本研究的第一部分中，設計了不同Al跟Ti含量的AlxCo1.5CrFeNi1.5Tiy系列高熵合金，並針對其組成相與微結構做研究。文中探討此系列合金之黏著磨耗行為與機制，並與常見的耐磨鋼材，SUJ2軸承鋼及SKH51高速鋼做比較。結果顯示Al跟Ti的含量會顯著地影響合金的組成相與微結構，特別是其中堅硬的η-(Ni, Co)3Ti相之數量與形貌。Al0.2Co1.5CrFeNi1.5Ti合金在相近的硬度表現下，其磨耗阻抗至少比常見的耐磨鋼材好一倍以上。這些高熵合金之所以會有如此傑出的磨耗阻抗主要是因為其優異的抗氧化性與抗高溫軟化性質。
在第二部分中，本研究使用Al0.3CrFe1.5MnNi0.5高熵合金，展示了一種利用在靠近表層區域局部析出的表面硬化處理方法。這種表面析出硬化法製程簡單，只需要在大氣下進行一般的時效處理，並且適用於複雜形狀的物體。實驗的結果顯示，經過此表面硬化的Al0.3CrFe1.5MnNi0.5高熵合金，其磨耗阻抗至少增加了百分之五十，並且只有些許的彎曲韌性損失。跟常見的SUJ2軸承鋼與SKD61熱作工具鋼比起來，此表面硬化處裡過的Al0.3CrFe1.5MnNi0.5合金有著更好的機械性質組合。

摘要 I
Abstract II
誌謝 III
Contents V
Figure Captions VIII
List of tables XIII
1. Introduction 1
2. Background 3
2.1. Wear 3
2.1.1. Wear behavior 3
2.1.2. Wear map of steels in dry sliding 8
2.1.3. Importance of wear 10
2.1.4. Wear prevention 11
2.2. High-entropy alloy 13
2.2.1. Concept of high-entropy alloys 13
2.2.2. Four core effects of high-entropy alloys 13
2.2.3. High-entropy alloy systems with good wear resistance 20
2.3. Motivation 21
3. Microstructure and wear behavior of AlxCo1.5CrFeNi1.5Tiy high-entropy alloys 23
3.1. Introduction 23
3.2. Experimental procedure 26
3.3. Results 31
3.3.1. Microstructure and Hardness 31
3.3.2. Wear test result 50
3.3.3. Oxidation weight gain test and hot hardness measurement 60
3.4. Discussion 63
3.4.1. Wear mechanism 63
3.4.2. Mechanism of the outstanding wear resistance in Al00Ti10 and Al02Ti10 65
3.5. Summary 69
4. Intrinsic surface precipitation hardening in an Al0.3CrFe1.5MnNi0.5 high-entropy alloy 71
4.1. Introduction 71
4.2. Experimental procedure 76
4.3. Results 80
4.3.1. Cross-sectional microstructure and hardened layer thickness 80
4.3.2. SEM/EDS and XRD analysis 88
4.3.3. Mechanical properties of the surface-hardened layer 92
4.4. Discussion 98
4.4.1. Strain energy and free surface effect 98
4.4.2. Temperature selection 105
4.4.3. Applicability 107
4.5. Summary 109
5. Conclusions 110
6. References 112
著作目錄 119

[1] Huang KH. A Study on the Multicomponent Alloy Systems Containing Equalmole Elements. Department of Materials Science and Engineering. Hsinchu: NTHU, Taiwan, 1996.
[2] Yeh JW, Chen SK, Lin SJ, Gan JY, Chin TS, Shun TT, Tsau CH, Chang SY. Nanostructured High-Entropy Alloys with Multiple Principal Elements: Novel Alloy Design Concepts and Outcomes. Advanced Engineering Materials 2004;6:299.
[3] Yeh JW, Chen YL, Lin SJ, Chen SK. High-entropy alloys - A new era of exploitation. Materials Science Forum 2007;560:1.
[4] Ranganathan S. Alloyed pleasures: Multimetallic cocktails. CURRENT SCIENCE 2003;85:1404.
[5] Yeh JW. Recent progress in high-entropy alloys. ANNALES DE CHIMIE-SCIENCE DES MATERIAUX 2006;31:633.
[6] Hsu CY, Yeh JW, Chen SK, Shun TT. Wear resistance and high-temperature compression strength of Fcc CuCoNiCrAl0.5Fe alloy with boron addition. Metallurgical and Materials Transactions a-Physical Metallurgy and Materials Science 2004;35A:1465.
[7] Huang PK, Yeh JW, Shun TT, Chen SK. Multi-Principal-Element Alloys with Improved Oxidation and Wear Resistance for Thermal Spray Coating. Advanced Engineering Materials 2004;6:74.
