Proceedings of the
9th International Conference of Asian Society for Precision Engineering and Nanotechnology (ASPEN2022)
15 – 18 November 2022, Singapore

Effect of ß-Ti on surface integrity in slot micro-milling multiphase titanium alloy Ti6Al4V

Yabo Zhang1,2, Yabo Zhang1,a and Hao Wang1,b

1School of Mechanical and Electrical Engineering, Harbin Institute of Technology, Harbin 150001, China

2Department of Mechanical Engineering, Faculty of Engineering, National University of Singapore, 9 Engineering Drive 1, Singapore 117575, Singapore


Surface integrity has a significant influence on the fatigue life of micro-components with complex structures. In the present study, surface topography and microstructure evolution of subsurface for the machined surface was 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 ß-Ti was considered in the study. The results show an apparent shear front on the free surface and gouging in the tool-chip contact surface. The up-milling and down-milling present leaf burrs and wave-type burrs with the larger up-milling burr width, respectively. The machined surface shows the obvious feed marks and adhesive materials accompanied by squeezed ß-Ti, split ß-Ti and plastic side flow ß-Ti. The subsurface of the machined surface can be divided into the amorphous layer (24.23 nm), nanocrystalline layer (124.74 nm), and elongated grain layer (197.42 nm), and bulk material due to the coupling effect of thermo-mechanical load. The nanocrystalline layer presents the 10-20 nm dynamic recrystallization grain with a flat shape and distorted elongated subgrains. The elongated grain layer shows the compressed and elongated grains along the slot width direction. The depth of the subsurface deformation layer around ß-Ti is 535 nm which is larger than the α-Ti zone. In the deformation layer of machined subsurface. The deformation coordination between α-Ti and ß-Ti can lead to the formation of a large number of nanocrystal grains and some enlarged grains in the phase boundary of the α-Ti side. The ß-Ti is full of elongated grains and sporadic dynamic recrystallization nanocrystalline. Our findings contribute to revealing the surface formation mechanism, surface integrity, and fatigue life of micro-milled multiphase parts.

Keywords: Surface topography, microstructure evolution, micro-milling, Ti6Al4V

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