Investigation on the machinability of metastable β titanium alloy M28

Abstract

Oriented to the application of new generation strategic aircraft, M28 (Ti-4Al-5Mo-5 V-6Cr-1Nb) is a novel metastable β 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.