Creep deformation of WC hardmetals with iron-based binders

Abstract

Iron is a candidate to replace cobalt in WC hardmetals, due to its lower cost and toxicity. A WC-FeCr hardmetal was compression tested at 900-1200 °C. Particular attention is paid to the steady-state creep rates and stress-exponents (n) during isostress treatments. Three regimes of n are observed. Two of these were previously reported for WC-Co: power law creep (n»3) at stresses below ~100MPa; and grain boundary sliding (n»1) at higher stresses. A previously unreported regime at very low stresses (<10MPa), with an exponent of n»2, is also observed. By combining electron microscopy with X-ray diffraction texture measurements, the low stress regime is attributed to viscous flow of the binder, which is accommodated by diffusional creep in the WC skeleton. The mechanism may be applicable to other hardmetals. Compared to analogous WC-Co materials, WC-FeCr shows improved creep resistance below 1000 °C, which can be explained by its lower self-diffusivity, and a lower solubility for WC than Co. However, at temperatures corresponding to liquid eutectic formation (~1140 °C), its creep resistance becomes inferior. These results indicate FeCr may be a suitable replacement for Co provided the eutectic temperature is not exceeded.