Effect of Re and C on mechanical properties of NbTaW0.4 refractory medium-entropy alloy at elevated temperature

The NbTaW0.4, Re0.1NbTaW0.4, NbTaW0.4C0.25 and Re0.1NbTaW0.4C0.25 refractory medium entropy alloys (RMEAs) were fabricated by arc melting. The effect of Re, C andRe + C on the microstructure and mechanical properties of NbTaW0.4 alloy was investigated. The NbTaW0.4 alloy consisted of disordered body-centered cubic (BCC) solid solution phase. The yield strength at room temperature and 1450 ℃ of NbTaW0.4 alloy were 912 MPa and 198 MPa, respectively. A small addition of Re (4 at%) has no significant effect on the microstructure and room temperature mechanical properties of the alloy, but can increase the yield strength by about 69% at 1450 ℃; when C (9.4 at%) or both Re and C (Re is 3.6 at%; C is 9.1 at%) were added to the alloy, the microstructure of the alloy was fine and uniform hypo-eutectic structure, and needle-like precipitates were dispersedly distributed within the grains in the matrix. The mechanical properties of the alloy were significantly improved when C or both Re and C were added. Compared with NbTaW0.4 alloy, the yield strength of NbTaW0.4C0.25 alloy and Re0.1NbTaW0.4C0.25 alloy increased by 316.6% and 233.3% at 1450 ℃, respectively. Re element can affect the morphology, quantity and distribution of Ta2C phase. Consequently, element Re shows an antagonistic effect on the enhancement of NbTaW0.4 alloy by C element. The NbTaW0.4C0.25 alloy exhibits excellent yield strength of 825 MPa at 1450 ℃ with decent ductility of 12.4% at room temperature.