AlxCrFe1.5MnNi0.5Mo0.1 (x = 0.15, 0.3, 0.5)高熵合金之腐蝕研究

Corrosion of AlxCrFe1.5MnNi0.5Mo0.1 (x = 0.15, 0.3, 0.5) High-Entropy Alloys

高逸帆(Yih-Farn Kao)

指導教授 ： 陳瑞凱 ； 徐統

國立清華大學/工學院/材料科學工程學系/碩士(2008年)

摘要

本研究以與316不□鋼成份相近的六元AlxCrFe1.5MnNi0.5Mo0.1 (x =0.15, 0.3, 0.5)高熵合金，進行包括線性極化LSV、電化學阻抗頻譜EIS、循環極化CV、浸泡實驗、複合動態線性極化與開路電位法LSV(t)-OCP(t)、以及OM, SEM, GXRD等的腐蝕研究。LSV結果顯示，(1)在0.5 M硫酸環境中，合金之抗蝕性隨Al的增加而變好，這和2006年張競謙AlxCrFe1.5MnNi0.5 (x = 0, 0.3, 0.5)和吳家豪AlxFeCoNiCrMo0.5(x = 0.5, 1, 1.5, 2)的實驗結果相反，顯示Al變量在硫酸內對抗蝕度的影響受合金背景元素的影響。(2)在0.5 M硫酸與0.25 M氯化鈉的混合溶液中，合金之抗蝕性隨Al的增加而變差，顯示在鈍化膜較不完整的情況下，本質金屬決定腐蝕性能。(3)而在1 M氯化鈉中Al含量對抗蝕性的影響則為不規律。
由0.5 M硫酸中的EIS測試結果得知，隨著Al含量的增加，形成雙層鈍化膜的機率變大且電阻總和也變大，呼應了極化曲線的實驗結果。而在0.5 M硫酸與0.25 M氯化鈉混合溶液中循環伏安CV測試中可知，隨著鋁含量的增加，正的遲滯環增大，造成孔蝕破壞的情形也越嚴重，對照OM金相可驗證。
由本實驗看出傳統浸泡實驗和掃描式線性極化實驗在定量上有著
極大的誤差(約100倍)，此現象在諸多文獻上皆可見到。藉著長時間
V開路電位對時間變化分析法，與長時間浸泡後線性線性極化法的比
較，亦即使用LSV(t)-OCP(t)法，觀察到兩者的差異係因隨著時間的增長，鈍化膜溶解造成了浸泡實驗的腐蝕速率的大量增加有關。以往有關此現象的解釋在文獻上不多見，本實驗成功減少浸泡實驗換算後電流密度，與傳統線性極化法定量上的巨大誤差。
與鑄造態相比較，其他不同的單一熱處理態如固溶化水淬態、爐冷態、500℃2小時時效態、500℃48小時時效態、與900℃2小時時效態、900℃48小時時效態等，並未對本研究材料在腐蝕性質上有明顯
的幫助或害處。
本研究亦由低掠角XRD實驗，觀察到固溶化水淬態合金在0.5 M硫酸中的腐蝕膜組成，與合金中Al含量是有關的。其中，x = 0.30與x =0.50較相近，x = 0.15則不一樣。

關鍵字

線性極化法 ； 循環極化法 ； 電化學阻抗頻譜法 ； 浸泡法 ； 開路電位與時間關係圖 ； 複合動態線性極化與開路電位法

並列摘要

In this study we use linear sweep voltammetry (LSV),
electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV),immersion test, a combined dynamic LSV(t)-OCP(t), OM, SEM, and glancing-angle XRD (GXRD) to investigate the corrosion properties of AlxCrFe1.5MnNi0.5Mo0.1 (x = 0.15, 0.3, 0.5) high-entropy alloys that is similar to 316 type stainless steel. LSV results show that (1) corrosion resistance of AlxCrFe1.5MnNi0.5Mo0.1 in 0.5 M sulfuric acid solution
increases with x, which is contrary to that of AlxCrFe1.5MnNi0.5 (x = 0, 0.3,0.5) of Chang, and that of AlxFeCoNiCrMo0.5 (x = 0.5, 1, 1.5, 2) of Wu in 2006, suggesting that the corrosion properties of alloys is influenced by the environmental alloying composition. (2) The corrosion resistance of alloys in 0.5 M sulfuric acid and 0.25 NaCl mixing solution decreases with x, showing that the intrinsic alloy determines the corrosion property
in this case of defective passive film. (3) There is irregular influence effect of x on corrosion property for alloys in 1 M NaCl solution.
EIS results in 0.5 M sulfuric acid show the double-layer passive film is likely to form and the total electrical resistance increases as time increases, conforming results from SLV. CV tests in 0.5 M sulfuric acid +0.25 M NaCl solution show that positive hysteresis loop enlarges as Al content, manifesting the severe pitting corrosion, and conforming results from OM.
There is an obvious deviation of about 100 times for results from conventional immersion test and from LSV, which has long been noticed but not explained in references in the past. By a combined dynamic LSV(t)-OCP(t) proposed by this study, we observe that an increase in corrosion rate due to the dissolution of the passive film after long-term immersion in corrosive solution, and the deviation between LSV and VII immersion results comes from this increase in corrosion rate. In this study we successfully reduce this deviation to a reasonable degree.
Compared to the as-cast, each of all the other states, such as the as-solutionized & quenched, the as-furnace-cooled, the 500℃ x 2 h-aged,the 500℃ x 48 h-aged, the 900℃ x 2 h-aged, and the 900℃ x 48 h-aged,has no obvious beneficial or detrimental effects on the corrosion
properties of alloys in this study. From G-XRD data we observe the composition of the corrosive film on the surface of the sample is related to the Al content in the alloy. Similar results are obtained for both x =
0.30 and 0.50, but different for 0.15.

並列關鍵字

Linear Sweep Voltammetry (LSV) ； Cyclic Voltamatry (CV) ； Electrochemical Impedance Spectroscopy (EIS) ； Immersion Tset ； Open Circuit Potential vs Time ； LSV(t)-OCP(t)

參考文獻

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11. M. G. Fontana, Corrosion engineering, 3rd ed. (Plenum Press, New York 1986), Chap. 9