Precipitation-hardened high strength alloys, such as nickel-based alloys, aluminum alloys and stainless steels, are susceptible to hot cracking during 3D printing. This issue is typically mitigated by reducing solute segregation or promoting columnar-to-equiaxed transition. Here, we demonstrate an alternative approach by increasing segregation solutes, especially Ti element, to reduce hot cracking during laser powder bed fusion (LPBF) additive manufacturing of a new austenitic stainless steel (ASS). Enhanced segregation triggers peritectic-like reactions at cell/grain boundaries, forming multiple phases that bridge FCC dendrites. As a result, the new ASS exhibited excellent printability across a broad range of processing parameters. The as-built (AB) steel displayed a heterogeneous columnar grain microstructure with fine L21/BCC/C14 precipitates partially decorating cell structures, achieving a yield strength (σ0.2) above 690 MPa and uniform elongation (εu) beyond 17.5 %. The epitaxial growth of the columnar grains was frequently interrupted by puddles of fine grains, leading to near-isotropic tensile properties. Following isochronal annealing at temperatures between 600 and 1150 °C for two hours, the AB steel underwent varying degrees of microstructure evolution, resulting in a broad range of mechanical properties (σ0.2 from 300 to 1460 MPa and εu from 59.5 % to 7.6 %). This high strength is attributed to the formation of the L21/σ/η multiple phases at cell and grain boundaries, in combination with coherent L12-ordered (γ') nanoparticles precipitated within cell interiors during aging. This study explored that compositional design leveraging the unique solidification behavior of the LPBF process can produce hierarchical-structured stainless steels with excellent printability and tunable mechanical performance.

中文翻译：

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一种新型时效硬化奥氏体不锈钢，具有卓越的可打印性


沉淀硬化的高强度合金，如镍基合金、铝合金和不锈钢，在 3D 打印过程中容易发生热裂纹。通常通过减少溶质分离或促进柱状到等轴状转变来缓解这个问题。在这里，我们展示了一种替代方法，通过增加偏析溶质，尤其是 Ti 元素，来减少新型奥氏体不锈钢 （ASS） 的激光粉末床熔融 （LPBF） 增材制造过程中的热裂纹。增强的离析会在细胞/晶界触发类似 peritectic 的反应，形成桥接 FCC 树晶的多个相。因此，新型 ASS 在广泛的加工参数范围内表现出出色的适印性。完工 （AB） 钢表现出非均质柱状晶粒微观结构，细小的 L21/BCC/C14 沉淀部分装饰细胞结构，屈服强度 （σ0.2） 超过 690 MPa，均匀伸长率 （εu） 超过 17.5 %。柱状晶粒的外延生长经常被细晶粒水坑打断，导致近各向同性的拉伸性能。在 600 至 1150 °C 的温度下等时退火 2 小时后，AB 钢经历了不同程度的微观组织演变，从而产生了广泛的机械性能（σ0.2 从 300 到 1460 MPa，εu 从 59.5 % 到 7.6 %）。这种高强度归因于在细胞和晶界形成 L21/σ/η 多相，以及在老化过程中在细胞内部沉淀的相干 L12 有序 （γ'） 纳米颗粒。 本研究探讨了利用 LPBF 工艺独特的凝固行为的成分设计可以生产出具有出色可打印性和可调机械性能的分层结构不锈钢。