Insight into the role of Sc on microstructure, mechanical properties and high temperature oxidation resistance of NiCoCrAlSiSc alloys

The microstructure and mechanical properties of Ni–20Co–20Cr–2Al–1Si-xSc (x = 0, 0.1, 0.3, 0.5, 1 wt. %) alloys were investigated, and the oxidation behavior of the alloys with different Sc contents at 1000oC was studied. The results indicate that NiCoCrAlSi alloy without Sc solidified into coarse columnar grains, with the addition of Sc, the grain size significantly decreased. Sc enriched at the grain boundaries of the alloy and promotes the segregation of Si and Ni towards the grain boundaries, forming the compound NiScSi. Within the range of 0∼1% (wt.%) Sc content, as the Sc content increased, there is an increase in the yield strength (σ0.2) of the alloy, a decrease in elongation, a little variation in tensile strength, and an enhancement in Vickers hardness. After cyclic oxidation at 1000oC and 120 hours for alloys with different Sc contents, composite oxide films were formed on the surfaces of the alloys, but the properties and microstructure of the oxide films were significantly different. As the Sc content rised, the integrity of the oxide films was significantly improved, and the oxidation resistance of the alloys gradually enhanced at a high temperature of 1000oC.