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

Abstract

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(Tl) = 6.62 mPa.s, η(Tl) = 6.9 mPa.s, and η(Tl) = 5.8 mPa.s in the same order. All processed specimens are solidified at an undercooling of ΔTu = 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 cP(av) = 1.30 ± 0.20 J (kg)−1 for all alloys. The thermal expansion between the room and solidus temperatures is measured by dilatometry.