| 英文摘要 |
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, corrosion 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% NaCl, 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 of 3.5wt% NaCl 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% HCl. |
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