Analyzing the Interplay of Sintering Conditions on Microstructure and Hardness in Indirect Additive Manufacturing of 17-4PH Stainless Steel

Abstract

Indirect additive manufacturing (AM) methods have recently attracted attention from researchers thanks to their great potential for cheap, straightforward, and small-scale production of metallic components. Atomic diffusion additive manufacturing (ADAM), a variant of indirect AM methods, is a layer-wise indirect AM process recently developed based on fused deposition modeling and metal injection molding. However, there is still limited knowledge of the process conditions and material properties fabricated through this process, where sintering plays a crucial role in the final consolidation of parts. Therefore, this research, for the first time, systematically investigates the impact of various sintering conditions on the shrinkage, relative density, microstructure, and hardness of the 17-4PH ADAM samples. For this reason, as-washed samples were sintered under different time–temperature combinations. The sample density was evaluated using Archimedes, computed tomography, and image analysis methods. The outcomes revealed that sintering variables significantly impacted the density of brown 17-4PH Stainless Steel samples. The results indicated more than 99% relative densities, higher than the value reported by Markforged Inc. (~ 96%). Based on parallel porosities observed in the computed tomography results, it can be suggested that by modifying the infill pattern during printing, it would be possible to increase the final relative density. The microhardness of the sintered samples in this study was higher than that of the standard sample provided by Markforged Inc. Sintering at 1330 °C for 4 h increased the density of the printed sample without compromising its mechanical properties. According to X-ray diffraction analysis, the standard sample provided by Markforged Inc. and “1330 °C—4 h” one had similar stable phases, although copper-rich intermetallics were more abundant in the microstructure of reference samples. This study is expected to facilitate the adoption of indirect metal AM methods by different sectors, thanks to the high achievable relative densities reported here.