The effect of average cooling rate from a temperature within beta single phase region on phase constitution and tensile properties of Ti-Fe-Cr alloys

The influence of cooling rate on phase constitution and tensile properties of Ti-2.9Fe-4.9Cr and Ti-4.2Fe-6.9Cr alloys was investigated by electrical resistivity and Vickers hardness measurements, X-ray diffraction, optical microstructure observation and tensile testing. In only Ti-2.9Fe-4.9Cr alloy quenched at an average cooling rate of 25 Ks(-1), reflections from isothermal omega phase were identified, whereas only reflections from beta phase were identified by XRD with no reflections of isothermal omega phase present in Ti-2.9Fe-4.9Cr alloy cooled at other cooling rates and Ti-4.2Fe-6.9Cr alloy quenched at all cooling conditions. HV for Ti-2.9Fe-4.9Cr alloy cooled at 25 Ks(-1), was about 400 and HV of Ti-4.2Fe-6.9Cr alloy cooled at all cooling conditions, even 25 Ks(-1), was around 320. Therefore, quench sensitivity of Ti-4.2Fe-6.9Cr alloy is lower than that of Ti-2.9Fe-4.9Cr alloy. Tensile strength and reduction in area of Ti-2.9Fe-4.9Cr alloy cooled at three different cooling rates except for 25 K s(-1) showed about 1200 MPa and 45%, respectively. About 1050 MPa in sigma(B) and 60% in phi were obtained in all quenched Ti-4.2Fe-6.9Cr alloys, respectively. The strength/ductility balances of Ti-4.2Fe-6.9Cr alloy quenched at four different cooling rates are comparable with those of developed beta titanium alloys in solution treated and quenched state.