激光增材制造不锈钢的凝固组织及调控方法研究进展

激光增材制造技术成形的制件具有自由度大、精度高、质量和性能好等优势，随着该技术的日益发展，其在不锈钢材料领域取得了显著的进展。激光增材制造技术成形不锈钢通常呈现出与传统制备工艺显著不同的非平衡凝固组织，表现出复杂的结构特征，而这些特征决定了合金的性能和应用。介绍了激光熔化沉积和选区激光熔化两种激光增材制造技术，选择典型的316L不锈钢及17-4PH不锈钢，综述了激光增材制造不锈钢凝固组织特征的研究现状，重点关注典型多尺度、层次性的组织结构（包括晶粒、宏观缺陷、熔池组织、胞状亚结构、氧化物夹杂等）。系统分析了激光增材制造不锈钢的组织调控方法，包括调整工艺参数、改变工艺环境及热处理等方式，通过组织调控能够影响晶粒的生长及熔池反应，进一步改善其内部微观组织，如形成间隙固溶体或颗粒夹杂物、细化晶粒及消除孔隙等，同时能促进不同相的析出和转变。通过合理地调控凝固组织，能够显著改善不锈钢的组织及机械性能。最后，对激光增材制造不锈钢的未来发展进行了展望。

Research Progress on Solidification Structure and Control Methods of Stainless Steel Fabricated by Laser Additive Manufacturing

The metal products fabricated by laser additive manufacturing have the advantages of large degree of freedom, high precision, and excellent performance and quality. With the growing development, laser additive manufacturing technology has made a significant progress in the field of stainless steel. Compared with the products prepared by conventional methods, the stainless steel fabricated by laser additive manufacturing possesses a completely different non-equilibrium solidification structure, and exhibits complex structural features that determine the properties and applications of the alloys. Two laser additive manufacturing technologies of laser melting deposition and selective laser melting were introduced. Typical 316L stainless steel and 17-4PH stainless steel were selected to investigate the research status of solidification structure characteristics of stainless steel fabricated by laser additive manufacturing, with the focus on the typical multi-scale and hierarchical structure (including grains, macro defects, molten pool structure, cellular substructure, oxide inclusions, etc.). All importantly, the structure control methods of stainless steel fabricated by laser additive manufacturing were systematically revealed, including the adjustment of process parameters, change of process environment and heat treatment. Structure control could affect the growth of grains and the reaction of molten pool, which further improved the internal microstructure, such as forming interstitial solid solutions or particle inclusions, refining grains and eliminating pores, and promoted the precipitation and transformation of different phases. The microstructure and mechanical properties of stainless steel could be significantly improved by rationally controlling the solidification structure. Finally, the future development of laser additive manufacturing for fabricating stainless steel was also prospected.