Precipitation of an ordered intermetallic phase in WC-10% Ni

Abstract

The cause of the variability of the intensity of magnetization of the nickel binder phase in cemented carbides was sought by electron diffraction and dark-field microscopy studies of fractured specimens, one of which was partially magnetic and the other almost non-magnetic. A coherent phase in the nickel binder having either a b c c or a CsCI-type structure was found on the boundaries of crack paths. A coherent non-randomly arranged CsCI-type phase was found in an epitaxial relationship with (12.0) planes of WC. The lattice parametera=0.295 nm for both coherent phases. This phase or phases occurs more frequently in non-magnetic than in magnetic nickel binders of hardmetals. When seen near WC grains the ordered phase is often accompanied by randomly arranged tungsten trioxide particles. The implication is that the ordered phase occurs more readily in carbon-deficient surroundings. The phase is postulated to be NiW because large quantities of tungsten are known to form solid solutions with nickel.