Nb變量對CrFeCoNiNbx合金微結構及腐蝕行為的影響

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Title:	Nb變量對CrFeCoNiNbx合金微結構及腐蝕行為的影響 Microstructures and corrosion behaviors of CrFeCoNiNbx alloys
Authors:	葉鎮宇
Contributors:	化學工程與材料工程學系奈米材料碩士班
Keywords:	高熵合金 high entropy alloys
Date:	2017
Issue Date:	2017-10-03 11:53:49 (UTC+8)
Abstract:	本論文主要在研究CrFeCoNiNbx高熵合金之電化學性質及其微結構，本論文研究合金分別為CrFeCoNiNb0.2、CrFeCoNiNb0.4、CrFeCoNiNb0.6三種合金來做研究及探討。結果顯示，在CrFeCoNi中添加不同比例的Nb，合金微結構從原本CrFeCoNi的晶粒狀組織結構變為CrFeCoNiNbx合金雙向的樹枝狀組織結構。同時隨著Nb含量之增加，具有HCP結構之Laves相就漸漸增加。本實驗再以恆電流/恆電位儀測量金屬合金在1M硫酸、1M鹽酸、1M硝酸及1M氯化鈉溶液，在30、40、50、60溫度下的極化曲線，來測定其腐蝕電位、腐蝕電流和鈍態區間電位，並相互比較及與304不銹鋼做些比較。在1M硫酸、1M鹽酸、1M硝酸及1M氯化鈉的去氧溶液中三種合金皆會產生鈍態區，但在有些溶液中因溫度的升高而導致鈍態區的消失，也會出現腐蝕電位Ecorr及腐蝕電流icorr不穩定的現象。此外我們會藉由場發射式電子顯微鏡(FE-SEM)及EDS分析來觀察其腐蝕表面孔洞和表面的成分比例。本論文的研究結果顯示，三種合金在各溶液中的耐腐蝕能力皆優於304不鏽鋼。 The purpose of this research is to investigate the electrochemical properties and microstructure of the CrFeCoNiNbx high entropy alloys (HEAs), including the CrFeCoNiNb0.2, CrFeCoNiNb0.4, and CrFeCoNiNb0.6 alloys. The microstructure changed from a granular structure of CrFeCoNi alloy into a dendritic structure of CrFeCoNiNbx alloys after added different proportions of Nb. The two phases in the CrFeCoNiNbx alloys were FCC and HCP-structured Laves phase. The Laves phase increased gradually as the Nb content increased. To further understand the electrochemical properties of the HEAs, the polarization curves of those HEAs were tested in the solution of 1 M H2SO4, 1M HCl, 1M HNO3, and 1M NaCl, and the testing temperatures were 30˚C, 40 ˚C, 50˚C, and 60˚C. Furthermore, the corrosion potential, the corrosion current and the passive range were tested through galvanostat/ potentiostat, and the results of CrFeCoNiNbx alloys also compared with those of 304 stainless steel (304SS). Results indicated that the HEAs in 1 M H2SO4, 1M HCl, 1M HNO3, and 1M NaCl solution remained passive regions, but the passive regions disappear in some solution while tested at higher temperatures. In addition, corrosion potential, Ecorr, and corrosion current density, icorr, became unstable at higher testing temperatures. The corrosion surfaces were examined by a field-emission scanning microscope (FE-SEM) with the energy dispersive spectroscopy (EDS). All of the results showed that CrFeCoNiNbx alloys had better corrosion resistances than commercial 304 stainless steel in these four solutions.
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