Influence of temperature, pressure, and cooling rate during hot isostatic pressing on the microstructure of an SX Ni-base superalloy

This work investigates the application of hot isostatic pressing for heat treatment of the single-crystal Ni-base superalloy ERBO/1. Recent progress regarding incorporation of quenching within hot isostatic pressing enables heat treatments to be performed so that the microstructures can be frozen at a desired point. The influence of the temperature, pressure, and cooling method (quenching, natural convection, and slow cooling) as well as the cooling rate after solutioning-HIP treatment on pore densification and gamma/gamma'-morphology was measured. Temperatures above gamma'-solvus resulted in a greater efficiency of the porosity reduction. At super-solvus temperatures, pressures above 75 MPa are sufficient enough to annihilate the porosity. The cooling rate after HIP-solutioning treatment has a major influence on the gamma'-particle size and shape. Quenching with 45-20 K/s at 100 MPa leads to high number density and monomodal distribution of gamma'-particles with sizes around 140 nm. In contrast, slow cooling rate of 0.33 K/s leads to gamma'-precipitate sizes of 720 nm. Moreover, an integrated heat treatment at 100 MPa, which consisted of solutioning and aging in the HIP, was successfully applied. It led to smaller gamma'-particle sizes and narrower gamma-channels compared to the conventionally heat-treated material and also almost no porosity. (C) 2016 Elsevier Ltd. All rights reserved.