Microstructure and mechanical properties of Ni-Fe-Cr-Al wrought alumina forming superalloy heat-treated at 600–1100 °C

Abstract

Haynes® HR-224® is a new wrought alumina-forming Ni–27.5Fe–20Cr–3.8Al alloy developed to be applied in aggressively oxidizing environments. Although the superior environmental resistance of Haynes® HR-224® has been already proved under various atmospheric conditions, very limited information is available on controlling its microstructure and mechanical properties through heat treatment processing. In this work, the effect of heat-treatment temperature on structural evolution and mechanical response of Haynes® HR-224® is systematically examined for the first time. The commercial sheet material in the solution annealed condition was subjected to 2 h annealing (aging) followed by water quenching at 600–1100 °C (with an interval of 100 °C). The SEM/EDS and TEM techniques were applied to examine a heat-treatment induced structural evolution of the material, while mechanical characteristics were evaluated in room temperature static tensile tests carried out by using non-standard miniaturized specimens. A prominent increase in room temperature tensile strength accompanied by a reduction of ductility was measured in samples heat-treated at 600–800 °C/2 h. Discontinuous precipitation (DP) of (γ + γ’)/M23C6 was recognized as the main structural process lying behind the observed mechanical behavior of the examined material.