Local variations of the chemistry in as-cast gamma-TiAl (TiBx) alloys and its consequence for thermomechanical treatments
The first part of the paper presents an accompanying investigation to a thermomechanical processing route of gamma-TiAl turbine blades. By means of scanning electron microscopy and energy dispersive X-ray (EDX) analysis, the chemical homogeneity and the microstructures of gamma-TiAl as-cast ingots, work pieces and the final turbine blades are determined. We find that the local Al-content in as-cast ingots can vary by more than 1.5 at.%. Large chemical inhomogeneities present in as-cast ingots can only be eliminated to a certain degree by subsequent thermomechanical processing. An additional aim of the study is to assess the influence of a thermomechanical processing on the morphology of titanium boride precipitates and the alpha2-Ti3Al-phase. The second part of the paper contains a detailed analytical study devoted to homogenization of a range of gamma-TiAl cast alloys. Different microstructures are generated in a laboratory-scale argon-arc furnace by both rapid and slow solidification rates and an additional homogenization treatment, respectively. Quantitative EDX analysis shows that only rapid solidification of ingots with a subsequent homogenization treatment leads to a nearly chemically homogeneous microstructure.
Sternitzke
M
GKSS Research Centre, Max-Planck-Str., D-21502 Geesthacht, Germany.
Appel
F
Wagner
R