Relief Formation on the Free Surface of Metallic Polycrystals upon Recrystallization Annealing

Abstract

The mechanism of the formation of a complicated relief first found on the recrystallized tungsten surface in studies performed by A.I. Belayeva and coauthors is described in this work. Its essence is the deformation of boundaries and near-boundary volumes of crystallites (grains) in the near-surface polycrystalline-metal layer upon cooling after high-temperature holding that is caused by the difference in the ultimate strength and thermal expansion coefficients of boundaries and bodies of grains. In the near-surface layer upon cooling of the metal, due to the difference in the size reduction of grain boundaries and grain bodies, cracks (grooves) arise at boundaries on whose banks identical ridges are formed. The bending of the boundary makes the profile of grooves asymmetric and creates rather shallow creases in front of ridges. The surface relief impairs the service properties of metals but its formation can be prevented, if articles become single-crystalline owing to recrystallization.