本研究釐清了不同的製程參數對於Incoloy-925的拉伸性質與腐蝕行為的影響。Incoloy-925藉由合金鋼廠的熱鍛造機與Gleeble熱壓模擬皆可達到75%的變形量，於後續的熱處理成功地細化晶粒至39μm。於室溫下，降伏強度與最大拉伸強度皆可以透過控制L12 γ'析出物之尺寸與體積百分比提升。根據差排模型，在weak-pair轉換至strong-pair coupling的瞬間所對應到的析出物尺寸為理論最高強度。然而研究過程中發現此合金於高溫650°C出現嚴重的延性下降情形，從室溫25%減少至3%。破裂分析結果顯示，隨著拉伸溫度提高，沿晶破裂的特徵更加明顯，晶界觀察發現有沿著晶界的γ'於650°C會轉變成針狀的η相並脆化晶界，導致高溫拉伸延性降低。因此本研究嘗試將晶界工程應用至Incoloy-925改變晶界分布的方式以改善材料性質。研究結果顯示晶界工程對於高溫拉伸延展性並無顯著的效益，因為晶界仍存在許多η相從而脆化晶界。然而藉由改變時效條件析出大量且分散的η相使得裂口到處分布，提升了高溫延展性。此外，此材料的腐蝕特性與表面穩定性於本研究中亦被探討，研究顯示此材料抗蝕能力十分優秀，而高溫氧化實驗中，抗氧化能力亦藉由晶界工程略有改進。

The present study investigates the effects of processing conditions on the tensile property and corrosion behavior of Incoloy-925. Grain refinement of the alloy can be achieved with both air hammer and Gleeble test. In addition, both yield strength and ultimate tensile strength at room temperature can be increased by controlling the size and volume fractions of L12 gamma-prime precipitates, and peak strength can be verified at the transition from strong-pair and weak-pair coupling models. However, significant hot ductility drop has been observed, experimental results show that the tensile strain has been decreased from 25 % at room temperature to 3 % at 650°C and fracture surfaces analysis has shown a ductile to brittle transition. Microstructure observations have revealed that primary gamma-prime phase along the grain boundaries can evolved into needle-like η phase at 650°C to cause hot ductility drop. Therefore, grain boundary engineering (GBE), which can change the distribution of grain boundaries, has been applied to Incoloy-925 to improve material properties. Experimental results indicate that effect of GBE doesn’t improve hot ductility drop a lot since there are a lot of η phases decorated along grain boundaries. However, increasing the aging temperature can homogeneously precipitate a great number of η phases, distributing uniform cracks over the bulk structure and increasing the hot ductility. Furthermore, corrosion behavior of Incoloy-925 has been investigated with salt spray test, polarization test, and oxidation test. Experimental results indicate that Incoloy-925 with and without GBE possesses good corrosion resistance. In addition, oxidation resistance with GBE is slightly improved.

Abstract I
摘要 II
Acknowledgements III
Table of Contents IV
List of Figures VI
List of Tables X
1. Introduction 11
2. Literature review 13
2.1. Incoloy-925 13
2.2. Thermal mechanical treatments on superalloys 15
2.3. Strengthening mechanisms on superalloys 16
2.4. Grain boundary engineering 19
2.5. The corrosion experiments 20
3. The Material and Methods 23
3.1. The material 23
3.2. The design of thermal-mechanical treatments and heat treatments 23
3.3. Optical microscopy (OM) 25
3.4. Scanning electron microscopy (SEM) 25
3.5. Differential thermal analyzer (DTA) 25
3.6. Gleeble3500 thermomechanical simulator 26
3.7. Hardness test 26
3.8. Tensile test 27
3.9. Grain boundary engineering 28
3.10. EBSD analysis 28
3.11. Salt spray test 29
3.12. Polarization test 30
3.13. Oxidation test 32
4. Results and discussions 33
4.1. Microstructure evolutions 33
4.1.1. Analysis of as-cast microstructure 33
4.1.2. Analysis of microstructure after SHT 34
4.1.3. Analysis of microstructure after hot forging and annealing 37
4.1.4. Analysis of microstructure after aging 39
4.1.5. Analysis of Gleeble3500 thermomechanical simulation 42
4.2. Tensile properties 45
4.2.1. Analysis of tensile test at room temperature 45
4.2.2. Analysis of tensile test at high temperature 49
4.2.3. Grain boundary engineering in Incoloy-925 53
4.3. Corrosion behavior 60
4.3.1. Salt spray tests 60
4.3.2. Polarization tests 61
4.3.3. Oxidation tests 63
5. Conclusion 67
6. Nomenclature 69
Reference 70

[1] M.J. Donachie, S.J. Donachie, Superalloys: a technical guide, ASM international, 2002.
