高熵合金Al0.5CoCrCuFeNiBx (x=0, 0.2, 0.6, 1.0)與AlxCrFe1.5MnNi0.5 (x=0, 0.3, 0.5)之腐蝕行為與陽極處理研究

Corrosion Behavior and Anodizing Treatment of the High-entropy Alloys Al0.5CoCrCuFeNiBx (x=0, 0.2, 0.6, 1.0) and AlxCrFe1.5MnNi0.5 (x=0, 0.3, 0.5)

李健平(Chien-Ping Lee)

指導教授 ： 施漢章

國立清華大學/工學院/材料科學工程學系/博士(2008年)

摘要

高熵合金為數種常用的合金元素如鋁、鈷、鉻、銅、鐵、矽以及鎳等所組成的新型多元合金。其打破傳統合金以單一元素為主要成份的觀念，藉由5種以上的主要元素相混合，各種元素之原子含量均大於5 atom%，小於35 atom%。高熵合金的結晶結構與物理性質皆與傳統合金不同。其具有許多優秀的性質，如(1)易產生非晶質相與奈米級的析出、(2)高硬度與耐磨耗性、(3)良好的熱穩定性、(4)抗均勻腐蝕。
此研究首先探討硼的添加對Al0.5CoCrCuFeNiBx合金腐蝕阻抗之影響。由極化掃瞄與電化學阻抗頻譜分析(EIS)可以明確得知：在酸性溶液中，Al0.5CoCrCuFeNi合金比商用304不□鋼具有較貴重的腐蝕電位(Ecorr)與較低的腐蝕電流密度(icorr)，但隨著硼成分的增加其均勻腐蝕的阻抗會下降。由循環極化掃瞄可以發現Al0.5CoCrCuFeNi與Al0.5CoCrCuFeNiB0.2合金呈現擬似鈍態的行為，而Al0.5CoCrCuFe- NiB0.6與Al0.5CoCrCuFeNiB1.0合金由於硼成分的增加，會造成活態且鈍態區域的完全消失。表面形態與化學成分分析指出含硼的高熵合金會產生CrB2的化合物，而減少合金表面的Cr2O3鈍化膜。
AlxCrFe1.5MnNi0.5合金在酸性的溶液中具有寬廣的鈍態區域（大於1000 mV），由極化掃瞄與電化學阻抗頻譜分析可以明確得知：在硫酸溶液中，隨著AlxCrFe1.5MnNi0.5合金中鋁成分的增加，會造成腐蝕阻抗下降。此外在CrFe1.5MnNi0.5合金中添加鋁會造成孔蝕電位下降，而削弱其在氯鹽環境中對孔蝕的阻抗。含有鋁成分的高熵合金在Nyquist圖中具有兩個電容的迴圈，分別代表了電雙層與表面吸附層的存在。由表面金相得知：AlxCrFe1.5MnNi0.5合金中隨著鋁成分的增加，會有較嚴重的均勻腐蝕與孔蝕。
由電化學阻抗頻譜分析可清楚顯示：未經陽極處理前的AlxCrFe1.5MnNi0.5 (x=0, 0.3, 0.5)高熵合金在含氯離子的溶液中之極化阻抗(Rp)會明顯的低於商用304不鏽鋼。利用AlxCrFe1.5MnNi0.5合金在硫酸溶液中具有大範圍的鈍態區域，與穩定的鈍態電流密度(ipass)，所以在硫酸溶液中將AlxCrFe1.5MnNi0.5合金的電位維持在鈍態區域，隨著陽極氧化時間的增加其電流密度會下降並趨於穩定，進而形成多元合金的陽極氧化膜。由X光光電子能譜術的分析可知在陽極處理後的Al0.3CrFe1.5MnNi0.5合金其表面會形成大量的鋁與鉻的氧化物，其皆為形成鈍態的主要化合物。陽極處理後的CrFe1.5MnNi0.5 與 Al0.3CrFe1.5MnNi0.5合金在含氯離子的溶液中，其EIS量測所得的極化阻抗明顯提升兩個數量級。因此陽極處理可有效改善高熵合金的表面結構，並減少對孔蝕的敏感性。

