Tertiary Creep in Nickel-base Single-Crystal Superalloys: a Case of Geometric Effect

Abstract

The tertiary creep in nickel-base single-crystal superalloys observed in conventional constant-load tests, for conditions where rafting of γ´ precipitates does not play a dominant role, represents a dynamic steady-state condition. The accelerating strain rate corresponds primarily to the increasing stress with decreasing cross-sectional area as the strain increases. Experiments on [001]-oriented CMSX-10 at 900 °C for the initially applied stresses of 500–700 MPa revealed this geometrically induced effect for the most part of the creep life. A power-law describes the stress dependence of creep rate. It is shown that one creep rupture test provides a stress-strain rate relationship for dislocation creep over a stress range of about 100 MPa. Consequently, this suggests an economical, time-saving experimental scheme for determining stress exponent n from one test for a short stress range or the variations in n over a larger stress range using only a few specimens. A simple nonlinear elasto-viscous creep mod...