Fatigue behavior of additively manufactured 17-4 PH stainless steel: The effects of part location and powder re-use

Abstract

In laser beam powder bed fusion (LB-PBF), an additive manufacturing method, powder is often reconditioned and re-used multiple times to save cost. Considering the assumption that powder characteristics may affect the LB-PBF part quality, it is essential to understand how such characteristics change by re-using the powder and how these changes affect the mechanical properties of the fabricated part. Therefore, this study systematically investigates the effect of powder re-use on the powder characteristics, microstructural features, and mechanical properties of LB-PBF 17−4 precipitation hardening (PH) stainless steel (SS) specimens in both as-built and machined surface conditions. In addition, the dependency of microstructural features and mechanical properties on the location of the specimen on the build plate and how the powder re-use affects such location dependencies are studied. No significant effect of powder re-use and location dependency was observed on tensile or fatigue behavior of LB-PBF specimens in the as-built surface condition. However, an improved fatigue resistance, specifically in the high cycle regime, was observed for machined specimens fabricated by heavily re-used powder. In addition, considerable location dependency on the fatigue behavior was observed for machined specimens fabricated by unused powder. This location dependency, however, decreased with increasing powder re-use. The observed dependency of the fatigue behavior to the location and the improved fatigue resistance are explained by the better flowability and less compressibility of the re-used powder due to the decreased number of very fine particles and agglomerates within the powder batch. These improved powder characteristics resulted in a more uniform powder distribution on the build plate and less and smaller defects in the specimens.