Investigation on the machinability of metastable β titanium alloy M28

Oriented to the application of new generation strategic aircraft, M28 (Ti-4Al-5Mo-5 V-6Cr-1Nb) is a novel metastable beta titanium alloy with outstanding strength. The research on the machining of such hard-to-machine material remains inadequate. To investigate the machinability of M28, milling experiments were made with the uncoated WC-Co carbide insert. The cutting force and tool life of M28 were compared with those of Ti-6Al-4 V in varying cutting speeds. The tool wear mode was also analyzed. The cutting force of M28 increases with cutting speed significantly, especially in high-speed cutting where it can reach as high as 132% of that of Ti-6Al-4 V. The "transgranular cut" of M28 contributes to the high cutting force. A much shorter tool life in cutting M28, ranging from 0.88% to 13.82% of that of Ti-6Al-4 V, was found in the experiment. Serious edge chipping occurred at the normal cutting speed as the result of stress concentration and abrasion of the secondary alpha precipitation. In high-speed cutting, chip adhesion, comb cracks, and tool plastic deformation were found at the edge as the result of the high temperature. In addition, the semi-crater at the worn edge tip was formed by the interaction of high-frequency cutting impact, carbide thermal softening, and diffusion wear. A better understanding of the machinability of M28 is conducive to the improvement in manufacture in the aviation industry.