Microstructure evolution and deformation mechanisms of the electroslag refined-continuous directionally solidified (ESR-CDS®) superalloy Rene88DT during isothermal compression

The microstructure evolution and deformation mechanisms of alloy Rene88DT prepared by ESR-CDS® during isothermal compression have been investigated by optical microscopy (OM), electron back scattered diffraction (EBSD) and transmission electron microscopy (TEM). The results showed that two cycles of dynamic recrystallization (DRX) occurred during the compressive deformation of the sample at super-solvus temperature with total true strain of 1.2, and this led to a near completely recrystallized fine-grained microstructure. For samples deformed at sub-solvus temperature, only one cycle of DRX occurred during compression with total true strain of 1.2, resulting in a partial recrystallized microstructure, and large misorientation formed in the un-recrystallized coarse grains. DRX is mainly initiated at the columnar grain boundaries or stimulated by the carbide particles within the grains. The main DRX mechanisms are grain boundary bulging and migration, second phase particles stimulation, sub-grain coarsening and migration.