Surface Tension, Viscosity, and Selected Thermophysical Properties of Ti48Al48Nb2Cr2, Ti46Al46Nb8, and Ti46Al46Ta8 from Microgravity Experiments

The surface tension and the viscosity of the alloys Ti₄₈Al₄₈Nb₂Cr₂, Ti₄₆Al₄₆Nb₈, and Ti₄₆Al₄₆Ta₈ are measured with the oscillating drop technique in an electromagnetic levitation device under reduced gravity conditions on board a parabolic flight airplane. The surface tensions as a function of temperature are obtained as σ(T) = (1.19 ± 0.02 − 3.80 × 10⁻⁴ (T − 1856 K)) Nm⁻¹ for Ti₄₆Al₄₆Nb₈, σ(T) = (1.21 ± 0.02 − 2.69 × 10⁻⁴ (T − 1879 K)) Nm⁻¹ for Ti₄₆Al₄₆Ta₈, and σ(T) = (1.20 ± 0.02 − 3.96 × 10⁻⁴ (T − 1776 K)) Nm⁻¹ for Ti₄₈Al₄₈Nb₂Cr₂, concentrations in atomic per cent. The viscosities at the liquidus temperatures are obtained as η(T_l) = 6.62 mPa^.s, η(T_l) = 6.9 mPa^.s, and η(T_l) = 5.8 mPa^.s in the same order. All processed specimens are solidified at an undercooling of ΔT_u = 220 ± 30 K. In addition, the solidus and liquidus temperatures and the enthalpies of fusion are determined by calorimetry. From the large undercooling and the enthalpy of fusion, the average specific heat capacity at an undercooling of 120 K is obtained as c_P(av) = 1.30 ± 0.20 J (kg)⁻¹ for all alloys. The thermal expansion between the room and solidus temperatures is measured by dilatometry.