Abstract
The application of titanium alloy micro-gears in microelectromechanical systems has been severely restricted, as the graphite mold is prone to abrasion or even to crack at high temperatures, mainly due to the forming load. We aimed to manufacture Ti-6Al-4V alloy micro-gears through hot extrusion under an electric field and to clarify the influence of holding time on the extrusion force. The results suggest that the formed gears had a complete filling and clear tooth profile. Moreover, the contact resistance and current density caused a gradient temperature distribution inside the billet, resulting in a carburized layer and inhomogeneous β grains. The extrusion force increased with an increased holding time, which can be ascribed to the increase in the thickness of the carburized layer and the β grain size. Among these two factors, β grain size played a leading role in the extrusion force. Continuous dynamic recrystallization dominated the deformation in a single β phase, and the misorientation of the transformed α laths from β grains followed the Burgers orientation relationship. This study may pave the way for the extrusion forming of other titanium alloy micro-components.
Highlights
Micro-gears are pivotal actuating elements in the transmission of power and motion and are used extensively in microelectromechanical systems (MEMS), including medical treatment, aviation, automobile, communication, and military applications [1]
Ye et al [4] investigated the dynamic recrystallization and strengthening-toughening effects in a near-α Ti-xSi alloy processed by hot extrusion
The Ti-6Al-4V micro-gears can be successfully fabricated by hot extrusion under thermal-mechanical coupled fields
Summary
Micro-gears are pivotal actuating elements in the transmission of power and motion and are used extensively in microelectromechanical systems (MEMS), including medical treatment, aviation, automobile, communication, and military applications [1]. Yang et al [5] studied the microstructure evolution and mechanical properties of P/M Ti-22Al-25Nb alloy during hot extrusion. There is much research on the macro-extrusion of titanium alloys, while there is little literature on the extrusion formation of micro-gears using difficult-to-deform Ti alloys, due to high strength, poor plasticity, and the mold’s vulnerability. These properties dictate that Ti alloy micro-gears should be formed at high temperatures. In terms of hot extrusion, H13 steel molds were used to extrude wide thin-ribbed sections at a temperature of 480 ◦ C [6]. Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations
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