Evaluation of Heat Treatment Parameters on Microstructure and Hardness Properties of High-Speed Selective Laser Melted Ti6Al4V

Abstract

This study presents the investigation on how heat treatment parameters, which are temperature, cooling method, and residence time, influence the microstructural and hardness properties of Ti6Al4V components produced on Ti6Al4V substrate using high speed selective laser melting technique. Heat treatment was performed on the produced samples before they were characterized for microstructure and hardness. The microstructure of the as-built sample contained large columnar β-grains that were filled with martensite α’ phase and had a high hardness of 383 ± 13 HV. At 1000 °C and residence time of maximum 4 h, better heat treatment parameters were seen for the selective laser melting (SLM) produced Ti6Al4V sample since an improved lamellar α + β microstructure was obtained at this condition. This microstructure is known to have improved tensile properties.

Additive Manufacturing of AlSi10Mg and Ti6Al4V Lightweight Alloys via Laser Powder Bed Fusion: A Review of Heat Treatments Effects

“…The as-built L-PBF-ed Ti6Al4V alloy shows a fully or majority martensitic (α′) microstructure within prior columnar β-grains that are arranged along the build direction ( Figure 32 a,b,d,f), as also reported by [ 32 , 59 , 211 , 212 ].…”

“…As previously reported, the other focal point is the cooling method; however, in this case, it also depends on the temperature from which the cooling pathway starts. The effects induced by the cooling rate are moderate if the samples are heat-treated in low-SSTRs, but they become very important when the samples are at temperature > T 0 , as previously discussed [ 32 , 212 , 265 , 271 , 276 , 285 ]. Focusing on this last temperature range, Etesami et al [ 285 ] reported a microstructure formed by primary α-phase containing β-particles and needle-like α′-martensite after 930 °C × 2 h (WQ).…”

“…The same authors reported a complete β transformation at 1008 °C. Lekoadi et al [ 212 ] did not show any observable microstructural changes after 700 °C × 2 h (FC), while Simonelli et al [ 59 ] highlighted the α′ → α + β transformation after 730 °C × 2 h (FC) showing a microstructure formed by α + β structure.…”

“…Longhitano et al [ 271 ] reported the same results after 650 °C × 3 h (FC). Finally, the morphology of the columnar β-grains is not affected during the SR heat treatments, while the quartic α′ is transformed into β phase and the other (primary, secondary and tertiary) into α phase ( Table 9 ) [ 59 , 212 , 227 , 233 , 245 , 265 , 268 , 271 , 285 ].…”

“…In fact, the same authors showed that the diameter of the equiaxed grains is the same as the columnar width. Lekoadi et al [ 212 ] reported an incomplete β-grains transformation after 1000 °C × 2 h, a fully α′ martensite decomposition into α + β lamellar with α-colonies after 4 h, and a globularization after 8 h ( Figure 46 ).…”