Microstructural refinement of alpha-brass and titanium-aluminum-vanadium alloys by equal channel angular extrusion processing: Modeling and experimental validation

Equal Channel Angular Extrusion (ECAE) has been used as one of the methods to develop ultra-fine grained (UFG) materials. Investigations to date have focused on producing UFG microstructures in ductile metals and alloys. It has been a challenge to produce by ECAE hard-to-work alloys such as Ti-6Al-4V because such materials readily fracture due to their limited ductility at room and intermediate temperatures. This necessitates processing the alloys at high temperatures. Selection of die materials which retain their strength at high temperature and fabrication of ECAE dies are additional challenges in processing of such alloys. Several researchers have conducted ECAE of Ti-6Al-4V alloys using the grain fragmentation method. However, investigations of ECAE process that results in grain structures containing relatively low density of dislocations are sparse. The present study is a fundamental investigation of aimed at determining process parameters for producing UFG in commercial Ti-6Al-4V and developing a mechanism based model for grain refinement. Finite element method was used to model the ECAE process and the FEM predictions were validated experimentally under various process conditions. A mechanism of grain refinement was developed based on microstructural observations. The mechanism satisfactorily accounts for grain refinement in two phase alpha + beta titanium alloys with prior lamellar and equiaxed alpha + beta microstructures.