Effect Of Gas Pressure On The Morphology Of Pore - Like Porosity

Metal-Gas eutectic solidification (also known as Gasar) is considered as a revolutionary technology of fabricating porous metals. Because that it can control the porosity, average pore diameter and the arrangement direction of porous structure easily. The gas pores of the porous materials fabricated by Gasar process grow along the solidification direction. Owing to this pore structure, gasar metals have more special mechanical and physical properties than the traditional porous metal materials. The special structure and properties herald potential and broad application prospects of lotus-type porous metal.In this paper, by use of the develoded’Gasar’apparatus, lotus-type porous silver samples had been fabricated in hydrogen/oxygen and argon or pure oxygen atmosphere. At the same time, the influence of the different gas pressure on the porosity, average pore diameter and the distribution of the lotus-type porous Ag were studied.The results showed that, in hydrogen and argon atmosphere, the porosity decreased with increasing pressure of hydrogen. However, the porosities of samples were all less than 10%. In others words, it was difficult to fabricate lotus-type porous Ag by hydrogen gas.It was found that, the oxygen and argon pressure had a significant influence on porosity of porous Ag. The porosity increased after decreased first with the increasing of the oxygen pressure PO2 when the PAr was constant; The porosity decreased with increasing pressure of argon pressure PAr when the PO2 was constant; When a pure oxygen was used as the atmosphere, the porosity increased with increasing of the oxygen pressure PO2.The size of the pores also had close relations with the gas pressure. For the lotus-type porous Ag obtained under pure oxygen atmosphere, the average diameter of the pores decreased with the increasing of the oxygen pressure Pot.According to the conduction of heat balance equation, we calculated the solidification rate of base metal Ag. At the same time, the solidification rate of base metal Ag and Cu and Mg had been compared and concluded that, VAg=10vCu; vAg=30vMg.According to the thermodynamics analysis of diffusion and mass transfer theory, the average diffusion rate of gas atmos at the forefront of solid-liquid interface had been deduced,The solidification rate v0 and gas diffusion rate v were represented in the Gasar solidification. Through analysing the Gasar solidification rate and gas diffusion rate in the process of solidification, the forming condition of the lotus-type porous structure had been obtained:when the solidification rate of metal matrix v≥the gas diffusion rate v, then the lotus-type porous structure can be formed.