Papers by Author: D. Voss

Abstract: The first results are presented of ESA MAXUS 8 sounding rocket benchmark experiment on γ-TiAl (Nb,B) intermetallics solidification, that was a part of the IMPRESS EU FP6 project. Having the aim to investigate the columnar and equiaxed primary microstructures formation at diffusion controlled melt growth, an experiment was designed applying the power-down directional solidification technique with fixing quench in automatic spaceborne furnace module TEM03-5M. Two related alloys were tested: one inoculated with boron grain refiner Ti-44Al-7.5Nb-2.7B (at.%); and the other Ti-45.5Al-8Nb (at.%) without grain refinement. The series of terrestrial reference processes has been performed accordingly in counter-gravity solidification direction. The numerical studies of heat-mass transfer, melt hydrodynamics and temporal solidification dynamics of these alloys have been implemented under the earth-and zero-gravity approximations using the GIGAN software package (IPPE). The comparison is performed of numerical model findings with the real microstructure and composition of samples, whose analyses were carried out by backscattered scanning electron microscopy (SEM) and X-ray microprobe (EDX) techniques. The convection-induced peritectic macrosegregation effect appearance and development in ground-based reference ingots is analytically observed and numerically studied. The achieved microstructure formation in space benchmarks is discussed.

Abstract: The authors are members of the integrated project Intermetallic Materials Processing in Relation to Earth and Space Solidification (IMPRESS), funded within the European Framework (FP6). One of the aims of IMPRESS is to develop new alloys and processes for the casting of TiAl-based turbine blades for the next generation of aero and industrial gas turbine engines. Within IMPRESS, two related issues have been identified during the primary solidification stage, namely, segregation and the columnar-to-equiaxed transition (CET). The authors have set out to isolate the effects of thermo-solutal convection, by designing a microgravity experiment to be performed on a European Space Agency platform. This experiment will investigate the CET formation during solidification. It is planned to use a sounding rocket providing a microgravity time of approximately twelve minutes. The results of this microgravity solidification experiment will be used as unique benchmark data for development and validation of new computational models of TiAl solidification. This in turn will produce accurate models and ultimately new robust industrial processes by project partners in the aerospace industry. The evolution of the design of the microgravity experiment is discussed and the results of preliminary ground reference experiments are presented. Future plans and objectives for the project are also highlighted.