本文主要是探討純鈦金屬在不同溫度及應變速率下之撞擊特性與微觀結構分析。利用壓縮式霍普金森桿撞擊試驗機(Hopkinson bar)及加溫裝置，分別於應變速率1000 s-1、3000 s-1和5000s-1及實驗環境溫度-100℃、25℃、800℃各條件下，進行純鈦之高速撞擊變形，以分析材料在塑變形為中巨觀與微觀結構變化，並導入構成方程式以描述材料之應力應變關係。
實驗結果顯示，在相同的溫度下，塑流應力值、加工硬化率及應變速率敏感性係數皆隨應變速率增加而上升；而當固定應變速率時，其塑流應力值、加工硬化率、應變速率敏感性係數則會隨溫度之增加而下降，而熱活化體積則是隨著溫度上升而增加。溫度敏感性係數則隨應變速率和應變量的上升而增加。可藉由Zerilli-Armstrong HCP構成方程式，針對純鈦不同溫度及應變速率下之塑變行為作準確的預測及描述。
在光學式顯微鏡下觀察可得純鈦金屬有絕熱剪切帶之形成與晶粒組織形貌改變，兩者皆受到溫度與應變速率的影響。而剪切帶伴隨著裂縫生成與結合，是導致材料發生破壞的主要原因。在微觀結構方面，由掃描式電子顯微鏡分析破壞面下，可觀察到不同區域分別會有代表延性破壞的韌窩及瘤狀物形貌，以及代表脆性破壞的劈裂形貌；另在穿透式電子顯微鏡觀察下則可發現差排密度隨著應變速率上升而上升，隨著溫度上升而下降。最後結合巨觀與微觀之結果可發現塑流應力值與差排密度有重要之相關性。

In this study, dynamic impact response and microstructural characteristics of pure titanium were investigated using a compressive split-Hopkinson bar. The specimens were deformed at different temperatures of -100ºC, 25ºC, 800ºC under strain rates of 1000s-1, 3000s-1 and 5000 s-1, respectively. The results reveal that the mechanical properties and microstructures of pure titanium were greatly affected by temperature and strain rate. At a constant temperature, the flow stress, work hardening rate, and strain rate sensitivity increase with increasing strain rate, but the thermal activation volume and activation energy decrease with the increasing strain rate. However, at a constant strain rate, flow stress, work hardening rate, strain rate sensitivity, and temperature sensitivity decrease but the thermal activation volume and activation energy increase with increasing temperature. The Zerilli-Armstrong model is shown to provide an adequate description of the stress-strain response of pure titanium specimens under the current testing conditions. Microstructural observations shown that the deformed grain of pure titanium are strongly dependent on strain rate. SEM fracture analysis indicates that the fracture feature are dominated by dimple, cleavage and knobble at different fracture area. Furthermore, according to the microscopic results, the relationship between the dislocation density and flow stress can be expressed using the Bailey-Hirsch equation.
Key words: pure titanium, split-Hopkinson bar, high strain rate, dislocation density

[1] M. Niinomi, T. Kobayashi, O. Toriyama, N. Kawakami, Y. Ishida, and Y. Matsuyama, "Fracture characteristics, microstructure, and tissue reaction of Ti-5Al-2.5 Fe for orthopedic surgery," Metallurgical and Materials Transactions A, vol. 27, pp. 3925-3935, 1996.
[2] D. Steinberg, S. Cochran, and M. Guinan, "A constitutive model for metals applicable at high‐strain rate," Journal of Applied Physics, vol. 51, pp. 1498-1504, 1980.
[3] F. E. Hauser, "Techniques for measuring stress-strain relations at high strain rates," Experimental Mechanics, vol. 6, pp. 395-402, 1966.
[4] R. Woodward, "The interrelation of failure modes observed in the penetration of metallic targets," International Journal of Impact Engineering, vol. 2, pp. 121-129, 1984.
[5] K. Wang, "The use of titanium for medical applications in the USA," Materials Science and Engineering: A, vol. 213, pp. 134-137, 1996.
[6] M. Peters, J. Hemptenmacher, J. Kumpfert, and C. Leyens, "Structure and properties of titanium and titanium alloys," Titanium and Titanium Alloys: Fundamentals and Applications, pp. 1-36, 2003.
[7] M. Niinomi, "Mechanical properties of biomedical titanium alloys," Materials Science and Engineering: A, vol. 243, pp. 231-236, 1998.
[8] M. J. Donachie, Titanium: a technical guide: ASM international, 2000.
[9] G. Welsch, R. Boyer, and E. Collings, Materials properties handbook: titanium alloys: ASM international, 1993.
