The mechanical properties of different lamellae and domains in PST-TiAl investigated with nanoindentations and atomic force microscopy

A nanoindenting atomic force microscope (NI-AFM) was used to determine the hardness and modulus of polysynthetically twinned TiAl on a nanometer scale. Samples with different orientation, (110)γ and (111)γ, were examined. The hardness of α2 lamellae is significantly higher than that of γ lamellae, whereas different γ domains only show small hardness variations. Compression deformed PST crystals show a large amount of twinning in some γ domains. The hardness of twinned and untwinned lamellae are compared. The plastic anisotropy in the γ-phase produces significant differences in the pile-up around the impressions left by nanoindentations. The atomic force microscope allows direct imaging of these impressions. Conical tips were used to study the asymmetric pile-up behavior of the impressions. These patterns are characteristic for the orientation of the lamellae and domains.