Beta titanium alloys possess an ideal combination of strength and low density for many aerospace applications including gas turbine compressor blades, vanes and related hardware. However, titanium is a very reactive metal element and may undergo sustained combustion under conditions encountered in gas turbine engine compressors, high pressure over 400psi (27.2atm) and high temperature over 850F (454.4C). If encountered, the alloys may burn by ignition followed by combustion and therefore it is important to prevent this kind of disaster. Three conditions are required in combustion, the source of ignition, the presence of an oxidizer, and finally the presence of fuel. It is inevitable that some sources of ignition such as friction will be present. The oxidizer is always present since it is the fluid being pumped. Any plan to reduce the risk and consequences of fires must therefore be concerned with fuel, that is materials.
The beta Ti-Cr-V ternary system, the composition range especially bounded by Ti-13Cr-22V, Ti-36Cr-22V and Ti-13Cr-40V (compositions are all in wt% specified otherwise), is known for an essential lack of combustibility in combination with high temperature strength properties. As these properties are correlated with microstructures and phase relations (for example, the presence of TiC$r_2$ Laves phase is known to be detrimental to mechanical properties such as ductility), the thermodynamic properties and phase equilibria of the anti-oxidation and anti-combustion Ti-Cr-V system are important. But the thermodynamic assessments and predictions have not been made and therefore ambiguities related to phase equilibria involving the high and low temperature modifications of TiC$r_2$ compounds have not been resolved nor any ternary thermodynamic parameter has been calculated and suggested.
In this study, the thermodynamic assessments of the Ti-Cr-V system are performed by the use of previously reported ternary experimental data and the relevant phase diagrams are calculated and compared with experimental measurements. The resultant information will be useful in understanding the ternary phase diagram in the entire composition range, but with an emphasis on the non-burning Ti-rich region, and in choosing optimum composition ranges for non-burning properties. Afterward, other alloy (Mo,Nb) addition effect is considered in the Ti-Cr-V system.
