Dynamic recrystallization of the hot isostatically pressed P/M superalloy FGH4096 in hot working process

The dynamic recrystallization (DRX) of the hot isostatically pressed P/M superalloy FGH4096 in isothermal working process was characterized and investigated by using optical microscope (OM) and transmission electron microscope (TEM) techniques. The P/M superalloy was first prepared by hot isostatically pressing. The isothermal compression tests of the P/M superalloy were then conducted in a Gleeble-1500D simulator at the temperature ranging from 1080 to 1140 °C and the strain rate from 0.02 to 1.0 s−1. The microstructure observation of the deformed samples showed that the necklace microstructure was obtained under the strain of 0.51 or below. The necklace microstructure is an intermediate microstructure for the complete recrystallized microstructure, which could be finally generated when the strain was about 0.69. In addition, it was found that the complete recrystallized grain quantity was increased with the increase of temperature and the decrease of strain rate. The DRX nucleation sites are classified into three regions, viz., (i) previous particle boundaries (PPBs), (ii) recrystallized grain boundaries, and (iii) twin sources. As the repeated DRX took place, the grain size was eventually refined from 30.0 to 4.0 μm after the multiaxially forging and the homogeneous bulk billet with fine DRX grains was finally obtained.