Correlation Between Microstructure and Tensile Properties of STS 316L and Inconel 718 Fabricated by Selective Laser...

Understanding how microstructure influences mechanical behavior is central to optimizing additive manufacturing techniques. Prior research has shown that selective laser melting (SLM) can produce complex geometries in metallic alloys, but the relationship between microstructural features and tensile properties remains unclear. Established knowledge includes the formation of columnar grains and dendrites during solidification, yet gaps persist in how these structures affect tensile elongation and strength. This uncertainty motivates investigations into how processing parameters influence microstructure and, in turn, mechanical performance. Current studies have not fully resolved how variations in melt pool geometry or porosity impact tensile outcomes. This gap drove the current work to explore the correlation between microstructure and tensile properties in SLM-processed alloys. The need for precise control of processing conditions is well recognized, but the specific mechanisms remain underexplored. This paper's contribution lies in analyzing how microstructural differences in STS 316L and Inconel 718 affect tensile properties across different build heights and planes.

The aim of this study is to investigate how microstructural features influence tensile properties in SLM-processed STS 316L and Inconel 718. The specific problem addressed is the lack of clarity regarding how directional solidification affects mechanical behavior in these alloys. The motivation stems from the need to optimize processing parameters for improved tensile performance. The study focuses on comparing microstructure and tensile properties across different build heights and planes. By examining columnar grains and dendrites, the researchers aim to understand how solidification patterns affect mechanical outcomes. The study also seeks to determine how porosity and melt pool geometry influence tensile elongation and strength. This work aims to provide insights into how processing conditions can be adjusted to enhance tensile properties. The ultimate goal is to inform the development of more effective SLM strategies for these alloys.

The study employed selective laser melting (SLM) to process STS 316L and Inconel 718 specimens. Microstructure analysis was conducted at various build heights—top, middle, and bottom—and across different planes (YZ, ZX, and XY). The researchers examined columnar grains and dendrites formed during directional solidification. They measured average melt pool width, depth, and scan track width to assess processing consistency. Tensile testing was performed to evaluate strength and elongation in both materials. Fractographic analysis was used to identify failure mechanisms and porosity distribution. The study compared microstructural features between the two alloys to determine their impact on tensile properties. The results were synthesized to explore how processing parameters influence microstructure and mechanical behavior.

SLM-processed STS 316L exhibited a tensile strength of 656 MPa and elongation of 75%, significantly higher than other SLM-processed STS 316L specimens. In contrast, SLM Inconel 718 showed moderate tensile strength (1165 MPa) and elongation (11.5%). Fine columnar grains with diameters of 0.5 μm and dense microstructures (0.35% porosity) in STS 316L contributed to enhanced tensile elongation. The melt pool width and depth were similar in both materials due to fixed processing parameters. Fractographic analysis revealed that lack of fusion pores and unmelted powder negatively impacted tensile properties. The study found that directional solidification led to columnar grain formation in both materials. The mechanical performance varied across build heights and planes, with top regions showing distinct microstructural features. These findings suggest that processing conditions must be carefully controlled to optimize tensile properties.

The study's findings suggest that microstructure significantly influences tensile properties in SLM-processed STS 316L and Inconel 718. The authors propose that fine columnar grains and low porosity in STS 316L enhance tensile elongation. They suggest that directional solidification during SLM leads to columnar grain formation, which affects mechanical behavior. The results indicate that processing parameters must be optimized to avoid lack of fusion pores and unmelted powder. The study highlights the importance of controlling melt pool geometry to improve tensile properties. The authors propose that build height and plane orientation influence microstructural variations. These variations, in turn, affect tensile strength and elongation. The study concludes that suitable processing conditions can enhance tensile performance in SLM-processed alloys.