Hardening mechanisms in a precipitation hardenable nickel-12·71 at. % aluminium alloy

Abstract

The reversible contribution to the flow stress in a polycrystalline Ni-12·71 at. % Al alloy was studied by temperature change between 303° and 77°K as a function of tensile strain up to 8% and of the degree of precipitation at 873° and 973°K, Strain-free values of the flow stress ratio and reversible change in flow stress were obtained by extrapolation to zero strain. Aluminium in solution greatly increased the temperature dependence of the flow stress over that of pure nickel. The temperature dependence was progressively decreased by coherent precipitation of γ’ (Ni₃Al) to a minimum in the peak aged condition, then increased again on over-ageing at 973°K. It was estimated that solution hardening comprised 28–36% of the peak aged flow stress, dislocation hardening 10–11%, coherency hardening 12–18%, and other mechanisms, taken to be order hardening and modulus mis-match hardening, 335–47%.