Effect of Prior Plastic Deformation on the α-Cr Precipitation in a Binary Ni-Cr Alloy

Abstract

The effect of prior plastic deformation on the discontinuous precipitation in a supersaturated binary Ni-Cr alloy (42 wt pct Cr) was investigated. Solutionised samples were cold rolled to different extents of reduction (20, 50 and 70 pct) and then subjected to aging heat treatments in the temperature range of 923 K to 1123 K (650°C to 850°C) for different time periods, resulting in the precipitation of a-Cr in various morphologies. The a-Cr precipitates were in the form of lamellar discontinuous precipitation, acicular continuous precipitation along the deformation bands, globularization and equiaxed precipitation concurrently with matrix recrystallization. The volume fraction of each morphology varied according to the heat treatments. Overall, the prior plastic deformation had a retarding effect on the kinetics of discontinuous precipitation and accelerated the kinetics of continuous precipitation. The retardation of discontinuous precipitation was attributed to the loss of supersaturation of the matrix due to the other competing modes of precipitation supported by deformation. Plastic deformation prior to aging is shown to be a possible route for engineering the microstructure in this alloy.