Creep in ODS copper reinforced with alumina short fibres—DRS copper

Abstract

Creep in copper dispersion strengthened with fine alumina particles (oxide dispersion strengthened (ODS) Cu) and reinforced with alumina short fibres—a DRS Cu composite—is investigated in two temperature intervals, namely 673–773 K, lower temperature interval (LTI) and 923–1023 K, higher temperature interval (HTI). It is shown that 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 the composite matrix (i.e. ODS copper) by a factor Λ, by which the flow stress in the matrix is reduced due to load transfer. The minimum creep strain rate is found to be 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 values of the apparent stress exponents are explained in terms of the true threshold stresses. The true threshold stress is identified with the athermal detachment stress σ d =σ OB 1−k R 2 , and its nonproportionality to the Orowan stress σ OB is explained by the relaxation factor k R increasing with temperature.