Understanding on processing temperature-metallographic microstructure-tensile property relationships of third-generation nickel-based superalloy WZ-A3 prepared by hot isostatic pressing

Abstract

A third-generation powder metallurgy nickel-based superalloy (WZ-A3) was prepared by hot isostatic pressing (HIP) at 1100 °C, 1150 °C, 1200 °C, and 1250 °C, respectively. The characteristics of grains, precipitates, and elemental distribution revealed its microstructural development. The samples prepared at a sub-solvus temperature (1100 °C) consisted of fine recrystallized grains and dendritic structures. However, the microstructure became a completely recrystallized structure when the HIP temperature reached or exceeded 1150 °C. The average grain size increased from 4.0 µm (1100 °C) to 53.1 µm (1250 °C) due to the promoted recrystallization and atom diffusion rate. Prior particle boundaries (PPBs) with continuously distributed precipitates were identified as a mixture of (Nb, Ti)C carbides and Hf0.5Zr0.5O2 oxides. By increasing the HIP temperature from 1100 °C to 1200 °C, the PPBs were reduced but not eliminated. As a result, samples prepared at 1200 °C experienced interparticle debonding with relatively high strengths, and the ultimate tensile strength values were 1388.7 MPa and 1228.3 MPa at room temperature (RT) and 700 °C, respectively. When the HIP temperature was 1250 °C, the presence of coarse grains, large carbides, as well as eutectic structures formed at the junction of grain boundaries caused dramatic drops of tensile strengths and brittle fractures. These results emphasized the importance of parameter optimization for controlling the microstructure and mechanical properties during the HIPing process.