Some new aspects concerning particle hardening mechanisms in γ' precipitating Ni-base alloys—I. Theoretical concept

Abstract

Strengthening of Ni-base alloys by coherent, stress-free, ordered particles is critically discussed in the light of more recent theories. In part I. a theoretical concept is developed which rests on existing hardening models estimating the increase of the yield stress due to pairwise particle cutting and anti-phase domain boundary (APB) formation. The effect of the anisotropy on the dislocation line tension of two-phase material and on the Orowan stress is taken into account. It is shown that conventional hardening models which are derived in the framework of the Fleischer-Friedel theory are strictly limited to dilute alloys. For Ni-base alloys containing large volume fractions of γ'(Ni 3Al) precipitates the Labusch theory holds. Consequently, the new theory of Labusch and Schwarz is applied to the operating APB hardening. The yield stress of an anisotropic γ' hardening model system is calculated for large variations of particle parameters. Experimental results obtained with the commercial alloys Nimonic PE 16 and Nimonic 105 to check the theoretical estimates will be reported in a subsequent paper (part II).