Liquid phase sintering of metal matrix composites containing solid lubricants

Abstract

Attempts to improve the wear properties of sintered high speed steels have been made by the simultaneous addition of hard ceramic particles (TiC) or (NbC) alongside particles with solid lubricative properties such as (MnS) or (CaF 2). Preliminary investigations carried out to study any interactions between such particles and a sintered high speed steel matrix indicated that the steel matrix carbides were modified by a chemical reaction which occurred between the added ceramic particle and its high speed steel matrix; the result of which was to give a substantial improvement in hardness. The solid lubricant remained chemically unaltered by the sintering process, and tended to reduce hardness. Both types of particulate addition raised the sintering temperature needed to achieve full density due to their effect on solidus/liquidus temperatures. Studies of the sintering kinetics in such materials confirmed that densification was due to a liquid phase sintering mechanism and that solution/re-precipitation of carbide phases played a major role in the densification process. Coarsening of the solid lubricant particles into large agglomerates occured during sintering by a process of the transportation of smaller particles into pore interstices by the liquid phase.