Forming Mechanism And Experimental Investigation Of Porous Metallic Material Prepared By Laser Sintering

Rapid Laser Sintering Manufacturing (RLSM), due to its flexibility in feedstock and shapes, exhibit a great potential for developing novel porous metallic material. However, laser sintering technology is still in its early stage of development. Significant further research and understanding are required in the aspect of basic theories producing porous metals in forming of gas pore and porous microstructure, and during the process of laser rapid solidification, the effect of temperature gradient, velocity of solidification on the microstructure involved in laser sintering. In this paper, by combining theoretical analysis, numerical simulation and experimental study, foaming mechanism of gas pore were analyzed thoroughly, and the basic theory which can control the technique of porous metallic material were achieved.Detailed the mechanism of nucleation and growth pattern of gas pore for rapid direction solidification in laser sintering, the thermodynamics and kinetic conditions of heterogeneous nucleation were achieved. Analyzed the forming mode of pore, introduced the gas separate from the melting metal and the surface of solidification, but only the gas came from the surface of solidification could grow with the solid and form into lotus-type porous.The research on the direction and velocity of the growth of gas pore in the sintering pool were studied. The effect of parameters on the growth of pore and the relationship between parameters and the microstructure were obtained. So, we can control the microstructure by changing the parameters which has the deeply effect on the growth of gas pore.The theoretical modes for calculating porosity and inter-pore spacing were established. A comparation between the obtained experimental data and the reuslts calculated using the present theoretical models was perfored, showing a good agreement.The microhardness of porous stainless steel samples were measured and qualitative the effect of laser parameters on it. The compressibility of porous stainless steel was stuied, by analyzing the deformation mechanism, a formula of stress-stain curve was established. The tensile strength was measured, through the application to the relative theoretical model, with the obtained experimental data, found out the formula which fit the relation between tensile strength and porosity of porous stainless steel.