Characterization of Shear Band Formation and Microstructure Evolution during Orthogonal Cutting of Ti-5553: Part I—Shear Angle, Strain and Strain Rate

Abstract

Ti-5553 (Ti-5Al-5Mo-5V-3Cr-0.5Fe) is a recently commercialized near-β titanium alloy employed in large-section forging of Boeing 787 landing gear. The machinability of Ti-5553 is low owing to its high strength at elevated temperature, low thermal conductivity and high chemical reactivity. Chip serration occurs during high-speed machining of Ti-5553, which is found to be attributed to the periodic formation of shear bands caused by thermoplastic instability within the primary shear zone. Microscopic observations indicate that the geometry and microstructure of shear bands are significantly related to the shear angle, shear strain and strain rate under the given cutting conditions. In this study, quick-stop turning tests were conducted to understand the chip formation mechanism in machining Ti-5553, and the machined chips were metallographically characterized to investigate their morphology and microstructure evolutions. In the Part I of this study, the shear angle, shear strain and strain rate were quantitatively determined, and the shear band microstructure was examined to reveal the effect of cutting conditions in dry turning of Ti-5553. This study advances the mechanism of shear band formation in machining Ti-5553 and develops a novel experimental approach to directly obtain the actual shear strain and strain rate based on the geometry of the machined chip.