BULK DEFORMATION OF TI-6.8MO-4.5FE-1.5AI (TIMETAL LCB-ASTERISK) ALLOY

Recently, a low-cost near-beta titanium alloy (Timetal LCB Ti-Q.8Mo-4. 5Fe-1.5Al wt %) containing iron and molybdenum has been developed. Thi s alloy is cold formable in the beta microstructure and can be aged to high strengths by precipitating the alpha phase. Due to its combinati on of cold formability and high strength, the alloy is a potential rep lacement 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-t emperature compression tests conducted over a strain-rate range of 0.0 1 to 5/s indicate that the bulk cold compression of the alloy is affec ted by two factors: the microstructure and the length-to-diameter aspe ct ratio of the specimen. In the aged condition, when the microstructu re has or-phase particles distributed along flow lines in the beta-pha se matrix, the alloy has the propensity for shear failure when deforme d in compression in a direction parallel to the flow lines. In the sol ution-heat-treated condition, the microstructure consists of beta grai ns with athermal omega phase. In this condition, the alloy can be cold compressed to 75 % reduction in height using specimens with aspect ra tio of 1.125, but fails by shear for a larger aspect ratio of 1.5. Pla stic deformation of the material occurs initially by single slip in mo st grains, but changes to multiple slip at true plastic strains larger than about 0.15. At a slow strain rate, the deformation is uniform, a nd 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. Al though there is a considerable rise in temperature (200 to 500 degrees C) during deformation, precipitation of the alpha phase was not obser ved.