镍基非晶微观有序结构对耐蚀性的影响

The corrosion resistance of Ni-P coating with amorphous structure is decreased due to the amorphous crystallization. In the course of crystallization, the lattice structure is translated from disorder to order, the resistant ability of the passive film for corrosive ions is decreased. However, it can not be understand very well for the effect of ordered or disordered structure in amorphous matrix on corrosion resistance and the structure of passive film at present. In this project, the different amorphous nickel base coating will be prepared by electroless plating, the local structure parameter will be analyzed. The corrosion rate and corrosion characteristics of amorphous coating will be obtained by corrosion experiment. The influence of ordered structure in amorphous matrix on composition and structure of passive film will be studied by measuring the structural characteristics of passive film. Based on the model of point defect (PDM), the point defect properties of passive film can be explained and concentration of point defect can be calculated by using Mott-Schottky curve. By studying the semiconductor type of passive film and calculating the band gap by using photoelectrochemistry, mobility of carrier can be judged. By comprehensive analysis the local structure of amorphous matrix and structural characteristics of passive film, it will be understand the formation mechanism of passive film on the Ni-base amorphous surface and relationship between the amorphous ordered structure and stability of passive film.

非晶镍磷镀层的晶化导致其耐蚀性能下降，晶化过程中，晶格排列由无序状态逐渐转化为有序结构，钝化膜对腐蚀性离子的阻碍能力降低，而目前对此类钝化膜有序无序转变过程中耐蚀性能的变化以及钝化膜的行为特点还缺乏足够的认识。本项目首先使用化学镀的方法获得成分不同的镍基非晶镀层，通过解析获得非晶组织中的有序结构参数；同时开展镍基非晶的腐蚀实验，获得非晶基体腐蚀速率、腐蚀特征数据。其次，离位测量非晶钝化膜的结构特征，研究有序结构对钝化膜成分结构的影响规律；进一步，以点缺陷模型（PDM）为理论基础，利用Mott-Schottky曲线可以确定钝化膜中点缺陷性质以及计算出点缺陷浓度，研究钝化膜半导体类型，利用光电化学谱计算禁带宽度，判断载流子的迁移率。综合非晶局域有序结构的解析和相关钝化膜结构特征的研究结果，最终确定镍基非晶表面钝化膜的形成，获得非晶有序结构与钝化膜稳定性之间的关系。

本研究以Ni-P二元合金以及Ni-P-X（X= Cu, W, Mo）三元合金为研究对象，采用变化成分及低温热处理手段获得不同的非晶组织，用X射线衍射解析非晶结构，结合电化学腐蚀试验及钝化膜的分析，研究微观局域结构与材料宏观耐蚀性之间的变化规律。对于高磷二元Ni-P合金，尽管是非晶基体，但里面的原子团簇的尺寸并不是固定的，随着低温热处理时间的延长，原子团簇的尺寸先减少后增大，对应的耐蚀性先增加后减小，说明对于二元Ni-P合金，耐蚀性和原子团簇的尺寸有关，原子团簇的尺寸越大，其与周围非晶基体的腐蚀电位相差越大。与二元Ni-P相比，Ni-P-Cu三元合金在和二元Ni-P磷含量相当的情况下，铜的加入对于提高耐蚀性是有利的。仅从非晶结构方面分析，发现Cu的加入尽管是增大原子团簇尺寸的，但是耐蚀性还是比Ni-P二元合金提高，因此原子团簇尺寸不是影响耐蚀性的唯一因素，合金元素的影响更重要。Ni-P-Cu三元合金耐蚀性好的原因在于可以形成n-p型钝化膜，钝化膜的钝化效果受钝化电位和钝化时间的影响。对于Ni-P-W三元镀层，与磷含量接近的二元Ni-P镀层相比，三元镀层的基体结构为非晶基体上分布有少量纳米相的混合体， W的添加并没有增加镀层的非晶化程度。对Ni-W-P三元非晶镀层进行低温热处理，随加热时间延长，镀层中有序团簇的尺寸先减小后增大，纳米相的析出也有增多的趋势。经低温热处理后，Ni-W-P镀层耐蚀性的变化表现为先提高后降低，这主要与纳米相的析出数量、有序团簇的尺寸及数量有关。对于Ni-P-Mo三元镀层，P与Mo的沉积表现出相互制约关系，P比Mo更能促进非晶的形成，同时在耐蚀性上表现出更好的耐蚀性；非晶Ni-Mo-P三元镀层在10% H2SO4溶液中的钝化膜具有p-n型半导体的性质，与磷含量相同的Ni-P二元镀层相比，形成的含Mo的钝化膜对于提高耐蚀性是有利的。