本研究主要測試Ti-6Al-4V合金於路易士酸性、中性與鹼性之AlCl3-EMIC離子液體中應力腐蝕破裂敏感性。並藉由再結晶退火熱處理改變Ti-6Al-4V合金中α相與β相之相比例，以探討相比例對Ti-6Al-4V合金於路易士酸性及中性離子液體中應力腐蝕破裂敏感性之影響。
進行應力腐蝕破裂敏感性測試前，先針對Ti-6Al-4V合金原材於三種不同路易士酸鹼性之AlCl3-EMIC離子液體的腐蝕行為進行研究。動電位極化測試的結果顯示，Ti-6Al-4V合金原材於路易士酸性AlCl3-EMIC離子液體中抗蝕性最差，並可觀察到α相優選溶解的現象；於路易士中性AlCl3-EMIC離子液體中，則可觀察到β相優選溶解的現象；於路易士鹼性AlCl3-EMIC離子液體中，α相或β相優選溶解的現象並不顯著。由此結果可知，Ti-6Al-4V合金原材於AlCl3-EMIC離子液體中的腐蝕行為受到離子液體中不同陰離子的作用所影響。除此之外，再針對經熱處理後以爐冷與空冷方式處理之Ti-6Al-4V合金於路易士酸性與中性AlCl3-EMIC離子液體的腐蝕行為進行研究。結果顯示，不論是以爐冷或空冷方式處理之Ti-6Al-4V合金於路易士酸性AlCl3-EMIC離子液體中皆呈現α相優選溶解的現象。然而經熱處理後以爐冷方式處理之Ti-6Al-4V合金於路易士中性AlCl3-EMIC離子液體中β相優選溶解的現象更加顯著；以空冷方式處理之Ti-6Al-4V合金於路易士中性AlCl3-EMIC離子液體中，α/β相界處因伽凡尼效應(galvanic effect) 的作用下，腐蝕現象較為顯著。
U型試片應力腐蝕試驗結果顯示，Ti-6Al-4V合金原材之U型試片於路易士酸性離子液體中表面呈現嚴重的腐蝕型貌。經熱處理後以爐冷與空冷方式處理之Ti-6Al-4V合金於路易士酸性離子液體中亦未發生應力腐蝕破裂的現象；於路易士中性與鹼性AlCl3-EMIC離子液體中皆會發生應力腐蝕破裂之現象，值得注意的是，熱處理後以空冷方式處理之Ti-6Al-4V合金於路易士中性離子液體中，應力腐蝕破裂敏感性明顯增加。

In this study, the susceptibility of Ti-6Al-4V alloy to stress corrosion cracking (SCC) in Lewis-acid, Lewis-neutral and Lewis-basic AlCl3-EMIC ionic liquids was investigated. In order to study the effect of β phase volume fraction on the susceptibility of Ti-6Al-4V alloy to SCC in Lewis-acid and Lewis-neutral AlCl3-EMIC ionic liquids, the volume fraction of the β phase was varied by means of recrystallization annealing.
The corrosion behavior of as-received Ti-6Al-4V alloy in Lewis-acid, Lewis-neutral and Lewis-basic AlCl3-EMIC ionic liquid was investigated prior to the U-bend SCC test. The results of potentiodynamic polarization curve measurement showed that as-received Ti-6Al-4V alloy exhibited the highest corrosion rate in Lewis-acid AlCl3-EMIC ionic liquid and the preferential corrosion of α phase in as-received Ti-6Al-4V alloy was observed after polarization test. In contrast, the preferential corrosion of  phase in Ti-6Al-4V alloy was observed after polarization test in Lewis-neutral AlCl3-EMIC ionic liquid.. However, the phenomenon of preferential corrosion was not found in Lewis-basic AlCl3-EMIC ionic liquid. That is, the corrosion behavior of Ti-6Al-4V alloy in AlCl3-EMIC ionic liquid is influenced by the anion contained in AlCl3-EMIC ionic liquid with different Lewis acidity. Furthermore, the effect of β phase volume fraction on the corrosion behavior in Lewis-acid and Lewis-neutral AlCl3-EMIC ionic liquid was also investigated. The preferential corrosion of α phase in Ti-6Al-4V alloys which were recrystallization annealed followed by furnace-cooled and air-cooled, respectively were found after polarization test in Lewis-acid AlCl3-EMIC ionic liquid. The distinct preferential corrosion of  phase in Ti-6Al-4V alloy with recrystallization annealing followed by furnace-cooling was observed after polarization test in Lewis-neutral AlCl3-EMIC. However, preferentially corrosion at α/β phase boundary resulted from galvanic effect was found in Ti-6Al-4V alloy with recrystallization annealing followed by air-cooling after polarization test in Lewis-neutral AlCl3-EMIC ionic liquid.
