Study on grain boundary distribution and formation mechanism in GH3536 superalloy strip and foil after annealing treatment

The grain boundary distribution characteristics and their formation mechanism in GH3536 superalloy strip and foil prepared by multi-pass "cold-rolling and annealing " at different annealing temperatures (including subsolvus and supersolvus temperatures) were studied in this paper. According to the results of this study, the grain size of strip and foil of a thickness of 200 mu m was unevenly distributed along the strip when annealed at 1050 ?. The deformation energy storage of the strip and foil of 200 mu m thickness was low, and its recrystallization temperature was higher than that of strip and foil with a thickness of 100 mu m and 50 mu m. Therefore, the annealing process at 1050 ? was conducive to promoting the interaction and decomposition of coincident site lattice (CSL) grain boundaries through the movement of dislocations in the recovery process, so that CSL grain boundaries formed low-energy grain boundary clusters and interrupted random grain boundaries. In the process of grain growth of GH3536 strip and foil, the "accidental " growth mechanism of sigma 3 annealing twin boundaries was dominant. With the increase in grain size, the proportion of sigma 3 grain boundary increased. The parallel sigma 3 twin boundary formed by this mechanism was not conducive to breaking the random grain boundary. After annealing at a supersolvus temperature of 1200 ?, the grains grew under the action of high thermal activation energy, the proportion of sigma 3 grain boundary decreased, and its reduction was more prominent in strip and foil of 50 mu m thickness with large cumulative deformation. When annealing twice at the selected supersolvus temperature, strain-induced grain boundary migration dominated, which reduced the dislocation density and deformation storage energy of the microstructure and was thereby conducive to the formation of sigma 3 grain boundaries by the "accidental " growth mechanism; furthermore, the proportion of sigma 3 grain boundary increased in the process of grain coarsening.