Al含量對AlxCoCrFeNi合金腐蝕行為機制之影響研究

Al content on Mechanism of Corrosion Behavior of AlxCoCrFeNi (x=0, 0.25, 0.50, 1.00) in 0.5M H2SO4

李宗達(Tsung-Dar Lee)

指導教授 ： 張一熙 ； 陳瑞凱

國立清華大學/工學院/材料科學工程學系/碩士(2009年)

摘要

Al含量顯著影響AlxCoCrFeNi (x = 0, 0.25, 0.50, 1.00)高熵合金在硫酸及含氯化物硫酸溶液中的腐蝕行為。為進一步探討腐蝕機制，本實驗利用動電位極化測試、電化學阻抗頻譜測試、XPS、AES、ICP及SEM等分析法，針對真空電弧熔煉配製的鑄造態AlxCoCrFeNi (x = 0, 0.25, 0.50, 1.00)合金，進行細部交叉比對研究，得到以下重要結論：
從x = 0合金比對x ≠ 0合金的結果顯示，在硫酸溶液中，含Al合金在室溫以下的抗蝕性優於不含Al合金，室溫以上則反是。數據顯示活化能正比於Al含量，Arrhenius plot的交點在室溫(約23~27oC)處，因而有以上的結果。
而硫酸溶液中，合金氧化層的厚度隨Al含量增加而增加，原因在於Al的氧化物易形成多孔隙結構。Al含量增加對腐蝕行為的影響有二：一為鈍化態之耐蝕性降低，因為多孔隙結構造成鈍化電流密度相對提升；二為合金因Al含量增加，轉變為BCC與FCC雙相結構，腐蝕集中於富Al、Ni之BCC相，局部電池效應將造成腐蝕加速而不利於抗蝕。
在含氯化物硫酸溶液中，不含Al合金之抗孔蝕性優於含Al合金；Al增量造成孔蝕電位下降，此性質與傳統合金類似。

關鍵字

高熵合金 ； 腐蝕 ； 動電位極化掃描 ； 電化學阻抗頻譜

並列摘要

Al content is a significant factor that affects the corrosion characteristics of AlxCoCrFeNi (x = 0, 0.25, 0.50, 1.00) in sulfuric acids with or without chlorides. In order to investigate the corrosion mechanism of AlxCoCrFeNi (x = 0, 0.25, 0.50, 1.00), by use of potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and analysis methods such as XPS, AES, ICP, and SEM to vacuum arc remelted and cast AlxCoCrFeNi (x = 0, 0.25, 0.50, 1.00), and after detailed cross comparison of experimental data, this study obtains the following important conclusions:
In comparison of results for alloy x = 0 with those of x ≠ 0, it shows that in sulfuric acid the latter possesses better corrosion characteristics than the former at temperatures lower than the room temperature, and vice versa. Data show the activation energy for corrosion is proportional to the amount of Al, x, in the alloys and the intersection point of lines for different x in the Arrhenius plot is at room temperature (around 23 ~ 27oC) and this obviously conforms the corrosion results mentioned above.
The thickness of oxides for alloys in sulfuric acid increases with increasing x in that it is easy to form porous structure for aluminum oxides in sulfuric acid. There are two main effects on corrosion characteristics for increasing aluminum amount in the alloys. One is the lowering anticorrosion of passive oxides because of the relative raise in passive current density in presence of porous structure of aluminum oxides. The other is the microstructural change of the alloys from single FCC to duplex BCC-FCC, where the corrosion process principally prevails in the Al, Ni-riched BCC phase and there is a local cell effect in this BCC-FCC duplex phase microstructure. Thus, the corrosion process accelerates.
In chloride bearing sulfuric acid solution the corrosion resistance of the alloys free from Al is better than that of the alloys with Al. Increase in Al amount in the alloys causes lowering in pitting potential of alloys, which is similar to that in conventional alloys.

並列關鍵字

high entropy alloys ； corrosion ； potentiodynamic polarization ； electrochemical impedance spectroscopy

參考文獻

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