扫描策略对激光选区熔化GH5188合金组织及力学性能的影响

Effect of scanning strategy on microstructure and mechanical properties of GH5188 alloy fabricated by laser powder bed fusion

摘要

系统研究长直线与短直线扫描策略对激光选区熔化（laser powder bed fusion，LPBF）成形 GH5188 高温合金微观组织及力学性能的影响。金相与扫描电镜结果表明：两种扫描策略均形成由柱状晶与等轴晶共同组成的混合组织。短直线策略的熔池熔深较小，因重熔不足而中心区保留更多的小晶粒，使平均晶粒尺寸得到进一步细化（17.17 μm）。相比之下，长直线策略的热流方向更稳定，柱状晶外延生长更充分，沿构建方向形成更强的〈001〉织构，平均晶粒尺寸略大（20.86 μm）。力学性能测试表明：两种策略成形试样的室温拉伸强度与塑性差异较小；980 ℃，高温拉伸强度相当，但长直线策略试样的伸长率较短直线策略提升 28.6%；927 ℃/90 MPa 持久测试，长直线策略试样的断裂时间（50.2 h±1.8 h）及塑性（10.1%±0.5%）显著优于短直线策略（45.3 h±2.1 h，7.6%±0.4%）。断面微观组织分析显示，短直线策略试样的裂纹分布更加密集，且晶界处伴随明显的碳化物析出与粗化，反映出更高的晶界损伤敏感性。断口形貌进一步验证了裂纹主要沿晶界扩展的特征。相比之下，长直线策略试样的晶粒较大、晶界数量较少，因此晶界相关的损伤与裂纹扩展明显减缓。

Abstract

This study systematically investigates the effects of long-line and short-line scanning strategies on the microstructure and mechanical properties of GH5188 superalloy fabricated by laser powder bed fusion (LPBF). Metallography and SEM results reveal that both strategies produce mixed microstructures composed of columnar and equiaxed grains. Due to the shallower melt pool and insufficient remelting, the short-line strategy retains finer grains at the melt-pool center, leading to further grain refinement (17.17 μm). In contrast, the long-line strategy provides a more stable heat-flow direction, resulting in stronger 〈001〉 texture development along the build direction and a slightly larger average grain size (20.86 μm). Mechanical testing shows that the two strategies lead to similar tensile strength and ductility at room temperature. At 980 ℃, the tensile strengths are comparable, while the elongation of the long-line specimens is 28.6% higher than that of the short-line specimens. Under the 927 ℃/90 MPa stress rupture condition, the long-line specimens exhibit a significantly longer rupture life (50.2 h±1.8 h) and higher ductility (10.1%±0.5%) than the short-line specimens (45.3 h±2.1 h; 7.6%±0.4%). Cross-sectional analysis shows that the short-line specimens contain more densely distributed cracks, along with pronounced carbide precipitation and coarsening at grain boundaries, indicating higher grain-boundary damage sensitivity. Fractographic analysis further confirms that cracks preferentially propagate along grain boundaries. These findings clarify the microstructural origins of high-temperature performance differences and provide guidance for optimizing LPBF scanning strategies for GH5188 alloy.

关键词

激光选区熔化 / 钴基合金 / 扫描策略 / 力学性能 / 持久性能

Key words

laser powder bed fusion (LPBF) / cobalt-based superalloy / scanning strategy / mechanical property / stress rupture property

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基金资助

辽宁省科技重大专项(2024JH1/11700038)

国家重点研发计划(2023YFB3712003)

中国科学院青年创新促进会项目(2020198)