The results of U-bend test indicated that severe corrosion was found in Ti-6Al-4V after U-bend test in the Lewis-acid AlCl3-EMIC ionic liquid. Furthermore, Ti-6Al-4V alloys after recrystallization annealing followed by furnace-cooling and air-cooling were also corroded severely after U-bend test in the Lewis-acid AlCl3-EMIC ionic liquid. However, Ti-6Al-4V alloy is susceptible to SCC in the Lewis-neutral and Lewis-basic AlCl3-EMIC ionic liquids. Moreover, the susceptibility of Ti-6Al-4V alloy with recrystallization annealing followed by air-cooling to SCC was significantly increased in the Lewis-neutral AlCl3-EMIC ionic liquids.

[1] S.A. Forsyth, J. M.Pringle, D.R. MacFarlane, Ionic Liquids - An Overview, Australian Journal of Chemistry, 57 (2004) 113-119.
[2] T. Welton, Ionic liquids in catalysis, Coordination Chemistry Reviews, 248 (2004) 2459-2477.
[3] J.F. Wishart, Energy applications of ionic liquids, Energy & Environmental Science, 2 (2009) 956-961.
[4] J.-K. Chang, S.-Y. Chen, W.-T. Tsai, M.-J. Deng, I.W. Sun, Electrodeposition of aluminum on magnesium alloy in aluminum chloride (AlCl3)–1-ethyl-3-methylimidazolium chloride (EMIC) ionic liquid and its corrosion behavior, Electrochemistry Communications, 9 (2007) 1602-1606.
[5] J.A. Whitehead, J. Zhang, N. Pereira, A. McCluskey, G.A. Lawrance, Application of 1-alkyl-3-methyl-imidazolium ionic liquids in the oxidative leaching of sulphidic copper, gold and silver ores, Hydrometallurgy, 88 (2007) 109-120.
[6] N.V. Plechkova, K.R. Seddon, Applications of ionic liquids in the chemical industry, Chemical Society Reviews, 37 (2008) 123-150.
[7] G. Sanderson, J.C. Scully, The stress corrosion of ti alloys in methanolic solutions, Corrosion Science, 8 (1968) 541-548.
[8] X.G. Zhang, J. Vereecken, Stress Corrosion Cracking Mechanism of Ti-6A1-4V in Acidic Methanol, Corrosion, 46 (1990) 136-141.
[9] C. Leyens, M. Peters, Titanium and Titanium Alloys: Fundamentals and Applications, Wiley-VCH Verlag GmbH & Co. KGaA, (2003).
[10] J. Matthew J. Donachie, Titanium: a technical guide, ASM International, (2000).
[11] G. Sanderson, D.T. Powell, J.C. Scully, The stress-corrosion cracking of Ti alloys in aqueous chloride solutions at room temperature, Corrosion Science, 8 (1968) 473-481.
[12] H. Niedermeyer, J.P. Hallett, I.J. Villar-Garcia, P.A. Hunt, T. Welton, Mixtures of ionic liquids, Chemical Society reviews, 41 (2012) 7780-7802.
[13] K.R. Seddon, A. Stark, M.-J. Torres, Influence of chloride, water, and organic solvents on the physical properties of ionic liquids, Pure and Applied Chemistry, 72 (2000) 2267-2275.
[14] Y. Chauvin, H. Olivier-Bourbigou, Nonaqueous Ionic Liquids as Reaction Solvents, CHMTECH, 25 (1995) 26-30.
[15] M.J. Earle, K.R. Seddon, Ionic liquids. Green solvents for the future, Pure and Applied Chemistry, 72 (2000) 1391-1398.
