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In-situ modification of thermal, microstructural, and mechanical responses by altering scan lengths in laser powder bed fusion additive manufacturing of Ti-6Al-4V.

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Title: In-situ modification of thermal, microstructural, and mechanical responses by altering scan lengths in laser powder bed fusion additive manufacturing of Ti-6Al-4V.
Authors: Promoppatum, Patcharapit1 (AUTHOR) patcharapit.pro@kmutt.ac.th, Chayasombat, Bralee2 (AUTHOR), Nyein Soe, Aung1 (AUTHOR), Sombatmai, Atikom1 (AUTHOR), Sato, Yuji3 (AUTHOR), Suga, Tetsuo3 (AUTHOR), Tsukamoto, Masahiro3 (AUTHOR)
Source: Optics & Laser Technology. Sep2023, Vol. 164, pN.PAG-N.PAG. 1p.
Subjects: Porosity, Yield stress, Powders, Finite element method, Lasers, Electron beam melting
Abstract: • The present study explored the effect of the scan lengths from 0.25 to 2 mm on thermal, microstructural, and mechanical responses. • Shorter scan lengths resulted in a noticeable increase in yield stress, but a reduction in strain at failure. • The increase in void fraction was found to be highly localized at the interface between hatch regions, especially at a small scan length. • The microstructure was mostly alpha prime martensite, but the lath size became smaller with shorter scan lengths. • Finite element analysis showed that shorter scan lengths led to higher cooling rates, which could explain the smaller lath size. • The study suggests that varying the scan length can be used to modify mechanical properties, but further research is needed for defect minimization. Although a laser powder bed fusion (LPBF) process involves a complex laser-material interaction, it allows the possibility of designing the process conditions to achieve a distinct thermal history. Thus, in-situ control of microstructures and mechanical properties is feasible. Among many process parameters, the scan length has been regarded as an important variable, which can have a strong effect on thermal responses. Therefore, the present study performed a numerical and experimental assessment of the effect of scan lengths on thermal, microstructural, and mechanical behaviors on the LPBF of Ti-6Al-4V. Four scan lengths of 0.25, 0.5, 1, and 2 mm were used. Overall, it was found that shortening scan lengths can result in a more rapid cooling. As a result, even though the phase fraction was indifferent in each sample, a lath size refinement was observed for the sample with a short scan length. By changing the scan length from 2 to 0.25 mm, the lath size changed from 1.05 to 0.76 µm, and the yield stress increased from 1031 MPa to 1125 MPa. Nonetheless, the ductility reduction was also observed, which was mainly driven by a significant void escalation at 0.25 mm scan length. In addition, not only was the void fraction higher with shorter scan lengths, but it also become more highly localized at the hatch interface, especially at a scan length of 0.25 mm. Therefore, the gain of yield stress with the loss of ductility at the short scan length was noted. Ultimately, the present work revealed comprehensively the interaction between thermal, microstructural, and mechanical responses under different built conditions. These understandings could be used further toward process optimization in the LPBF technology. [ABSTRACT FROM AUTHOR]
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Database: Engineering Source
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Abstract:• The present study explored the effect of the scan lengths from 0.25 to 2 mm on thermal, microstructural, and mechanical responses. • Shorter scan lengths resulted in a noticeable increase in yield stress, but a reduction in strain at failure. • The increase in void fraction was found to be highly localized at the interface between hatch regions, especially at a small scan length. • The microstructure was mostly alpha prime martensite, but the lath size became smaller with shorter scan lengths. • Finite element analysis showed that shorter scan lengths led to higher cooling rates, which could explain the smaller lath size. • The study suggests that varying the scan length can be used to modify mechanical properties, but further research is needed for defect minimization. Although a laser powder bed fusion (LPBF) process involves a complex laser-material interaction, it allows the possibility of designing the process conditions to achieve a distinct thermal history. Thus, in-situ control of microstructures and mechanical properties is feasible. Among many process parameters, the scan length has been regarded as an important variable, which can have a strong effect on thermal responses. Therefore, the present study performed a numerical and experimental assessment of the effect of scan lengths on thermal, microstructural, and mechanical behaviors on the LPBF of Ti-6Al-4V. Four scan lengths of 0.25, 0.5, 1, and 2 mm were used. Overall, it was found that shortening scan lengths can result in a more rapid cooling. As a result, even though the phase fraction was indifferent in each sample, a lath size refinement was observed for the sample with a short scan length. By changing the scan length from 2 to 0.25 mm, the lath size changed from 1.05 to 0.76 µm, and the yield stress increased from 1031 MPa to 1125 MPa. Nonetheless, the ductility reduction was also observed, which was mainly driven by a significant void escalation at 0.25 mm scan length. In addition, not only was the void fraction higher with shorter scan lengths, but it also become more highly localized at the hatch interface, especially at a scan length of 0.25 mm. Therefore, the gain of yield stress with the loss of ductility at the short scan length was noted. Ultimately, the present work revealed comprehensively the interaction between thermal, microstructural, and mechanical responses under different built conditions. These understandings could be used further toward process optimization in the LPBF technology. [ABSTRACT FROM AUTHOR]
ISSN:00303992
DOI:10.1016/j.optlastec.2023.109525