Impregnation of Porous P/M Bodies with Molten Alloy under High Centrifugal Force

This work explored porous metal impregnation via a high temperature centrifugation process. Impregnation was accomplished by combining a low Tm (411 K) Sn-Bi alloy and P/M-processed stainless steel or alumina matrices (normally exhibiting poor wettability by the alloy) in a capsule, followed by heating to 673 K. This capsule was subsequently set in a heat-insulating vessel and rotated in a centrifuge up to 10,000 rpm. By this process, the molten alloy was forcibly impregnated into the pores of the matrices. The minimum pore size at which the alloy penetrated the matrix was found to increase as the centrifugal force was increased. At the maximum centrifugal force, the alloy could be impregnated into pores only several microns in size. The impetus for impregnation was found to be the pressure applied to the molten alloy by the centrifugal force. The pore size that could be impregnated at a given centrifugal force (which correlated with the pressure generated) could be readily predicted using the Washburn equation.