關鍵字

高熵合金 ； 腐蝕 ； 陽極處理 ； 極化曲線 ； 交流阻抗分析

並列摘要

High entropy alloys (HEAs) are a newly developed family of multi-component alloys that consist of various major alloying elements, including copper, nickel, aluminum, cobalt, chromium, iron and others. Each element in the alloy system is present in between 5 and 35 atom %. The crystal structures and physical properties of HEAs differ completely from those of conventional alloys.
First, this investigation discusses the corrosion resistance of the Al0.5CoCrCuFeNiBx alloys with various amounts of added boron. The potentiodynamic polarization curves and electrochemical impedance spectra (EIS) clearly revealed that the Al0.5CoCrCuFeNi alloy was more resistant to general corrosion than type 304 stainless steel (higher corrosion potential, lower corrosion current density) in acid solution. However, the general corrosion resistance of Al0.5CoCrCuFeNiBx alloy decreased as the concentration of boron increased. The cyclic polarization curve of the Al0.5CoCrCuFeNi and Al0.5CoCrCuFeNiB0.2 alloy were referred to as a pseudo-passive curve; however, the passive regions of the Al0.5CoCrCuFeNiB0.6 and Al0.5CoCrCuFeNiB1.0 alloy were totally disappeared and referred to active curve due to the increasing effect of boron. Surface morphological and chemical analyses verified that the production of CrB2 for the boron-containing HEA was reducing the Cr2O3 passive film on the alloy surface
The AlxCrFe1.5MnNi0.5 alloys exhibited a wide passive region, which extended ＞ 1000 mV in acidic environments. The potentiodynamic polarization and EIS of the AlxCrFe1.5MnNi0.5 alloys, obtained in H2SO4 solutions, clearly revealed that the corrosion resistance decreased as the concentration of aluminum increased. Moreover, the alloying of aluminum in the CrFe1.5MnNi0.5 alloys decreased the pitting potential (Epit) and impaired the pitting resistance in chloride environments. The Nyquist plots of the Al-containing alloys had two capacitive loops, which represented the electrical double layer and the adsorptive layer. Scanning electron microscopy (SEM) micrographs revealed that the general and pitting corrosion susceptibility of the AlxCrFe1.5MnNi0.5 alloys increased as the amount of aluminum in the alloy increased.
The EIS clearly revealed that the polarization resistance (Rp) values of the AlxCrFe1.5MnNi0.5 (x=0, 0.3, 0.5) alloys were markedly lower than that of the 304 stainless steel in chloride environments. At passive potential, the corresponding current declined with the anodizing time accounting, causing passivity by the growth of the multi-component anodized film in H2SO4 solution. X-ray photoelectron spectroscopy (XPS) analyses revealed that the surface of anodized Al0.3CrFe1.5MnNi0.5 alloy formed aluminum and chromium oxide film which was the main passivating compound on the alloy. This anodic treatment increased the corrosion resistance in the EIS measurements of the CrFe1.5MnNi0.5 and Al0.3CrFe1.5MnNi0.5 alloys by two orders of magnitude in chloride environment. Accordingly, the anodic treatment of the AlxCrFe1.5MnNi0.5 alloys optimized their surface structures and minimized their susceptibility to pitting corrosion.

並列關鍵字

High-entropy Alloy ； Corrosion ； Anodizing Treatment ； Potentiodynamic polarization curve ； EIS

參考文獻

[65] C.H. Wu, H.C. Shih, Corrosion and electrochemical properties of AlxFeCoNiCrMo0.5 six-component high entropy alloys, Master's Thesis, National Tsing-Hua University, Hsinchu, Taiwan, 2006.

[66] C.C. Chang, H.C. Shih, Corrosion and electrochemical properties of AlxCrMnFe1.5Niy high entropy alloys, Master's Thesis, National Tsing-Hua University, Hsinchu, Taiwan, 2006.

[61] K.L. Chang, H.C. Shih, Electrochemical studies of the CrN coating on steels, PhD's Thesis, National Tsing-Hua University, Hsinchu, Taiwan, 2004.

[5] W. Klement, R.H. Willens, P. Duwez, Non-crystalline structure in solidified gold-silicon alloys, Nature 187 (1960) 869-870.

[6] P. Duwez, Structure and properties of alloys rapidly quenched from the liquid state, Trans. ASM 60 (1967) 607.