中熵超級沃斯田鐵系不鏽鋼抗蝕與抗菌性質之研究

Study of Corrosion Property and Antibacterial Property of Medium-Entropy Super Austenitic Stainless Steel

陳子恩(Tzu-En Chen)

指導教授 ： 李岳聯

國立臺灣大學/工學院/工程科學及海洋工程學研究所/碩士(2020年)

https://doi.org/10.6342/NTU202004173

摘要

超級沃斯田鐵系不鏽鋼不僅有良好的耐腐蝕性質，也優異的機械性能，在未來的應用上潛力無窮，相較於一般常見的304或316不鏽鋼，超級不鏽鋼添加了高含量的合金元素，包括鉻、鎳、鉬、銅等等，不同的合金元素對超級不鏽鋼之機械性質或耐腐蝕性質有不同層面的作用。本研究探討新開發之中熵超級沃斯田鐵系不鏽鋼(Medium-entropy Super Austenitic Stainless Steel)冷軋鋼板在700°C不同時效熱處理時間會對材料表現出的性能有什麼影響，並與已被妥善研究的商用超級不鏽鋼(S31254)與抗菌不鏽鋼(304-Cu)做比較。第一部分探討材料硬度的改變，富銅相在底材內均勻析出使不鏽鋼達到析出硬化的效果，在4小時的熱處理條件下達到頂時效；爾後，晶粒內部的第二相析出物也會造成硬度提升。第二部分探討抗腐蝕性質的變化，在動電位循環極化曲線中只有48小時熱處理試片的抗蝕能力有明顯下降，然而在陽極定電位極化與EIS試驗中可以觀察到每個熱處理條件之間的差異，時效熱處理時間越長，所得的鈍化區穩態電流逐漸增大，且鈍化膜提供的阻抗隨之下降；粒間腐蝕測試明顯可看出敏化的現象跟熱處理的時間呈正相關。第三部分研究材料抗菌效果隨熱處理時間的演變，隨熱處理時間的加長，在固態瓊脂培養基中生成的菌落數遞減，表現出抗菌的能力。微結構分析發現，較長時間的時效熱處理除了讓富銅相析出，也讓晶界上生成富鉬的第二相析出物，即是造成材料抗蝕能力下降的原因。根據XPS分析結果，48小時長時間時效的試片，表面形成的鈍化膜組成成分與固溶不鏽鋼與4小時時效熱處理的試片不同，成分中含有較高比例的氫氧化鉻，而會形成穩定鈍化膜的氧化鉻比例下降，是造成抗蝕能力下降的原因。最後，由於長時間時效的中熵超級不鏽鋼的抗蝕能力下降，代表底材更容易氧化溶解，釋放較多的銅離子即為抗菌能力提升的原因。

關鍵字

中熵超級不鏽鋼 ； 時效處理 ； 析出物 ； 抗蝕性 ； 抗菌性

並列摘要

Super stainless steels with high portion of alloy, chromium, nickel, molybdenum and copper, possess excellent anti-corrosion resistant and remarkable mechanical properties which has high potentials for engineering applications. In this thesis, the effect of 700°C aging treatment for various time on behaviors of a novel Medium-entropy Super Austenitic Stainless Steel were thoroughly studied while making a comparison with commercial super austenitic stainless steel S31254 and anti-bacterial copper-bearing 304Cu-SS. First of all, we illustrated the effects on hardness variation. Cu-rich phase was precipitated on matrix and leads to precipitate hardening with peak aging occurring on 4 hours aged specimen. Secondly, we discuss the anti-corrosion abilities of specimens. Based on cyclic potentiodynamic polarization curves, only 700°C 48hr specimen shows obvious decrease in corrosion resistance. However, the difference of anti-corrosion properties is distinct for each specimen in anodic potentiostatic polarization. Additionally, the protection from passive films varied among specimens. Aging time has huge impact on these properties. With prolonged aging time, the steady state current densities increase gradually and the impedance provided by passive films decayed. The level of intergranular corrosion are positively related to aging time as well. Thirdly, we investigated the antibacterial properties of ME-ASS. the number of incubated colonies drops with increased aging time which shows the ability to kill bacteria.
We found second phase precipitation on grain boundaries on specimens aged more than 12 hours by TEM, this is the main cause of worse anti-corrosion properties of the stainless steels. From XPS analysis, 48 hours aged stainless steel possessed a passive film with higher portion of chromium hydroxide and less chromium oxide which is the key to form stable passive films. As a result, 48 hours aged specimen performed a inferior anticorrosion ability. Lastly, the materials are prone to corrosion and release more metallic ions when the anticorrosion properties are poor. The released copper ions are the main factor to enhanced antibacterial behaviors.

並列關鍵字

Medium-entropy Super Austenitic Stainless Steel ； Aging treatment ； Precipitation ； Corrosion resistance

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