High‐Temperature Creep Properties of an Additively Manufactured Y2O3 Oxide Dispersion‐Strengthened Ni–Cr–Al–Ti γ/γ’ Superalloy

Abstract

The effects of the modification of a high‐γ' Ni–8.5Cr–5.5Al–1Ti (wt%) model superalloy with 0.5 wt% Y2O3, manufactured by laser powder bed fusion, on the microstructure and compressive creep resistance, are investigated. Compared with the base alloy, the oxide dispersion‐strengthened (ODS) alloy exhibits 8–10 times slower creep rates at 800 °C, over a wide range of compressive stresses (35–250 MPa). Two creep regimes are observed: diffusional creep, hypothesized to be due to grain boundary sliding, and dislocation creep, with stress exponents n of 2 and 5, respectively. Compared with the horizontal direction, the vertical build direction is characterized by lower creep rates, due to the vertically elongated grain structure. Nonetheless, the ODS alloy's weakest (horizontal) direction shows better creep resistance than the non‐ODS alloy in its strongest (vertical) direction, despite a higher number of as‐built defects (slag, cracks) in the ODS alloy. The strengthening potential of ODS modification of additively manufactured nickel‐based superalloys is thus demonstrated. The development of successful commercial ODS nickel superalloys for additive manufacturing processing requires further additions of grain boundary strengthening elements as the dispersoids do not significantly increase the grain boundary strength, as their cracking is prevalent in the ODS alloy.