Structure and grindability of cast Ti–5Cr– xFe alloys

Abstract

The purpose of this study was to investigate the structure, microhardness and grindability of Ti–5Cr and a series of ternary Ti–5Cr– xFe alloys with 0.1, 0.5, 1, 3 and 5 wt.% Fe, respectively. This study evaluated the phase and structure of Ti–5Cr and Ti–5Cr– xFe alloys, using an X-ray diffraction (XRD) for phase analysis and optical microscope for microstructure of the etched alloys. In addition, grindability was evaluated by measuring the amount of metal volume removed after grinding for 1 min at each of the four rotational speeds of the wheel (500, 750, 1000 or 1200 m/min), with the goal of developing a titanium alloy with better machinability than commercially pure titanium (c.p. Ti). The results showed that the structure of Ti–5Cr– xFe alloys is sensitive to the Fe content. With Fe contents higher than 0.5 wt.%, the equi-axed β phase is entirely retained, while ω phase was found in the Ti–5Cr, Ti–5Cr–0.1Fe, Ti–5Cr–0.5Fe and Ti–5Cr–1Fe alloys. The largest quantity of ω phase and highest microhardness were found in Ti–5Cr–0.5Fe and Ti–5Cr–1Fe alloys. The grinding rates of the Ti–5Cr and Ti–5Cr– xFe alloys showed a similar tendency to the microhardness. The Ti–5Cr, Ti–5Cr–0.1Fe, Ti–5Cr–0.5Fe and Ti–5Cr–1Fe alloys exhibited the best grindability, especially at 500, 750 and 1000 m/min. Furthermore, the grindability of the tested metals increased in proportion to grinding speed up to 1000 m/min, with a decrease after 1200 m/min. This study concluded that Fe may be used to harden titanium and improve the grindability.