Experimental investigation of process parameter variations on the microstructure and failure behavior of IN718 structures in PBF-LB/M

Abstract

Conventional manufacturing technologies, such as milling or casting, are limited in terms of the manufacturable complexity of the parts to be produced. They are also restricted in terms of the local modifiability of the mechanical properties. Additive manufacturing, specifically the Powder Bed Fusion of Metals using a Laser Beam (PBF-LB/M), is a novel method, which is capable of addressing both limitations. However, the resulting parts are often prone to cracking during PBF-LB/M and in the service afterward because of high thermally induced local stress intensities. Selectively modifying the process parameters during the fabrication can be a suitable strategy to locally reduce the failure susceptibility. Over the course of this study, samples made from the nickel-based superalloy Inconel 718 were manufactured with varying laser powers, hatch distances, and scan speeds. The samples were divided into stress crack specimens as well as static and dynamic tensile test specimens. The grain structure was investigated, and correlations between the microstructure and the cracking susceptibility were determined. It was found out that variations in the laser power had the most pronounced effect on the grain structure and the failure behavior. An increasing grain size enhanced the fracture resistance in the stress crack samples while the static and dynamic mechanical properties deteriorated. Based on these results, the application area of PBF-LB/M could potentially be widened due to the manufacturability of parts otherwise susceptible to stress-induced cracking. The mechanical properties of as-built parts can remain unchanged utilizing a local process parameter adaption.