Bulk deformation of Ti-6.8Mo-4.5Fe-1.5Al (Timetal LCB) alloy

Recently, a low-cost near- beta titanium alloy (Timetal LCB Ti-6.8Mo-4.5Fe-1.5Al wt.%) containing iron and molybdenum has been developed. This alloy is cold formable in the beta microstructure and can be aged to high strengths by precipitating the alpha phase. Due to its combination of cold formability and high strength, the alloy is a potential replacement for steel components in the automotive industry. The current study was undertaken to evaluate the cold bulk forming characteristics of Timetal LCB for use in lightweight automotive applications. Room-temperature compression tests conducted over a strain-rate range of 0.01-5/s indicate that the bulk cold compression of the alloy is affected by two factors: the microstructure and the length-to-diameter aspect ratio of the specimen. In the aged condition, when the microstructure has alpha -phase particles distributed along flow lines in the beta -phase matrix, the alloy has the propensity for shear failure when deformed in compression in a direction parallel to the flow lines. In the solution-heat-treated condition, the microstructure consists of beta grains with athermal omega phase. In this condition, the alloy can be cold compressed to 75% reduction in height using specimens with aspect ratio of 1.125, but fails by shear for a larger aspect ratio of 1.5. Plastic deformation of the material occurs initially by single slip in most grains, but changes to multiple slip at true plastic strains larger than approx0.15. At a slow strain rate, the deformation is uniform, and the material work hardens continuously. At high strain rates, shear bands develop, and the localized deformation and temperature rise due to deformation heating leads to flow softening during compression. Although there is a considerable rise in temperature (200-500 deg C) during deformation, precipitation of the alpha phase was not observed.