THERMOCHEMICAL ASPECTS OF MULTIPHASE DIFFUSION DURING BRAZING OF HARDMETAL

During brazing of WC cemented carbide parts (hard metal) on steel usin g pure copper as a braze material an intermetallic compound is formed at the hard metal/braze interface whereas pores are generated in the b order zone of the hard metal. As a result, the tensile strength of the joint is greatly reduced with fracture occurring preferentially in th e border area of the hard metal. The calculation of the molar Gibbs en ergies of the different phases and of some of the element chemical pot entials, as well as the experimental determination of some potential g radients, are used to explain the different processes (phase formation and multiphase diffusion) taking place during brazing. An explanation for the formation of pores is proposed.