20钢复合渗铬生长纳米结构Cr2N/CrN层

Formation of nanostructured Cr_2N/CrN layer on plain 20 carbon steel by duplex chromizing process

对经离子渗氮处理的20钢,进行610℃下不同保温时间的盐浴渗铬,获得了不同时期的复合渗铬层。利用光学显微镜、X射线衍射仪、扫描电镜及能谱仪、透射电镜对这种复合渗铬层的形成过程进行研究。结果表明,复合渗铬层主要由铬氮化合物相组成,其形成是在消耗原离子渗氮化合物层的基础上实现;并且,在复合渗铬初期,复合渗铬化合物层主要由CrN相组成,在复合渗铬后期,原CrN相化合物层的最表层开始转变为Cr2N相,因而形成较致密的Cr2N/CrN双层结构渗铬层。横截面透射电镜观察表明,所制备的Cr2N/CrN双层结构为纳米结构渗铬层（CrN晶粒在100nm以下,Cr2N晶粒在100～300nm之间）。摩擦学性能测试显示,这种纳米结构复合渗铬层有降低渗层摩擦系数的趋势。

The process was carried out at 610 ℃ in salt bath on plasma nitrided plain 20 steel, and duplex chromizing coatings at different stage of the process were obtained. The growing process of the coatings was studied by means of optical microscopy, X-ray diffraction, scanning electron microscopy, X-ray energy dispersive spectroscopy and transmission electron microscopy. The results show that the chromized compound layer is composed of chromium nitrides, and it forms at the cost of the iron nitrides layer formed by plasma nitriding. In addition, at early stage of the chromizing process, the formed compound layer is chromium nitride（CrN）, whereas, the CrN layer can be transformed into Cr2N because of the exhausting of nitrogen atoms at the coming ehromizing stage, therefore, a dense bilayer of Cr2N/CrN is formed. TEM results on cross-sectional of the layer indicates that the formed Cr2N/CrN bilayer consists of nanocrystalline chromium nitrides grains （CrN grains are below 100nm, Cr2N grains range in 100- 300nm）. Tribological tests indicate that the surface nanocrystallized layer has the effect of reducing the coating＇s friction coefficients.