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

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. Keywords: Creep, EBSD, Grain boundary connectivity, Laser deposition, Small punch test, Wilshire equations