本研究根據以前的學長以及學姊的研究，以CrFeCoNi為基礎，添加不同元素對材料的腐蝕性質及孔蝕形貌進行研究，例如添加Nb [CrFeCoNiNbX,(X=0.2、0.4、0.6、1.0)]，添加Ta[CrFeCoNiTaX,(X=0.1、0.3、0.5]，添加V[CrFeCoNiVX,[X=0.2、0.5、1.0]，以及CrFeCoNiNb0.15Mo0.15、CrFeCoNiNb0.3Mo0.3、CrFeCoNiNb0.5Mo0.5、CrFeCoNiNb0.25Mo0.75、CrFeCoNiNb0.75Mo0.25、CrFeCoNiMo。本研究利用恆電流/恆電位儀測進行電化學阻抗頻譜法(EIS)量測，分別在1M鹽酸、1M硫酸、1M硝酸以及1M氯化鈉除氧溶液中進行，量測後進行等效電路圖模擬，將Nyquist圖和試片阻抗值(Rp)以及學長姐量測極化曲線的數據進行相互比較。而臨界孔蝕溫度量測在1M氯化鈉溶液中進行，使用定電壓的方式對試片電流密度進行量測，之後再利用SEM對蝕孔形貌進行觀察。
電化學阻抗頻譜法(EIS)量測中發現到試片阻抗值(Rp)以CrFeCoNi的表現較好，推測可能因為添加而外的元素使材料結構以及Cr含量發生改變，使試片阻抗值(Rp)下降。而臨界孔蝕溫度可以看到CrFeCoNiNb0.15Mo0.15的抗孔蝕能力最佳，可以承受遠高於其它試片1300mV(SHE)，1300mV(SHE)的電壓下臨界孔蝕溫度約68℃。
This thesis investigated the corrosion behaviors of CrFeCoNiX (X = Nb, Mo, Ta or V) high-entropy alloys. The electrochemical behaviors of CrFeCoNiX high-entropy alloys were tested, included the electrochemical impedance spectroscopy (EIS) method and the critical pitting temperatures (CPTs) of these alloys. The EIS were tested in an Autolab PGSTAT30 Potential / Galvanostat, and the four solutions were 1M H2SO4, HNO3, HCl and NaCl solutions, respectively. The equivalent circuits of EIS of these alloys in the solutions were analyzed by the software of Autolab PGSTAT30 Potential / Galvanostat. The CPTs of these alloys were done according to standard of ASTM-G150-99, and corrosion morphologies were observed by a scanning electron microscope.
Results indicated that the CrFeCoNi alloy had a best impedance (Rp) among these alloys, because it had a single-phased granular structure and higher Cr-content of 0.25 molar fraction. Additionally, the CrFeCoNiNb0.15Mo0.15 alloy had the best pitting resistance in 1M NaCl solution, and the CPT of CrFeCoNiNb0.15Mo0.15 alloy was 68℃ under the potential of 1300mV (SHE).
