Kirkendall pore formation within WC-Co tool inserts during the machining of titanium alloys

Recent research has indicated that machining of titanium alloys with uncoated cemented tungsten carbide tools fulfil the criteria for Kirkendall porosity. If this occurs during machining, it could contribute to the type and rate of tool wear, compromising the tools structural integrity close to the edge line within the contact zone. In this study, voids were observed at the tool-workpiece contact zone close to the cutting edge of worn milling inserts, generated due to the 10 000 times higher outward diffusion of Co into Ti than Ti into Co. To investigate the nature of the Kirkendall diffusion process, diffusion couples between titanium alloys and WC-6Co at pressures between 0 to 2.5 GPa and temperatures between 800 and 1200 °C were made and analysed. Porosity was found in the 1200 °C Ti-6Al-4V/WC-6Co 2.5 GPa and 1000 °C Ti-5Al-5Mo-5V-3Cr/WC-6Co 35 MPa samples in addition to the inserts. These findings highlight the need for further research into porosity-driven wear mechanisms to improve the cemented carbide tools for machining titanium alloys.