The effects of Fe and Al on the phase transformations and mechanical behavior of -Ti β alloy Ti-11at.%Cr

Alloy composition is important for developing desired microstructures in beta-titanium (beta-Ti) alloys during thermomechanical processing. In this work, the relatively low-cost alloying elements iron (Fe) and aluminum (Al) were added to a base Ti-11at.%chromium (Cr) alloy and in-situ and ex-situ examination of the microstructural evolution and mechanical properties during tension, hardness, elevated temperature X-ray diffraction (XRD) and resonance ultrasound spectroscopy (RUS) were performed. The 400 degrees C XRD revealed that Ti-11at.%Cr underwent beta-to-omega and beta-to-alpha transformations. Adding 0.85 at.% Fe reduced the volume fraction of the omega- and alpha-phases, and adding 5.3 at.% Al inhibited the beta-to-omega transformation. The 400 degrees C RUS showed that the alloys containing the omega phase exhibited an increase in shear modulus of -140%, while the omega-free alloys exhibited an increase of only -102%. The hardness and strength values of the omega-containing Ti-11Cr and Ti-11Cr-0.85Fe increased with increased omega-phase volume fraction when the omega/alpha ratio was greater than 0.25. The relationship between omega/alpha volume fraction ratio and mechanical properties is discussed.