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.

Specific objective functions and algorithms are presented, which by means of dedicated finite element simulation software, calculate optimized control variables for an industrial Bridgman casting furnace. A gradient method and an evolution strategy have been integrated into an efficient optimization tool in order to minimize an objective function which characterizes the quality of directional solidified (DS) or single crystal (SC) turbine blades. The goal is to minimize the manufacturing costs for a desired quality. For a dummy turbine blade geometry, the macrograin structures produced by the optimized withdrawal velocity profile and an equivalent constant velocity, which had the same total process time, are compared. This comparison shows that the developed optimization techniques are applicable to the casting of DS/SC turbine blades.

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