Research on High Layer Thickness Fabricated of 316L by Selective Laser Melting.

Shuo Wang,Yingyi Ma,Jin Yang,Wentian Shi,Feifei Zhang,Dong Han,Yude Liu,Bin Qi

doi:10.3390/ma10091055

Abstract

Selective laser melting (SLM) is a potential additive manufacturing (AM) technology. However, the application of SLM was confined due to low efficiency. To improve efficiency, SLM fabrication with a high layer thickness and fine powder was systematically researched, and the void areas and hollow powders can be reduced by using fine powder. Single-track experiments were used to narrow down process parameter windows. Multi-layer fabrication relative density can be reached 99.99% at the exposure time-point distance-hatch space of 120 μs-40 μm-240 μm. Also, the building rate can be up to 12 mm3/s, which is about 3–10 times higher than the previous studies. Three typical defects were found by studying deeply, including the un-melted defect between the molten pools, the micro-pore defect within the molten pool, and the irregular distribution of the splashing phenomenon. Moreover, the microstructure is mostly equiaxed crystals and a small amount of columnar crystals. The averages of ultimate tensile strength, yield strength, and elongation are 625 MPa, 525 MPa, and 39.9%, respectively. As exposure time increased from 80 μs to 200 μs, the grain size is gradually grown up from 0.98 μm to 2.23 μm, the grain aspect ratio is close to 1, and the tensile properties are shown as a downward trend. The tensile properties of high layer thickness fabricated are not significantly different than those with a coarse-powder layer thickness of low in previous research.

Highlights

Selective laser melting (SLM) is a type of promising metal additive manufacturing (AM) technology, in which functional complex parts can be formed into arbitrary shapes by melting layers of powder particle selectively and successively without traditional processing [1,2,3]
At a point distance of 50 μm, the spheroidization phenomenon was observed with the exposure time increased from 80 μs to 160 μs, for which the line-energy density of single track is relatively lower, and the powder cannot be melted fully
As the exposure time increased from 80 μs to 200 μs, the track width kept expanding from 230.79 μm to 364.41 μm, indicating that molten pool size depended on the exposure time

Summary

Introduction

Selective laser melting (SLM) is a type of promising metal additive manufacturing (AM) technology, in which functional complex parts can be formed into arbitrary shapes by melting layers of powder particle selectively and successively without traditional processing [1,2,3]. SLM has a new potential development of the most innovate laser manufacturing technology, which has been widely used in aerospace, medicine, and automotive fields because of generated metal parts with fine surface roughness, high relative density, high mechanical properties, and even arbitrary complex structures [4,5,6,7,8,9,10,11,12]. During the SLM fabrication process, the formation of low layer thickness can result in high surface precision [13,14,15,16,17,18,19]. Kamath et al investigated the selective laser melting 316L low layer thickness (30 μm) formation process, in which high relative density can be reached 99.81% [20]. Sun et al reported SLM fabrication of 316L with the layer thickness of 50 μm, which was aimed at obtaining a high relative density of 99.9% [22]

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