Improving fatigue performance of metal parts with up-facing inclined surfaces produced by laser powder bed fusion and in-situ laser remelting

It is well known that the relatively poor surface quality of metal parts produced by Laser Powder Bed Fusion (LPBF) compared to conventionally manufactured parts has a negative effect on their fatigue life. To enhance fatigue life, time consuming post-processing (e.g. machining, polishing) is typically applied to improve the surface quality. Laser remelting is a promising technique for surface quality improvement, applicable to variable shapes. However, laser remelting is traditionally only used as post-process since surfaces inclined with respect to the powder bed are covered with loose powder during building. Recently, the authors have developed a dual laser technique, which enables improving the quality of up-facing inclined surfaces during building. The technique consists of two steps: (1) selectively removing powder from inclined surfaces by laser-induced shock waves, (2) laser remelting newly exposed surfaces. This paper shows a clear improvement in three-point bending fatigue of such treated samples from maraging steel 18Ni-300 and titanium alloy Ti-6Al-4V, compared to as-built state. This performance was quantified by the number of load cycles until failure at a fixed maximum tensile stress level. The improved performance could be linked to reduced surface roughness, total notch depth, critical stress concentration factor and a lower density of surface asperities. The remolten layer exhibited no visible defects and a decreased microhardness, which could beneficially impact the crack nucleation. This technique shows large potential for reducing the time and cost of metal parts produced by LPBF with enhanced fatigue performance by limiting or avoiding the need for surface post-processing.

Automated summary

This paper introduces a method for improving the surface quality and fatigue life of metal parts produced by Laser Powder Bed Fusion (LPBF) through laser remelting. By selectively removing powder from inclined surfaces and performing laser remelting, the fatigue performance of the metal parts is significantly improved. This technique has the potential to reduce the time and cost of post-processing, and enhance the efficiency of LPBF manufacturing.