Abstract
In this study, electrically-assisted micro-compression (EAMC) tests were conducted for cylindrical specimens of Ti-6Al-4V alloy with four geometric sizes and three initial microstructures. The result showed that the specimen temperature nonlinearly increased with the square of current density. The quasi-static heat equilibrium equation was established to quantify the effects of the scale factor on the Joule heat temperature. Moreover, it was demonstrated that the Joule temperature scale effect had a greater effect on the flow stress than the sample size effect for specimens of different dimensions. It was noted that the 0.5 mm diameter sample displayed abnormal deformation behavior, which was related to surface oxidation leading a brittle surface layer. By comparison of the microstructures, it was found that the α→β phase transformation occured below the β transus temperature, which was attributed to the local Joule heat effect and the scattering of drift electrons during EAMC. Furthermore, the flow curves showed a strong dependence of the strength and ductility on the initial microstructure. The widmannstatten microstructure exhibited higher strength, smaller hardening rate and more easy flow localization compared with basket-weave microstructures, which was attributed to the low β phase content and narrow interlamellar spacing of α lamellae grains in the widmannstatten microstructure.
Highlights
In recent years, people are paying more attention to means of energy conservation and environmental protection due to the pressures of promoting growth while saving resources and protecting the environment
When the electric current passes through materials, the plasticity of materials is improved and the forming force is significantly reduced, which is called the electroplastic effect (EPE) [1,2,3]
The electrically-assisted micro-compression (EAMC) tests were conducted for cylindrical specimens of Ti-6Al-4V alloy with four geometric dimensions and three initial microstructures in this study
Summary
People are paying more attention to means of energy conservation and environmental protection due to the pressures of promoting growth while saving resources and protecting the environment. Electrically-assisted forming (EAF) has shown great potential in heating efficiency, environmental friendliness, increasing formability and optimizing microstructures. When the specimen size is scaled down to the mesoscale, the flow stress and friction behavior of materials become different from those of the macroscale one due to the so-called size effects [13,14], and the experience of the traditional forming process is no longer applicable in the field of micro-forming. The effects of the geometric dimensions on EAMF behavior of titanium alloys have been little investigated. Electrically-assisted micro-forming has shown great potential in increasing formability and optimizing microstructures. The effects of initial microstructure and geometric dimension on the micro-deformation behavior in Ti-6Al-4V alloys have been little investigated. For better understand the deformation behaviors, the microstructure evolution and surface morphology were studied by optical microscopy (OM), field emission scanning microscopy (FE-SEM) and transmission electron microscopy (TEM)
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