[2] S. Metals, http.//www. specialmetals. com/products/data—925. htm, (2002).
[3] R.E. Reed-Hill, R. Abbaschian, (1973).
[4] R.C. Reed, The superalloys: fundamentals and applications, Cambridge university press, 2006.
[5] W. T., Res Mechanica, 11 (1984) 47.
[6] E.L. Hibner, S. Tassen, CORROSION 2001, NACE International, 2001, pp. No. 01102.
[7] E.L. Hibner, L.E. Shoemaker, CORROSION 2000, NACE International, 2000, pp. No. 00602.
[8] Z. Shi, J. Xu, Z. Qiu, Z. Wang, B. Gao, JOM, 55 (2003) 63-65.
[9] K. Prasad, R. Sarkar, P. Ghosal, V. Kumar, Materials & Design, 31 (2010) 4502-4507.
[10] Y. Lin, J. Deng, Y.-Q. Jiang, D.-X. Wen, G. Liu, Materials & Design, 55 (2014) 949-957.
[11] N. Saunders, U. Guo, X. Li, A. Miodownik, J.-P. Schillé, JOM, 55 (2003) 60-65.
[12] N. Saunders, Z. Guo, X. Li, A. Miodownik, J.-P. Schille, Proceedings of the 10th International Symposium on Superalloys, 2004, pp. 849-858.
[13] M. Oehring, F. Appel, T. Pfullmann, R. Bormann, Applied physics letters, 66 (1995) 941-943.
[14] W. Mangen, E. Nembach, Acta Metallurgica, 37 (1989) 1451-1463.
[15] E. Nembach, Scripta Metallurgica et Materialia, 24 (1990) 787-792.
[16] C. Wei, H. Bor, C. Ma, T. Lee, Materials chemistry and physics, 80 (2003) 89-93.
[17] R. Kozar, A. Suzuki, W. Milligan, J. Schirra, M. Savage, T. Pollock, Metallurgical and Materials Transactions A, 40 (2009) 1588-1603.
[18] A. Vattré, B. Devincre, A. Roos, Intermetallics, 17 (2009) 988-994.
[19] d.F.J. Preuss M, Grant B, Knoche E, Moat R, Daymond M, Superalloys 2008. Champion (PA): The Minerals, Metals and Materials Society, 2008, pp. 405-414.
[20] A. Ardell, Metallurgical Transactions A, 16 (1985) 2131-2165.
[21] M.C. Flemings, Metallurgical transactions, 5 (1974) 2121-2134.
[22] V. Garat, J.-M. Cloue, D. Poquillon, E. Andrieu, Journal of Nuclear Materials, 375 (2008) 95-101.
[23] M. Mirzaee, H. Keshmiri, G.R. Ebrahimi, A. Momeni, Materials Science and Engineering: A, 551 (2012) 25-31.
[24] M.S. Salehi, S. Serajzadeh, Computational Materials Science, 49 (2010) 773-781.
[25] L. Cheng, H. Chang, B. Tang, H. Kou, J. Li, Materials Letters, 92 (2013) 430-432.
[26] G.E. Dieter, D.J. Bacon, Mechanical metallurgy, McGraw-Hill New York, 1986.
[27] D.L. Gv Boittin, A. Rafrayl, P. Caron, P. Kanoutél, F. Gallerneaul, G. CailletaudZ, Superalloys 2012, (2012) 167-176.
[28] A. Heckl, S. Neumeier, M. Göken, R. Singer, Materials Science and Engineering: A, 528 (2011) 3435-3444.
[29] M. Meyers, K. Chawla, Englewood Cliffs, NJ, (1999) 92.
[30] M. Yoo, J. Horton, C. Liu, Acta Metallurgica, 36 (1988) 2935-2946.
[31] A. Devaux, L. Nazé, R. Molins, A. Pineau, A. Organista, J. Guédou, J. Uginet, P. Héritier, Materials Science and Engineering: A, 486 (2008) 117-122.
[32] S. Zhao, X. Xie, G.D. Smith, S.J. Patel, Materials letters, 58 (2004) 1784-1787.
[33] L. Brown, R. Ham, Strengthening methods in crystals, (1971) 9-135.
[34] W. Huther, B. Reppich, Zeitschrift fur Metallkunde, 69 (1978) 628-634.
[35] F. Hargreaves, R. Hills, J. Inst. Met, 41 (1929) 257.
[36] M. Kronberg, F. Wilson, AIME TRANS, 185 (1949) 501-514.
