Tribological Properties of Typical NiAlCoCrFeTi Series High Entropy Superalloys

Two typical high entropy superalloys (HESAs), namely NiAlCoCrFeTi (HESA-1) and NiAlCoCrFeTiTaMoW (HESA-2) were prepared by vacuum arc melting technology. Their microstructures, mechanical properties and tribological properties from 25 to 900 ℃ were studied. The results showed that both of the HESAs were composed of γ phase with disordered face-centered cubic (FCC) structure and γ´ phase with ordered FCC structure. The γ phase rendered the HESAs with good ductility and fracture toughness, and the γ´ phase made the HESAs had high hardness and strength. From 25 to 900 ℃, the friction coefficients and wear rates of the HESAs decreased obviously with increasing temperature. At 25 ℃, the main wear mechanism was abrasive wear, which made the HESAs have larger friction coefficients and higher wear rates. Above 400 ℃, under the combined action of friction induced oxidation and thermal oxidation, a few discontinuous oxide glaze layers were formed on the worn surfaces of the HESAs, which made the friction coefficients and wear rates decreased significantly. At 900 ℃, a lot of dense oxide glaze layers were formed on the worn surfaces, which played an important role in decreasing the friction coefficients and wear rates. The friction coefficients were reduced to 0.26 and 0.25, respectively, and the wear rates of the HESA-1 and the HESA-2 were reduced to 13.3×10⁻⁶ and 8.0×10⁻⁶ mm³/(N·m), respectively. Due to the combined effect of friction induced oxidation and thermal oxidation, the active elements such as Al, Cr, Ni and Co on the surfaces of the HESAs formed a lot of dense oxide glaze layers on the worn surfaces, which made the HESAs have good high-temperature tribological properties. At high temperatures, the wear resistance of the HESA-2 containing refractory metal elements was better than that of the HESA-1, which mainly due to the HESA-2 had higher high-temperature hardness than HEAS-1.