Hot deformation behavior of Ti–6.0Al–7.0Nb biomedical alloy by using processing map

doi:10.1016/j.jallcom.2013.10.132

Journal of Alloys and Compounds

Volume 587, 25 February 2014, Pages 183-189

https://doi.org/10.1016/j.jallcom.2013.10.132 Get rights and content

Highlights

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Hot deformation behavior of Ti–6.0Al–7.0Nb biomedical alloy was investigated.
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Constitutive equation represented temperature, strain rate and true strain was developed.
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Power dissipation maps built at different strains exhibit similar features.
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Processing map approach was adopted to optimize hot forging process for biomedical alloy.

Abstract

Ti–6.0Al–7.0Nb is a dual phase biomedical alloy used for artificial bone. Isothermal compression tests of Ti–6.0Al–7.0Nb biomedical alloy has been taken carried out on a Gleebe 3500 simulator at the strain rates of 0.001–1.0 s¹ and temperatures of 750–900 °C. A constitutive equation represented as a function of temperature, strain rate and true strain was developed, and the hot deformation apparent activation energy is calculated about 341 kJ/mol. Processing maps were constructed on the basis of the experimental data for evaluation of the flow instability regime and optimization of processing parameters. Processing maps predict a single flow instability region occurred around the temperature range of 750–770 °C and the strain rate range of 0.03–1.0 s⁻¹. The power dissipation maps at different strains exhibit similar features indicating that the processes involved in hot working have very short transient and are essentially of steady–state type. Ti–6.0Al–7.0Nb biomedical alloy can be deformed at the condition of (T_opi: 850 °C, ${\dot{ε}}_{opi}$ : 1.0 s⁻¹) with the peak η of 0.46 to obtain fine kinked and globular α phase for artificial bone.

Introduction

Titanium alloys are widely used on medicine because of their high strength, small density, excellent mechanical properties and toughness, especially resistance to corrosion, biocompatibility and nonmagnetic [1], [2], [3]. A large number of titanium alloys have been used for human implant, mainly are used for artificial joint or as implant and repair material for other hard tissue. In the early, the pure titanium and Ti–6Al–4 V are widely used on human implant. However, pure titanium has low strength, and Ti–6Al–4 V also contains harmful element (V), which is harmful to hematopoietic system and irritation of respiratory secretion, even leads to cancer [4], [5]. Biological titanium alloy Ti–6.0Al–7.0Nb [6] was developed for surgical implant by Swiss Sulzer medical technology company. Its mechanical property is as good as Ti–6Al–4 V alloy, and it does not contain toxic element V [7], [8]. After a long-term clinical application, it has been recognized by the world medical community. In recent years, many countries are committed to research and develop new biological Ti–6.0Al–7.0Nb alloy. Cui et al. [9] determined the high temperature deformation behavior of this alloy, optimized the hot deformation conditions, and established the effect of processing conditions on structure evolution. Guo et al. [10] investigated the oxidation behavior and wear resistance of this biomedical Ti-alloy. Pilehva et al. [11] performed the constitutive modeling of the working process for this alloy. But they did not develop processing maps and investigat the plastic instability.

As a α + β type alloy, Ti–6Al–7Nb alloy has moderate strength and good high temperature plasticity. This biomedical alloy has been used for human implant, i.e. artificial joint, bone and other hard tissue. However, this alloy is rather difficult to deform into shape. Microstructure and hot workability of this alloy are sensitive to processing parameters, such as deforming temperature and strain rate [9]. Meanwhile, hot deformation behavior of biomedical alloy, especially the deforming flow stress model under the high deforming temperature becomes the focus of base research. In this work, hot deformation behavior of Ti–6.0Al–7.0Nb biomedical alloy has been investigated based on the isothermal compression tests conducted at different deformation temperatures and strain rates. The approach of processing map has been adopted to understand the deformation mechanism during hot processing, and to optimize process parameters for this biomedical alloy.

