Effect of al content on phase constitution and tensile properties of Ti-13mass%Cr-1mass%Fe-Al alloys

The influence of Al content on phase constitution and tensile properties of Ti-13mass%Cr-1mass%Fe-Al alloys was investigated by measurement of electrical resistivity and Vickers hardness, X-ray diffractometry (XRD) and tensile test. For all solution treated and quenched (STQed) specimens, only P reflection was detected by XRD. Resistivity at room and liquid nitrogen temperatures increased monotonically with Al content. Vickers hardness kept almost the same value as STQed specimen up to 3.0mass%Al and then increase with Al content. In the isochronal heat treatment, two minima of resistivity ratio (pLN/pRT) were observed at 623K and 823K, respectively. The former is due to the precipitation of isothermal omega phase and the latter is a precipitation. The temperature of resistivity minimum attributing to omega phase precipitation gradually increases with Al content. In the alloys with 4.5mass%Al and more, the minimum of resistivity associated with omega precipitation disappeared and the minimum caused by alpha precipitation remained. It is considered that Al content above 4.5msss% was suppressed isothermal omega precipitation and enhanced a precipitation. In STQed alloys, tensile strength increased slightly with Al content and elongation at fracture kept almost constant value. Ti-13mass%Cr-1mass%Fe-Al alloys in STQed state without isothermal omega precipitation bad the comparable tensile properties to Ti-22mass%V-4mass%Al, one of the most popular beta titanium alloy.