Tool wear induced the gradient distribution of surface integrity with process-microstructure-property characteristics after turning Ti-6Al-4 V

Abstract Since high-speed machining faces the challenge of rapid tool wear, the gradient thermo-mechanical loads modify the surface integrity with gradient microstructure-property characteristics. This study investigates on depth gradient surface integrity issues after turning Ti-6Al-4 V considering tool wear states, involving the analysis of microstructural evolution and mechanical behaviors. The microstructure observation demonstrates that the gradient distribution of grain boundary, crystallographic textures and phase compositions from the machined surface to the substrate. The grain boundaries provide crucial evidences of plastic activity in localized deformation layers. The fiber texture is generated with the attenuation of texture strength from the surface 9.7 to the substrate 2.3. The α-phase with peak broadening presents the tendency of initial decreasing and then increasing from the substrate to the surface. The nanohardness exhibits the trend of surface hardening-hardening weakening-substrate along the depth gradient at VB = 0 mm, while presents the surface hardening-hardening strengthening-hardening weakening-substrate at VB = 0.3 mm. The stress states change from tensile state of machined surface to compressive state below the machined surfaces. The surface tensile stress and peak compressive stress both enhance with the progressive of tool wear state. This work provides a meaningful opportunity to improve surface integrity via controlling the depth gradient distribution.