目的 研究不同扫描参数对激光粉末床熔融（Laser powder bed fusion, LPBF）加工Ti-6Al-4V合金表面粗糙度的影响,为优化LPBF工艺提供理论依据。方法 采用条纹和棋盘2种扫描路径,并设置0.11、0.14 mm等2种扫描间距制备试样,结合电子背散射衍射（EBSD）和三维轮廓仪对试样的微观组织及表面粗糙度进行定量分析。结果 相较于条纹路径,采用棋盘路径能够优化热输入分布,显著促进晶粒细化和取向随机化,其平均晶粒尺寸降低了10.78%,晶粒长宽比下降了7.29%,晶粒取向散度（Grain orientation spread, GOS）提升了3.03%,表明柱状晶生长受到有效抑制,晶粒趋于等轴化。当棋盘单元由3 mm缩小至1 mm时,晶粒取向进一步趋于均匀,GOS值从0.68°提升至0.8°,提升幅度为17.65%,但平均晶粒尺寸回升18.15%,晶粒长宽比回升1.98%,表明晶粒细化效果趋于稳定。在表面质量方面,条纹路径因往复扫描造成热积累,导致表面粗糙度较高,Sa为(71.978±3.02) µm;棋盘路径显著改善了熔池流动均匀性,使Sa降至(46.325± 2.85) µm,改善幅度达到35.65%。在棋盘单元从3 mm减至1 mm后,表面粗糙度进一步降至(45.131± 2.10) µm,改善幅度为2.58%。此外,虽然缩小扫描间距在一定程度上促进了晶粒细化,但热积累增强,导致晶粒择优生长加剧,表面粗糙度改善效果不明显。结论 通过优化扫描策略,可有效调控熔池稳定性和晶粒组织演化,进而降低成形件的表面粗糙度。
Abstract
The work aims to systematically investigate the effect of scanning strategy and hatch spacing on the surface roughness and microstructural evolution of Ti-6Al-4V alloy fabricated with Laser Powder Bed Fusion (LPBF), to provide theoretical guidance for process optimization. Ti-6Al-4V samples with dimensions of 5 mm×5 mm×1 mm were manufactured with an EOS M280 LPBF system under various processing conditions. The resulting microstructure and surface quality were quantitatively characterized through electron backscatter diffraction (EBSD) and white-light three-dimensional optical profilometry. The experimental design incorporated two distinct scanning strategies, namely stripe and chessboard patterns, in combination with two different hatch spacing. The hatch spacing of 0.14 mm represented a commonly recommended value, while 0.11 mm corresponded to a higher overlap ratio, aiming to explore the impact of varying overlap on melt pool stability and surface roughness. To further investigate the interaction between scanning strategy and localized thermal behavior, a multi-factorial approach was employed by introducing two chessboard unit sizes of 3 mm and 1 mm. This setup allowed for a comprehensive evaluation of the combined effects of scanning parameters on grain morphology and surface characteristics.
Compared with the stripe scanning pattern, the chessboard strategy significantly improved the uniformity of heat input distribution. This improvement facilitated grain refinement and enhanced the randomness of grain orientation. Under stripe scanning conditions, the average grain size was measured at 2.236 µm. When the chessboard strategy was applied, the average grain size decreased to 1.995 µm, indicating a reduction of 10.78 percent. Additionally, the peak of the grain aspect ratio probability density curve shifted from 1.743 to 1.616, corresponding to a 7.29 percent decrease. These changes collectively suggested effective suppression of columnar grain growth through the chessboard pattern. In terms of crystallographic texture, the peak grain orientation spread (GOS) increased from 0.66° under stripe scanning to 0.68° with the chessboard pattern, indicating an increase of 3.03 percent. A further reduction in chessboard unit size from 3 mm to 1 mm led to a continued increase in GOS to 0.8°, reflecting a 17.65 percent enhancement in grain orientation uniformity. However, this change also resulted in a rise in average grain size to 2.357 µm, representing an 18.15 percent increase, and the grain aspect ratio reached 1.648, marking a slight increase of 1.98 percent. These observations indicated that excessive local heat accumulation began to offset the benefits of refinement and texture weakening, leading to a saturation effect. With respect to surface roughness, the stripe scanning strategy resulted in the highest Sa value of (71.978±3.02) µm due to pronounced thermal accumulation. In contrast, the chessboard strategy significantly improved melt pool homogeneity, reducing the Sa value to (46.325±2.85) µm, which corresponded to a 35.65 percent reduction in surface roughness. Further reduction of the chessboard unit size to 1 mm led to a Sa value of (45.131±2.10) µm, with a marginal additional improvement of 2.58 percent. When the hatch spacing decreased from 0.14 mm to 0.11 mm under stripe scanning conditions, the Sa value was reduced to (52.515±2.54) µm, reflecting a 27.05 percent improvement. However, this enhancement was still less significant than that achieved with the chessboard strategy. Although reducing hatch spacing can promote grain refinement to a certain extent, it also intensified thermal accumulation, which favored directional grain growth and limited further improvements in surface quality.
The findings indicate that optimizing the scanning strategy effectively regulates melt pool behavior and grain evolution, thereby reducing the surface roughness and improving the surface quality of Ti-6Al-4V components manufactured by LPBF.
关键词
激光粉末床熔融 /
扫描参数 /
Ti-6Al-4V /
表面粗糙度 /
晶粒取向 /
晶粒尺寸
Key words
laser powder bed fusion /
scanning parameters /
Ti-6Al-4V /
surface roughness /
grain orientation /
grain size
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基金
国家自然科学基金（52175384）; 上海市现代纺织前沿科学研究基地（X11012301）
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