EFFECT OF PRECIPITATES ON RECRYSTALLISATION TEMPERATURE IN Cu-Cr, Cu-Zr AND Cu-Zr-Cr ALLOYS.

Abstract

In a previous paper it was reported that the high recrystallization temperature of Cu-Cr, Cu-Zr, and Cu-Zr-Cr alloys was due to the formation of fine precipitates during recrystallization, which obstructed dislocation climb, glide, and grain boundary migration. In the present paper, the same alloys quenched, tempered (at 350, 450, 500, 550, and 700 degree C), heavily cold worked, and annealed at various temperatures were studied by the resistometric method, measurements of mechanical properties, and transmission electron microscopy. No fine precipitates were detected at dislocations or subboundaries in the low temperature annealing stage, but fine precipitates, which retard recovery, must exist since electric resistivity decreased during low temperature annealing. Retardation of recovery is due to the binding of dislocation jogs by fine precipitates. In the high annealing temperature range, the growth of precipitates and crystal grains was observed by transmission electron microscopy, and the effect of precipitates on the retardation of recrystallization was also detected. The size of precipitates formed during tempering before cold working did not affect the recrystallization temperature, because the precipitates were broken up by heavy cold work and were thus made a constant size.