T8钢液相等离子体电解渗碳的扩散过程和光谱学分析

Diffusion Coefficient and Spectroscopy Analysis during Plasma Electrolytic Carburizing on T8 Carbon Steel

采用阴极液相等离子体电解渗技术实现了T8碳钢表面的快速渗碳。测量了样品内部温度与外加电压的关系,并评估了在不同电压下碳在钢中的扩散过程和等离子体放电的光谱特征。结果表明,T8碳钢在甘油水溶液中经1min渗碳处理后可得到20-30μm厚的硬化层。在外加电压为360 V电压、样品表面温度约为650℃的条件下,碳的扩散系数为6.7×10-8cm2·s-1;在外加电压为380 V、样品表面温度约800℃的条件下,碳的扩散系数为1.5×10-7cm2·s-1。气膜放电击穿产生的等离子体处于局部热平衡状态,电子温度为5000-12000 K。等离子体区的瞬时高温为有机物的分解和碳的快速扩散提供了有利条件,碳的扩散系数比同温度下传统固体渗碳提高了一个数量级,扩散激活能也明显降低。

Fast carburization of T8 carbon steel was carried out by plasma electrolytic carburizing（PEC） method in glycerol aqueous solution. The dependence of temperature on the applied voltage for the steel sample was measured with a thermocouple, and the influence of the applied voltage on the diffusion process of carbon and the optical emission spectral features of the plasma discharge was investigated. It was found that a hardening layer of 20-30 μm thick formed after 1min discharge in glycerol aqueous solution; by applied voltage 360 V, the surface temperature of the steel was about 650℃and the diffusion coefficient of carbon was about 6.7×10-8cm2·s-1; while by applied voltage 380 V, the surface temperature of the steel and the diffusion coefficient of carbon were about 800℃ and1.5×10-7cm2·s-1, respectively. In addition, the discharge plasma within the gaseous envelope by the above two voltages was in local thermal equilibrium（LTE） state with temperatures in the range of 5000-12000 K. The transient high temperature promotes the decomposition of electrolyte and the diffusion of carbon. In comparison with the conventionbal pack cementation process at the same temperature, the diffusion coefficient of carbon was enhanced by an order of magnitude with an obviously reduced activation energy for the PEC process.