Effects of heat treatment on microstructure and creep properties of a laser powder bed fused nickel superalloy

S.J Davies,S.P Jeffs,M.P Coleman,R.J Lancaster

doi:10.1016/j.matdes.2018.08.039

Abstract

Nickel-based superalloy C263 has been consolidated with Laser Powder Bed Fusion (LPBF) with two perpendicular build orientations and exposed to either of two heat treatment programmes. This study analyses the effects of build orientation and heat treatment on the resulting microstructures produced in LPBF C263 variants, evaluated against a cast equivalent. Results show that although a strongly anisotropic microstructure was present in standard heat-treated (HT1) LPBF material, this was eradicated following an alternate heat treatment regime (HT2) through recrystallisation, aided by high local strain. Subsequently, their mechanical properties have been assessed by means of the Small Punch (SP) creep test. A contrasting presence of Σ3 formations was observed between the two LPBF heat treatment programmes with the resulting random grain boundary network (RGBN) revealing shorter potential intergranular crack paths in the HT2 material, although grain boundary carbides were found to be the dominant strengthening mechanism for improved creep resistance. Adapted Wilshire equations have been implemented to predict the long-term creep lives of the C263 variants and their apparent activation energies have been determined.

Highlights

The purpose of this study is to evaluate the effects of build orientation and post-process heat treatment on the microstructure of C263 produced via Laser Powder Bed Fusion (LPBF)
An in-depth analysis of five C263 variants was conducted to determine the influence of heat treatments on their microstructures and mechanical properties
The higher temperature solution heat treatment in HT2 has successfully alleviated microstructural anisotropy by reducing texture and the columnar grain structure in LPBF variants

Summary

Introduction

Davies et al / Materials and Design 159 (2018) 39–46 inputs upon structure and properties in metallic components [1,2] One such process is Laser Powder Bed Fusion (LPBF). Ni based superalloys are prominently utilised for applications within aerospace and industrial gas turbine engines where good mechanical properties are required at high temperatures. Much of these high temperature properties are derived from γ’ precipitates, with superior creep rupture strength influenced by grain boundary carbides [6,7]. The Ni based superalloy C263 gains a large proportion of its high temperature properties from a fine globular dispersion of Cr-rich M23C6 carbides, typically precipitating following casting or as a result of heat treatments [8]. The successful precipitation of this phase following an AM processing route is yet to be determined in this alloy

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