[10] J. Holt and Z. Munir, "Combustion synthesis of titanium carbide: theory and experiment," Journal of Materials Science, vol. 21, pp. 251-259, 1986.
[11] D. Curran, L. Seaman, and D. Shockey, "Linking dynamic fracture to microstructural processes," in Shock Waves and High-Strain-Rate Phenomena in Metals, ed: Springer, 1981, pp. 129-167.
[12] U. Lindholm and L. Yeakley, "High strain-rate testing: tension and compression," Experimental Mechanics, vol. 8, pp. 1-9, 1968.
[13] W.-S. Lee and C.-F. Lin, "Plastic deformation and fracture behaviour of Ti–6Al–4V alloy loaded with high strain rate under various temperatures," Materials Science and Engineering: A, vol. 241, pp. 48-59, 1998.
[14] J. Fagbulu and O. Ajaja, "Dislocation distributions and creep mechanisms," Journal of materials science letters, vol. 6, pp. 894-896, 1987.
[15] D. Klahn, A. Mukherjee, and J. Dorn, "STRAIN-RATE EFFECTS," California Univ., Berkeley. Lawrence Radiation Lab.1970.
[16] J. Campbell and A. Dowling, "The behaviour of materials subjected to dynamic incremental shear loading," Journal of the Mechanics and Physics of Solids, vol. 18, pp. 43-63, 1970.
[17] J. Campbell and W. Ferguson, "The temperature and strain-rate dependence of the shear strength of mild steel," Philosophical Magazine, vol. 21, pp. 63-82, 1970.
[18] A. Seeger, "CXXXII. The generation of lattice defects by moving dislocations, and its application to the temperature dependence of the flow-stress of fcc crystals," The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science, vol. 46, pp. 1194-1217, 1955.
[19] W. Ferguson, A. Kumar, and J. Dorn, "Dislocation damping in aluminum at high strain rates," Journal of Applied Physics, vol. 38, pp. 1863-1869, 1967.
[20] D. Klahn, A. Mukherjee, and J. Dorn, "Proceedings of the Second International Conference on the Strength of Metals and Alloys," 1970.
[21] B. Dodd, "Adiabatic shear localization: occurrence, theories, and applications," 1992.
[22] Z. Gronostajski, "The constitutive equations for FEM analysis," Journal of Materials Processing Technology, vol. 106, pp. 40-44, 2000.
[23] L. Meyer, N. Herzig, T. Halle, F. Hahn, L. Krueger, and K. Staudhammer, "A basic approach for strain rate dependent energy conversion including heat transfer effects: An experimental and numerical study," Journal of materials processing technology, vol. 182, pp. 319-326, 2007.
[24] D. Umbrello, R. M’saoubi, and J. Outeiro, "The influence of Johnson–Cook material constants on finite element simulation of machining of AISI 316L steel," International Journal of Machine Tools and Manufacture, vol. 47, pp. 462-470, 2007.
[25] U. Andrade, M. Meyers, and A. Chokshi, "Constitutive description of work-and shock-hardened copper," Scripta metallurgica et materialia, vol. 30, pp. 933-938, 1994.
[26] F. J. Zerilli and R. W. Armstrong, "Constitutive equation for HCP metals and high strength alloy steels," High strain rate effects on polymer, metal and ceramic matrix composites and other advanced materials, pp. 121-126, 1995.
[27] F. J. Zerilli and R. W. Armstrong, "Dislocation‐mechanics‐based constitutive relations for material dynamics calculations," Journal of Applied Physics, vol. 61, pp. 1816-1825, 1987.
[28] J. Murray and H. Wriedt, "The O− Ti (oxygen-titanium) system," Journal of Phase Equilibria, vol. 8, pp. 148-165, 1987.
[29] H. Conrad, "Thermally activated deformation of metals," JOM, vol. 16, pp. 582-588, 1964.
[30] M. Meyers, D. Benson, O. Vöhringer, B. Kad, Q. Xue, and H.-H. Fu, "Constitutive description of dynamic deformation: physically-based mechanisms," Materials Science and Engineering: A, vol. 322, pp. 194-216, 2002.
[31] W.-B. Lee, C.-Y. Lee, W.-S. Chang, Y.-M. Yeon, and S.-B. Jung, "Microstructural investigation of friction stir welded pure titanium," Materials Letters, vol. 59, pp. 3315-3318, 2005.
[32] D. R. Chichili, K. Ramesh, and K. J. Hemker, "Adiabatic shear localization in α-titanium: experiments, modeling and microstructural evolution," Journal of the Mechanics and Physics of Solids, vol. 52, pp. 1889-1909, 2004.
