The melting diagram of the Ti-corner of the Ti-Zr-Si system and mechanical properties of as-cast compositions

Phase equilibria in the Ti-corner of the Ti-Zr-Si system were studied by the methods of metallography, differential thermal analysis, X-ray and microprobe analyses of as-cast samples. The results are given in the way of the melting diagram and of polythermal sections at 10 and 20 at.% Si. At 1300 degreesC invariant four-phase equilibrium of eutectic type L <----> <beta-Ti>(beta) + (Ti5Si3)(Z) + <(Ti, Zr)(2)Si> (S-2) was shown to occur in the concentration interval studied. The location of the eutectic point E was determined to take place at similar to78Ti-11Zr-11Si. The ternary compound S2 formed from the melt by peritectic reaction L + Z --> S2. Microhardness of the primary silicide grains and of eutectics microconstituents has shown that zirconium additions decrease the strength of the Z-phase and of the beta + Z eutectic, while they do not change the strength of the S2-silicide and of the beta + S2 eutectic. Based on the results of hot hardness measurements, below 550 degreesC the potential for attractive high-temperature structural properties is controlled by refinement of the microstructure, while above this temperature the alpha --> beta transformation temperature of Ti limits the application. (C) 2004 Elsevier B.V. All rights reserved.