Some new aspects concerning particle hardening mechanisms in γ' precipitating nickel-base alloys—II. Experiments

Abstract

Experiments are presented examining the theoretical concept described in the preceding paper (part I). The RT yield stress of the γ'(Ni 3Al) strengthened Nickel base alloys Nimonic PE 16 and Nimonic 105 has been measured in compression, the γ'-particle diameter (3–720 nm) and the precipitated volume fraction (4–51%) being varied over a wide range. The analysis of the experimental data starts from the assumption that solid solution hardening of matrix and γ'-particle hardening do not superimpose by linear addition, but according to the ‘ 3 2 -law’. The measured relationships can be described but qualitatively by conventional hardening models which actually hold for small volume fractions. In particular, the transition from cutting of γ'-particles by paired dislocations to single dislocation Orowan looping occurs at large (overaged) spherical particles as expected by theory. However, in the range of small particles considerable discrepancies arise. Here, the new theory of Labusch and Schwarz has to be applied, fitting experimental data thoroughly to the respective model. The interpretation of the mechanical relationships is supported by TEM observation of the dislocation structure.