Creep strength of a tungsten–rhenium–hafnium carbide alloy from 2200 to 2400 K

The high–temperature creep behavior of tungsten–4 wt.% rhenium-0.32 wt.% hafnium carbide (W-4Re-0.32HfC) was evaluated at temperatures ranging from 2200 to 2400 K and stresses ranging from 40 to 70 MPa in a vacuum less than 1.33×10–6 MPa (1.0×10–8 torr). The effects of temperature and stress on the steady–state creep rate were determined. The stress exponent for creep was 5.2, and the activation energy for creep was 594 kJ mol−1. The creep strength of W-4Re-0.32HfC was compared with that of pure tungsten (W) and tungsten–5 wt.% rhenium (W–5Re) at a creep rate of 10−6 s−1 as a function of temperature. The temperature-compensated creep rate of W–4Re–0.32HfC was approximately two orders of magnitude less than that of pure W and one order of magnitude less than that of W–5Re. The creep strength of W–4Re–0.32HfC was correlated with its microstructural development during the high-temperature deformation. Transmission electron microscope (TEM) study of the creep tested samples revealed that the high creep strength of this alloy resulted from finely dispersed submicron-sized HfC particles. The strengthening effect of the HfC particles could be attributed to direct and indirect particle strengthening. Direct particle strengthening was caused by the retardation of subboundary dislocation movement by direct particle/dislocation interaction. Indirect particle strengthening was caused by the formation of subgrains, which in turn reduces the distance that dislocations can move before being immobilized at subgrain or grain boundaries. The strengthening effect of HfC particles was reduced as HfC particle diameter increased.