STUDY INTO STRUCTURAL EVOLUTION OF TWO-PHASE TITANIUM ALLOY DURING THERMAL DEFORMATION PROCESSING

Abstract

This paper studies Ti–3,5Fe–4Cu–0,2B two-phase titanium alloy behavior during its thermal deformation processing under uniaxial compression. Boron was added to obtain a fine-grained structure in the cast state. Samples of alloys 6 mm in diameter were obtained by melting pure components in a vacuum induction furnace with their subsequent crystallization into a solid copper mold. Uniaxial compression tests with a true strain of 0,9 were performed using the Gleeble 3800 thermal-mechanical physical simulation system at 750, 800 and 900 °C and strain rates of 0,1; 1 and 10 s–1. Scanning electron microscopy was used to study the microstructure of the alloy in its initial and deformed states. A model of flow stress dependence on temperature and strain rate was built as a result of the tests. It is shown that pressure treatment involves recrystallization of the initial cast structure containing solid solutions based on α-Ti, β-Ti and titanium diboride aggregates. During the deformation process, the volume fraction of α-titanium solid solution grains decreases with rising temperature, and the fraction of the β phase, on the contrary, increases. In this case, the average grain size of solid solutions based on α-Ti and β-Ti varies insignificantly after deformation in almost all of the studied modes. It is shown that the preferred mode of hot pressure treatment for obtaining a high complex of mechanical properties in the investigated alloy is a temperature range of 750– 800 °C, since α-phase grain sizes increase from 2,2 to 4,5 μm with an increase in temperature to 900 °C.