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采用等离子体源渗氮技术经450℃×6 h在304L奥氏体不锈钢表面获得了厚度约为15μm、峰值氮浓度高达25 at%的单一面心结构的γΝ相改性层。研究了γΝ相改性层在3.5%NaCl溶液中的耐腐蚀性能,分析了其钝化膜的化学组成,并与原始304L不锈钢相比较。结果表明:γΝ相改性层的阳极极化曲线未发生明显的点蚀击穿,自腐蚀电位比原始不锈钢提高了323 m V(SCE),维钝电流密度低一个数量级。γΝ相钝化膜的EIS与原始不锈钢钝化膜相比,其容抗弧直径增大,相位角平台变宽,采用等效电路Rs-(Rct//CPE)拟合的电荷转移电阻Rct由原始不锈钢3.05×10~4Ω·cm~2增至1.98×105Ω·cm2,计算的双电层电容Cdl由313μF/cm~2降低至70.3μF/cm~2。γΝ相钝化膜具有双层结构,外层是Fe、Cr氢氧化物和氧化物构成,内层以Cr_2O_3为主,N主要以离子键类型的Fe Nx和Cr Nx形式存在。与原始奥氏体不锈钢相比,γΝ相钝化膜更加致密,具有保护性的Cr_2O_3阻碍层增厚,增强了γΝ相改性层的耐蚀性能。
A single side-centered γN modified layer with a thickness of about 15 μm and a peak nitrogen concentration of up to 25 at% was obtained on the surface of 304L austenitic stainless steel by plasma nitriding at 450 ℃ for 6 h. The corrosion resistance of γN phase modified layer in 3.5% NaCl solution was studied. The chemical composition of the passivation film was analyzed and compared with the original 304L stainless steel. The results show that there is no obvious pitting breakdown in the anodic polarization curves of the γ-N modified layer, and the self-corrosion potential is increased by 323 mV (SCE) compared with the original stainless steel. Compared with the original stainless steel passivation film, the EIS of the γΝ -phase passivation film is larger than that of the original stainless passivation film, and the phase angle platform is widened. The charge-transfer resistance Rct fitted by the equivalent circuit Rs- (Rct // CPE) The original stainless steel increased from 3.05 × 10 ~ 4Ω · cm ~ 2 to 1.98 × 105Ω · cm2, and the calculated electric double layer capacitance Cdl decreased from 313μF / cm ~ 2 to 70.3μF / cm ~ 2. The γN phase passivation film has a double-layer structure, the outer layer is composed of Fe, Cr hydroxide and oxide, the inner layer is mainly Cr_2O_3, and N mainly exists in the form of Fe Nx and Cr Nx with ionic bond. Compared with the original austenitic stainless steel, the passivation film of γN phase is denser, the protective Cr_2O_3 barrier layer is thicker, and the corrosion resistance of γN phase modified layer is enhanced.