Effect of interlayer temperature on melt-pool morphology in laser powder bed fusion

Considering the high correlation of melt-pool size and build quality of a part fabricated by a laser power bed fusion (L-PBF) process, it is important to understand what are the major thermal factors that affect melt-pool size during the build process. This paper conducts an experimental investigation on how interlayer temperature affects the melt-pool morphology through a case study of a square-canonical part of Inconel 718 built with the EOS M280 system. Interlayer temperature is the layer temperature after powder spreading but before scanning a new layer. This paper examines variations in melt-pool morphology across representative layers with a large difference in interlayer temperature. It also investigates how the melt-pool size variation is affected by local temperature change caused by switching the laser scanning direction from hatch-to-hatch within a single layer. It is observed that the melt-pool half-width has increased by 40% - 100% when the interlayer temperature has increased from 100 °C to 300 °C. On the other hand, the variation of melt-pool dimensions due to local temperature change is less significant under a low interlayer temperature at 100 °C. The difference in melt-pool dimensions due to laser turnaround gets amplified when the interlayer temperature reaches high at 300 °C. Moreover, a trend of melt-pool morphology transitioning from a conduction to a convective heat transfer mode is observed at the interlayer temperature of 300 °C. Results of this paper demonstrate that interlayer temperature plays a critical role in thermal effects on melt-pool morphology, indicating a need of controlling interlayer temperature to improve build quality.