Advanced Materials Research Vols. 154-155

Abstract: Ferrite stainless steel has been widely used in foreign automobile vent pipe. During the production of domestic automobile vent pipe, because the crystal grains of welding Joint heat-affected zone are not refined by heat treatment and become very big, forming properties of cold machining of ferrite stainless steel become bad. In order to optimize welding technology, the temperature field of laser welding joint of stainless steel automobile vent pipe is simulated. The temperature field model of laser welding joint of 409 L stainless steel pipe is built based on the pair heat source model. At the same time, the affecting factors are considered, such as thermal radiation, phase change latent heat, thermophysical properties of materials with temperature changes and the spread of convective heat in the liquid metal in the model. The temperature field in different welding parameters are simulated. The impact of process parameters on the temperature distribution is acquired. The experimental results can help works, such as accurately understanding laser welding thermal process, predictive control of welding stress and deformation, and improving cold forming quality of automobile vent pipe.

Abstract: High purity spherical nano-powder materials can be synthesized using high-frequency plasma chemical vapor deposition (HF-PCVD) by electrodeless discharge. A generalized two-dimensional mathematical model for the reactive synthesis titanium dioxide (TiO2) nanoparticles using HF-PCVD was developed based on reaction engineering theory, the model can theoretically describe the distribution of temperature and conversion of titanium tetrachloride(TiCl4) reactant in reactor. The model was proved by using experiment conditions. It was reasonable explained by simulation results of the model that why the average particle sizes of TiO2 nanoparticles product is vary in different experiment conditions, that is, at shorter residence time and a lower concentration of TiCl4 reactant, the particle sizes of TiO2 nanoparticles is smaller and more uniform distribution, but a lower conversion rate of TiCl4 reactant，vice versa.

Abstract: The crystal structure of hafnium tungstate displays unusual property of isotropic negative thermal expansion in a wide temperature range which brings about a number of important potential applications. In this work, densely packed hafnium tungstate blocks are rapid synthesized by CO2 laser. The result of XRD and Raman spectra show that the samples contain single cubic phase of α-HfW2O8 with space group P213. The SEM observations show that the sample is composed of nano-rods which grow horizontally on the surface and in the interior. The nano-threads in the interior are composed of densely packed nano-crystallites.

Abstract: Micro-arc oxidation coatings were prepared on magnesium alloy AZ91D substrates at the different applied voltages in aluminate solution. The morphologies, phase components, and corrosion resistances of the coatings were investigated. The effect of the applied voltages on the microstructure and corrosion resistance of the coatings was also discussed. The results indicate that the coatings are uniform in thickness, and mainly composed of MgAl2O4 and MgO. There were many residual discharging channels on the coatings surface. The coatings improved the corrosion resistances of magnesium alloy AZ91D considerably. With the increase of the applied voltage, the thickness and the MgAl2O4 content of the coatings increase, while no significant variation is observed in the MgO content. The coatings surface becomes lower porosity and larger pore size with increasing of the applied voltage. In addition, the corrosion resistances of the coatings on magnesium alloy AZ91D surface are obviously superior to the magnesium alloy AZ91D substrate in the 3.5 wt. % NaCl solutions, and the effect is more remarkable at higher voltage.

Abstract: The evolution of composition and corrosion resistance of PIII nitrided M50 steel with various process parameters was investigated. Besides nitrogen, the oxygen also was detected in modified layer, which came from the H2O and CO2 desorbed from chamber walls at high temperature. The results show that the content and diffusion distance of oxygen and nitrogen increase with temperature firstly; while the temperature exceeds 350 , the content and diffusion distance of oxygen and nitrogen reduce dramatically, because of the external diffusion of oxygen and nitrogen in form of NOx gas. The implantation current density is beneficial to increase the content and diffusion distance of oxygen and nitrogen. The corrosion tests show that the sample with higher oxygen and nitrogen content has better corrosion resistance.

Abstract: The microstructure and microhardness of plasma welding (PAW) joint with surfacing welded cobalt-based alloy have been investigated by using Optical microscope (OP) ,X-ray, scanning electron microscope (SEM),and microhardness testing. The results show that the surfacing layer microstructure is made up of the dendrite (γ-Co) and eutectic (γ-Co+M7C3). The microhardness decreases from surfacing layer to substrate. The highest hardness on the surfacing layer obtains with 550HV up. The fusion zone’s and substrate’s microhardness is about 380HVand 280HV respectively.

Abstract: In order to improve the surface properties of the aluminum alloy, an amorphous composite coating was prepared on the surface of the aluminum alloy substrate by electrothermal explosion spraying with fully amorphous Fe-Si-B ribbons. The microstructure, phase structure and micro-hardness of the coating were characterized by SEM, XRD and Vickers hardness tester. The results show that the composite coating is composed of amorphous phase and nanocrystal phase. The coating has dense structure and low porosity. It has not been seen rough laminar microstructure that is frequently obtained by other thermal spray techniques. The amorphous composite coatings with different thickness present higher hardness and show good mechanical properties.

Abstract: The periodic microstructures on 65Mn plate were induced by the irradiation of the femtosecond laser with the laser wavelength of 800 nm and the pulse length of 130 fs. The parallel periodic ripples structures were observed at the laser fluence of 1 J/cm2 with different pulses number( N=5,50,400,800) which lied parallel to the laser electric polarization field vector. For 400 pulses, the nano-holes arrays were generated to interrupt the consistent ripples structures.For 800 pulses, initial nano-holes evolution to the grooves, which the direction were uncertainly. Further experiments have been made to induce large area consitent ripple structures by scanning, at the laser fluence of 1 J/cm2 with speed v=500μm/s. 2D arrays were induced by accurate processing control

Abstract: During the resin flow of Resin Transfer Molding, the permeability of fiber performs is an important parameter, which reflects the interaction between the resin and fiber. In this paper the Darcy’s law was used as the fundamentals to determine the permeability of fiber performs, an experiment installation was designed, and do some experimental study on the one-dimensional permeability of resin in the multilayer fibrous plaids at a constant flow rate. The installation was designed base on condition of different flow rates and different fiber volumes (or porosity), and compared the results of the permeability of different flow rates. Then analyzed the results, and some content conclusions were obtained.

Abstract: In this study, the tensile shear strength and the fracture behavior of friction stir spot welded AZ61 joints in lap-shear configuration were investigated. The heat input was measured in FSSW to help analyze the effect of welding parameters on the strength. The tensile shear failure test was performed in a material testing system. The cross section of the joints and the fracture surface of the failed specimens were analyzed using optical microscopy and scanning electron microscopy. Results show that the weld diameter and the tensile shear load increase with increasing the input heat. The path of the material flow formed during FSSW process would provide a good way for crack propagation. All failed specimens in this study appear the same fracture features and show a circumferential failure mode under tensile shear loading conditions. The failure is initiated from a notch tip in the upper sheet loading side, and then propagates along the interface of the upper and lower sheets, then through the stir zone circumference; finally, a small portion of the lower sheet in the lower sheet loading side is torn off with some part of the stir zone.