基于空心阴极效应的奥氏体不锈钢表面氮化行为的研究

Plasma nitriding is an effective materials surface modification process employed for improving surface hardness, wear resistance and the corrosion properties of various steels such as austenitic stainless steel. However, it has some inherent shortcomings, such as damage caused to parts by arcing, the 'edging effect', 'hollow cathode effect' and difficulty in maintaining a uniform chamber temperature, particularly in fullworkloads of components with varied dimensions. Several models have been proposed in the past to explain the mass transfer mechanism in plasma nitriding. These include the models of sputtering and deposition, nitrogen adsorption, and neutral and ion adsorption. However, any of these models can easily be explained the phenomenon of plasma nitriding process. In order to overcome above shortcomings, this project proposed surface nitriding with hollow cathode discharge. Using hollow cathode discharge effect exiting between inner and outer layers the large screen is easily to be heated to higher temperature. Radiation provides the heat that brings components to the required temperature for treatment. Hollow cathode discharge can be able to increase ionization and intensity of discharge, the plasma density increased, the production of ions rised and the ion flux density at the components surface increases. A basic consideration of nitriding processes is to decouple the plasma generation from the components to be nitrided, the arcing damage and the edge effect are eliminated.As such, very complex shaped components can be treated and the active species can even enter blind holes, producing uniform modified layers on all types of geometrical shape and size in a heavily loaded chamber. A high quality modified layer was formed quickly by reaction diffusion of nitrogen atoms into the surface. It offers the equipment and technology advantages, particularly in terms of reduced gas and energy consumption, mass production of complex shape workpiece. Based on the theories of plasma discharge and the principles of the thermochemical surface treatment, flexible change potential of samples in the plasma environment, this includes cathodic, anodic (zero) and floating potential, to investigate the influence of the nitrogen ions and neutral nitrogen particle on the plasma nitriding, providing experimental data for the establishment of the plasma nitriding model. There is an increase in the flexibility and performance of the plasma nitriding process.

针对目前金属材料表面渗扩技术和理论中存在的问题与不足，提出利用低压低温等离子体异常辉光放电过程中的空心阴极效应进行材料表面渗氮改性处理。本项目采用双层网状圆筒组成空心阴极结构环绕工作空间，气体经过空心阴极放电电离向工作空间提供高浓度高活性的工作介质，同时还可作为高效热源辐射加热工件。奥氏体不锈钢工件可不再作为传统的放电阴极，避免了离子轰击和辉光放电特性所引起的表面打弧和边缘效应等问题。可保持原有的光洁度，获得组织性能均匀的改性层。具有明显的设备和工艺优势，节省能源，可批量生产形状复杂的工件。借助空心阴极放电结构设计的特点，灵活改变工件所处电位，研究含氮正离子和中性粒子对渗氮行为的影响，期望对长期存在争议的渗氮机理和控制渗氮过程的关键因素进行有益的探索，为低温等离子体在奥氏体不锈钢氮化应用方面提供技术和理论支持。

在传统离子渗氮处理过程中，奥氏体不锈钢工件作为放电系统的阴极，受辉光放电特性和电场效应的影响,存在表面打弧与边缘效应等弊端。特别是工件几何形状的变化导致表面电场强度的差异，造成离子轰击强度不同，导致改性层组织与性能不均匀。在借鉴活性屏渗氮技术的优点基础上，项目组提出了基于空心阴极放电效应下的离子渗氮新技术，实现低经济成本和操作简单的改性处理。该技术克服了活性屏渗氮技术中辉光放电强度低的弊端。采用多种空心阴极结构环绕工作空间，产生空心阴极放电产生高浓度高活性的等离子体源，关键摩擦副可不作为放电阴极，在避免传统渗氮中的弊端的同时，完成渗氮处理。.根据能量和质量守恒原理，借助气体热力学和传热学理论，用数值分析方法模拟空心阴极放电周围空间温度场,建立了传质传热方程。本项目组与清华大学摩擦学国家重点实验室合作，完成了新型空心阴极离子源渗扩装置的设计与制造。研究空心阴极放电产生的各类粒子与奥氏体不锈钢表面相互作用过程，放电参数、放电特性对改性层的影响，阐述了改性层（特别是S 相）形成的微观机制与物理本质。研究了奥氏体不锈钢氮化前后的电化学腐蚀与摩擦学行为，重点分析了不同渗氮改性对奥氏体不锈钢表面摩擦磨损行为的影响。基于大量的实验与模拟分析，提供切实可行的基于空心阴极放电的奥氏体不锈钢阳极氮化与高温快速氮化新方法。研究了含氮正离子和中性含氮粒子等含氮颗粒对渗氮行为的影响，提出了基于空心阴极放电的渗氮新模型。