Processing of Submicron-Grained Billets of Ti-6A1-4V Titanium Alloy by Multiple Forging

摘要

This report results from a contract tasking the Institute for Metals Superplasticity Problems as follows: The project will study sub-microcrystalline structure formation in a Ti-6A1-4V titanium alloy during large plastic deformation by multiple isothermal forging; and to produce large (diameter up to 2OOmm) billets with homogeneous microstructure and a grain size of no more than 0.5 microns. The results of the project will establish the connection between microstructural changes resulting in the formation of a sub-microcrystalline structure and resulting mechanical behavior in a Ti-6A1-4V alloy during large plastic deformation at temperatures about half the melting temperature and reveal whether dynamic recrystallization is the pertinent metallurgical process. The influence of temperature and rate of deformation as well as the initial microstructure (grain size, phase volume fraction, thickness of plates of a and p-phases) on the kinetics of structure formation, its uniformity, and mechanical properties will be shown. The influence of initial microstructure on cavitation and workability will also be determined. Based on the experimental studies, computer modeling of multi-step isothermal forging in a special die set unit will also be conducted. Optimum routes of multiple isothermal forging in the special die set will be determined.