[33] B. Viguier, "Dislocation densities and strain hardening rate in some intermetallic compounds," Materials Science and Engineering: A, vol. 349, pp. 132-135, 2003.
[34] S. Esmaeili, L. Cheng, A. Deschamps, D. Lloyd, and W. Poole, "The deformation behaviour of AA6111 as a function of temperature and precipitation state," Materials Science and Engineering: A, vol. 319, pp. 461-465, 2001.
[35] D. Chu and J. Morris, "The influence of microstructure on work hardening in aluminum," Acta materialia, vol. 44, pp. 2599-2610, 1996.
[36] J. Harding, "Effect of temperature and strain rate on strength and ductility of four alloy steels," Metals Technology, vol. 4, pp. 6-16, 1977.
[37] L. Shi and D. Northwood, "The mechanical behavior of an AISI type 310 stainless steel," Acta metallurgica et materialia, vol. 43, pp. 453-460, 1995.
[38] P. Lefranc, V. Doquet, M. Gerland, and C. Sarrazin-Baudoux, "Nucleation of cracks from shear-induced cavities in an α/β titanium alloy in fatigue, room-temperature creep and dwell-fatigue," Acta Materialia, vol. 56, pp. 4450-4457, 2008.
[39] U. Lindholm and L. Yeakley, "Dynamic deformation of single and polycrystalline aluminium†," Journal of the Mechanics and Physics of Solids, vol. 13, pp. 41-53, 1965.
[40] J. Lifshitz and H. Leber, "Data processing in the split Hopkinson pressure bar tests," International Journal of Impact Engineering, vol. 15, pp. 723-733, 1994.
[41] B. Dodd and Y. Bai, "Ductile fracture and ductility," 1987.
[42] L. Bolzoni, E. M. Ruiz-Navas, and E. Gordo, "Influence of sintering parameters on the properties of powder metallurgy Ti–3Al–2.5 V alloy," Materials characterization, vol. 84, pp. 48-57, 2013.
[43] Q. Li, Y. Xu, and M. Bassim, "Dynamic mechanical behavior of pure titanium," Journal of Materials Processing Technology, vol. 155, pp. 1889-1892, 2004.
[44] J. Jonas, C. Sellars, and W. M. Tegart, "Strength and structure under hot-working conditions," Metallurgical Reviews, vol. 14, pp. 1-24, 1969.
[45] L. Farbaniec, A. Abdul-Latif, J. Gubicza, and G. Dirras, "Ultrafine-grained nickel refined by dislocation activities at intermediate strain rate impact: deformation microstructure and mechanical properties," Journal of Materials Science, vol. 47, pp. 7932-7938, 2012.
[46] W. Cui, Z. Jin, A. Guo, and L. Zhou, "High temperature deformation behavior of α+ β-type biomedical titanium alloy Ti–6Al–7Nb," Materials science and engineering: A, vol. 499, pp. 252-256, 2009.
[47] M. E. Backman and S. A. Finnegan, "The propagation of adiabatic shear," in Metallurgical Effects at High Strain Rates, ed: Springer, 1973, pp. 531-543.
[48] W.-S. Lee and C.-F. Lin, "Effects of prestrain and strain rate on dynamic deformation characteristics of 304L stainless steel: Part 1—Mechanical behaviour," Materials science and technology, vol. 18, pp. 869-876, 2002.
[49] J. H. Giovanola, "Adiabatic shear banding under pure shear loading part ii: fractographic and metallographic observations," Mechanics of Materials, vol. 7, pp. 73-87, 1988.
[50] P. Partridge, "The crystallography and deformation modes of hexagonal close-packed metals," Metallurgical reviews, vol. 12, pp. 169-194, 1967.
[51] R. Ham, "The determination of dislocation densities in thin films," Philosophical Magazine, vol. 6, pp. 1183-1184, 1961.
[52] Y. Tomota, P. Lukas, S. Harjo, J. Park, N. Tsuchida, and D. Neov, "In situ neutron diffraction study of IF and ultra low carbon steels upon tensile deformation," Acta materialia, vol. 51, pp. 819-830, 2003.
[53] Y. G. Ko, D. H. Shin, K.-T. Park, and C. S. Lee, "An analysis of the strain hardening behavior of ultra-fine grain pure titanium," Scripta Materialia, vol. 54, pp. 1785-1789, 2006.
[54] J. Bailey and P. Hirsch, "The dislocation distribution, flow stress, and stored energy in cold-worked polycrystalline silver," Philosophical Magazine, vol. 5, pp. 485-497, 1960.