非晶Ni-Mo-P化学镀层的应力和抗腐蚀性能

Stress and corrosion performance of amorphous Ni-Mo-P electroless deposits

研究了非晶Ni Mo P沉积层的应力、成分及气孔率,它们对镀层在5%NaCl中的抗腐蚀性能的影响,同时研究了气孔、应力产生的原因。研究结果表明:在合适的Na2MoO4浓度及pH值下获得的非晶Ni Mo P沉积层具有最佳抗腐蚀性。随着镀液中Na2MoO4含量的增加,镀层应力很快从压应力向拉应力转变,镀层的气孔率增加。当Na2MoO4浓度大约为0.05g/L时,容易获得低孔隙率、低应力的非晶镀层。镀层气孔率、应力增加,镀层的耐蚀性显著降低。试样的长期腐蚀抵抗主要取决于镀层的应力,短期腐蚀抵抗则取决于镀层的气孔率。镀层具有低应力无气孔时,非晶镀层中Mo的含量越高,镀层在5%NaCl中的抗腐蚀性越好,而P含量的变化对镀层抗腐蚀性能无明显影响。镀层的应力采用X射线应力仪测定,并通过观察试样在5%HCl中浸泡25d后的外观进一步验证。采用浸泡腐蚀测试、硝酸变黑腐蚀测试、气孔率贴滤纸测试及电化学腐蚀测试技术对比研究了沉积层的腐蚀行为。

This study investigated the stress, porosity and composition of amorphous NiMoP electroless deposits obtained from typical acid pH=4.6 and alkaline pH=8.0, their effects on corrosion performance of deposits in 5% NaCl and the generation mechanism of stress and porosity. The results indicate that the deposit obtained at a certain pH and Na2MoO4 concentration has the best corrosion resistance in 5% NaCl. With the increase of Na2MoO4 concentration, the stress was quickly changed from compressive to tensile stress, and the porosity was also increased. The higher were the stress and porosity, the poorer was remarkably the corrosion resistance. When the Na2MoO4 concentration was about 0.05g/L, the deposit with the highest corrosion resistance in neutral 5% NaCl was easily obtained. The corrosion resistance in the long time was mainly decided by the stress of deposits; the corrosion resistance in short time was mainly decided by the porosity of deposits. When deposits have no pore and low stress, the amorphous NiMoP alloys with higher Mo have better corrosion resistance; P in amorphous NiMoP films hasn′t obviously influences on corrosion resistance. The stress were measured by Xray analyzer and checked by the appearance immersed in 5% HCl for 35days. The corrosion performance was investigated by immersion corrosion tests, HNO3 corrosion blacking tests, porosity ferroxyl indicator tests and electrochemical corrosion technique. 