鋼材被覆不同組成的鈦鎳薄膜之窩蝕行為

Cavitation Erosion Behavior of Steel Coated with TiNi Films in Different Compositions

鈦鎳介金屬被公認有優異的擬彈性而能抵抗窩蝕，但其昂貴的價格促成薄膜化的動機。本研究以陰極電弧放電沉積法在S48C中碳鋼表面被覆鈦鎳薄膜，藉改變靶組成來控制鍍膜成份，並探討鍍膜之成份、微結構對鍍膜電化學特性的影響，以及在不同環境中鍍層抗窩蝕性的實證效果。研究結果顯示使用成份Ti50Ni50、Ti55Ni45及Ti60Ni40的靶材進行被覆，分別得到Ti51Ni55、Ti45Ni51及Ti51Ni49的鍍膜組成，鍍膜結晶性隨含鈦量增加而提高。窩蝕結果顯示：三種鍍膜在純水、3.5wt% NaCl及3.5wt% HCl水溶液中皆有保護基材的效果，但是在鹽水及鹽酸溶液腐蝕性環境中的保護能力降低，其中以Ti60Ni40、Ti55Ni45靶材所製得之鍍膜在此二環境有較低的窩蝕損失。在純水中，不同組成的鍍膜有著幾乎相同的抗窩蝕效果，但在後二者的環境中，有了電化學腐蝕反應的共同參與，使得原本在純水中並非重要因素的鍍膜組成，其重要性就被突顯出來了。富鈦的鍍膜組成或較高的結晶性會降低鍍膜在鹽水中的腐蝕電流及提高孔蝕保護電位，或因降低鹽酸溶液中的腐蝕電流，故顯現出較低的窩蝕損失。

TiNi intermetallic compound is considered for its pseudoelasticity to the application of cavitation resistance. It is however expensive and motivated the introduction of thin film process. Cathodic arc plasma deposition was therefore used to deposit TiNi films on S48C medium carbon steel substrate to reveal the film composition and microstructure effect on the cavitation resistance, as well as electrochemical behavior in different environments. Experimental result shows that the film compositions were Ti45Ni55, Ti49Ni51 and Ti51Ni49 when target composition Ti50Ni50, Ti55Ni45 and Ti60Ni40 were used. Cavitation resistance of all coated specimens in fresh water were significantly increased. Whereas in 3.5 wt% NaCl solution and 3.5 wt% HCl solution, the cavitation weight loss of specimen is higher than the specimen in fresh water. In fresh water, the films with different compositions almost have the same weight loss. Film composition does not influence the cavitation resistance of films in this regard. It however causes the difference in weight loss of specimens by suffering the electrochemical reactions that occurs in NaCl solution and HCl solution. Ti-rich film composition may reduce Icorr and give rise to Epp of specimens in 3.5wt% NaCl solution, or reduce Icorr of specimens in 3.5wt% HCl solution. This explains that the films prepared by using Ti60Ni40 and Ti55Ni45 target have superior cavitation resistance.