Machinability maps – Towards a mechanistic understanding of the machining of TI-6AL-4V and TIMETAL 407

Abstract

In recent years, new titanium alloys with improved “machinability” have been developed, to provide manufacturers with alloys that can be machined to final dimensions at higher metal removal rates. One such alloy, TIMETAL® 407 (Ti-407), was developed to replace Ti-6Al-4V (Ti-64) in applications where energy absorption prior to failure is a key property requirement. In this study, a combination of large scale turning trials was used to characterise the full range of machining criteria, including: (1) tool life, (2) chip formation and (3) subsurface microstructural deformation. The machining response of the two alloys was summarised in easy-to-visualise machinability maps: to aid the machining supply chain in selecting feed rates and cutting speeds to generate certain chip forms, to extend tool life and minimise subsurface deformation for specific titanium alloys. Assessment of these key characteristics has provided an understanding of the effects of mechanical twinning on the poor chip control through increasing the accommodation of strain prior to fracture.