Obstructed and unobstructed growth of expanded austenite layers

该研究项目的目标是研究在等离子体辅助热化学扩散处理奥氏体不锈钢（ASS）过程中，利用钢铁和碳制造的活性筛网阻碍和畅通扩展奥氏体层生长的基本方面。重点是研究不同表面处理状态下AISI 316L ASS表面处理过程中最重要的挑战之一，即由不同机制启动的必要表面活化。这种表面活化是形成厚而均匀的扩展奥氏体层的先决条件。主动筛选技术与热化学处理的结合开辟了独特的可能性，例如根据处理类型产生不同类型的反应物质，通过改变主动筛选等离子体功率来调节处理气氛中的物质浓度，以及处理样品的可变偏压等离子体功率。这些独特的机会使得在等离子体渗氮、等离子体渗碳和等离子体氮化渗碳过程中设计不同的表面活化方案以及扩展奥氏体层生长。系统地研究了不同表面活化机制对AISI 316L的影响，以及N/ c供应等离子体浓度和时间依赖性处理对膨胀奥氏体层形成的影响。这涉及到使用激光吸收光谱进行原位等离子体分析，以确定等离子体和活性屏蔽材料表面相互作用产生的反应气体种类和浓度。这些数据将使用表面敏感技术与材料响应相关联，并深入分析N和/或C掺入膨胀奥氏体引起的微观结构演变。结合定量分析方法的结果，对膨胀奥氏体层的阻碍生长和无阻碍生长有了全面的认识。根据热化学扩散处理的类型和ASS的表面处理条件，这些知识可以确定最有效的表面活化机制，以产生厚而均匀的膨胀奥氏体生长。此外，将根据扩展当前的膨胀奥氏体形成理论和转移到传统的等离子辅助处理（无活性筛）的观点来评估这些发现。

The goal of the research project is studying the fundamental aspects of obstructed and unobstructed growth of expanded austenite layers during plasma-assisted thermochemical diffusion treatment of austenitic stainless steels (ASS) by utilizing steel-made and carbon-made active screens. The focus will be to study one of the most important challenges during surface treatment of AISI 316L ASS with different surface finishing states, namely the necessary surface activation initiated by different mechanisms. This surface activation is a prerequisite to form thick and uniform expanded austenite layers.Combination of active screen technology with thermochemical treatment opens up unique possibilities, such as the generation of different kind of reactive species depending on treatment type, adjustable species concentrations in the treatment atmosphere by varying the active screen plasma power, and variable bias plasma power at the treated samples. These unique opportunities enable to design different scenarios for surface activation as well as expanded austenite layer growth during plasma nitriding, plasma carburizing and plasma nitrocarburizing. The effectiveness of different surface activation mechanisms on AISI 316L and the influence of concentration- and time-dependent treatments by the N/C-supplying plasma on the formation of expanded austenite layers are systematically investigated. This involves the use of laser absorption spectroscopy for in-situ plasma analysis to determine the types and concentrations of reactive gas species generated by the interaction of plasma and active screen material surface. These data will be correlated to the resulting material response using surface sensitive techniques as well as in-depth analysis of the microstructure evolution induced by incorporation of N, and/or C, into the expanded austenite. The full understanding of obstructed and unobstructed growth of expanded austenite layers is obtained by combining the results of the quantitative analysis methods. This knowledge allows the identification of the most effective surface activation mechanism to yield thick and uniform growth of expanded austenite depending on the type of thermochemical diffusion treatment and surface finishing condition of the ASS. Furthermore, the findings will be assessed in view of extending current theories of expanded austenite formation and in view of a transfer to conventional plasma-assisted treatments (without active screen).