Section snippets

Experimental materials and procedures

Ti–6Al–7Nb biomedical alloy used in this work was supplied as a forged bar with diameter of 15 mm, and the chemical composition is listed in Table 1. The micrograph of the as-received alloy is shown in Fig. 1, which presents typical duplex microstructure. The cylindrical compression specimens with the dimension of ϕ 8 × 12 mm were machined from the post forged bar. The end surfaces of the cylindrical samples were grooved for holding the glass lubricant in hot compression process.

Isothermal hot

Flow behavior of Ti–6.0Al–7.0Nb biomedical alloy

Typical true stress–true strain curves of Ti–6.0Al–7.0Nb alloy obtained at various deformation temperatures and strain rates are presented in Fig. 2, where correspond to deformation temperatures of 750, 800, 850 and 900 °C, respectively. As shown in Fig. 2, flow curves are sensitive to the deformation temperature and strain rate. Generally, the flow stress decreases with the raising deformation temperature and decreasing strain rate. The stress increases sharply until a peak stress at a very

Conclusions

Hot deformation behavior (Flow behavior, constitutive model, processing map and microstructure characterization) of Ti–6.0Al–7.0Nb biomedical alloy has been investigated at a temperature range of 750–900 °C and a strain rate range of 0.001–1.0 s⁻¹. The following conclusions are drawn from this research:

(1)
True stress–true strain curves of Ti–6.0Al–7.0Nb biomedical alloy are sensitive to the deformation temperature and strain rate. Generally, the flow stress decreases with the raising deformation

Acknowledgements

This work was financially supported by the National Natural Science Foundation of China (Grant No. 51101119) and the Postdoctoral Science Foundation of China (Grant No. 2012T50818).

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Citation Excerpt :
Generally, the efficiency values associated with DRV, DRX and super-plasticity are about 0.30, 0.30–0.50, and 0.60, respectively. When the efficiency is less than 0.3, DRV is the dominating softening mechanism during the hot deformation [14]. Therefore, combining with the PM (Fig. 5) and microstructure evolution (Fig. 10), sub-structure and fine grains existed in most of grains, and grain boundaries were saw-teeth shape after deformation, indicating that DRV and DRX occurred obviously after thermal compression of the Ti-645 alloy.
We investigated the deformation behavior of a new biomedical Cu-bearing titanium alloy (Ti-645 (Ti-6.06Al-3.75V-4.85Cu, in wt%)) to optimize its microstructure control and the hot-working process. The results showed that true stress–true strain curve of Ti-645 alloy was susceptible to both deformation temperature and strain rate. The microstructure of Ti-645 alloy was significantly changed from equiaxed grain to acicular one with the deformation temperature while a notable decrease in grain size was recorded as well. Dynamic recovery (DRV) and dynamic recrystallization (DRX) obviously existed during the thermal compression of Ti-645 alloy. The apparent activation energies in (α + β) phase and β single phase regions were calculated to be 495.21 kJ mol⁻¹ and 195.69 kJ mol⁻¹, respectively. The processing map showed that the alloy had a large hot-working region whereas the optimum window occurred in the strain rate range of 0.001–0.1 s⁻¹, and temperature range of 900–960 °C and 1000–1050 °C. The obtained results could provide a technological basis for the design of hot working procedure of Ti-645 alloy to optimize the material design and widen the potential application of Ti-645 alloy in clinic.

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Hot deformation behavior of Ti–6.0Al–7.0Nb biomedical alloy by using processing map

Highlights

Abstract

Introduction

Section snippets

Experimental materials and procedures

Flow behavior of Ti–6.0Al–7.0Nb biomedical alloy

Conclusions

Acknowledgements

Biomaterials

Mater. Lett.

Mater. Sci. Eng. C

Biomaterials

J. Alloys Comp.

Mater. Sci. Eng. A

J. Alloys Comp.

Mater. Sci. Eng. A

Mater. Des.

Mater. Sci. Eng. A