[16] F. Endres, S. Zein El Abedin, Air and water stable ionic liquids in physical chemistry, Physical Chemistry Chemical Physics, 8 (2006) 2101-2116.
[17] F. Endres, Ionic Liquids:Solvents for the Electrodeposition of Metals and Semiconductors, ChemPhysChem, 3 (2002) 144-154.
[18] Q. Zhao, Y. NuLi, T. Nasiman, J. Yang, J. Wang, Reversible Deposition and Dissolution of Magnesium from Imidazolium-Based Ionic Liquids, International Journal of Electrochemistry, 2012 (2012) 1-8.
[19] I. Mukhopadhyay, C.L. Aravinda, D. Borissov, W. Freyland, Electrodeposition of Ti from TiCl4 in the ionic liquid l-methyl-3-butyl-imidazolium bis (trifluoro methyl sulfone) imide at room temperature: study on phase formation by in situ electrochemical scanning tunneling microscopy, Electrochimica Acta, 50 (2005) 1275-1281.
[20] R. Al-Salman, J. Mallet, M. Molinari, P. Fricoteaux, F. Martineau, M. Troyon, S. Zein El Abedin, F. Endres, Template assisted electrodeposition of germanium and silicon nanowires in an ionic liquid, Physical chemistry chemical physics : PCCP, 10 (2008) 6233-6237.
[21] R. Al-Salman, S.Z. El Abedin, F. Endres, Electrodeposition of Ge, Si and SixGe1-x from an air- and water-stable ionic liquid, Physical chemistry chemical physics : PCCP, 10 (2008) 4650-4657.
[22] A. Lewandowski, A. Świderska-Mocek, Ionic liquids as electrolytes for Li-ion batteries—An overview of electrochemical studies, Journal of Power Sources, 194 (2009) 601-609.
[23] P. Wang, S.M. Zakeeruddin, P. Comte, I. Exnar, a.M. Gra¨tzel, Gelation of Ionic Liquid-Based Electrolytes with Silica Nanoparticles for Quasi-Solid-State Dye-Sensitized Solar Cells, Journal of the American Chemical Society, 125 (2002) 1166-1167.
[24] M.-T. Lee, W.-T. Tsai, H.-F. Cheng, I.W. Sun, J.-K. Chang, Effect of electrolyte temperature on the pseudo-capacitive behavior of manganese oxide in N-butyl-N-methylpyrrolidinium–dicyanamide ionic liquid, Journal of Power Sources, 233 (2013) 28-33.
[25] C. Ke, J. Li, X. Li, Z. Shao, B. Yi, Protic ionic liquids: an alternative proton-conducting electrolyte for high temperature proton exchange membrane fuel cells, RSC Advances, 2 (2012) 8953-8956.
[26] A. Bösmann, L. Datsevich, A. Jess, A. Lauter, C. Schmitz, P. Wasserscheid, Deep desulfurization of diesel fuel by extraction with ionic liquids, Chemical Communications, (2001) 2494-2495.
[27] F. Zhou, Y. Liang, W. Liu, Ionic liquid lubricants: designed chemistry for engineering applications, Chemical Society Reviews, 38 (2009) 2590-2599.
[28] J.S. Wilkes, J.A. Levisky, R.A. Wilson, C.L. Hussey, Dialkylimidazolium chloroaluminate melts: a new class of room-temperature ionic liquids for electrochemistry, spectroscopy and synthesis, Inorganic Chemistry, 21 (1982) 1263-1264.
[29] J. Armand A. Fannin, D.A. Floreani, L.A. King, J.S. Landers, B.J. Piersma, D.J. Stech, R.L. Vaughn, J.S. Wilkes, J.L. Williams, Properties of 1,3-dialkylimidazolium chloride-aluminum chloride ionic liquids. 2. Phase transitions, densities, electrical conductivities, and viscosities, The Journal of Physical Chemistry, 88 (1984) 2614-2621.
[30] A.a.K. Abdul-Sada, A.M. Greenway, K.R. Seddon, T. Welton, Upon the existence of [Al3Cl10]− in room temperature chloroaluminate ionic liquids, Organic Mass Spectrometry, 24 (1989) 917-918.
