Materials Science Forum Vols. 697-698

Abstract: In this paper, the microstructure and microhardness of laser shock processed (LSP) Ti-6Al-2.5Mo-1.5Cr-0.5Fe-0.3Si titanium alloy with and without annealing were examined and compared. The titanium alloy samples were LSP processed with 3 layers at 4.24GW/cm². Some of the samples were vacuum annealed at 623K for 10 hours. The microscopic structure with and without annealing were tested and analyzed by SEM, TEM. The results indicated that after LSP, the shock wave provided high strain rate deformation and led to the formation of ultra-fine grain. Comparing with the samples without annealing, the dislocation density was lower and the grain-boundary was more distinct in the annealed samples, but the sizes of the ultra-fine grain didn’t grow bigger after annealing. On the other hand, the microhardness measurement was made on the cross-section. It is obviously that the laser shock processing improved the microhardness of the Ti-6Al-2.5Mo-1.5Cr-0.5Fe-0.3Si for about 12.2% at the surface, and the hardness affected depth is about 500 microns. The microhardness after annealing is 10 HV_0.5 lower, but the affected depth is not changed. The titanium alloy after LSP is thermostable at 623K; thus break the USA standard AMS2546, in which titanium parts after LSP are subjected in subsequent processing should not exceed 589K.

Abstract: Through design of balancing movement controller of large size workpiece for applying to LDMC-100 type ion nitriding furnace, the structure and principle of mechanism were introduced, the balance of mechanical transmission and influencing to nitriding layer of workpiece surface were analysed. In this mechanism, the planetary gear system was adopted, the single axis was adopted in this supporting mechanism, and the electric and insulating on workpieces were used. The balancing influencing of movement and techniques parameters for nitriding layer were discussed. The results indicate, the nitriding period is related with input speed and number of driven gear teeth. The re-nitriding rate and blank nitriding rate are related with gear modulus, workpiece outside diameter, number of drive and driven gear teeth. When the mechanism structure parameter is fixed, the effect of nitriding was completed by changing speed of input axis.

Abstract: For bio-electrodes implanted in deep brain, electrode materials will affect the fibrous encapsulation formed on the interface of bio-electrodes and brain tissue which would reduce the operating effect of the bio-electrodes. To reduce or eliminate the fibrous encapsulation layer, N₂/H₂ plasma treatment process is used to modify the polyurethane which is the most materials of the bio-electrode. The amino groups are produced on the polyurethane surface. After these amino groups have a polymerization reaction with the polypeptide molecule, a layer of the polypeptide molecule is formed on the polyurethane surface of the bio-electrode. These modified bio-electrodes are implanted in the deep brain of the rats for two weeks to observe the immune response and the morphology of the cells on the interface of the bio-electrodes. The results of the experiments indicate that the polypeptide molecules on the polyurethane can improve the immune response of the cells and affect the growth of the fibrous encapsulation on the interface of the bio-electrodes.

Abstract: The substrate temperature has great influence on the growth rate and quality of diamond films by hot filament chemical vapor deposition (HFCVD). In order to deposit polycrystalline diamond films of uniform thickness over large areas and improve the growth rate of diamond films, the substrate temperature uniformity need to be further improved. Thus three-dimensional finite volume simulation has been developed to predict substrate temperature distribution, and optimize the deposition parameters like the size and arrangement of filaments which have a profound effect on the substrate temperature. Based on the simulation results, the optimum parameters of diamond deposition are found. Subsequently, experiments of depositing diamond films on silicon (100) wafers are done when the deposition parameters are fixed at optimum values gained from the simulation results. According to the results of scanning electron microscopy (SEM) and Raman spectroscopy, the thickness and quality of diamond films are homogeneous, which validate that the simulated deposition parameters are conducive to fabricate the high quality diamond films.

