电沉积Fe-P非晶镀层工艺及机理研究

【作者】 罗少林；

【导师】 张英杰；

【作者基本信息】 昆明理工大学 ， 材料学， 2007， 硕士

【摘要】 电沉积非晶态Fe-P镀层有很好的耐蚀性和较高的硬度，有着很好的应用前景。但是根据目前已有的报道，非晶态Fe-P镀层仍存在着一些不足之处，因此影响了其使用范围，如晶化温度较低，经过400℃热处理及离子氮化后才可使其硬度达到HV1000。本论文针对这些不足之处，对电沉积非晶态Fe-P合金的工艺进行了优化和改进，制备出了高耐蚀、高硬度及高晶化温度的Fe-P非晶镀层，并研究了电沉积Fe-P非晶合金镀层耐蚀机理及强化机理，主要内容包括以下几个方面：分析了Fe-H₂O系电位-pH图与Fe-Cl-H₂O系的电位-pCl图，结果表明：只有将电位控制在Fe-H₂O系电位-pH图中①线的下方pH较小的区域，而且镀液中氯离子的浓度必须大于0.4mol／L时，Fe才能正常沉积。对比了以硫酸亚铁为铁盐和氯化亚铁为铁盐时各自的优、缺点，最终选择了电流效率高、沉积速度快且易形成非晶态结构的氯化物体系进行实验。通过查阅资料，确定了镀液配方和工艺条件的大致范围，在250ml赫尔槽和160ml矩形槽中对各因素进行考察。将各因素按对镀层耐蚀性的影响大小分为主要因素和次要因素，通过多次实验最后确定了电沉积Fe-P非晶合金镀层的最佳镀液组成及工艺条件，并考察了各因素对镀层耐蚀性的影响。用EPMA-1600电子探针测量了Fe-P非晶镀层中P的含量，发现在最佳工艺条件下，镀层中含P约21（wt）％。X射线衍射实验结果表明，此时镀层结构为非晶态。采用腐蚀失重法测量了镀层的耐蚀性，发现电沉积Fe-P非晶镀层在0.5mol／L H₂SO₄中的腐蚀失重约为0.08g·m^-2·h^-1。采用维氏硬度实验方法对镀层的硬度进行了测试，发现在镀态时Fe-P非晶镀层的硬度为HV550，经过380℃热处理后镀层的硬度即可达到HV1100。此外，对镀层在热处理时的氧化增重情况也进行了考察，发现在温度低于400℃时，镀层的抗氧化性能非常好，而温度升至400℃以上时镀层氧化增重率迅速升高，说明该镀层在氧化性环境中使用时，温度不宜超过400℃。用电化学工作站测量了镀层在0.5mol／LH₂SO₄中的阳极极化曲线，在曲线上可以看到有明显的钝化区域，说明Fe-P非晶镀层耐蚀的原因是在酸中发生了钝化。用成相膜理论和吸附理论分析了镀层钝化的机理，钝化的根本原因是Fe和P原子核外有空轨道，而O^2-有剩余的孤电子对，因此可形成氧化物层或吸附层，从而减缓镀层的腐蚀速率。将热分析方法和X射线衍射方法结合起来研究了镀层的晶化过程，镀层的DSC图结果显示，在300℃左右镀层开始剧烈放热，说明此时镀层开始由亚稳的非晶态向晶态转变，而位于330℃和368℃左右的两个放热峰则反映了铁的磷化物从过饱和a-Fe（P）固溶体中脱溶及铁的磷化物之间的转变。从X射线衍射结果可推断出，镀层在热处理过程中发生了固溶强化与弥散强化，因此硬度会升高，而当热处理温度升至380℃以上时，由于脱溶物长大粗化，因此硬度值又下降。更多还原

【Abstract】 The application prospect of electrodeposited Fe-P amorphous film is bright because of its good corrosion resistance and high hardness.Its application range,however,has been affected by some deficiency ,such as lower crystallization temperature , the hardness of the film can up to HV1000 only by the ion nitriding after 400℃heat treatment.Fe-P amorphous films with better corrosion resistance,higher hardnes and higher crystallization temperature have been obtained in this paper,the electrodeposition process of Fe-P amorphous film has been studied as well as the mechanism of corrosion and reinforcement.The main results are as follows:The results of thermodynamics analysis show that the Fe atoms can only be deposited in the zone which the pH value is small enough if the potential is lower than line①and the concentration of Cl^- must be exceeded 0.4mol/L.Chloride bath has been chosen because of its higher electrical current efficiency and can form amorphous structure much more easily and promptly if compared with sulfate bath.All of the factors involved have been divided into two sets.those whom made greater influence to the corrosion resistance were named primary factors,and the rest were named secondary factors.The most favorable values of both the primary factors and the secondary factors have been gained after several sets of 267ml Hull cell tests and 160ml rectangular cell tests,the influence of some factors to the corrosion resistance have also been detected.The content of P in Fe-P amorphous film under the best process condition is approximately 21（wt）%.The result of XRD approves that this film is amorphous in structure.Weight loss corrosion measurement has been introduced to determine the corrosion rate of Fe-P films.It is suggests that the value of corrosion rate of Fe-P films in 0.5mol/L H₂SO₄ solution is about 0.08g·m^-2·h^-1.The result of Vickers hardness test show that the hardness of Fe-P films is about HV550 without being heat treatment,but can up to HV1100 after 380℃heat treatment.Furthermore,the oxidation weight gain rate of the film has also been determined when heated,the result demonstrates that Fe-P films can be used under 400℃normally.The electrochemistry workstation has been adopted to study the anode polarization of the Fe-P film.The anode polarization curve with clear passivation section conforms that Fe-P films tend to passivate in 0.5mol/L H₂SO₄ solution.According to the membrane theory and the adsorption theory,it is the extranuclear empty tracks of Fe and P atoms combine with the electron pairs of O^2- that contribute to the formation of the oxide layer or the adsorption layer.thus the corrosion rate of Fe-P films is reduced. The motheds of thermal analysis and X-RAY diffraction were used to study the structural transformation of Fe-P amorphous films after being heated.the relationship between hardness and heat treatment temperature was studied by Vickers hardness test.It is suggests that the Fe-P amorphous films begin to crystallize at 300℃,the hardness of the film increases and maximizes at 380℃in consequence of solid solution reinforcement and disperse reinforcement, and then decreases out of Ostwald coarsening.更多还原