Machinability of cast titanium alloy Ti-6Al-4V with addition of boron

Abstract

Cast titanium products generally have coarser microstructures compared to wrought, which explains their limited mechanical properties. However, instead of additional thermo-mechanical processing steps, as in the case of wrought components, the microstructure of castings can be refined by additions of boron. This enhances yield strength, tensile strength and ductility. In order to investigate the influence on machining of this microstructural refinement, cutting tests were performed in three different Ti-6Al-4V castings, having 0, 0.06 and 0.11 wt.% boron. Five machinability criteria were studied; cutting force, chip breakability, burr formation, surface roughness and tool wear. The results show anisotropic deformation behavior in chips when alpha colony size is on the same order of magnitude as the primary deformation zone, or larger. There was little or no influence on cutting forces and burr formation, however chip breakability and tool life was reduced when boron was added. Surface roughness showed a more complex behavior where 0.06 wt.% boron resulted in rougher surfaces compared to the other compositions at low feed rate.