Influence of strain rate and temperature on the deformation mechanisms of a fine-grained Ti-6Al-4V alloy

MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING

卷:790

Article

Despax, Laurie¹  Vidal, Vanessa¹  Delagnes, Denis¹  Dehmas, Moukrane²  Matsumoto, Hiroaki³  Velay, Vincent¹ 

[1] Univ Toulouse, ISAE SUPAERO, CNRS, ICA,IMT Mines Albi,UPS,INSA, Campus Jarlard, F-81013 Albi 09, France

[2] Univ Toulouse, CNRS, CIRIMAT, 4 Allee Emile Monso,BP 44362, F-31030 Toulouse 04, France

[3] Kagawa Univ, Fac Engn, Dept Adv Mat Sci, 2217-20 Hayashi Cho, Takamatsu, Kagawa 7610396, Japan

关键词: Titanium alloys;    Mechanical behaviour;    Superplasticity;    Interrupted tensile test;    Texture;    beta-phase;    Electron backscatter diffraction (EBSD);   

DOI  :  10.1016/j.msea.2020.139718

来源: Elsevier

【 摘 要 】

Depending on their initial microstructure, titanium alloys, as the Ti-6Al-4V may have activation of different deformation mechanisms during hot forming processes. In this work, interrupted tensile tests and heat treatments are used to improve the understanding of the mechanical and microstructural behaviour of a fine-grained Ti-6Al-4V alloy at two temperatures (750 degrees C and 920 degrees C) and so for two different beta phase fractions. The microstructural features like, alpha grain size and phase fraction, were determined by Scanning Electron Microscope (SEM) and image analysis. Moreover, evolution of the preferred crystallographic orientation of alpha grains and local misorientations between and inside grains were obtained by Electron Backscatter Diffraction (EBSD). The strain rate sensitivity parameter as well as the activation energy were deduced from mechanical tests. It appears, from all these microstructural and mechanical data, that several mechanisms are activated depending on the strain level and on the temperature range. At 750 degrees C, for a high strain rate, the deformation is mainly controlled by dislocations activity in the alpha phase (texture changes, dynamic recrystallization) and, at very low strain rate, by probably GBS accommodated with dislocations activity into alpha (recovery) and beta. On the contrary at 920 degrees C, a clear decrease of the overall texture intensity associated with a high m value suggests that GBS is the dominant mode of deformation. Nevertheless, as the alpha/beta volume fraction is around 48 %/52 % at this temperature, not only the alpha phase but also the beta phase as well as alpha/alpha and beta/beta boundaries might contribute to the flow behaviour. During long deformation time (low strain rate and high temperature), dynamic coarsening behaviour (both into alpha and beta), that is controlled by bulk diffusion, can occur and modify the type, the distribution and decrease the number of alpha/beta, alpha/alpha and beta/beta boundaries. This can be partly related to the flow hardening observed at 920 degrees C and 10(-4) s(-)(1).

【 授权许可】

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