Abstract: Ti-bearing high-entropy superalloys (HESAs) often suffer from severe intergranular embrittlement and terrible oxidation degradation at intermediate temperatures. Here we showcase that minor Si addition can effectively mitigate the intergranular embrittlement and improve the oxidation resistance of the a (Ni₂Co₂FeCr)₉₂Ti₄Al₄ HESA at 700 °C simultaneously. Experimental analysis revealed that the intergranular G phase induced by 2 at% Si addition can effectively suppress the inward diffusion of oxygen along grain boundaries at 700 °C, thus enhancing the tensile ductility of the alloy from ∼8.3% to ∼13.4%. Besides, the 2 at% Si addition facilitated the formation of a continuous Al₂O₃ layer during oxidation, contributing to a remarkable reduction in the growth rate of the oxide scale to a quarter of the Si-free HESA. Our results demonstrate that Si can be a favorable alloying element to design advanced HESAs with synergistically improved thermal-mechanical performance.

Key words: High-entropy superalloy, Mechanical property, Oxidation behavior, Intermediate temperature, Silicon addition