Passivation Layer Tailoring Using Laser Powder-Bed Fusion Additive Manufacturing: A Tribocorrosion Study

Abstract

Laser powder-bed fusion is an additive manufacturing high-energy laser beam creating near-end shape parts directly from a digital computer model. This technique has revealed new trends in manufacturing industry by producing parts with complex geometry and with topology optimizing the weight to strength ratio of structures. In this research, we characterize the corrosion behavior of a Ti6Al4V and AlSi12 alloy fabricated by using laser powder-bed fusion (L-PBF) when they were exposed to corrosive and tribocorrosion conditions. Two synthesis pathways (vertical and horizontal) were employed to produce alloy disks by using high and low laser power resulting in four different thermo-history profiles. The superfine microstructure of L-PBFed Ti6Al4V was revealed using EBSD and XRD, identified as α’ structure (an oversaturated HCP phase) with an n-type titanium oxide passive layer. The surface property was tailored by different 3D printing parameter resulting in a 30% increase in hardness 60% in wear loss and 28% decrease in the oxygen vacancies. The difference in oxygen vacancies tuned the corrosion to wear ratio from 25% to 15% at 2N normal load in simulated body fluid. The corrosion behavior of L-PBFed AlSi12 was tested in simulated acid water. The two different melt pool microstructure (shown in Fig1 (a) and (b)) engineered by the L-PBF building direction results in a difference in the suspiciously of pitting corrosion. The horizontal built specimens show better in pitting resistance, but with a broader probability distribution, which increases the uncertainty in engineering structurer design. The coarse grain silicon precipitation at melt pool boundary result in localized cathode barrier that deflects the pit propagation resulting in shallow pits. However, the heterogeneity of grain boundaries leads to the weakness in forming a protective surface layer under Cl- attack. Figure 1 (a) Pit morphology and (b) melt pool structure and (c) accumulated pitting probability of AM-AlSi12 in dilute Harrison’s solution Figure 1