Titanium-boride eutectic materials: Phase equilibria and constitution of alloys in the Ti-rich portion of the Ti-V-B system

Abstract

Phase equilibria and constitution of alloys were experimentally investigated in the Ti-TiB-(Ti∼0.5V∼0.5)B-Ti ∼40V∼60 region using metallography (optical microscopy and SEM/EPMA), differential thermal analysis (DTA), and X-ray diffraction (XRD). The phase diagram in the melting (solidification) temperature range has been constructed as solidus and liquidus surfaces projections and a vertical section at 9 at.% B. The V alloying was found to decrease melting temperatures from 1500 °C for the binary (Ti) + TiB eutectic to 1430 °C for the ternary invariant equilibrium Le ↔ (Ti 0.63V0.37) + (Ti0.74V0.26)B and then to increase them. At that, the composition of (βTi,V) + (Ti,V)B monovariant eutectic becomes richer in boron, from 7.07.5 at.% B in the Ti-B binary to about 8.5 at.% B at 40 at.% V. The V contents in metal and boride phases after partition are comparable. Vanadium sharply decreases the α ↔ βtransition temperature, so that at ∼10 to ∼15 at.% V as-cast arc melted alloys are multiphase and at ∼20 at.% V practically completed β-stabilization is observed.