窩蝕是材料在使用環境中被流體侵蝕而常發生的損壞過程。尋求一種合適的表面改質技術來提昇材料的窩蝕抵抗性，其經濟效益與使用壽命有可能比更換材料更俱優勢。氮化速度較快、硬化層較厚、變形較小且基材選擇彈性大的離子氮化是早被證實提昇金屬耐磨耗、耐腐蝕及耐疲勞最有效的方法之一。因此，本研究之目的在探討碳鋼結構材於離子氮化後之窩蝕行為。而窩蝕試驗依照ASTMG32-的之規範分別在純水、. 3.5wt% NaCI及3.5wt% HCl水溶液中進行窩蝕試驗。實驗結果顯示:碳鋼離子氮化後所生成之氮化層在純水中能有效降111窩蝕速來，因離子氮化後所形成的氮化層屬於高硬度組織，能有效抵抗窩蝕所產生的液流衝擊。在3.5wt%NaCI及3.5wt% HCl溶液中因有電化學 腐蝕反應的參與，使得氣化層窩蝕抵抗性變差，但在3.5wt%NaCl容液中仍比未氮化之試片有較低的流失速 4率。在3.5wt% HCI溶液中電化學腐蝕作用力大於窩蝕機械破壞力，更因為氮化鐵在鹽酸溶液中有較大的腐蝕 電流使得氮化層失去保護作用，導致窩蝕損失大於碳鋼原材。由此可知，表面改質必須特別針對使用環境加以選擇，普通碳鋼離子氮化後在純水和3.5wt%NaCI中可有效抵抗窩蝕作用。

Cavitation is a common deterioration process of a material resulting from high speed fluid attack. Surface treatments are usually preferably considered to promote cavitation resistance because economic reason and longer durability. Ion nitriding， known to have a higher nitriding rate， larger case depth， less distortion of work piece as well as flexibility in substrate material， is the most effective process for the nitriding of metals to improve their wear， co付oSlOn and fatigue resistance. Hence， the cavitation behavior of ion nitrided carbon steel will be studied. An ASTM G32-85 standard method was conducted to proceed cavitation test in fresh water， 3.5wt% NaC!， and 3.5wt% HCl， respectively.

Experimental results show that nitriding of steel reduces cavitation rate in fresh water. This indicates that surface hardening caused by ion nitriding is the reason to resist mechanical damage. Electrochemical corrosion plays a part in the case of3.5wt% NaCI and 3.5wt% HCl solution. Ion nitrided specimens in the former solution therefore become less protective than in fresh water with however lower cavitation rate than blank steel. Ion nitrided specimen in the later solution subjecting primarily to electrochemical attack to the nitriding layer， which has high corrosion current， shows inferior cavitation resistance than blank substrate. We learned from this study that method of surface modification should be properly determined depending on the electrolyte used. Ion nitriding of carbon steel in our case is suitable for fresh water and 3.5wt% NaCl， but not for 3.5wt% HC!.