【作者】 邢志强；

【导师】 朱雪梅；

【作者基本信息】 大连交通大学 ， 材料学， 2010， 硕士

【摘要】 采用自行设计研制的LDL-50型直流脉冲等离子氮化设备,对316不锈钢进行活性屏离子渗氮改性。利用X射线衍射(XRD)和扫描电子显微镜(SEM)分析改性前后316不锈钢的表面相结构、成分和形貌;利用显微硬度计研究渗氮前后316不锈钢的硬度变化;通过阳极极化曲线,电化学交流阻抗谱以及Mott-Schottky曲线的测试,研究了渗氮改性前后316不锈钢在3.5% NaCl溶液中的自钝化及钝化膜的半导体特性,进一步探索了γN改性层钝化膜的耐蚀性机理。研究结果表明:当气压一定时,随着渗氮温度升高,合金表面氮含量增加,在500 Pa下,由400℃的4.15 at%升高到450℃的24.72 at%;当温度一定时,对样品施加250 V负偏压,可显著增加γN层的厚度,提高改性层的均匀性和致密性。直流脉冲等离子体源活性屏渗氮改性316不锈钢的最佳工艺参数为250 V负偏压作用下450℃,500 Pa,渗氮6 h。γN改性层的厚度13μm,平均硬度达HV0.1N 1.39GPa,比316不锈钢提高了五倍。改性前后316不锈钢在3.5% NaCl溶液中均能实现自钝化,但316不锈钢钝化膜在200 mV时发生点蚀击穿,γN改性层无点蚀出现,随着浸泡时间的延长,γN改性层EIS图谱中的容抗弧直径增大,相位角平台变宽,高度增加,浸泡3 h时,低频端的“峰”变平,相位角接近90°,说明γN改性层钝化膜的致密性远优于316不锈钢。从Mott-Schottky曲线可知,改性前后316不锈钢的钝化膜在负于平带电位范围内表现为p型半导体,在高于平带电位范围内表现为n型半导体,说明钝化膜层由两部分组成,内层为Cr2O3,外层为Fe2O3;与316不锈钢相比,γN改性层钝化膜的空间电荷层电容、厚度、施主浓度及受主浓度均降低了一个数量级,施主平带电位负移,氧扩散系数提高了近一个数量级,说明钝化膜的内部缺陷降低、电容特性增大、氧化性增强、保护能力提高。更多还原

【Abstract】 developed in our laberatory. The phase microstructure, composition and surface morphology of 316 austenitic stainless steel andγN phase layer were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM); the hardness of 316 austenitic stainless steel andγN phase layer are studied by microhardness tester; the passivation of high-nitrogen f.c.c. (γN) phase formed on AISI 316 austenitic stainless steel and the semiconductor characteristics of the passive film were studied by using anodic polarization, electrochemical impedance spectroscopy (EIS), and Mott-Schottky plot, to explore the pitting corrosion mechanism of the stainless steel. The self- passivation of theγN phase layer in 3.5 % NaCl solution was observed. The results indicate that:At a fixed nitriding pressure, the content of nitrogen in surface increases with the increase of the permeability nitrid temperature, from 4.15 at.% of 400℃to 24.72 at % of 450℃.At a fixed nitriding temperature applying 250V negative bias consideraloly enhanced, the thickness ofγN layer improved its uniformity. And it showed the uniform structure.The optimal working parameters of direct current pulsed plasma source ion nitriding 316 stainless steel are 250V as well as negative bias 450℃500 Pa, 6h,γΝphase layer is about 13μm thick, and the average microhardness of nitried 316 stainless steel isΗV0.1N1.39GPa, five times higher than that of 316 stainless steel.Both the original and nitrided presented self-passivation in 3.5% NaCl solution. At 200mV, the 316 stainless steel showed pitting breakdown.γN phase layer had no pitting breakdown. With the marinated time extension, the EIS of 316 stainless steel andγN phase layer in 3.5% NaCl solution shows that, the diameters of the capacitive increase, the phase angle platform widened, highly increasing. After 3h immersion, the |z|-logf ofγN phase layer low-frequency peak change flat, phase angle increased height closer to 90°, the passive film ofγN-phase-modified layer was more compact than 316 stainless steel.The Mott-Schottky plot shows that the passivation films ofγN/316 stainless steel behave as n-type and p-type semiconductor in the potential range about and below the flat band potential. It showed that: the passive film had two parts, the endothecium was Cr2O3, the deep space was Fe2O3, compare to the 316 stainless steel, the capacitance of space charge, donor density and accept density ofγN decreased by 1 order. The flat-band moved negatively, the value of oxygen vacancy diffusion coefficient increased by 1 order, it restricted the self-catalysed- The surface modification of 316 stainless steel has been investigated by the direct current pulsed plasma source ion nitriding (DCPPSIN) apparatus LDL-50, which designed and acidification, decreased the disfigurement of passive film, increased the capacitive character and the oxidation and protect capability of passive film toned up.更多还原