[8] Tong CJ, Chen MR, Chen SK, Yeh JW, Shun TT, Lin SJ, Chang SY. Mechanical performance of the AlxCoCrCuFeNi high-entropy alloy system with multiprincipal elements. Metallurgical and Materials Transactions a-Physical Metallurgy and Materials Science 2005;36A:1263.
[9] Tong CJ, Chen YL, Chen SK, Yeh JW, Shun TT, Tsau CH, Lin SJ, Chang SY. Microstructure characterization of AlxCoCrCuFeNi high-entropy alloy system with multiprincipal elements. Metallurgical and Materials Transactions a-Physical Metallurgy and Materials Science 2005;36A:881.
[10] Chen MR, Lin SJ, Yeh JW, Chen SK, Huang YS, Chuang MH. Effect of vanadium addition on the microstructure, hardness, and wear resistance of Al0.5CoCrCuFeNi high-entropy alloy. Metallurgical and Materials Transactions a-Physical Metallurgy and Materials Science 2006;37A:1363.
[11] Chen MR, Lin SJ, Yeh JW, Chen SK, Huang YS, Tu CP. Microstructure and properties of Al0.5CoCrCuFeNiTix (x=0-2.0) high-entropy alloys. Materials Transactions 2006;47:1395.
[12] Wu JM, Lin SJ, Yeh JW, Chen SK, Huang YS. Adhesive wear behavior of AlxCoCrCuFeNi high-entropy alloys as a function of aluminum content. Wear 2006;261:513.
[13] Zhou YJ, Zhang Y, Wang YL, Chen GL. Solid solution alloys of AlCoCrFeNiTix with excellent room-temperature mechanical properties. Applied Physics Letters 2007;90:181904.
[14] Wang XF, Zhang Y, Qiao Y, Chen GL. Novel microstructure and properties of multicomponent CoCrCuFeNiTix alloys. Intermetallics 2007;15:357.
[15] Wang YP, Li BS, Ren MX, Yang C, Fu HZ. Microstructure and compressive properties of AlCrFeCoNi high entropy alloy. Materials Science and Engineering a-Structural Materials Properties Microstructure and Processing 2008;491:154.
[16] Hsu CY, Wang WR, Tang WY, Chen SK, Yeh JW. Microstructure and Mechanical Properties of New AlCoxCrFeMo0.5Ni High-Entropy Alloys. Advanced Engineering Materials 2010;12:44.
[17] Zhu JM, Zhang HF, Fu HM, Wang AM, Li H, Hu ZQ. Microstructures and compressive properties of multicomponent AlCoCrCuFeNiMo(x)under-bar alloys. Journal of Alloys and Compounds 2010;497:52.
[18] Hsu CY, Sheu TS, Yeh JW, Chen SK. Effect of iron content on wear behavior of AlCoCrFexMo0.5Ni high-entropy alloys. Wear 2010;268:653.
[19] Wikipedia: http://en.wikipedia.org/wiki/Tribology.
[20] Takadoum J. Materials and Surface Engineering in Tribology: ISTE, 2008.
[21] Neale MJ, Gee MG. Guide to wear problems and testing for industry: William Andrew Pub., 2001.
[22] Stachowiak GW. Wear: materials, mechanisms and practice: Wiley, 2005.
[23] Lim SC, Ashby MF. Overview no. 55 Wear-Mechanism maps. Acta Metallurgica 1987;35:1.
[24] Bhushan B. Introduction to tribology: John Wiley & Sons, 2002.
[25] CIA, The World Factbook, https://www.cia.gov/library/publications/the-world-factbook/fields/2195.html.
[26] Yeh JW, Lin SJ, Chin TS, Gan JY, Chen SK, Shun TT, Tsau CH, Chou SY. Formation of simple crystal structures in Cu-Co-Ni-Cr-Al-Fe-Ti-V alloys with multiprincipal metallic elements. Metallurgical and Materials Transactions A 2004;35:2533.
[27] Tong CJ, Chen YL, Yeh JW, Lin SJ, Chen SK, Shun TT, Tsau CH, Chang SY. Microstructure characterization of AlxCoCrCuFeNi high-entropy alloy system with multiprincipal elements. Metallurgical and Materials Transactions A 2005;36:881.
[28] Chen ST, Tang WY, Kuo YF, Chen SY, Tsau CH, Shun TT, Yeh JW. Microstructure and properties of age-hardenable AlxCrFe1.5MnNi0.5 alloys. Materials Science and Engineering: A 2010;527:5818.