[37] D. Brandon, Acta metallurgica, 14 (1966) 1479-1484.
[38] S. Ranganathan, Acta Crystallographica, 21 (1966) 197-199.
[39] V. Randle, M. Caul, Materials Science and Technology, 12 (1996) 844-850.
[40] R. V., Mater. Sci. Technol. , 26 (2010) 253.
[41] A. Telang, A.S. Gill, M. Kumar, S. Teysseyre, D. Qian, S.R. Mannava, V.K. Vasudevan, Acta Materialia, 113 (2016) 180-193.
[42] Q. Li, N. Richards, Metallography, Microstructure, and Analysis, 2 (2013) 21-29.
[43] S.-L. Lee, N. Richards, Materials Science and Engineering: A, 390 (2005) 81-87.
[44] Q. Li, B. Guyot, N. Richards, Materials Science and Engineering: A, 458 (2007) 58-66.
[45] V. Randle, Acta materialia, 47 (1999) 4187-4196.
[46] G. Palumbo, Google Patents, 1998.
[47] E. Dix, J. Bowman, Symposium on Corrosion Testing Procedures, ASTM International, 1937.
[48] B. ASTM, ASTM International (1997 Edition), (1997).
[49] V. Chawla, D. Puri, S. Prakash, B.S. Sidhu, Journal of Minerals and Materials Characterization and Engineering, 8 (2009) 693.
[50] F. Erler, C. Jakob, H. Romanus, L. Spiess, B. Wielage, T. Lampke, S. Steinhäuser, Electrochimica Acta, 48 (2003) 3063-3070.
[51] L. Dobrzański, Z. Brytan, M.A. Grande, M. Rosso, Journal of Materials Processing Technology, 192 (2007) 443-448.
[52] C.A. Walton, H.J. Martin, M. Horstemeyer, P.T. Wang, Corrosion Science, 56 (2012) 194-208.
[53] D.A. Jones, Principles and prevention of corrosion, Macmillan, 1992.
[54] K.B. OLDHAM, F. MANSFELD, Corrosion, 27 (1971) 434-435.
[55] P. Xu, L. Zhao, K. Sridharan, T. Allen, Journal of Nuclear Materials, 422 (2012) 143-151.
[56] L. Tan, K. Sridharan, T. Allen, Journal of nuclear materials, 348 (2006) 263-271.
[57] L. Tan, X. Ren, K. Sridharan, T. Allen, Corrosion Science, 50 (2008) 3056-3062.
[58] S. Yang, U. Krupp, H.J. Christ, V. Braz Trindade, Advanced Engineering Materials, 7 (2005) 723-726.
[59] H. Czichos, T. Saito, L. Smith, Springer handbook of materials measurement methods, Springer Berlin, 2006.
[60] H. Hindman, G. Burr, Transactions of the American Society of Mechanical Engineers, 71 (1949) 789-796.
[61] Y.-j. CHEN, J. Hjelen, H.J. Roven, Transactions of Nonferrous Metals Society of China, 22 (2012) 1801-1809.
[62] K.P. Mingard, B. Roebuck, E.G. Bennett, M.G. Gee, H. Nordenstrom, G. Sweetman, P. Chan, International Journal of Refractory Metals and Hard Materials, 27 (2009) 213-223.
[63] V. Randle, I.o. Materials, The Role of the Coincidence Site Lattice in Grain Boundary Engineering, Institute of Materials, 1996.
[64] M. Stern, A.L. Geary, Journal of the electrochemical society, 104 (1957) 56-63.
[65] C.E. Campbell, W.J. Boettinger, U.R. Kattner, Acta Materialia, 50 (2002) 775-792.
[66] E. Nembach, G. Neite, Progress in Materials Science, 29 (1985) 177-319.
[67] F.M. Shore, M. Morakabati, S.M. Abbasi, A. Momeni, R. Mahdavi, ISIJ international, 54 (2014) 1353-1360.
[68] M. Qian, J. Lippold, Acta Materialia, 51 (2003) 3351-3361.
[69] A. Ardell, Metallurgical and Materials Transactions B, 1 (1970) 525-534.
[70] H. Eiselstein, Metallurgy of a columbium-hardened nickel-chromium-iron alloy, Advances in the Technology of Stainless Steels and Related Alloys, ASTM International, 1965, pp. 62-79.
[71] V. Randle, Materials Science and Technology, 26 (2010) 253-261.
[72] J. Kim, P. Xiang, K. Kim, Corrosion, 61 (2005) 174-183.
[73] P. De Tiedra, Ó. Martín, M. San-Juan, Journal of Alloys and Compounds, 673 (2016) 231-236.