Abstract: In this investigation, conventional microcrystalline diamond (MCD) and boron doped diamond (BDD) films are deposited onto commercially available cemented tungsten carbide (WC-Co) Ball-nose endmills by using hot filament chemical vapour deposition (HFCVD). The quality and properties of the as-deposited diamond film are characterized by field emission scanning electron microscope (FESEM) and Raman spectroscopy. Milling tests of graphite materials using MCD, BDD coated and uncoated tool are carried out. Experiment results reveal that BDD films possess higher adhesive strength to the substrate than that of MCD films, and the BDD coated mills allow to be given smaller flank wear and longer tool life, when compared with MCD coated and uncoated WC-Co tools. Cutting performances of WC-Co mills in graphite milling are greatly improved by BDD coating, and typically more than 10 times the tool life is obtained. The research results are of great significance for high efficiency and quality machining of graphite materials.

Abstract: Thin diamond films are deposited on commercial tungsten carbide micro ball end mill by using hot filament chemical vapour deposition (HFCVD) technique. Raman spectrum results confirm the high purity of sp³-carbon bond diamond of as-deposited films. The scanning electron microscope (SEM) investigation exhibits continuous fine grained diamond films are uniformly deposited on micro ball end mill. Milling of graphite is chosen to check the cutting performance of fabricated diamond coated micro ball end mill. For the sake of comparison, milling test is also carried out using uncoated micro ball end mill under the same cutting parameters. The milling test results show that the tool life of diamond coated micro ball end mill is about 10 times than that of uncoated one, which may attribute to high hardness, wear resistance, low sticking to graphite of deposited diamond films and strong adhesive strength between them and substrate surfaces.

Abstract: In this paper, the microstructure and microhardness of Ti-6.5Al-3.5Mo-1.5Zr-0.3Si titanium alloy with and without laser shock peening (LSP) were examined and compared. The titanium alloy samples were treated with different layers, at the same power density. X-ray diffraction (XRD), Transmission Electron Microscope (TEM) and microhardness techniques were used to analyse microstructure and mechanical. X-ray diffraction analysis shows that there was not any phase transformation and no new crystalline phases have been formed. TEM studies demonstrate that both α and β phase can been refined in the surface layer with LSP. The microhardness measurements with LSP demonstrate that Hardness of crystallization surface is high up to 418MPa, which is more than the sample without LSP, the shock wave improved the microhardness for about 8%, and the affected depth is about 400 microns from the surface.

Abstract: This study applies the finite element method (FEM) in conjunction with an abductive network to predict the surface parameters for strain hardening material of asperity flattening in metal forming process. To verify the prediction of FEM simulation for surface parameters, the experimental data are compared with the results of current simulation. Contact area ratio, surface roughness, skewness and kurtosis are investigated for different process and material parameters, such as normal pressure, bulk strain rate, yielding stress, strength coefficient and strain hardening exponent of surface asperity flattening in metal forming, by finite element analysis. The abductive network is then utilized to synthesize the data sets obtained from numerical simulations, and the prediction model is established for predicting surface parameters. The predicted results of the surface parameters from the prediction model are in good agreement with the results obtained from the FEM simulation.

Abstract: Based on the characteristics of raw materials in EAF-TSCR, the composition of VN micro-alloyed was designed, the processes of the steelmaking, continuous casting, soaking, rolling, cooling were controlled, and at last the VN Micro-alloying high strength steel with ultra-fine grain was developed. The ferrite grain size of the steel reaches 3.0 to 4.0 microns, and the yield strength of which reaches 550MPa. Besides, the steel processes good toughness, cold formability and weldability. In the end, the strengthening mechanism of the ultra-fine steel was discussed.

Abstract: The Al-40Si alloy was modified by 0.5 wt% Sr addition and heat treated using the solution treatment and aging treatment. Its deforming capacity and hardness variance were investigated. The microstructures of the deformed samples were analyzed using optical microscope. The results show that the hardness increases with increasing of the deformation degree. When the deformation ratio exceeds 10.1 %, the hardness sharply increases. When the deformation ratio exceeds 20.4 %, the hardness maintains almost unchanged. In addition, although the cracks are not observed on the surface when the deformation ratio is less than 14.6 %, the primary Si phase is cracked. Thus the critical deformation ratio of the studied Al-40Si alloy is 10.1 %.