Microstructure and deformation behavior of MoReW in the temperature range from 25°C to 1500°C

Abstract

Refractory alloys which retain high strength above 1000 °C and, at the same time, have excellent malleability, are in high demand for high temperature structural applications. Here we report the microstructure and mechanical properties of an equiatomic MoReW alloy, which has demanding combination of strength and ductility in the temperature range of 25 °C to 1500 °C. The alloy was prepared by arc melting followed by hot isostatic pressing at 1400 °C, 207 MPa for 5 h and it has a single-phase BCC structure with the average grain size of ∼170 μm. The alloy yield stress is relatively low (555 MPa) at 25 °C, but it has weak temperature dependence resulting in remarkably good yield stress values at high temperatures, e.g. 402 MPa at 1000 °C and 247 MPa at 1400 °C. The alloy shows strong strain hardening at 25–1000 °C, with the true flow stress tripled at 25 °C and doubled at 1000 °C after true strain of 0.4. The microstructural analysis of the deformed specimens reveals extensive deformation twinning activity at the beginning of deformation and activation of other deformation modes at later deformation stages in this temperature range. This is unusual behavior as generally activation of twinning occurs at high stresses, after extensive dislocation activity, and deformation twinning in refractory alloys has never been reported above 400 °C. To understand and explain the observed behaviors of the alloy, a detailed analysis of strengthening mechanisms associated with screw and edge dislocation glide, as well as with twin nucleation and propagation, has been conducted and reasonable qualitative models of yielding, strain hardening and ductility of the studied MoReW alloy have been proposed.