Phase equilibria in the titanium corner of hypoeutectic alloys in the Ti-Nb-Si-Al system

Physicochemical analysis methods have been applied to the phase equilibria in the Ti-Nb-Si-Al system in the region of alloys rich in titanium. It is found that the crystallization conditions for hypoeutectic alloys with constant 5 at.% aluminum content control the niobium contents up to 17.5 at.%, for which there are two groups. After the primary crystallization of the β phase in alloys in these groups, binary eutectics are formed with different intermetallic phases. The properties of the alloys are dependent on the phase compositions in the eutectic mixtures. The temperature and concentration stability of the phases have been determined. It is shown that a peritectic reaction may give rise to a second intermetallide phase in alloys approximating to equilibrium as a result of subsequent annealing, which does not affect the structure of the cast alloys.