鎳鋁介金屬鍍膜之抗窩蝕行為

Cavitation Erosion Behavior of Ni-Al Intermetallic Coatings

本研究採取陰極電弧放電離子被覆技術製備Ni-Al薄膜於AISI 1045中碳鋼基材表面上，評估應用Ni-Al於抗窩蝕功能方面的可行性。研究中採用三種不同成份的靶材，包括有原子百分比Ni52Al48、Ni60Al40及Ni70Al30，以製備出不同組成的Ni-Al鍍膜，並觀察鍍膜微結構與成份隨靶材成份的變化，以了解組成對於抗鍍膜窩蝕性的影響。結果顯示：使用三種靶材所獲致的鍍膜成分別得到Ni62Al38、Ni63Al37及Ni69Al31，鍍膜鎳含量隨靶材鎳含量增加而增加。三種鍍膜的相組成均以Ni3Al為主，富鎳Ni70Al30靶材所得鍍膜除了Ni3Al相之外，尚含有部份鎳相。觀察刮痕試驗結果發現，刮痕呈密合型與拉伸破裂型裂紋，顯示出鍍膜有極強的附著性，同時亦反映在鍍膜的抗窩蝕性上。在純水中，所有成份的Ni-Al鍍膜試片均能提高中碳鋼基材的抗窩蝕性達十倍。在3.5 wt% 鹽水與3.5 wt% 鹽酸中亦分別有兩倍、三倍的效果。而在三種測試環境中，三種鍍膜試片間的窩蝕損失差別均不明顯，無法看出鍍膜組成對抗窩蝕性的影響。從動電位極化曲線上可以看出鍍膜試片均能大幅提高基材在鹽酸與鹽水溶液中的抗蝕性，然而由於窩蝕破壞所形成的孔洞中會因為孔蝕導致腐蝕損失加劇，因而鍍膜試片在腐蝕溶液中之抗窩蝕效果低於電化學量測結果中所預期的保護效果。

A cathodic arc plasma ion plating process was demonstrated to deposit Ni-Al film on AISI 1045 carbon steel to evaluate the cavitation protection. Three target materials with Ni52Al48, Ni60Al40, and Ni70Al30 compositions were used to investigate the microstructural and compositional effects on cavitation erosion behaviors of coatings. Experimental results show that the nickel content in these deposits increased with the nickel content of the target material. The major phase of deposited film was Ni3Al regardless of the target materials. A nickel phase was produced if nickel-rich target Ni70Al30 was used. The scratch test indicated that all of the as-deposited films presented very strong adhesion. This reflects their cavitation erosion behavior in fresh water. All coatings increased the cavitation erosion resistance of the bare substrate 10 fold. These coatings also enhanced the cavitation resistance 2-fold or greater in 3.5 wt.% NaCl and 3-fold in 3.5 wt.% HCl electrolyte. The potentiodynamic polarization data of coated specimens in these two electrolytes indicated that the coated specimens exhibited higher corrosion potential and lower corrosion current density than the bare substrate material. It is believed that the cavitation erosion induced pitting corrosion into the substrate accelerated the mass loss rate of the substrate.