Factors influencing the equal-channel angular pressing of Ti-6Al-4V alloy having lamellar microstructure

A study was made to investigate the factors influencing the formability on equal-channel angular (ECA) pressing of Ti-6Al-4V alloy, as a typical hard-to-work material, with a variation of ram speed. ECA pressings of Ti-6Al-4V alloy with initial lamellar microstructure were carried out by utilizing a set of die for isothermal condition. In this study, the equation for the effective strain rate during ECA pressing was evaluated by considering the geometry of both die and sample. Quantitative measurement showed that strain rate less than 0.27 s(-1) was found to be the optimum condition for sound deformation while specimens showed the noticeable shear cracking with stain rate above 0.67 s(-1). In spite of optimum condition determined here, however, shallow shear segments were still found in a specimen. This was mainly attributed to the flow localization associated with the flow softening behavior of lamellar microstructure. Such behavior was dependent on the lamellar structure per se, which was in discussion on the relation and the ability to transmit slip across either colony boundaries or alpha/beta lamellae interfaces as a slip filter. (C) 2007 Elsevier B.V. All rights reserved.