Kinetic Analysis for High-Temperature Coarsening of γ″ Phase in Ni-Based Superalloy GH4169.

Cheng Zhang,Hui Wang,Liming Yu

doi:10.3390/ma12132096

Abstract

The growth of precipitates in Ni-based superalloy GH4169 is critical as it controls the mechanical properties and long-term stability of the alloy. In this paper, the coarsening behavior of the main strengthening phase γ″ in the temperature range from 800 °C to 900 °C is investigated. Two heat treatment steps, i.e., pre-precipitation of γ″ phase and coarsening of precipitates at high temperatures, were performed on the GH4169 alloy. It was found that there were three morphological forms of γ″ phase in chronological order: lip-shape, disc-shape, and irregular rectangle-shape with larger size. The coarsening kinetics of γ″ phase followed the Lifshitz-Slyozov-Wagner (LSW) time-law for diffusion-controlled growth, and the activation energies of γ″ phase before and after losing the coherent relationship with matrix were 261 kJ mol−1 and 271 kJ mol−1, respectively.

Highlights

GH4169 (US brand name Inconel 718) is a Ni-based superalloy that has been extensively used under high temperature environment such as turbine engine, cogeneration, and heat treatment equipments.Its excellent high-temperature performance, especially the mechanical properties, is significantly affected by various precipitates [1,2,3]
At 800 ◦ C, the precipitation rate of δ phase is extremely slow and only a small amount of round particles precipitate at grain boundaries (Figure 1a,b)
The grain/twin boundary precipitation and intra-granular precipitation of δ phase both occur during the aging processes at 850 ◦ C and 900 ◦ C

Summary

Introduction

GH4169 (US brand name Inconel 718) is a Ni-based superalloy that has been extensively used under high temperature environment such as turbine engine, cogeneration, and heat treatment equipments.Its excellent high-temperature performance, especially the mechanical properties, is significantly affected by various precipitates [1,2,3]. GH4169 (US brand name Inconel 718) is a Ni-based superalloy that has been extensively used under high temperature environment such as turbine engine, cogeneration, and heat treatment equipments. Previous studies have shown that there are three major precipitates in GH4169: equilibrium γ0 phase (Ni3 (Al,Ti) composition and L12 structure), equilibrium δ phase (Ni3 Nb composition and D0a structure), and metastable γ” phase (Ni3 Nb composition and D022 structure) [4]. Both the spherical-shaped γ0 and the disc-shaped γ” contribute to the age-hardening process of GH4169.

Methods

Results

Conclusion