Mutation in TCP phases and superior stress rupture life led by W/Mo ratio in Ni-based single crystal superalloys

• The precipitation behavior of TCP phases was mutated by tuning W/Mo ratio. • The μ phase formed in the high W/Mo ratio alloy. • Small P phase particles formed in the low W/Mo ratio alloy. • The stress rupture life was increased for the low W/Mo ratio alloy. Balancing the strengthening effect and microstructure instability led by refractory elements is crucial for superalloys. In this work, comparative study was conducted on two second-generation Ni-based single crystal superalloys which have similar components and total content of W + Mo except for different W/Mo ratios. It has been evidenced that μ phase precipitated in the high W/Mo ratio alloy after isothermal exposure for 1,500 h at 950 °C, whereas only sub-micron P phase particles formed in the low W/Mo ratio alloy even after 10,000 h of isothermal exposure. Striking increase in stress rupture life was achieved for the low W/Mo ratio alloy experienced 10,000 h of isothermal exposure. The mutation in TCP phases and enhanced stress rupture life were ascribed to the dendrite segregation of W and Re, and partitioning behavior of Cr and Re in γ and γ′ phases induced by W/Mo ratio.