Abstract：The hot deformation behavior and microstructural evolution were investigated during subtransus hot deformation of a Ti- 6Al- 4V alloy with two initial microstructures (Widmansttten microstructure and α′ martensitic microstructure) by compressive deformation in a Gleeble simulator. When deformed at a temperature of 700 ℃ and 750 ℃, specimens with a Widmansttten microstructure exhibited flow instability. These microstructures exhibited flow localization bands due to the adiabatic conditions and the bands became diffused with increasing temperatures and decreasing strain rates. Specimens with α′ martensitic microstructure exhibited extensive flow softening, especially, a homogeneous ultra- fine grained structure was achieved at all deformation conditions. The new ultrafine grains mainly formed through the process of continuous dynamic recrystallization (CDRX). The phase transformation of α′/α+β was strongly contributed to the microstructure refinement.
[1] C L, M P. Titanium and Titanium Alloys [M]. Cologne: Wiley-VCH Verlag GmbH, 2003.[2] DING R, GUO Z X. Microstructural evolution of a Ti–6Al–4V alloy during β-phase processing: experimental and simulative investigations [J]. Materials Science and Engineering: A, 2004, 365: 172-179.[3] S.L. Semiatin, V. Seetharaman, I. Weiss, The thermomechanical processing of alpha/beta titanium alloys, JOM, 49 (1997) 33-39. [4] ZHEREBTSOV S V, SALISHCHEV G A, GALEYEV R M, et al. Production of submicrocrystalline structure in large-scale Ti–6Al–4V billet by warm severe deformation processing [J]. Scripta Materialia, 2004, 51(12): 1147-1151.[5] KO Y G, JUNG W S, SHIN D H. Effects of temperature and initial microstructure on the equal channel angular pressing of Ti–6Al–4V alloy [J]. Scripta Materialia, 48(2003):197-202.[6] KO Y G, KIM W G. Microstructural influence on low-temperature superplasticity of ultrafine-grained Ti-6Al-4V alloy [J]. Materials Science and Engineering A, 410-411(2005):156-159.[7] SEMENOVA I P, RAAB G I. The effect of equal-channel angular pressing on the structure and mechanical behavior of Ti–6Al–4V alloy [J]. Materials Science and Engineering A, 387-389(2004): 805-808.[8] DING R, GUO Z, WILSON A. Microstructural evolution of a Ti-6Al-4V alloy during thermomechanical processing [J]. Materials Science and Engineering A, 2002, 327(2): 233-245.[9] SESHACHARYULU T, MEDEIROS S C, MORGAN J T, et al. Hot deformation mechanisms in ELI grade Ti-6Al-4V [J]. Scripta Materialia, 1999, 41(3): 283-288.[10] SESHACHARYULU T, MEDEIROS S C, MORGAN J T, et al. Hot deformation and microstructural damage mechanisms in extra-low interstitial (ELI) grade Ti-6Al-4V [J]. Materials Science and Engineering A, 2000, 279(1-2): 289-299.[11] H. Matsumoto, L. Bin, S.-H. Lee, Y. Li, Y. Ono, A. Chiba, Frequent Occurrence of Discontinuous Dynamic Recrystallization in Ti-6Al-4V Alloy with α′ Martensite Starting Microstructure, Metallurgical and Materials Transactions A, 44 (2013) 3245-3260.[12] SEMIATIN S L, BIELER T R. The effect of alpha platelet thickness on plastic flow during hot working of Ti-6Al-4V with a transformed microstructure [J]. Acta Materialia, 2001, 49(17): 3565-3573.[13] SEMIATIN S L, SEETHARAMAN V, WEISS I. Flow behavior and globularization kinetics during hot working of Ti-6Al-4V with a colony alpha microstructure [J]. Materials Science and Engineering A, 1999, 263(2): 257-271.[14] PRASAD Y, SESHACHARYULU T, MEDEIROS S C, et al. Influence of oxygen content on the forging response of equiaxed (alpha+beta) preform of Ti-6Al-4V: commercial vs. ELI grade [J]. Journal of Materials Processing Technology, 2001, 108(3): 320-327.[15] H. Matsumoto, S.-H. Lee, Y. Ono, Y. Li, A. Chiba, Formation of Ultrafine-Grained Microstructure of Ti-6Al-4V Alloy by Hot Deformation of α′ Martensite Starting Microstructure, Advanced Engineering Materials, 13 (2011) 470-474.[16] H. Matsumoto, H. Yoneda, D. Fabregue, E. Maire, A. Chiba, F. Gejima, Mechanical behaviors of Ti–V–(Al, Sn) alloys with α′ martensite microstructure, Journal of Alloys and Compounds, 509 (2011) 2684-2692.[17] H. Matsumoto, H. Yoneda, K. Sato, S. Kurosu, E. Maire, D. Fabregue, T.J. Konno, A. Chiba, Room-temperature ductility of Ti–6Al–4V alloy with α′ martensite microstructure, Materials Science and Engineering: A, 528 (2011) 1512-1520.[18] H. Matsumoto, B. Liu, S.H. Lee, Y.P. Li, K. Sato, Y. Ono, A. Chiba, Tms, Hot deformation behavior of Ti-6Al-4V alloy with alpha' martensite starting microstructure, Minerals, Metals & Materials Soc, Warrendale, 2012.[19] H. Matsumoto, L. Bin, S.-H. Lee, Y. Li, Y. Ono, A. Chiba, Frequent Occurrence of Discontinuous Dynamic Recrystallization in Ti-6Al-4V Alloy with α′ Martensite Starting Microstructure, Metallurgical and Materials Transactions A, 44 (2013) 3245-3260.[20] H. Beladi, Q. Chao, G.S. Rohrer, Variant selection and intervariant crystallographic planes distribution in martensite in a Ti–6Al–4V alloy, Acta Materialia, 80 (2014) 478-489.[21] Q. Chao, P.D. Hodgson, H. Beladi, Ultrafine Grain Formation in a Ti-6Al-4V Alloy by Thermomechanical Processing of a Martensitic Microstructure, Metallurgical and Materials Transactions A, 45 (2014) 2659-2671.
2017, Vol. 24 
