Investigation on Microstructure and Mechanical Properties of Hastelloy-X Thin Wall Specimens obtained by PBF-LB/M

Powder Bed Fusion—Laser Beam/Metal (PBF-LB/M) is considered one of the most versatile and promising among the Additive Manufacturing (AM) techniques, enabling the fabrication of dimensionally precise parts due to the lower thermo-mechanical distortions introduced in the process. Moreover, PBF-LB/M facilitates the manufacturability of several metal alloys, such as nickel-based ones, retaining acceptable structural integrity that can be improved with the aid of different post-process operations on the final part. These advantages and capabilities of the process allow the manufacturing of geometrically and dimensionally complex parts, such as thin walls and intricate structures. The aim of this work is to study the impacts on microstructure and mechanical properties based on tensile specimens’ thickness produced in Hastelloy-X alloy. The specimens were produced as per ASTM E8/E8M-24. The material microstructure is evaluated through a grain size and orientation and porosity percentage analysis using an optical microscope. The material mechanical properties are assessed through a tensile test at room temperature on dog bone specimens that were fabricated both parallel and perpendicular to the building direction. The results obtained in this work show a significant reduction in mechanical properties as a function of specimen thickness, resulting from a gradual decrease from the baseline to 40% of it. Specifically, there was a 16% decrease in the Ultimate Tensile Strength, a 23% reduction in the Young's Modulus, and a 41% decrease in the Elongation at Break. In addition, it has been observed that specimens’ printing orientation has an important influence on mechanical properties, regardless of the specimen thickness. An analysis of porosity, grain size, and orientation evaluates the microstructure of tested specimens, revealing significant differences between horizontal and vertical specimens.