Microstructural characterization and evolution mechanism of adiabatic shear band in a near beta-Ti alloy
Research highlights
▶ The thermo-mechanical history during the shear localization was calculated for the first time in this new beta-Ti alloy. ▶ The microstructures within the adiabatic shear band were observed by means of TEM. ▶ The β → ω(althermal) phase transformation was observed within adiabatic shear band in the near β-phase Ti alloy for the first time.
Introduction
Adiabatic shear band, a narrow region with highly localized plastic deformation, frequently appears in metallic materials subjected to dynamic loading events, such as ballistic impact, machining, and high-speed deformation processing [1], [2], [3], [4], [5], [6], [7]. Scientists have great interest in this phenomenon due to the extreme thermo-mechanical history and the complex ultrafine microstructure in the shear localization regions.
The shear band is one of the most important deformation and failure mechanisms and often occurs in a very short time. Therefore, it is quite helpful to examine the residual structure within shear band to deduce the possible evolution mechanism. Meyers et al. [8], [9], Andrade et al. [10] and Yang et al. [11] have studied the microstructure within shear bands using transmission electron microscopy in 304 L stainless steel, Ta, copper and pure Ti, respectively. Fine microstructure within shear bands has been reported in these materials subjected to different loading conditions. These TEM examinations have yielded extensive information about the process of adiabatic shearing localization.
The study on deformation history is mainly by calculating the mechanical response data during the formation of shear band. Some excellent articles by Hine and Vecchio [12] and Shih et al. [13] are available. However, there are few reports about this aspect in Ti alloys, especially in the beta phase Ti alloys.
ASBs are easily produced in titanium and its alloys due to the properties of low heat conductivity and high adiabatic shearing sensitivity. Therefore, the localized shear deformation of Ti alloys has been studied extensively in recent years [14], [15], [16]. Now it is widely considered that the fine equiaxed subgrains in the ASB are formed by dynamic recovery and continuous dynamic recrystallization [17], [18]. In addition, some articles have reported the observation of the phase transformation within the ASB in Ti alloys [19], [20], [21].
Ti-1300 titanium alloy used in this article is a near beta-Ti alloy that is developed by China. This alloy has great forgeability and high hardenability, and optimum matching of plasticity and ductility under 1300 MPa condition. There are some studies on the mechanical property of this alloy under static condition. However, little work on the microstructure changes under dynamic loading was investigated. This would limit its application in aerospace engineering.
The purpose of this study is to present and discuss the microstructural characterization and evolution mechanism of the ASB produced during SHPB in this alloy.
Section snippets
Materials and methods
Ti-1300 alloy was used in the present work. The as-received material was previously processed solution heat treatment in order to obtain single β-phase microstructure. The experimental configuration and the procedures used to produce ASB are described in Fig. 1 [22].
The samples for TEM are cut parallel to the surface of the bisected hat-shaped specimens, followed by mechanical thinned to ∼60 μm and a twinjet polishing technique using a solution of 300 ml methanol, 175 ml 1-butanol and 30 ml
Mechanical response at super high strain rate
It is well known that once shear localization has initialed, sheep shear strain and strain rate together with temperature rise would concentrate into the shear band. According to Andrade et al. [10] and Culver [23], the shear stress, strain rate, nominal strain and the true shear strain can be calculated by the following equations from Eqs. (1), (2), (3), (4).where E0 and C0 are the elastic modulus and elastic wave speed in SHPB, L
Conclusions
Thermal/mechanical evolutions during the formation of shear band are described by combining dynamic response data and the quantitative calculation of adiabatic temperature rise and drop. The temperature within the shear band rises from 293 K to 1409 K within 29 μs during shear deformation. Then, it takes 31 μs for the shear band to cool down from 1409 K to ambient temperature when the shear localized deformation ceases. So, the cooling rate is as high as 3.6 × 107 K/s. The temperature can rise above
Acknowledgements
This work is supported by the projects National Nature Science Foundation of China (No. 50671121, No. 50971134), the project of Pre-research Fund of the PLA General Armament Department (No. 9140A12011610BQ1901), and the key project of State Key Laboratory of Explosion Science and Technology (No. KFJJ09-1). Ti-1300 alloy used in this study is offered by Prof. Y.Q. Zhao and Senior engineer P. Ge in the Northwest Nonferrous Metal Research Institute. Y.Q. Zhao and P. Ge are gratefully acknowledged.
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