Microstructure and High Temperature Stress Rupture Properties of Ru-Containing Directionally Solidified Ni-Base Superalloy

摘要

In this investigation, 3wt.% Ru was added to a low Cr and high W content superalloy with a nominal composition of Ni-10Co-1.5Cr-2.0Mo-1.0Nb-5.5Al-1.2Ti-0.1C-0.02B (wt.%) and both the Ru-free and the Ru-bearing alloys were directionally solidified. The multi-step heat treatment, thermal exposure and stress rupture test were performed. The results indicate that Ru is a weak positive segregation element (k'=C_(interdendrite)/ C_(dendrite)= 1.03). The solubility of Ru in γ phase is 30% higher than that of in γ' phase. Ru hardly enters into MC carbides, but can effectively retard the formation of M_6C carbides. Ruthenium reduces the amount of eutectic (γ+γ'), decreases solid solution temperature of γ' phase, and promotes the rafting tendency of γ/γ' at elevated temperatures. Ru-bearing alloy possesses rather higher life at 1100℃/118MPa due to decrease of the film-like M_6C carbides. The addition of Ru can inhibit the formation of M_6C and eutectic γ', which hinder the initiation and propagation of cracks.