Hot Plastic Deformation of Titanium Alloys Reflected on Process Maps

Abstract

Maps are plotted for the hot plastic deformation of titanium-based alloys with a high-temperature polymorphic transformation, namely, martensitic 23A, 5VA and PT3V alloys. Hot plastic compression is modeled using a DIL 805 A/D dilatometer. Samples in the form of null 5 x 10 mm cylinders are compressed to a strain of 0.3 in the temperature range 600-1100 degrees C at a strain rate from 10(-3) to 10 s(-1). The alpha <-> beta transformation temperatures are 800-900 degrees C in alloy 23A, 880-900 degrees C in 5VA, and 900-920 degrees C in PT3V, and they fall into the temperature range of hot compression. The process maps show the effect of mechanical energy dissipation in changing the shape and structure of the samples. The dissipation of introduced mechanical energy is found to be due to the operation of the following two structural mechanisms: accommodative elastoplastic relaxation in ensembles of lattice defects with eta approximate to 25% and the hcp <-> bcc crystallographic transformation with an efficiency eta approximate to 15%.