Improved surface quality and fatigue life of high-strength, hybrid particle reinforced (Ti+B4C)/Al-Cu-Mg metal matrix composite processed by dual-laser powder bed fusion

Abstract

High surface roughness observed in the as-built condition is still a limiting factor for metal parts processed by laser powder bed fusion (L-PBF). This is mainly due to the highly degrading effect of poor surface quality on fatigue performance. As a promising in-process alternative, the dual-laser powder bed fusion (dL-PBF) technique has recently been proven to increase the surface quality and fatigue life of L-PBF metal parts with up-facing inclined surfaces, reducing the need for additional post-treatments. This paper shows the beneficial effect of dL-PBF on the three-point bending fatigue life of lightweight high-strength hybrid particle reinforced (Ti+B4C)/Al-Cu-Mg metal matrix composite coupons, while comparing the dL-PBF processed to the as-built (AB), electric-discharge machined (EDM) and conventionally machined (milled) conditions. The effect of different surface conditions on several fatigue-influencing factors, i.e., surface roughness and concomitant roughness-induced stress concentration factor, surface residual stress, and hardness is discussed, as well as the resultant fatigue performance. The 73 % surface roughness reduction is identified as the major dL-PBF-influenced factor, leading to significantly enhanced fatigue life values that approach those of conventionally machined surfaces.