Threshold stress for creep in dispersion-strengthened alloys

Abstract

The bypass of particles by climb necessarily results in an increase in length of a dislocation, provided its ends are anchored at network nodal points. The energy associated with this length increase is provided by the applied stress. It follows that a critical threshold stress for the climb process, and hence for recovery creep, can be defined as that required to maintain the minimum length increase during bypass. A model of the process is presented on the basis that climb is aided solely by the local normal stress; the average contribution of the shear stress through forward slip of the climbing dislocation is considered to be negligible.The computed value of threshold stress is only weakly dependent upon applied stress and, for practical purposes, can be considered to be independent. There is a strong dependence on the dispersion parameter r/λ, where r is the particle radius and λ the surface-to-surface particle separation. A preliminary comparison of the theory is made with results on a TiN dispersion-strengthened austenitic steel and satisfactory agreement is found.