Abnormal grain growth in bulk Cu - The dependence on initial grain size and annealing temperature

The dependence of abnormal grain growth (AGG), also termed secondary recrys tallization, on annealing temperature in the range between 600 degreesC and 1050 degreesC has been observed in pure bulk Cu specimens compressed to va rious levels between 5 and 75 pct. There is no grain texture after annealin g. The average grain size after primary recrystallization, which represents the initial grain size for secondary recrystallization during further anne aling, decreases with increasing deformation and is nearly independent of t he annealing temperature, in agreement with previous observations. The incu bation time for AGG decreases and the number density of abnormally large gr ains increases with increasing deformation (hence, a decreasing initial gra in size) and increasing annealing temperature. At low temperatures, most of the grain boundaries are faceted, with some facet planes probably of singu lar structures corresponding to cusps in the polar plots of the grain-bound ary energy vs the grain-boundary normal. With increasing temperature, the g rain boundaries become defaceted and, hence, atomically rough. The observed grain-growth behavior appears to be qualitatively consistent with the move ment of faceted grain boundaries by two-dimensional nucleation of boundary steps. The temperature dependence appears to be consistent with roughening of grain boundaries. Before the onset of AGG, stagnant growth of the grains occurs at low rates, probably limited by slow two-dimensional nucleation o f boundary steps, and, at low deformations and low annealing temperatures, the stagnant growth persists for 100 hours. The specimens with relatively s mall initial grain sizes (because of high deformation) show double AGG when annealed at high temperatures.