NdFeB基体ZrN涂层的耐腐蚀性能

Corrosion Resistance of ZrN Coating on NdFeB

采用离子镀技术在NdFeB基体上沉积ZrN、ZrN／Zr多层和TiN／Ti多层涂层，考察了其耐腐蚀性能，分析了腐蚀过程。采用静态全浸腐蚀试验（20％NaCl，20℃）测定其失重曲线，扫描电子显微镜（SEM）分析腐蚀前、后的涂层表面形貌变化及腐蚀过程，用CH1600B系列电化学分析仪测试极化电位。试验发现：未镀层NdFeB基体在4h后明显失重，随时间延长失重速率增加。施加涂层基体10h后失重，随时问失重速率增加，但小于未镀层试样。NdFeB基体的自腐蚀电位约-1．037V，腐蚀电流1．69×10^-3A／cm^2；施加涂层后自腐蚀电位向正向移动0．131V（TiN／Ti）-0．258V（ZrN），腐蚀电流10^-5～10^-6A／cm^2；ZrN／Zr涂层由7层增加到14层后，腐蚀电位提高0．037V，腐蚀电流降低。结果说明：离子镀沉积ZrN系列涂层显著提高NdFeB耐腐蚀性能。增加ZrN／Zr周期能够提高耐蚀性能。腐蚀源首先在涂层表面缺陷与基体结合部位形成。一旦形成腐蚀源，NaCl晶体即在基体上结晶并生长，随着此过程进行，涂层逐步腐蚀。

The corrosion resistance of ion-plated ZrN, ZrN/Zr and TiN/Ti coatings on NdFeB substrates were investigated. The electrolyte, 20 % NaCI , was used for potentiodynamic polarization. The corrosion morphology in 20 % salt water was analyzed by scanning electron microscopy （SEM）. It was found that： the uncoated NdFeB appears mass loss after 4 hours, and the corrosion rate became faster with increasing time, however ZrN-coated NdFeB appears mass loss after 10 hours, and the corrosion rate is lower than that of uncoated NdFeB. The corrosion potential of uncoated NdFeB is - 1.037 V, and become more positive（0.131 V-0.258 V） when coated ZrN coatings, the corrosion rate decreases by 2-3 orders of magnitude after ion-plated ZrN coatings. The increase of the number of ZrN/Zr layers can lead more positive corrosion potential and lower corrosion current density. The corrosion of ZrN-coated NdFeB origins from the surface defects, such as pin-hole. NaCl crystallizes and grows up on the interface between substrate and coating and corrupt the coating finally. It could be concluded that ion-plated ZrN coatings can increase significantly the corrosion resistance of NdFeB magnets.