Study of the Structural Evolution of a Two-Phase Titanium Alloy during Thermodeformation Treatment

Abstract

The behavior of the Ti–3.5Fe–4Cu–0.2B two-phase titanium alloy during thermal-deformation treatment under uniaxial compression is investigated. Boron is introduced to form a fine-grained structure in a cast state. Alloy samples 6 mm in diameter are formed by alloying pure components in a vacuum induction furnace and subsequent accelerated crystallization in a massive copper mold. The tests for uniaxial compression with true deformation of 0.9 are performed using a Gleeble 3800 physical simulation system of thermomechanical processes at 750, 800, and 900°C and strain rates of 0.1, 1, and 10 s^–1. The alloy microstructure in the initial and deformed states is investigated using scanning electron microscopy. The tests result in a model of the dependence of the flow stress on temperature and strain rate. It is shown that the recrystallization of the initial cast structure containing solid solutions based on α-Ti, β-Ti, and titanium diboride colonies occurs during pressure treatment. The volume fraction of the solid solution grains based on α-titanium decreases during deformation with an increase in temperature, while the fraction of the β phase, on the contrary, increases. Herewith, the average grain size of solid solutions based on α-Ti and β-Ti varies insignificantly after deformation according to almost all studied modes. It is shown that the preferential mode of the pressure heat treatment for attaining the high complex of mechanical properties in the alloy under study is a temperature range of 750–800°C because the grain size of the α phase increases from 2.2 to 4.5 μm with an increase in temperature up to 900°C.