In-situ X-ray imaging reveals the effect of spatter on single melt track at high layer thickness during laser powder bed melting

Abstract

Through in-situ micro-focus X-ray imaging technology, the formation processes of melt tracks for 316L were investigated at high layer thicknesses. Some lager size (d > 150 μm) were observed, named ’agglomeration spatter’, which originated at the front of the melt pool. More interestingly, the agglomeration spatter is not always harmful under the experimental conditions of this study, some spatter incorporate into the melt pool can be advantageous for forming the continuous melt track due to their supplement for liquid mass. This also proves a newly identified role of the spatter on the melt track formation. Moreover, direct correlations between the spatter (>50 μm) and defects of the melt track were established. If one large solidified spatter falls and coalesces with another on the melt track surface, it can form balling or protrusion. Sometimes, large spatter clusters fail to incorporate into the melt pool in time, thereby compromising the height consistency of the melt track. The violent surface fluctuations of the melt pool induced by the incorporates of agglomeration spatter results in fish-scale bumps on surface of the melt track. The drop point deviation of the agglomeration spatter even causes discontinuity of the melt track. We also found that the agglomeration spatter can serve as a monitoring indicator after statistical analysis, and the agglomeration spatter with an ejection velocity higher than 0.08 m/s will cause defects. This study provides deep insight into the role of spatter on melt track formation in LPBF.