Study of recarburised eta-phase by transmission electron microscopy

On resintering, eta-phase changes chemically to Co and WC sometimes retaining a rosette-like appearance. Large Co contents remaining localised, consist of an allotropic mixture of Co and, at times of Co/sub 7/W/sub 6/, indicating a residual C-deficiency. Neighbouring small lakes of f.c.c. Co are C-sufficient. It is postulated that C-deficient regions attract Co which flows until eta-phase has formed and remains trapped until a C balance is restored. Carbide grain growth occurring in enlarged Co lakes is ascribed to the recrystallisation of W from solution during recarburisation of eta-phase