Hot working behavior of near alpha titanium alloy analyzed by mechanical testing and processing map
(Faculty of Material &Manufacturing Technologies, Malek-Ashtar University of Technology, Shabanlou Street, Tehran, Iran)
Abstract: The hot deformation characteristics of the Ti-5.7Al-2.1Sn-3.9Zr-2Mo-0.1Si (Ti-6242S) alloy with an acicular starting microstructure were analyzed using processing map. The uniaxial hot compression tests were performed at temperatures ranging from 850 to 1000 °C and at strain rates of 0.001-1 s-1. The developed processing map was used to determine the safe and unsafe deformation conditions of the alloy in association with the microstructural evolution by SEM and OM. It was recognized that the flow stress revealed differences in flow softening behavior by deformation at 1000 °C compared to the lower deformation temperatures, which was attributed to microstructural changes. The processing map developed for typical strain of 0.7 in two-phase field exhibited high efficiency value of power dissipation of about 55% at 950 °C and 0.001 s-1, basically due to extensive globularization. An increase in strain rate and a decrease in temperature resulted in a decrease in globularization of α lamellae, while α lamellar kinking increased. Eventually, the instability domain of flow behavior was identified in the temperature range of 850-900 °C and at the strain rate higher than 0.01 s-1 reflecting the flow localization and adiabatic shear banding. By considering the power efficiency domains and the microstructural observations, the deformation in the temperature range of 950-1000 °C and strain rate range of 0.001-0.01 s-1 was desirable leading to high efficiencies. It was realized that (950 °C, 0.001 s-1) was the optimum deformation condition for the alloy.
Key words: Ti-6242S; hot deformation; processing map; microstructure; globularization