Creep deformation of WC hardmetals with iron-based binders

TL;DR

This study investigates the creep behavior of WC-FeCr hardmetals, revealing a new low-stress creep regime and suggesting FeCr as a potential cobalt substitute in hardmetals below 1000°C.

Contribution

The paper identifies a previously unreported low-stress creep regime in WC-FeCr and analyzes its mechanisms, proposing FeCr as a cost-effective and less toxic alternative to cobalt in hardmetals.

Findings

Three creep regimes identified: power law, grain boundary sliding, and viscous flow.

WC-FeCr shows better creep resistance than WC-Co below 1000°C.

Creep resistance decreases above 1140°C due to eutectic formation.

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 {\deg}C. Particular attention is paid to the steady-state creep rates and stress-exponents (n) during isostress treatments. Three regimes of stress dependence are observed. Two of these were previously reported for WC-Co: power law creep (n~3) at medium stresses; and grain boundary sliding (n~1) at higher stresses, generally >100MPa. A previously unreported low stress (<10MPa) regime 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 {\deg}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 {\deg}C), its creep resistance becomes inferior. These results indicate FeCr may be a suitable replacement for Co provided the eutectic temperature is not exceeded.