Creep in copper dispersion strengthened with fine alumina particles and reinforced with alumina short fibres—an ODS copper matrix composite

Abstract

Creep in copper dispersion strengthened with fine alumina particles (ODS copper) and reinforced with alumina short fibres—an ODS copper matrix composite—is investigated in two temperature intervals, namely lower temperature interval (LTI) 673–773 K and higher temperature interval (HTI) 923–1023 K. In both intervals, creep is associated with true threshold stresses decreasing with increasing temperature more strongly than the shear modulus of copper. The true threshold stress in the composite is higher than that in its matrix by a factor Λ≅2 in both LTI and HTI, by which the flow stress in the matrix is reduced due to load transfer. The minimum creep strain rate is dislocation core diffusion controlled in LTI and lattice diffusion controlled in HTI. High values of the apparent activation energies are fully explained in terms of the temperature dependence of the true threshold stress in LTI as well as in HTI. Also the high values of the apparent stress exponents are explained in terms of the true threshold stresses. The true threshold stress is identified with the detachment stress, i.e. the stress necessary to detach a dislocation from a fine interacting particle without assistance of thermal activation, σ d =σ OB 1−k R 2 . Its nonproportionality to the Orowan stress σ OB is explained by the relaxation factor k R that represents the relative strength of the attractive dislocation/particle interaction, increasing with temperature.