High-Temperature Stress-Strain Behavior and Fractographic Characterization of Additively Manufactured Inconel 939

Abstract

This study investigated the stress-strain behavior of additively manufactured IN939 over a temperature range from room temperature to 1000˚C. The results reveal a systematic decrease in ultimate tensile strength (UTS) above 600˚C, accompanied by a non-monotonic variation in yield strength and an abrupt reduction in strain at 800˚C. After completion of the mechanical tests, one side of each fractured specimen was sectioned near the necked region for cross-sectional analysis, while the opposite side was prepared for fractographic examination; both analyses were conducted using scanning electron microscopy (SEM). Failure below 600˚C was characterized by a high γ ’ precipitate density and predominantly intergranular fracture. The anomalous strain response observed at 800˚C is examined in detail, and a transition in deformation mechanisms associated with temperature-induced changes in the alloy’s microstructure is proposed. At 800˚C, fracture surfaces exhibited microcracks, reduced γ ’ density, micro-scale voids, and small discontinuities. At 1000˚C, incipient melting zones were observed, and no ductile dimples were present.