Microstructure-sensitive creep models for nickel-base superalloy single crystals

Abstract

Microstructure-sensitive creep models have been developed for Ni-base superalloy single crystals. Creep rupture testing was conducted on fourteen single crystal alloys at two applied stress levels at each of two temperatures, 982 and 1093°C. The variation in creep lives among the different alloys could be explained with regression models containing relatively few microstructural parameters. At 982°C, γ−γ′ lattice mismatch, γ′ volume fraction, and initial γ′ size were statistically significant in explaining the creep rupture lives. At 1093°C, only lattice mismatch and γ′ volume fraction were significant. These models could explain from 84% to 94% of the variation in creep lives, depending on test condition. Longer creep lives were associated with alloys having more negative lattice mismatch, lower γ′ volume fractions, and finer γ′ sizes. The γ−γ′ lattice mismatch exhibited the strongest influence of all the microstructural parameters at both temperatures. Although a majority of the alloys in this study were stable with respect to topologically close packed (TCP) phases, it appeared that up to ∼2vol% TCP phase did not affect the 1093°C creep lives under applied stresses that produced lives of ∼200–300h. In contrast, TCP phase contents of ∼2vol% were detrimental at lower applied stresses where creep lives were longer.