Novel reactive, liquid phase processes and the development of advanced materials

High temperature intermetallic compounds and metal-ceramic composites are difficult and costly to process using conventional casting, forming and machining routes due to their high melting temperature, high hardness and limited ductility. The fabrication of these materials through pressing and sintering of powders has the advantage of the fabrication of near net shape parts, reducing the need for forming and machining. For the specific case of reactive sintering (RS), the use of a mixture of relatively low cost pure powders, which react during sintering to form the desired compounds or composites, has the added benefits of lower processing temperatures and economic production. However RS suffers for the production of a porous, inhomogeneous finished product which has limited the commercial application of this technology. Our recent studies on RS of NiTi shape memory alloy (SMA) has revealed that low sintered densities result from the development of a poorly distributed liquid phase which becomes isolated into discontinuous "pockets". In this proposal, novel reactive liquid phase (RLP) processing will be developed with the aim of achieving high densities and increased homogeneity in a sintered part made from pure powders. The Ni + Ti system will serve as a test case. Cu will be added as a liquid phase sintering aid and a novel selection of Ni, Ti and Cu powder sizes will be used to create a well distributed, continuous liquid phase. This liquid will densify the mixture and accelerate the reaction between Ni and Ti to produce CuNiTi ternary SMA as the final product. This novel RLP approach will be further developed to create new CuNiTi-TiC composites through the addition of carbon powder to the original Cu, Ni, Ti mixture. The successful development of the RLP process will lead to a breakthrough in reactive sintering technology thus increasing its use in commercial applications. Economically produced, high density CuNiTi SMA and CuNiTi-TiC composites will have applications in important sectors of the Canadian economy including the automotive, tool and die and mining industries.