The effect of precipitation on the mechanical properties of the Cu-1.9% Co and the Cu-2% Co-6% Zn systems

A study of the effect of coherent precipitates on the surface topography produced by deformation of copper-2 wt. % cobalt alloy single crystals

“…According to their equations, a plot of (AT/VI) versus (R/b) should be a straight line passing through the origin. In practice, however, the increase in flow stress as experimentally determined by Livingston (15), Phillips (1), Koepke and Scott (16), and Olson (17) agrees with the predic ted theoretical curve only for small sizes of precipitate O particles (R<64 A). For larger particle sizes the increase in flow stress seems to be controlled by the dislocation bow-out mechanism originally proposed by Orowan (18).…”

“…According to Hollomon as cited by Kuhlmann-Wilsdorf and Wilsdorf (42) the stress required to activate such sources is about half of the stress needed for the initiation of a Frank-Read source within a crystal. This amount of stress is still slightly larger (17) than the observed flow stress for the specimens used in this research. Yet, discontinuities at the surfaces could produce a local stress concentration sufficient to activate disloca tion sources.…”

“…The stress required to initiate the FrankRead sources decreases with an increase in the precipitate particle size or the interparticle spacing. However, in these 0 specimens, even for precipitate of radius 90 A, the stress for activating Frank-Read sources remains higher than the flow stress of the material (17).…”

“…Obviously a large number of dislocations are generated, but the mechan ism of the dislocation generation is not well established for this alloy. The usual Frank-Read source mechanism of genera tion is not possible in this alloy because the stress required in its operation is higher than the observed flow stress of the crystals (17). The stress required to initiate the FrankRead sources decreases with an increase in the precipitate particle size or the interparticle spacing.…”

“…The specimen surface appears through the eyepiece to be inter The size of the precipitate particles of cobalt was deter mined by means of a magnetic technique described by Becker (5) and used by several others (6)(7)(8)(9)16,17). Cobalt precipitate particles are ferromagnetic and are finely dispersed in the matrix of copper which is very weakly paramagnetic.…”