The effect of solution annealing on additively manufactured and hot isostatically pressed René 80 Ni-based superalloy

Abstract

The effect of solution annealing temperature on the microstructure, morphology, size, and volume fraction of γ′ precipitates, and hardness of the material was investigated in this work. Samples were fabricated by Laser Based Powder Bed Fusion (LB-PBF) process and post processed with Hot isostatically Pressing (HIP). Next, different solution annealing conditions were applied to assess their impact on γ′ precipitation. The microstructure of the samples was characterized by light optical microscopy (LOM), field emission scanning electron microscopy (FE-SEM), and electron backscattered diffraction (EBSD). Defects were assessed by treating LOM images through ImageJ. The hardness was also measured by Brinell hardness. The results showed that HIP process densified the samples and increased the relative density to more than 99.98%. Performing HIP and solution annealing at a sub-solvus temperature resulted in irregular-shaped γ′ precipitates and grains remained elongated along the building direction. By increasing the solutioning temperature above solvus treatment, organized and cubic precipitates formed. Moreover, by increasing the solutioning temperature from 1230 to 1270 °C the grain size increased from 15 to 46 μm, and consequently, the hardness decreased by about 6%. The results also revealed that the γ′ volume fraction was not greatly affected by the solutioning temperature and remained within the range of 20.4–22.3% after aging. Finally, a thermal setpoint of 1260 °C resulted the most promising condition for solution annealing PBF-LB René 80 superalloy to obtain cubic secondary γ′ precipitates, minimizing the presence of irregular γ’ at grain boundaries and providing a robust process against thermal oscillations within industrial furnaces.

Keywords

• Nickel superalloy
• René 80
• Additive manufacturing
• Precipitation
• Microstructure