Effect of Aging Heat Treatment on Residual Stress of Hastelloy X Produced by Laser Powder Bed Fusion

Laser powder bed fusion (L-PBF) is a metal additive manufacturing process that fabricates three-dimensional shapes by layering metal powder and irradiating a laser on it. It has the advantage of being able to manufacture parts with complex shapes with high precision. However, due to the rapid local heat input and cooling caused by the laser, high residual stress occurs in the fabricated materials, which can lead to defects such as distortion, delamination and cracking in the L-PBF components. Therefore, it is important to predict and control the formation behavior of residual stresses. Meanwhile, Hastelloy X alloy, a nickel-based age-hardenable alloy, is widely used due to its excellent corrosion and oxidation resistances. This study aimed to analyze the residual stress of Hastelloy X produced by the L-PBF process and its annealing during aging heat treatment. Cantilever beam-shaped specimens were designed and fabricated for evaluating the residual stress. Cantilever samples aged at 800 ℃ for different times were cut from the supporting legs, and the resulted bending deformations of the cantilever beams was measured. The deformations were quantitatively analyzed by finite element simulations to evaluate the residual stress in the cantilever beams. It was shown that the level of the residual stress in the as-built Hastelloy X is about 520 MPa and is reduced to 140 - 200 MPa by the 800 ℃ heat treatment.