Abstract
To clarify the hot deformation characteristics of Ti alloys, flow behaviour, micro structural evolution and deformation mechanisms were investigated in a Ti-6Al-2Sn-4Zr-2Mo alloy with two initial micro structure: an ultra-fine grained (UFG) and a fine-grained (FG) microstructure (dα=0,8 µm and dα=3 µm respectively) by isothermal interrupted tensile tests, SEM observations and through electron back scatter diffraction experiments. Depending on the test conditions and on the initial α grain size, the flow behaviour can exhibit steady state flow and/or hardening and/or softening. The microstructure and texture evolutions have been studied mainly by using electron backscatter diffraction (EBSD) technique and SEM observations. They evidenced in particular the occurrence of α grains growth as well as dynamic recrystallization (DRX). The different flow behaviour associated to the microstructure evolution is shown and discussed to clarify the main deformation mode that could be assume to occur depending on the microstructure, the temperature and the strain rate.
Highlights
Because of its superior high-temperature properties compared to the popular Ti-6Al-4V alloy, Ti-6Al-2Sn-4Zr-2Mo (Ti-6242) alloy can be used in aerospace structures requiring creep resistance at elevated temperatures
This paper focuses on the interaction between the microstructure evolution and the hot deformation and superplastic behaviour of a Ti6242 alloy sheets characterized by different initial microstructure: ultra-fine grained (UFG) and fine grained (FG) samples have respectively an α nodule size of around dα=0,8 μm and dα=3 μm
The influence of the initial microstructure on the flow behaviour of the Ti6242 alloy at temperature ranging from 700°C to 850°C and for a strain rate between 10-2 s-1 and 10-4 s-1 was shown
Summary
Because of its superior high-temperature properties compared to the popular Ti-6Al-4V alloy, Ti-6Al-2Sn-4Zr-2Mo (Ti-6242) alloy can be used in aerospace structures requiring creep resistance at elevated temperatures. Superplasticity is mainly explained by grain boundary sliding (GBS) associated with different accommodation mechanisms such as dynamic recrystallization, grain growth, slip in grains, grain boundary migration, diffusion, phase transformation etc [2,3] All of these mechanisms may depend on the temperature, the strain rate and on the initial alloy microstructure (preferred orientation, size and shape of the grains, phase fraction and distribution). We are currently studying the deformation behaviour, of a Ti6242 alloy under different hot deformation conditions (temperature from 600°C to 960°C and strain rate between 10-2s-1 and 10-4 s-1) and for different initial α grain sizes (from 0.8 μm to 5 μm) ; the final objectives being (i) to understand the effect of the initial microstructure on the hot deformation behaviour and (ii) to be able to propose adequate thermo-mechanical behaviour models taking into account microstructural considerations [4,5,6,7]. Results of the associated microstructural evolution are shown and discussed in terms of mechanisms of hot deformation
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