Ultra-High Temperature Creep Properties and Failure Mechanism of W-Re-HfC Alloy

Abstract:

The creep properties of W-4Re-0.27HfC (wt%) alloy at temperatures of 1800, 1900, and 2000 ℃ was investigated by SEM, EBSD, and density functional theory (DFT). The grain size, grain type, dislocation density, fracture morphology, and the mechanism of creep failure of W-4Re-0.27HfC alloy ware analyzed after creep at different temperatures. The results indicate that the steady-state creep rates at creep temperatures of 1800, 1900 and 2000 °C are 9.8×10^-6, 1.0×10^-5, and 2.1×10^-5 s^-1, respectively. With the increase in creep temperature, the proportion of low-angle grain boundaries decreases while the proportion of high-angle grain boundaries increases, resulting in the increase in average grain size. During the creep process, grain undergoes plastic deformation, forming numerous ductile dimples. The poor deformation compatibility of high-angle grain boundaries leads to the formation of voids, accelerating creep failure. EDS results illustrate that the HfC particles in W-4Re-0.27HfC alloy are oxidized severely. DFT calculations show that the interface binding energy between HfC and matrix decreases from –11.221 J/m² to –3.935 J/m² after HfC oxidation, reducing the strengthening effect of the second phase.