W-Re-HfC合金的超高温蠕变性能与失效机制

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

摘要:

研究了W-4Re-0.27HfC（wt%）合金在1800、1900、2000 ℃下的蠕变性能，结合扫描电子显微镜（SEM）、背向散射电子衍射（EBSD）、第一性原理计算（DFT）等方法，分析了蠕变后W-4Re-0.27HfC合金的晶粒尺寸、晶粒类型、位错密度、断口形貌等，讨论了W-4Re-0.27HfC合金蠕变失效的机制。结果表明，蠕变温度为1800、1900、2000 ℃时，稳态蠕变速率分别为9.8×10^-6、1.0×10^-5、2.1×10^-5 s^-1。随着蠕变温度的升高，小角度晶界占比下降而大角度晶界占比增高，平均晶粒尺寸增加。蠕变过程中晶粒发生塑性变形，大角度晶界在塑性变形阶段变形相容性差，促进形成孔洞，加速蠕变失效。蠕变过程中第二相粒子HfC氧化严重，DFT计算结果表明HfC氧化后与基体间的界面结合能将从–11.221 J/m²降低至–3.935 J/m²，降低第二相的强化作用。

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.