TEMPERATURE SENSITIVE DUCTILITY IN FACE CENTERED CUBIC COPPER ALLOYS

According to the various analyses of the ductile brittle transition of body-centered cubic metals, the restrictions on plastic flow are the determining conditions for the breakaway of cleavage cracks from microcracks that may form either by dislocation coalescence, interface separation at twin or grain boundaries, or inclusion cracking. Although cleavage has never been observed in face-centered cubic metals, restricted plastic flow is possible as evidenced by yield points, temperature sensitivity of the yield stress, and discontinuous flow. How these factors influence the ductility of FCC metals is not well understood and has formed the basis of this study. Variations of tensile ductility of nine alpha solid solution copper alloys were dependent upon test temperature, solute species, solute content, and grain size. Temperature sensitive ductility losses were greatest in a Cu-Sb alloy and resulted from the onset of grain boundary cracking. Ductility losses below ambient temperature in alloys of copper with tin, silicon, or aluminum were correlated with the ease of formation and the extent of localized plastic shear zones. Dilute alloys had broad zones at all test temperatures and the ductility changes were small. In the high solute alloys, where the ductility losses were greatest, shear layers were more concentrated at low temperatures. (Author)