Prediction of creep properties for two nickel-base superalloys from stress relaxation testing

Abstract

The creep properties derived from stress relaxation tests are compared to those from creep tests in the temperature range from 705 °C to 800 °C and stresses from 200 MPa to 750 MPa for the nickel base superalloys IN738LC and modified Waspaloy. The creep behaviour of IN738LC exhibits an extended period of steady state strain rate, while creep of modified Waspaloy exhibits only a minimum creep strain rate. The results indicate that stress relaxation tests can be used to estimate the creep steady state or minimum strain rates, time to 1 per cent creep strain, and the creep stress exponent for both superalloys. Stress relaxation tests can generate these properties in a significantly more time-efficient and specimen-efficient manner than creep tests, regardless of whether the superalloy creep behaviour exhibits a steady state or minimum creep strain rate.