TY - JOUR
T1 - Peculiar microstructural evolution and hardness variation depending on laser powder bed fusion-manufacturing condition in Ti–6Al–2Sn–4Zr–6Mo
AU - Cobbinah, Prince Valentine
AU - Matsunaga, Sae
AU - Toda, Yoshiaki
AU - Ozasa, Ryosuke
AU - Okugawa, Masayuki
AU - Ishimoto, Takuya
AU - Liu, Yuheng
AU - Koizumi, Yuichiro
AU - Wang, Pan
AU - Nakano, Takayoshi
AU - Yamabe-Mitarai, Yoko
N1 - Publisher Copyright:
© 2024 The Authors
PY - 2024/1
Y1 - 2024/1
N2 - This study aims to comprehensively analyze the phase and microstructure evolution and related hardness variations of the Ti–6Al–2Sn–4Zr–6Mo wt.% (Ti6246) alloy produced by laser powder bed fusion (LPBF) under various laser conditions and to gain insight into the mechanisms of these changes using numerical thermal analysis. Higher laser volumetric densities (VEDs) resulted in a finer α/α' microstructure and increased hardness, exhibiting a positive correlation with the VED, except under extremely high conditions. This contrary trend, reported for the first time, is attributed to the solid-phase transformation from the β phase to metastable α' martensite during LPBF induced by rapid cooling. Despite the finer microstructure, the samples under very high VED conditions showed lower hardness, deviating from the overall trend. The X-ray diffraction peaks in the high-VED samples suggested a partial decomposition of α' to α + β owing to laser-induced reheating of the underlying layers, which is considered a contributing factor to the hardness reduction. The numerical analysis showed that the underlying layer was exposed to high temperatures for a relatively long time under high-VED conditions. It was revealed that the hardness of LPBF-fabricated Ti6246 was influenced by unique thermal processes: rapid cooling and reheating of the pre-solidified part, leading to the formation of a metastable α' phase and partial decomposition into α + β. These findings provide insights for tailoring Ti6246 with desired physical properties via LPBF.
AB - This study aims to comprehensively analyze the phase and microstructure evolution and related hardness variations of the Ti–6Al–2Sn–4Zr–6Mo wt.% (Ti6246) alloy produced by laser powder bed fusion (LPBF) under various laser conditions and to gain insight into the mechanisms of these changes using numerical thermal analysis. Higher laser volumetric densities (VEDs) resulted in a finer α/α' microstructure and increased hardness, exhibiting a positive correlation with the VED, except under extremely high conditions. This contrary trend, reported for the first time, is attributed to the solid-phase transformation from the β phase to metastable α' martensite during LPBF induced by rapid cooling. Despite the finer microstructure, the samples under very high VED conditions showed lower hardness, deviating from the overall trend. The X-ray diffraction peaks in the high-VED samples suggested a partial decomposition of α' to α + β owing to laser-induced reheating of the underlying layers, which is considered a contributing factor to the hardness reduction. The numerical analysis showed that the underlying layer was exposed to high temperatures for a relatively long time under high-VED conditions. It was revealed that the hardness of LPBF-fabricated Ti6246 was influenced by unique thermal processes: rapid cooling and reheating of the pre-solidified part, leading to the formation of a metastable α' phase and partial decomposition into α + β. These findings provide insights for tailoring Ti6246 with desired physical properties via LPBF.
KW - LPBF
KW - Metastable phase
KW - Polycrystalline microstructure
KW - Rapid cooling
KW - Thermal history
KW - Ti6246
UR - http://www.scopus.com/inward/record.url?scp=85200915330&partnerID=8YFLogxK
U2 - 10.1016/j.smmf.2024.100050
DO - 10.1016/j.smmf.2024.100050
M3 - 学術論文
AN - SCOPUS:85200915330
SN - 2772-8102
VL - 2
JO - Smart Materials in Manufacturing
JF - Smart Materials in Manufacturing
M1 - 100050
ER -