高熵合金Al_XFeNiCoCrMo0.5之腐蝕及電化學特性研究

Corrosion and Electrochemical Properties of AlXFeCoNiCrMo0.5 High Entropy Alloys

AlXFeNiCoCrMo0.5六元高熵合金，其中部份成分與一般商業用的316型不銹鋼相近，以316型不銹鋼而言，Fe為主要成分，而Cr的添加有助於鈍態膜的形成，Mo之添加則有助於抗氯鹽之孔蝕。本高熵合金成分與316型不銹鋼相較，Al成分為最大差異之元素，所以改變Al成分之莫耳比進行探討並與316型不銹鋼相比較。由金相照片可知Al成分的增加使合金中的樹枝相明顯增加，相對的也會對其腐蝕結果造成影響。不同的成分在0.5 M硫酸水溶液中之極化結果顯示，隨著Al成分的增加腐蝕電位越趨向於活態，而腐蝕電流也隨之增加。然而在1 M氯化鈉水溶液中，Ecorr和Icorr成分沒有明顯的差異，但Al為0.5莫耳比時明顯有較高的孔蝕電位。由以上結果以及EIS的測試結果可以知道Al為0.5莫耳比時性質較好，故隨後以該成分與316不銹鋼相比較。由EIS圖譜分析可以看出，在OCP的條件下不論在0.5 M硫酸水溶液或是1 M氯化鈉水溶液中，Al0.5FeNiCoNiCrMo0.5合金比316型不銹鋼具有較大的腐蝕阻抗值（RP）。然而藉由在含不同濃度氯化鈉之0.5 M硫酸水溶液的極化測試，可以知道本高熵合金對氯鹽較為敏感，較容易發生孔蝕現象，當氯化鈉含量低至0.1 M時即有孔蝕現象的發生。

Six-element AlxFeNiCoCrMo0.5 high entropy alloys (HEAs) comprise several components that are the same as those in 316 stainless steels (316SS). For 316SS, Fe is the major element. Al is the most active component between the HEAs and 316SS. For a comparison in corrosion property with 316SS, the molar ratio of Al in the HEA was varied. The dendrite phase in the alloy increased distinctly when the Al content was increased, and that would affect the corrosion property of this alloy. Potentiodynamic polarization analyses in 0.5 M H2SO4 solutions indicated that the corrosion potential (Ecorr) would be more active and the corrosion current (Icorr) would increase when the Al component increased in the HEAs. At a 0.5 molar ratio of Al, the HEA had a relatively high pitting corrosion potential in a 1 M NaCl solution, signifying a better pitting resistance of this alloy. Subsequent potentiodynamic polarization analyses showed that this HEA was more resistant to general corrosion than 316SS, both in 0.5 M H2SO4 and in 1 M NaCl solutions. However, the polarization results also demonstrated that pitting could be induced in this alloy in a Cl－- containing (0.1 M NaCl) H2SO4 solution.