[29] Tang WY, Chuang MH, Chen HY, Yeh JW. Microstructure and mechanical performance of new Al0.5CrFe1.5MnNi0.5 high-entropy alloys improved by plasma nitriding. Surface & Coatings Technology 2010;204:3118.
[30] Chuang MH, Tsai MH, Wang WR, Lin SJ, Yeh JW. Microstructure and wear behavior of AlxCo1.5CrFeNi1.5Tiy high-entropy alloys. Acta Materialia 2011;59:6308.
[31] Singh S, Wanderka N, Murty BS, Glatzel U, Banhart J. Decomposition in multi-component AlCoCrCuFeNi high-entropy alloy. Acta Materialia 2011;59:182.
[32] Tung CC, Yeh JW, Shun TT, Chen SK, Huang YS, Chen HC. On the elemental effect of AlCoCrCuFeNi high-entropy alloy system. Materials Letters 2007;61:1.
[33] Davis JR. Superalloys. In: Davis JR, editor. ASM Specialty Handbook: Nickel, Cobalt, and Their Alloys. Ohio: ASM International, 2000. p.68.
[34] Davis JR. Metallography and Microstructures of Heat Resistant Alloys. In: Davis JR, editor. ASM Specialty Handbook: Nickel, Cobalt, and Their Alloys. Ohio: ASM International, 2000. p.298.
[35] Heo Y-U, Takeguchi M, Furuya K, Lee H-C. Transformation of DO24 [eta]-Ni3Ti phase to face-centered cubic austenite during isothermal aging of an Fe-Ni-Ti alloy. Acta Materialia 2009;57:1176.
[36] Schnitzer R, Schober M, Zinner S, Leitner H. Effect of Cu on the evolution of precipitation in an Fe-Cr-Ni-Al-Ti maraging steel. Acta Materialia 2010;58:3733.
[37] Saito Y, Harada H. The Monte Carlo simulation of ordering kinetics in Ni-base superalloys. Materials Science and Engineering: A 1997;223:1.
[38] He Y, Liu H, Shin K, Lee CG. Cellular automata simulation of the ordering process in Ni-Al-Ti (Cr, Co) ternary alloys. Journal of Alloys and Compounds 2008;463:546.
[39] Kitashima T, Yokokawa T, Yeh AC, Harada H. Analysis of element-content effects on equilibrium segregation at [gamma]/[gamma]' interface in Ni-base superalloys using the cluster variation method. Intermetallics 2008;16:779.
[40] Zhao J, Ravikumar V, Beltran A. Phase precipitation and phase stability in nimonic 263. Metallurgical and Materials Transactions A 2001;32:1271.
[41] Cui CY, Gu YF, Ping DH, Harada H, Fukuda T. The evolution of [eta] phase in Ni-Co base superalloys. Materials Science and Engineering: A 2008;485:651.
[42] Gui C, Sato A, Gu Y, Harada H. Microstructure and yield strength of UDIMET 720LI alloyed with Co-16.9 Wt Pct Ti. Metallurgical and Materials Transactions A 2005;36:2921.
[43] Muzyka DR. The Metallurgy of Nickel-Iron Alloys. In: Sims CT, Hagel WC, editors. The superalloys. New York: Wiley-Interscience, 1972.
[44] Asgari S. Age-hardening behavior and phase identification in solution-treated AEREX 350 superalloy. Metallurgical and Materials Transactions A 2006;37:2051.
[45] Li X, Zhang J, Rong L, Li Y. Cellular [eta] phase precipitation and its effect on the tensile properties in an Fe-Ni-Cr alloy. Materials Science and Engineering: A 2008;488:547.
[46] Cui C, Sato A, Gu Y, Ping D, Harada H. Phase stability and yield stress of Ni-base superalloys containing high Co and Ti. Metallurgical and Materials Transactions A 2006;37:3183.
[47] Committee AIH. ASM Handbook: Friction, lubrication, and wear technology: ASM International, 1992.
[48] Ashby MF, Abulawi J, Kong HS. Temperature Maps for Frictional Heating in Dry Sliding. Tribology Transactions 1991;34:577
[49] Suh NP. Delamination Theory of Wear. Wear 1973;25:111.
[50] Suh NP. Overview of Delamination Theory of Wear. Wear 1977;44:1.
[51] Rigney DA, Chen LH, Naylor MGS, Rosenfield AR. Wear Processes in Sliding Systems. Wear 1984;100:195.
[52] Lim SC, Ashby MF. Wear-mechanism maps. Acta Metallurgica 1987;35:1.
[53] Quinn TFJ. Review of oxidational wear: Part I: The origins of oxidational wear. Tribology International 1983;16:257.
[54] Stott FH. The role of oxidation in the wear of alloys. Tribology International 1998;31:61.
