鎳磷合金奈米晶粒電鍍層之腐蝕行為研究

Study on the Corrosion Behavior of Nanocrystalline Ni-P Electrodeposited Coatings

本研究的目的是探討鎳磷合金鍍層在5% NaCl溶液中之腐蝕行為。利用動態電位極化曲線量測發現活性→鈍化→過鈍化之行為轉變，隨腐蝕電位與腐蝕溶液溫度提高，腐蝕速率越快，重量損失及表面磷含量也增加。腐蝕表面形貌經FESEM觀察由細小蝕孔轉變較大蝕孔約30μm，蝕孔孔內龜裂，鍍層出現層狀剝離，腐蝕深度也隨之加深。由XPS分析鍍層表面形成鈍化膜，且富含磷的腐蝕，透過TEM觀察鎳磷合金腐蝕區域為多孔晶質結構。

The main objective of this paper is to investigate the corrosion behavior of electrodeposited Ni-P coatings in a 5% NaCl solution. Potentiodynamic polarization curves obtained for the coating showed transition characteristics from active, passive, to transpassive as the applied potential increased. In the meantime, the weight loss and the measured P-content on the surface of the tested specimens were observed to increase with increases in applied potential and solution temperature. Under the examination of FESEM, it was observed that the corrosion pits on the specimen at higher potential and solution temperature evolved from smaller sizes to the ones of nearly 30μm in diameter. Moreover, within the developed corrosion pit, which penetrated through the coating, there existed cracks and delaminations. Results from XPS analysis showed that a passivated film which was richer in phosphor content was formed during corrosion. The microstructure of the corroded Ni-P coating was found to be porous and nanocrystalline under TEM examinations.