Microstructure effects on surface integrity in slot micro-milling multiphase titanium alloy Ti6Al4V

Abstract

Material microstructure in micro-cutting, such as the phase boundary for multiphase material, plays a dominant role in governing the surface integrity that strongly influences the fatigue life of micro-components with complex structures. In the present study, surface formation, subsurface deformation, and subsurface microstructure evolution for the machined surface were investigated by slot micro-milling multiphase titanium alloy Ti6Al4V in terms of chip morphology, burrs formation, surface roughness, surface defects, and subsurface deformation. In particular, the effect of β-Ti was considered in the study. The results show that the machined surface shows the obvious feed marks and adhesive materials accompanied by squeezed β-Ti, split β-Ti and plastic side flow β-Ti. The subsurface of the machined surface can be divided into the amorphous layer (around 24 nm), nanocrystalline layer (around 124 nm), elongated grain layer (around 197 nm), and bulk material. The deformation layer thickness of the β-Ti zone is larger than the α-Ti zone. In the deformation layer of the machined subsurface, the synergetic deformation between α-Ti and β-Ti can lead to the formation of a large number of nanocrystalline grains and some enlarged grains in the phase boundary of the α-Ti side, and the β-Ti side is full of elongated grains and sporadic dynamic recrystallization nanocrystalline. Our study enhances the understanding of the surface formation and subsurface formation mechanism in micro-milling Ti6Al4V, which can provide a theoretical basis and practical reference for achieving high surface integrity for polycrystalline or multiphase material by micro-milling.