Concurrent enhancement in mechanical properties and oxidation resistance of AlCrMoNbTi RHEAs via Cr addition

Concurrent enhancement in mechanical properties and oxidation resistance of AlCrMoNbTi refractory highentropy alloys was achieved via Cr addition. The effects of Cr content on its phase, microstructure, mechanical properties, and high-temperature oxidation resistance of AlCrxMoNbTi (x = 1, 1.2, 1.4, 1.6, 1.8, 2, 2.2) RHEAs were elucidated. After Cr addition, AlCrMoNbTi, which was originally in a BCC structure, contains both BCC and C14 phases. Consequently, the hardness increased monotonically with increasing Cr content, reaching the maximum of 781 Hv at AlCr2.2MoNbTi, 44.6% higher than AlCrMoNbTi. Cr addition also enhanced the compression yield strength and fracture strain. Those of AlCr2MoNbTi reach 2122 MPa and 7.52%, respectively, 55.1% and 37.2% higher than those of AlCrMoNbTi. The formation of the Laves phase is believed to be responsible for the enhancement in compression yield strength, while the improvement in fracture strain is mainly due to grain boundary strengthening. Notably, the specific yield strength of AlCr2MoNbTi reached 322 MPa cm3 g(-1), which is superior to that of lighterweight RHEAs. In addition, Cr addition promoted the isothermal oxidation resistance of AlCrxMoNbTi RHEAs. The mass gain per unit area of AlCr2MoNbTi was reduced to 3.3 mg cm(-1) after 50 h oxidation at 1000 degrees C, primarily attributed to the formation of Cr2O3, which serves as an effective barrier against oxygen diffusion, and the formation of the AlNbO4 phase, which effectively mitigate the oxidation of Mo.