Surface morphology and affected layer in disc-milling grooving of titanium alloy

Disc-milling grooving experiment was carried out to measure milling force and temperature for titanium alloy samples. After machining, surface roughness, surface topography, residual stress, microstructure and microhardness under different milling conditions were analyzed. The results show that the surface roughness of the center on milling surface is lower than that of the edge; moreover, the surface roughness decreases with the increase of the spindle speed, but increases with the increase of depth of cut and feed speed. The residual compressive stress is produced on the machined surface and subsurface, and gradually declines to zero with increase of the depth. The microstructure of lattice tensile deformation is found along feed direction under the effect of milling force, progressing from the initial equiaxed structure to long flake lattice. The metallographic structure of plastic deformation zone changes with the temperature, transforming from the initial equiaxed microstructure to a lamellar microstructure when the temperature is up to β-phase transition temperature. The combination of mechanical and thermal loads increases the microhardness on the machined surface and subsurface.