Effect of niobium filaments on mechanical response and fracture characteristics of dispersion strengthened copper alloy and copper–niobium microcomposite

Abstract

In this study, the microstructure, tensile deformation, cyclic stress amplitude-controlled fatigue and final fracture behavior of a microcomposite based on an oxide dispersion strengthened copper matrix were examined. Specimens of the microcomposite and an unreinforced dispersion strengthened copper counterpart were cyclically deformed, over a range of cyclic stress amplitudes, at both ambient and elevated temperatures. Increase in test temperature was found to have a detrimental influence on the cyclic fatigue life of the copper–niobium microcomposite. Temperature was found to have little influence on the cyclic fatigue life of the unreinforced dispersion strengthened microstructure. For both the unreinforced and reinforced materials macroscopic fracture was reminiscent of brittle failure over the entire range of stress amplitudes. However, on a microscopic scale cyclic fracture revealed features reminiscent of locally brittle and ductile mechanisms. The mechanical properties and cyclic fatigue behavior of the microcomposite are discussed in light of the mutually competitive influences of intrinsic composite microstructural effects, cyclic stress amplitude, test temperature and macroscopic aspects of fracture. The conjoint influence of the reinforcing niobium filaments and the oxide dispersoids in governing the response of the copper matrix is also discussed.