ATI 425® Alloy Formability: Theory and Application

Abstract

ATI 425® Alloy, nominal composition Ti-4.0Al-2.5V-1.5Fe-0.25O, is a new alpha/beta Ti alloy of significant commercial interest as a viable replacement for Ti-6Al-4V, CP-Ti, and other titanium alloys in a variety of aerospace applications. ATI 425® Alloy offers properties comparable to Ti-6Al-4V alloy with significant improvements in formability, both at room and elevated temperatures. The reasons for the improved formability, particularly at low temperatures, are not well understood. The development of a thorough understanding is complicated by the wide array of phases, microstructures, and deformation paths available via thermomechanical processing in alpha/beta titanium alloys. In this paper, theories of strengthening and dislocation mobility in titanium and HCP metals will be reviewed and applied to better understand why ATI 425® Alloy offers a unique combination of strength and formability not obtainable by conventional alpha/beta titanium alloys. Subsequently, the application of the improved formability to a range of product forms including sheet, tubing, and forgings will be discussed.