of dry skimming wear, cast Fe-B-C alloy has excellent abrasion resistance. Its abrasion resistance is more excellent than that of Ni-hard white cast iron, GCr15 and Cr12MoV, nears to that of high chromium white cast iron. Cast Fe-B-C alloy has simple melting process and good casting property, there are no costly nickel and molybdenum elements and low production cost.

The effect of applied strains field on the microstructure produced during α2 phase to O-phase (orthorhombic phase) transformation in Ti-25Al-10Nb (at. %) alloy is studied by computer simulation using a phase field model. It is shown that not only the applied strain magnitude but also the applied strain direction affects the microstructure significantly. The effect of strain direction on the volume fraction of O-phase is up to 24% but strain magnitude up to 60%. The fully lamellar microstructure can be formed in Ti-25Al-10Nb alloy when the strain is loaded along <11-20> of α2 phase with magnitude greater than a half of the stress-free transformation strain.

The structure and electronic properties of IVB and VB transition metal carbides and their surfaces are systematically investigated by first-principles method. The some important questions are studied and discussed, such as, the common characteristics and distinctions of the surface ripples on the (001) surfaces of different IVB and VB transition metal carbides, the effects of the surface ripple on the surface energy and the surficial charge distribution, the trends of the cohesive energy and surface energy of these IVB and VB transition metal carbides and their surfaces, and the correlation between the surface energy and the cohesive energy which is the inherent property of the bulk. A new viewpoint is suggested that the cohesive energy of the bulk carbides and the ripple ratio of the (001) surface affect and determine the surface energy of (001) surface of IVB and VB transition metal carbides together.