SLM-316L不锈钢纳米尺度界面结构特征及其对晶间腐蚀的影响机制

Selective laser melting (SLM), which is one of the rising 3D-printing technologies, could exactly fabricate the components with complex shapes and have great application potential in the energy and medical fields. The excellent corrosion resistance of stainless steels is one of the critical factors for their extensive application. However, the dendritic growth during the solidification results in a complex interfacial structure in the SLM stainless steels, which would make the SLM stainless steels suffer from intergranular corrosion. Now, both the intergranular corrosion mechanism of SLM stainless steels and the effect on the interfacial structure on the initiation and extension are unclear. Based on this, the current study aims to investigate the influence of the interfacial structure on the intergranular corrosion of SLM-316L stainless steel following the line of research: dendritic growth-interfacial structure-precipitates from grain boundaries-intergranular corrosion. The advanced microstructure characterization technologies is used to deeply investigate the dendritic growth and the corresponding interfacial structures, and reveal the relationship between the interfacial structure and the formation of the precipitated phases at the grain boundaries. The effect of the interfacial structures on the initiation and extension of intergranular corrosion of SLM stainless steels is studied using the nano-electrochemical in-situ testing technology. Finally, the methods for improving the resistance against intergranular corrosion of SLM stainless steels are obtained based on the research results of this study.

选区激光熔化技术（SLM）是一种新兴的金属3D打印技术，能够快速精密加工结构复杂的不锈钢零件，在能源、医疗等领域中有非常广阔的应用前景。良好的耐蚀性能是不锈钢广泛应用的关键性能之一，然而SLM不锈钢冷却凝固过程中的枝晶生长导致其具有复杂的界面结构，这使得SLM不锈钢将面临严重的晶间腐蚀风险。目前，SLM不锈钢的晶间腐蚀性能以及界面结构特征对其晶间腐蚀性能的作用机制等关键性问题尚未解决。基于此，本项目将围绕枝晶生长-界面结构-晶界析出相-晶间腐蚀的研究思路开展研究工作，采用先进的材料结构表征分析手段，深入研究SLM不锈钢熔池不同部位枝晶生长情况及所对应的纳米尺度界面结构特征，阐明SLM不锈钢界面结构对晶界析出相特征的作用规律，采用电化学纳米原位测试技术从纳米尺度揭示界面结构影响SLM不锈钢晶间腐蚀萌生、扩展的机制，探索优化SLM不锈钢耐晶间腐蚀性能的调控机制。

选区激光熔化技术（SLM）是一种新兴的金属3D打印技术，能够快速精密加工结构复杂的不锈钢零件，在能源、医疗等领域中有非常广阔的应用前景。良好的耐蚀性能是不锈钢广泛应用的关键性能之一，然而SLM不锈钢冷却凝固过程中的枝晶生长导致其具有复杂的界面结构，这使得SLM不锈钢将面临严重的晶间腐蚀风险。基于此，本项目SLM-316L不锈钢为研究对象，重点关注激光熔池内组织结构的不均匀性，围绕枝晶生长-界面结构-晶界析出相-晶间腐蚀的研究思路开展工作。研究了SLM-316L不锈钢的腐蚀行为，探究了SLM-316L不锈钢特征组织结构与点蚀、钝化之间的内在关联，结果表明，SLM-316L不锈钢的耐点蚀行为通常优于传统轧制316L不锈钢，SLM-316L不锈钢的点蚀主要其起源于加工气孔；高密度位错、晶内胞状结构等能够促进钝化膜的形核，进而提高钝化性能；研究了后热处理对SLM-316L不锈钢组织结构的影响规律，揭示了SLM-316L不锈钢特征结构的演变机制，结果表明，650 ºC和900 ºC热处理时SLM-316L不锈钢打印痕迹、位错和晶内胞状结构逐渐消失，1150 ºC热处理时SLM-316L不锈钢发生再结晶，并且晶界出有MnS等颗粒物析出。研究了SLM-316L不锈钢晶间腐蚀的萌生、扩展机制，阐明了后热处理对SLM-316L不锈钢晶界腐蚀的作用机理，结果表明，900 ºC后热处理试样的晶界处析出碳化物，因而表现出最大的晶间腐蚀敏感性；1150 ºC后热处理试样的晶界处MnS形成，成为SLM-316L不锈钢晶间腐蚀的敏感位置，提高晶间腐蚀敏感性。本项目的研究结果不仅能够推进有关纳米尺度下局部腐蚀行为与机理的深层次研究，还能为 SLM 不锈钢工业应用的安全性和寿命评估提供理论依据。