Abstract
The purpose of this study is to investigate the effects of laser spot size on the mechanical properties of AISI 420 stainless steel, fabricated by selective laser melting (SLM), process. Tensile specimens were built directly via the SLM process, using various laser spot diameters, namely 0.1, 0.2, 0.3, and 0.4 mm. The corresponding volumetric energy density (EV) is 80, 40, 26.7, and 20 J/mm3, respectively. Experimental results indicate that laser spot size is an important process parameter and has significant effects on the surface roughness, hardness, density, tensile strength, and microstructure of the SLM AISI 420 builds. A large laser spot with low volumetric energy density results in balling, un-overlapped defects, a large re-heated zone, and a large sub-grain size. As a result, SLM specimens fabricated by the largest laser spot diameter of 0.4 mm exhibit the roughest surface, lowest densification, and lowest ultimate tensile strength. To ensure complete melting of the powder and melt pool stability, EV of 80 J/mm3 proves to be a suitable laser energy density value for the given SLM processing and material system.
Highlights
Selective laser melting (SLM) is one of the popular additive manufacturing (AM) techniques in fabricating metallic components [1,2]
The final quality of the SLM build is significantly dependent on the heat input, which is controlled by the laser process parameters
As an extension of our earlier work [26], the aim of this study is to investigate the relationship of the spot size with the surface finish and mechanical properties of SLM built AISI 420 parts
Summary
Selective laser melting (SLM) is one of the popular additive manufacturing (AM) techniques in fabricating metallic components [1,2]. There are numerous studies investigating the correlation between process parameters (e.g., laser heat input, scanning strategy, and build direction) and the SLM build qualities (such as density, surface roughness, and mechanical properties) [3,4,5,6,7,8]. Among the SLM process parameters, the spot size of the laser is an effective variable in controlling the laser energy density, so as to adequately melt the powder and build parts of acceptable quality [17]. There is lack of study on the effects of laser spot size on the microstructure, surface finish, and mechanical properties of AISI 420 fabricated via SLM. The AISI 420 stainless steel powder (Sanyo Special Steel Corporation, Ltd., Hyogo-ken, Japan) is Materials 2021, 14, 4593
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