On the elasto-viscoplastic behavior of the Ti5553 alloy
Introduction
Titanium alloys are heavily used in aeronautic applications owing to a low density, good corrosion behavior, and excellent mechanical properties. The well-known Ti–6Al–4V is the most commonly selected Ti alloy in aerospace components. It accounts for more than 50% of the Ti production. However, the need to increase, for weight reduction reasons, the strength of Ti–6Al–4V components combined with the inherent limited strain hardening capacity has created an impetus for the development of new alloys. Over the past few years, Ti5553 has been identified as a promising candidate to advantageously replace Ti–6Al–4V in some components [1], [2], but the mechanical data available for supporting such a choice are still scarce. Near β Ti5553 alloy (Ti–5Al–5V–5Mo–3Cr) [3] is a variation of the Russian alloy VT22 [4] and an alternative to the alloy Ti-10-2-3 [5].
The aim of the present work is to investigate the elastoviscoplastic mechanical response of the alloy Ti5553 under two heat treatment conditions (leading to two different microstructures named hereafter Ti5553-1 and Ti5553-3) involving a comparison with the Ti–6Al–4V alloy. The first objective of this paper is to identify the elastic constants and the Norton–Hoff viscoplastic parameters [6] based on uniaxial tensile tests carried out under four different strain rates (5×10−5 s−1, 2×10−4 s−1, 4×10−3 s−1, 10−2 s−1) and at two temperatures (room temperature and 150 °C). The second objective is to analyze the elastic and plastic anisotropy in view of modeling structural applications of forming operations. The anisotropy is investigated on the basis of compression tests, uniaxial tensile tests in different directions, plane strain tests and shear tests.
The outline of the work is the following:
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In Section 2, the chemical composition and heat treatment of the different microstructures are presented.
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In Section 3, the different mechanical parameters (elasticity, viscoplasticity) are identified after the presentation of the experimental procedure and results.
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In Section 4, the elastic and plastic anisotropy of the two alloys is analyzed.
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In Section 5, the identified elastoviscoplastic model is validated by comparing experimental results on notched and one plane strain specimens with FE predictions.
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In Section 6 the overall conclusions are highlighted.
Section snippets
Materials
As for any metallic alloys, the mechanical properties of Ti alloys are very sensitive to the initial microstructure, thermo-mechanical loading history, and chemical composition [7], [8], [9], [10]. From a microstructural point of view, the Ti–6Al–4V and Ti5553 alloys are significantly different in terms of volume fraction and morphology of the primary α phase and of the transformed β phase. A detailed comparison between the microstructures of the two alloys can be found in [2].
Identification of the elastic and viscoplastic properties
This section is organized in the following way. The experimental procedures and test results are presented and discussed in 3.1 Mechanical test procedures, 3.2 Experimental results, respectively. The elastic and viscoplastic parameters are identified for the different alloys in the Section 3.3. The effect of some parameters on the elastoviscoplastic behavior is analyzed in the Section 3.4.
Study of the elastic and plastic anisotropy
In the previous sections, the behavior of the Ti–6Al–4V and of the two microstructures of Ti5553 was assumed to be elastically and plastically isotropic. The purpose of this section is to check the validity of this assumption using different mechanical tests (see Table 10). Three specimens or more are tested for each mechanical test. The anisotropy directions are defined in Figs. 1 and 3 for the Ti–6Al–4V and Ti5553 alloys, respectively.
Validation of the elastoviscoplastic constitutive law by FE simulations
The identified constitutive elastoviscoplastic model has been validated by comparing, at the global and local levels, numerical simulations and experimental tests on notched and plane strain specimens not used for the identification process.
Conclusions
A wide mechanical testing campaign has been performed to characterize the elastoviscoplastic behavior of two microstructures of the Ti5553 alloy and of a reference Ti–6Al–4V alloy. The isotropic elastic parameters and the Norton–Hoff viscoplastic parameters were identified at room temperature and at 150 °C from uniaxial tensile tests. On the basis of the experimental data available, it can be concluded that the tensile strength of the Ti5553-1 and Ti5553-3 microstructures is larger than that of
Acknowledgments
The authors thank the Walloon Region (Titaero Project), the Belgian Scientific Research Fund FNRS, Belgium which finances A.M.H. and the Interuniversity Attraction Poles Program, Belgian Science Policy P7/21 INTEMATE, for their financial support.
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