Multi-laser powder bed fusion of Ti-6.5Al-2Zr-Mo-V alloy powder: Defect formation mechanism and microstructural evolution

Multi-laser powder bed fusion (ML-PBF) has attracted much attention due to its advantage of directly building complex-structured and large-size components. In this work, this technique was conducted to fabricate Ti6.5Al-2Zr-Mo-V (TA15) parts using sequential and synchronized scan strategies. The defect formation mechanism and the effect of the laser beam number (up to four) on density, microstructure, and microhardness were clarified. We find that the densification gradually deteriorates as increasing the number of involved laser beams. The laser-switching induced pores are dominated in the sequential scan strategy, which cause a directional pore distribution along the overlap lines. The synchronized scan strategy has a similar phenomenon. Moreover, the laser intersection induced by the synchronized scan strategy leads to a potential transition of molten pool mode and an increase of recoil pressure, which significantly deteriorates the densification. ML-PBF processed Ti-6.5Al-2Zr-Mo-V parts are composed of near-full acicular martensite ?'. ML-PBF induces the low angle grain boundary to transfer to the high angle grain boundary due to the heat accumulation effect. Consequently, slow grain coarsening of acicular martensite ?' occurs with more laser beams involving in. This leads to the microhardness of single-, dual-, and quadruple- L-PBF processed samples value from -423 Hv to -388 Hv. The microstructure-property correlation in ML-PBF is in good agreement with the Hall-Petch relationship. Multi-laser powder bed fusion (ML-PBF) has attracted much attention due to its advantage of directly building complex-structured and large-size components. In this work, this technique was conducted to fabricate Ti6.5Al-2Zr-Mo-V (TA15) parts using sequential and synchronized scan strategies. The defect formation mechanism and the effect of the laser beam number (up to four) on density, microstructure, and microhardness were clarified. We find that the densification gradually deteriorates as increasing the number of involved laser beams. The laser-switching induced pores are dominated in the sequential scan strategy, which cause a directional pore distribution along the overlap lines. The synchronized scan strategy has a similar phenomenon. Moreover, the laser intersection induced by the synchronized scan strategy leads to a potential transition of molten pool mode and an increase of recoil pressure, which significantly deteriorates the densification. ML-PBF processed Ti-6.5Al-2Zr-Mo-V parts are composed of near-full acicular martensite ?'. ML-PBF induces the low angle grain boundary to transfer to the high angle grain boundary due to the heat accumulation effect. Consequently, slow grain coarsening of acicular martensite ?' occurs with more laser beams involving in. This leads to the microhardness of single-, dual-, and quadruple-L-PBF processed samples value from-423 Hv to-388 Hv. The microstructure-property correlation in ML-PBF is in good agreement with the Hall-Petch relationship. ? 2021 Elsevier B.V. All rights reserved.

Automated summary

Multi-laser powder bed fusion (ML-PBF) is used to fabricate TA15 parts with different laser beam numbers for observing the effect on density, microstructure, and microhardness. Densification deteriorates as the number of laser beams increase. Laser-switching induced pores show different distribution patterns in different scanning strategies.