Materials Science Forum Vols. 675-677

Abstract: Selective laser melting (SLMing) is a new advanced material processing technology which is used in fabricating parts with complex shape. Hot isostatic pressing (HIPing) is a manufacture technology which forms parts by imposing high heat and pressure on metal powders or semi-manufactured parts. Considering the advantages of both the technologies, they can be combined to produce higher-quality parts free from the limitation of the shape of parts. AISI316L stainless steel is widely used in manufacturing varies of complex metal parts. In this research, three AISI316L stainless steel samples with different relative densities were acquired by controlling the fabricating parameters in SLM. The SEM and optical microscopy analysis were employed to characterize the relative density, microstructure, deformation by comparing the differences between SLM samples and SLM-HIPped samples. In addition, the influence of HIP process on microstructures of samples in different laser fabricating parameters was investigated by analyzing the mechanisms of SLM and HIP. The results show that HIP can close vacuum crack and pore, consequently, the relative density of SLM samples increases after HIP, making the property of the samples improved and microstructure better-distributed. Moreover, the increment of relative density under the same HIP condition is also discussed.

Abstract: Low frequency electromagnetic (LFE) field was applied during the conventional hot-top casting process. Thermocouples were used to measure the cooling curves from the border to the center of the ingot during steady-state of casting process, cooling curves were obtained, and effects of low frequency electromagnetic field on the solidification, macrostructure during the conventional hot-top casting for 6063 aluminum alloy process were analyzed. The experimental results show that the forced convection caused by the low frequency electromagnetic (LFE) filed can make the melt temperature uniform, promote the evacuation of superheat, make the temperature in the liquid pool lower than the liquidus temperature of 6063 aluminum alloy, increase the number of floating nuclei, make the ingot with fine and homogeneous macrostructure, though there is no addition of any grain refiners.

Abstract: In this paper, one thin microwave absorbing sheet employing carbonyl-iron powder (CIP) and chlorinated polyethylene (CPE) was prepared. The pattern and static magnetic properties of CIP were characterized by scanning electron microscope (SEM) and vibrating sample magnetometer (VSM), respectively. The electromagnetic parameters and loss mechanisms of CIP were measured and discussed. The microwave absorption properties of composite sheets with different thicknesses and CIP ratios in matrix were investigated by measuring reflection loss (RL) in 2-18GHz. The results showed that the microwave absorption properties could be optimized by controlling CIP content and thickness of sheet. For the sample with the weight ratio (CIP:CPE) of 10:1 and 1mm thickness, the absorption bandwidth (RL below -4dB) achieved 14GHz (4-18GHz).

Abstract: A computational analysis is achieved during laser deep penetration welding. Multiple reflection and absorption are implemented simultaneously with the ray tracing technique in the keyhole. With all the governing equations including continuity, momentum and energy equation, the VOF method is adopted to trace the free surface of the molten pool. Temperature field is achieved by numerical simulation. The laser keyhole welding experiments on 304 stainless steel sheet showed that the computational results agree well with experimental results.

Abstract: In this paper, the coating of Fluoridated hydroxyapatite / Carbon nanotubes (HAF/CNTs) was generated upon titanium substrate coated by the means of radio frequency magnetron sputtering (RF-MS). The coating’s microstructure of interface and surface, phase constitution, as well as elemental composition were charactered by scanning electron microscope (SEM) and energy dispersive spectrum (EDS), whereas the cohesiveness of samples was measured by scratching adhesive tester (WS-2005). The results indicated that the surface was rough and porous and CNTs were uniformly distributed. Furthermore, line scanning of EDS showed that layer about 5μm in the coating interface, elements of titanium, calcium, phosphorus and oxygen diffused with one another, which demonstrated that the composite coating and titanium substrate were combined tightly. The bonding strength of HAF/CNTs/Ti composite coating composites was 83.1MPa, which indicated significant improvement compared with 71.40MPa of non-CNTs ones. It also proved that RF magnetron sputtering technique could provide remarkably high bonding strength for the coating/substrate composites.

Abstract: In this paper, removal of iron from metallurgical grade silicon with pressure leaching is carried out. We investigated the factors such as the concentration of hydrochloric, particle size of raw material ground, temperature, pressure and reaction time, which influenced on the removal of iron. The results show that the optimum operating conditions for pressure leaching in hydrochloride are: acid concentration 4 mol/L, diameter for raw material less than 50 μm, leaching temperature 160 0C，leaching pressure 2.0 MPa, leaching time 2.0 h. The content of iron residual in MG-Si powder was reduced to about 200 ppmw. The removal efficiency of iron is up to 90.90 %.

Abstract: The effects of Li2CO3 on melting temperature, viscosity, fluidity, surface tension and Al2O3 inclusion adsorption of mould flux for high speed continuous casting were studied. The results showed that with the increase of Li2CO3 content, melting temperature, viscosity and viscous activation energy of mould flux decreased obviously, fluidity increased, surface tension changed little, and Al2O3 inclusion adsorption of mould flux increased. In order to play an effective role, the Li2CO3 content should be less than 4 per cent. The results will play a guiding role in designing of mould flux for high speed continuous casting.

Abstract: In this paper, the View Cast software was used in the optimization of cast-steel rear axle production. The simulation results were adopted in the design of the gating system (including the dimensions of the gating system, the number of the risers and its dimensions) and the iron chills. Practical trial-manufacturing, compared with the numerical simulation, has shown that the new design had effectively eliminated the defect and improved the cast.

Abstract: A three-dimensional finite element model of hydro-drawing parabola workpieces was built in this study. By finite element analysis, the deformation was obtained. Based on simulation, the changing trends of stress and strain were obtained. In addition, thinning and FLD were studied. These results might provide useful reference on design improvement of the hydro-drawing process.

Abstract: Starting from the requirement that the principle of determinism be satisfied, two constitutive inequalities are derived for one-dimensional strain- and stress-based continuum damage models. The one-dimensional constitutive inequality corresponding to the strain-based formulation turns out to be much less restrictive than the one associated to the stress-based formulation and is extended to the three-dimensional case. This extension gives a general constitutive inequality for the damage of elastic-brittle materials.