奥氏体不锈钢碳梯度过饱和复合改性机制研究

In order to solve the scientific problem of combined improvements in the corrosion resistance and interfacial contact resistance of the austenite stainless steel bipolar plates for polymer electrolyte membrane (PEM) fuel cell, a new solution of the corrosion resistance modification for inner surface of the metal and the electrical contact modification for outer surface of the metal is proposed. The plasma source ion carburizing process with an independent intellectual property rights is utilized to modify AISI 316 austenite stainless steel. It could produce a carburized layer with a controllable and independent carbon distribution of the concentration and its depth, whose gradient concentration distribution consists of superhigh-saturated carbon (SHS-C> 3 wt.%) in the outer surface, super-saturated carbon (SS-C) in the subsurface and saturated carbon (S-C) in the matrix. The thermodynamics and kinetics of non-equilibrium phase transformation are investigated and revealed in the austenite with different saturated carbon concentration. A relationship between the composition, morphology, microstructure of the SHS-C/SS-C/SS-C gradient carbon alloy layer and the properties of corrosion resistance and surface contact resistance is established. The modification mechanism will be explored for the gradient carburized layer as carbide precipitation sublayer/supersaturated carbon solid solution sublayer/saturated carbon solid solution sublayer. The austenite stainless steel bipolar plates, whose inner surface has good corrosion resistance as well as outer surface with low surface contact resistance, are prepared by the combined surface modification under the optimized process conditions. It could provide the theoretical basis and the technical support for the production of the metallic bipolar plates used in the commercial PEM fuel cell.

针对燃料电池低成本、高强度、易加工的双极板材料-奥氏体不锈钢存在的抗腐蚀性能和界面接触电阻性能难以同时改善的难题，提出了"金属内表面抗蚀改性和外表面电接触改性"的复合解决方案。采用自主知识产权的等离子体源离子渗碳技术改性处理AISI 316奥氏体不锈钢，制备碳浓度及其深度分布独立可控的，外表面呈超高过饱和(SHS-C>3 wt.%)、亚表面呈过饱和(SS-C)到内部呈饱和(S-C)状态的碳梯度分布渗碳层。研究不同碳饱和浓度的奥氏体非平衡相变热力学和动力学，建立SHS-C/SS-C/SS-C梯度合金化表面成分、形貌、组织结构与腐蚀和电接触性能的关系，探明碳化物析出亚层/碳过饱和固溶亚层/碳饱和固溶亚层的梯度渗碳改性机制。在优化的工艺条件下，制备具有内表面抗蚀改性和外表面电接触改性复合作用的表面改性奥氏体不锈钢双极板，为解决质子交换膜型燃料电池用金属双极板发展的瓶颈问题提供理论基础和技术保障。