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

In this study, the microstructure, tensile deformation, cyclic stress ampli tude-controlled fatigue and final fracture behavior of a microcomposite bas ed on an oxide dispersion strengthened copper matrix were examined. Specime ns of the microcomposite and an unreinforced dispersion strengthened copper counterpart were cyclically deformed, over a range of cyclic stress amplit udes, at both ambient and elevated temperatures. Increase in test temperatu re was found to have a detrimental influence on the cyclic fatigue life of the copper-niobium microcomposite. Temperature was found to have little inf luence on the cyclic fatigue life of the unreinforced dispersion strengthen ed microstructure. For both the unreinforced and reinforced materials macro scopic fracture was reminiscent of brittle failure over the entire range of stress amplitudes. However, on a microscopic scale cyclic fracture reveale d features reminiscent of locally brittle and ductile mechanisms. The mecha nical properties and cyclic fatigue behavior of the microcomposite are disc ussed in light of the mutually competitive influences of intrinsic composit e microstructural effects, cyclic stress amplitude, test temperature and ma croscopic aspects of fracture. The conjoint influence of the reinforcing ni obium filaments and the oxide dispersoids in governing the response of the copper matrix is also discussed. (C) 1999 Elsevier Science S.A. All rights reserved.