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

Abstract

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’=Cinterdendrite / Cdendrite= 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 M6C 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°C/118MPa due to decrease of the film-like M6C carbides. The addition of Ru can inhibit the formation of M6C and eutectic γ', which hinder the initiation and propagation of cracks.

Influence of withdrawal rate on the microstructure of Ni-base single-crystal superalloys containing Re and Ru

“…However, the addition of refractory elements (i.e. Re and W) also leads to many problems, such as: (1) severe segregation [4,5]; (2) increasing tendency of grain defects formation [6]; (3) complicated solution heat treatments [7]; (4) increasing tendency of detrimental topologically-closed-packed (TCP) phases formation [8]. To overcome above-mentioned problems, approximately 2-6 wt.% Ru has been added to the newly developed single-crystal superalloys.…”

Effects of Re and Ru on the Solidification Characteristics of Nickel-Base Single-Crystal Superalloys

“…There has been much research focused on the solidification characteristics of Re-and Ru-containing superalloys. [13][14][15][16] However, because Ni-base superalloys are multicomponent and multiphase alloys, it is difficult to independently investigate the effects of individual elements. A better understanding of solidification characteristics of Re-and Ru-containing single-crystal superalloys is significantly important for enhancing the high-temperature capability of Ni-base superalloys.…”