The effect of heat treatment on microstructure, microhardness, and pitting corrosion of Ti6Al4V produced by electron beam melting additive manufacturing process

Abstract

There has been limited studies on corrosion behaviour of post-processed Electron Beam Melted (EBM) Ti6Al4V, given that the factors affecting corrosion resistance of AM Ti6Al4V remain unclear. This paper proposes using heat treatment method to improve the pitting corrosion resistance of EBM Ti6Al4V. Different treatment profiles alter the microstructure of EBM Ti6Al4V. A clear trend is observed between microhardness and α lath width. As-printed EBM Ti6Al4V exhibits an inferior pitting potential, while heat treatment provided a significant improvement in the corrosion resistance. This study finds that the β phase fraction is a better indicator than the α lath width for pitting corrosion resistance. Solution air-cooled & ageing heat treated EBM Ti6Al4V exhibits good mechanical and corrosion properties, and even performs better than commercial cast Ti6Al4V.

Effect of Heat Treatment and Hot Isostatic Pressing on the Corrosion Behavior of Ti6Al4 V Parts Produced by Electron Beam Melting Additive Manufacturing Technology

“…Nevertheless, Ti and V element concentration decreased in the corroded area (Figure ). The increase in the Al element can indicate the high presence of the α-lath phase as reported in the literature . Meanwhile, it was noted that the pitting corrosion occurs predominantly at the α-phase, while the β-phase seems more resistant against corrosion for EBM Ti 6 Al 4 V. On the other hand, carbon quantity was found higher in the corroded area for HIP1 (Figure and Table ).…”

“…This may be explained by the presence of the β-phase and continuous grain boundary α gb phases, which act as protective barriers against corrosion degradation. According to Xiu et al, both α and β phases had almost similar composition, and β-phase had slightly higher V and Fe, while the α-phase had higher Al element . Regrading to the EDS area of HT1, the V and Ti were higher compared to corroded area of EBM (Table ), which may explain the better corrosion resistance of HT1 versus EBM.…”

“…According to the corrosion test results conducted by Carrozza et al in a stimulated body fluid, they reported that HT at 680 °C for 4 h, followed by furnace cooling, did not have a significant effect on the corrosion behavior. 33 Xiu et al 34 found that postprocessing of EBM Ti 6 Al 4 V revealed that the β phase, rather than the α phase, exhibited better resistance to pitting corrosion. Furthermore, employing a HT involving solution annealing and air-cooling, followed by aging, resulted in improved corrosion resistance.…”

Energy consumption assessment in manufacturing Ti6Al4V electron beam melted parts post-processed by machining

“…Electron beam melting (EBM) is among the most widely used AM techniques to additively build titanium parts layer by layer for lots of applications, such as biomedical, automotive, and aerospace [ 5 ]. The EBM process is carried out in a vacuum at an elevated temperature to obtain stress-relaxed objects having mechanical and material properties better than wrought forging or cast.…”

“…Thus, post-treatment is always required so that the additively manufactured parts reach a better surface finishing. According to the literature, heat treatments [ 5 , 6 ], electrochemical polishing [ 7 ], laser polishing [ 8 ], and machining [ 9 ] are among the most employed post-treatments to improve the surface roughness of EBM parts.…”