Influence of High-Speed Milling Process on Mechanical and Microstructural Properties of Ultrafine Grained Profiles Produced by Linear Flow Splitting

The effects of milling parameters on the surface quality, microstructures and mechanical properties of machined parts with ultrafine grained (UFG) gradient microstructures are investigated. The effects of the cutting speed, feed per tooth, cutting tool geometry and cooling strategy are demonstrated. It has been found that the surface quality of machined grooves can be improved by increasing the cutting speed. However, cryogenic cooling with CO2 exhibits no significant improvement of surface quality. Microstructure and hardness investigations revealed similar microstructure and hardness variations near the machined groove walls for both utilized tool geometries. Therefore, cryogenic cooling can decrease more far-ranging hardness reductions due to high process temperatures, especially in the UFG regions of the machined parts, whilst it cannot prevent the drop in hardness directly at the groove walls.