# The Effect of Thermal Processing on the Microstructure and Properties of a Novel Nickel-Based Powder Metallurgy Superalloy

## TL;DR

This study compares two thermal processing methods for a nickel-based superalloy, finding that one method improves mechanical properties at high temperatures.

## Contribution

The study introduces a novel nickel-based powder metallurgy superalloy and evaluates the impact of different thermal-mechanical processes on its microstructure and properties.

## Key findings

- The IF-HT alloy exhibited finer γ′ precipitates and more uniform substructures compared to the As-HIP-HT alloy.
- The IF-HT alloy showed better creep resistance and stable plasticity at high temperatures due to its microstructural characteristics.
- The As-HIP-HT alloy had higher yield strength at lower temperatures but experienced reduced plasticity as temperature increased.

## Abstract

A novel nickel-based powder metallurgy superalloy was processed using two different thermal–mechanical processes, including hot isostatic pressed (As-HIP) and hipped + hot extruded + isothermally-forged (IF) heat treatments following two processed alloys, designated as As-HIP-HT and IF-HT. The objective of this study is to investigate the microstructure and mechanical property evolution in a nickel-based powder disk alloy fabricated by two processes. The findings revealed that both As-HIP and IF alloys underwent substantial recrystallization, with grains in the IF alloy being finer. Notable Prior Particle Boundaries (PPBs) were identified in the As-HIP samples. The IF-HT alloy exhibited a larger grain size due to a greater amount of stored energy. Significant differences in the secondary γ′ precipitates were observed between the two processes. More uniform substructures in the IF-HT alloy led to a higher density of finer γ′ precipitates. At temperatures of 704 °C and 760 °C, the As-HIP-HT alloy displayed a higher yield strength, but its plasticity significantly declined as temperature increased, while the IF-HT alloy showed a relatively stable plasticity. The presence of PPBs in the As-HIP-HT alloy minimally affected the alloy’s strength but reduced its plasticity. The creep property of the two processes was compared at 800 °C/330 MPa; the IF-HT alloy demonstrated lower creep rates and a longer creep life, which was attributed to its finer γ′ precipitates. Dominant creep deformation mechanisms in the As-HIP-HT alloy included Orowan dislocation loops and deformation twinning, while the primary mechanisms in the IF-HT alloy involved dislocation cutting through γ′ precipitates, dislocation slip, and micro-twins. These findings support the use of isostatic pressing + hot extrusion+ isothermally-forging process for critical high-temperature components.