[55] Lim SC. The relevance of wear-mechanism maps to mild-oxidational wear. Tribology International 2002;35:717.
[56] Vardavoulias M. The role of hard second phases in the mild oxidational wear mechanism of high-speed steel-based materials. Wear 1994;173:105.
[57] Serna MM, Rossi JL. MC complex carbide in AISI M2 high-speed steel. Materials Letters 2009;63:691.
[58] Soderberg S, Hogmark S. Wear mechanisms and tool life of high speed steels related to microstructure. Wear 1986;110:315.
[59] Quinn TFJ. Role of Oxidation in Mild Wear of Steel. British Journal of Applied Physics 1962;13:33.
[60] Quinn TFJ. Oxidational Wear. Wear 1971;18:413.
[61] Burakowski T, Wierzcho*n T. Surface engineering of metals : principles, equipment, technologies. Boca Raton, Fla.: CRC Press, 1999.
[62] Kalpakjian S. Manufacturing engineering and technology. Upper Saddle River, NJ: Prentice Hall, 2001.
[63] Davis JR. Surface hardening of steels: understanding the basics: ASM International, 2002.
[64] Barbu A, Ardell AJ. Irradiation-induced precipitation in Ni-Si alloys. Scripta Metallurgica 1975;9:1233.
[65] Rehn LE, Okamoto PR, Potter DI, Wiedersich H. Effect of solute misfit and temperature on irradiation-induced segregation in binary Ni alloys. Journal of Nuclear Materials 1978;74:242.
[66] Russell KC. Phase stability under irradiation. Progress in Materials Science 1984;28:229.
[67] Sagaradze VV, Nalesnik VM, Lapin SS, Aliabev VM. Precipitation hardening and radiation damageability of austenitic stainless steels. Journal of Nuclear Materials 1993;202:137.
[68] Noordhuis J, De Hosson JTM. Surface modification by means of laser melting combined with shot peening: A novel approach. Acta Metallurgica et Materialia 1992;40:3317.
[69] Juijerm P, Altenberger I. Effect of high-temperature deep rolling on cyclic deformation behavior of solution-heat-treated Al-Mg-Si-Cu alloy. Scripta Materialia 2007;56:285.
[70] Liao Y, Ye C, Kim B-J, Suslov S, Stach EA, Cheng GJ. Nucleation of highly dense nanoscale precipitates based on warm laser shock peening: AIP, 2010.
[71] Brenner B, Tietz F. Process for producing wear-resistant edge layers in precipitation-hardenable materials. United States: Fraunhofer-geselleschaft V, Zur Foerderung Der Angewandten Forschung E. (Munich, DE), 2003.
[72] Tang WY, Chuang MH, Chen HY, Yeh JW. Microstructure and Mechanical Performance of Brand-New Al0.3CrFe1.5MnNi0.5 High-Entropy Alloys. Advanced Engineering Materials 2009;11:788.
[73] Tang WY. Study on the Microstructure and Properties of Hign-entropy Alloys Treated by Plasma Nitriding. Department of Materials Science and Engineering, vol. PhD. Hsinchu: NTHU, Taiwan, 2009.
[74] Porter DA, Easterling KE, Sherif MY. Phase transformations in metals and alloys. Boca Raton, FL: CRC Press, 2009.
[75] Tong HC, Wayman GM. Order-disorder transformations in CuAu thin films. Acta Metallurgica 1973;21:1381.
[76] Somorjai GA. Surface Science. Science 1978;201:489.
[77] Suezawa M, Ishioka S. Strain energy near a free surface. Materials Science and Engineering 1979;37:283.
[78] Kubo H, Wayman M. Spinodal decomposition of beta brass. Metallurgical and Materials Transactions A 1979;10:633.
[79] Geng C, Chen L-Q. Spinodal decomposition and pattern formation near a crystalline surface. Surface Science 1996;355:229.
[80] Gutkin MY, Mikaelyan KN, Verijenko VE. Heterogeneous nucleation of martensite near free surface. Acta Materialia 2001;49:3811.
[81] Lovey FC, Chandrasekaran M. Diffraction effects in Cu-Zn and Cu-Zn-Al: Surface martensite transformation and microstructure. Acta Metallurgica 1983;31:1919.
[82] Lovey FC, Ferron J, De Bernardez LS, Ahlers M. On the stability of surface martensite in [beta]-phase Cu-Zn alloys. Scripta Metallurgica 1983;17:501.
[83] Koster U. The Influence of the Specimen Surface on Thermally Induced Structural Changes. Kristall und Technik 1979;14:1369.
[84] Balluffi RW, Allen SM, Carter WC, Kemper RA. Kinetics of materials. Hoboken, N.J.: J. Wiley & Sons, 2005.