Phenomenological foundations of methods of predicting long-time strength and creep of metallic materials for lengthy service

Abstract

The article examines the possibilities of reliable prediction of the characteristics of long-time strength for service times exceeding 100,000 h by temperature-time methods including the method suggested earlier on by the present author. The experimental data that are used are the results of long-time strength tests of a Japan-made superalloy on a base of 60,000 h at 700, 800, 900, and 1000°C. The article shows that the reliability of the predicted characteristics of long-time strength can be substantially enhanced by correctly selecting the extrapolation method based on physical prerequisites coinciding with the regularities of long time temperature-time failure of the investigated material. The adopted criterion of physically substantiated prediction of the results of tests with limited length in the temperature-time alternative is the characteristic of ductility of the material at failure (ɛ and ψ) and the graphic regularity of its change in dependence on the stress and temperature. These regularities of change of residual plastic deformation in dependence on the temperature and stress make it possible to establish the ranges of single time and temperature intervals of temperature-time similarity for the characteristics of long-time strength, which ensures the reliability of prediction.