[31] A.a.K. Abdul-Sada, A.M. Greenway, K.R. Seddon, T. Welton, A fast atom bombardment mass spectrometric study of room-temperature 1-ethyl-3-methylimidazolium chloroaluminate(III) ionic liquids. Evidence for the existence of the decachlorotrialuminate(III) anion, Organic Mass Spectrometry, 28 (1993) 759-765.
[32] R.J. GALE, B. GILBERT, R.A. OSTERYOUNG, Raman spectra of molten aluminum chloride-1-butylpyridinium chloride systems at ambient temperatures, Inorganic Chemistry, 17 (1978) 2728-2729.
[33] R.J. GALE, R.A. OSTERYOUNG, Infrared spectral investigations of room-temperature aluminum chloride-1-butylpyridinium chloride melts, Inorganic Chemistry, 19 (1980) 2240-2242.
[34] J.L. Gray, G.E. Maciel, Aluminum-27 nuclear magnetic resonance study of the room-temperature melt aluminum trichloride butylpyridinium chloride, Journal of the American Chemical Society, 103 (1981) 7147-7151.
[35] D. Appleby, C.L. Hussey, K.R. Seddon, J.E. Turp, Room-temperature ionic liquids as solvents for electronic absorption spectroscopy of halide complexes, Nature, 323 (1986) 614-616.
[36] C.L. Hussey, Room temperature haloaluminate ionic liquids.Novel solvents for transition metal solution chemistry, Pure and Applied Chemistry, 60 (1988) 1763-1772.
[37] M.-H. Chuang, J.-K. Chang, P.-J. Tsai, W.-T. Tsai, M.-J. Deng, I.W. Sun, Heat-treatment induced material property variations of Al-coated Mg alloy prepared in aluminum chloride/1-ethyl-3-methylimidazolium chloride ionic liquid, Surface and Coatings Technology, 205 (2010) 200-204.
[38] C.-H. Tseng, J.-K. Chang, J.-R. Chen, W.T. Tsai, M.-J. Deng, I.W. Sun, Corrosion behaviors of materials in aluminum chloride–1-ethyl-3-methylimidazolium chloride ionic liquid, Electrochemistry Communications, 12 (2010) 1091-1094.
[39] P.-C. Lin, I.W. Sun, J.-K. Chang, C.-J. Su, J.-C. Lin, Corrosion characteristics of nickel, copper, and stainless steel in a Lewis neutral chloroaluminate ionic liquid, Corrosion Science, 53 (2011) 4318-4323.
[40] C. Gabler, C. Tomastik, J. Brenner, L. Pisarova, N. Doerr, G. Allmaier, Corrosion properties of ammonium based ionic liquids evaluated by SEM-EDX, XPS and ICP-OES, Green Chemistry, 13 (2011) 2869-2877.
[41] I. Perissi, U. Bardi, S. Caporali, A. Lavacchi, High temperature corrosion properties of ionic liquids, Corrosion Science, 48 (2006) 2349-2362.
[42] I. Perissi, U. Bardi, S. Caporali, A. Fossati, A. Lavacchi, Ionic liquids as diathermic fluids for solar trough collectors’ technology: A corrosion study, Solar Energy Materials and Solar Cells, 92 (2008) 510-517.
[43] R.L. Perry, K.M. Jones, W.D. Scott, Q. Liao, C.L. Hussey, Densities, Viscosities, and Conductivities of Mixtures of Selected Organic Cosolvents with the Lewis Basic Aluminum Chloride + 1-Methyl-3-ethylimidazolium Chloride Molten Salt, Journal of Chemical and Engineering Data, 40 (1995) 615-619.
[44] C.R. Brooks, Heat treatment, structure, and properties of nonferr ous alloys, American Society for Metals, (1982).
[45] S.L. Semiatin, S.L. Knisley, P.N. Fagin, D.R. Barker, F. Zhang, Microstructure evolution during alpha-beta heat treatment of Ti-6Al-4V, Metallurgical and Materials Transactions A, 34 (2003) 2377-2386.
[46] K.R. Seddon, Ionic Liquids for Clean Technology, Journal of Chemical Technology and Biotechnology, 68 (1997) 351-356.