High temperature creep of WC-Co alloys

Abstract

The high temperature deformation of tungsten carbide-cobalt composites has been performed in the 1050 to 1350° C temperature range either in compression or in three point bending. The creep behaviour of these materials exhibits a sigmoidal log $$\mathop \varepsilon \limits^ \circ - log$$ σ plot with three domains of steady state creep rate possessing a different value of the stress exponent. From recent microscopical and analytical results a microstructural model of the composite is proposed. This model assumes the existence of carbide chains formed of crystals linked with coincidence grain boundaries and takes the number of coincidence grain boundaries into account. It has been used to interpret the creep results. The controlling component of the composite is the tungsten carbide and two deformation processes, grain boundary sliding and intragranular deformation, are the main mechanisms which are involved in the explanation of the creep behaviour. The results of the creep tests are discussed in correlation with transmission electron microscope (TEM) investigations on annealed then deformed samples. TEM microstructural studies of the carbide phase after deformation show an extensive intragranular deformation which has been carefully analysed. Attention has also been paid to the defect structure of grain boundaries.