A study of solution cooling rate on γ’ precipitate and hardness of a polycrystalline Ni-based superalloy using a high-throughput methodology

Abstract

In powder metallurgy Ni-based superalloys, the mechanical properties such as strength, creep and fatigue resistance at the elevated temperature closely rely on the solution cooling rate during heat treatment. Understanding the precipitation mechanisms upon different quenching media can offer a bridge across cooling rate to mechanical response. To date, extensive works have been done to construct the relationship between cooling rate and mechanical performance only using a limited quantity of quenching media such as water, oil and air, resulting in the inadequacy of process-microstructure-property database. In this work, a high-throughput approach based on the Jominy end quenching technique was developed to produce a gradient distribution of γ’ precipitates within an individual specimen by introducing a wide range of cooling rates from 35 °C/min to 6346 °C/min. A transformation from unimodal to bimodal γ’ Particle Size Distribution (PSD) was observed along the end quenched specimen. The average size of γ’ precipitates is inversely proportional with cooling rate in logarithmic scale. The hardness measurements display a strong dependence on cooling rate, which is explained by phase field simulation to provide deeper insight into the interaction between dislocation and γ’ precipitates.