Correlation of creep elongation and substructure in aluminum-stainless steel composites

Abstract

The tensile creep behavior and associated substructural detail have been characterized in aluminum-stainless steel composites at ambient temperature. Volume fractions in the range 0 to 0.33 were tested under constant load conditions (in the range 1.0 to 4.0 times macroscopic yield stress) with the load applied parallel to the direction of reinforcement. In both unreinforced aluminum and the composites, steady-state creep conditions are established in <100 hr; creep rates are in the range 1.2×10⁻⁷ in. per in. per hr to 5×10⁻⁴ in. per in. per hr, depending on stress and volume fraction reinforcement. The stainless steel reinforcement significantly reduces the creep rate at a given stress level. The steady-state creep rates are in good agreement with behavior predicted by an exponential form of the rule-of-mixtures equation relating creep rate to applied stress and volume fraction reinforcement. The matrix (experimental) and stainless steel wire (rule-of-mixtures analysis) give an exponential dependence of creep rate on stress with power exponents of 2.7 and 3.3, respectively. At a given level of creep strain dislocation substructure in the aluminum matrix is independent of distance from the interface; alternatively, the substructure is independent of volume fraction of reinforcement and is controlled only by the total strain in the composite. Similar behavior has been established previously in this system for time-independent uniaxial tensile or compressive loading.