The Nb-Ti-Si ternary phase diagram: Evaluation of liquid-solid phase equilibria in Nb- and Ti-rich alloys

Phase equilibria in ternary Nb-Ti-Si alloys have been investigated using scanning electron microscopy, XRD, and electron beam microprobe analysis. Alloys containing up to four phases, Nb(Ti)(5)Si-3, Ti(Nb)(5)Si-3, (Nb,Ti)(3)Si, and (Nb,Ti,Si) mere directionally solidified using cold crucible Czochralski crystal growth, A broad range df Nb and Ti compositions were investigated fur Si concentrations up to 35.0 %. Microstructural and microchemical evidence provided a clear definition of the Nb-Ti-Si liquidus surface and indicate that the metal-rich end of the ternary phase diagram possesses two transition reactions: L + Nb(Ti)(5)Si-3 --> (Nb,Ti)(3)Si + Ti(Nb)(5)Si-3 L + (Nb,Ti)(3)Si --> (Nb,Ti,Si) + Ti(Nb)(5)Si-3 The first of these transition reactions occurs at a composition of approximately Nb-66Ti-19Si, and probably at a temperature between 1600 and 1650 degrees C, The second of these transition reactions occurs at a composition of approximately Nb-76Ti-13.5Si and a temperature of approximately 1350 degrees C. No ternary eutectic was observed in the compositions that were investigated.