journal article

Impact of microstructure on elastic properties in the alloy Ti-42Al-8.5Nb

Abstract

The microstructure of a γ-TiAl alloy containing niobium undergoes continuous transformations during annealing at 550 °C. These take place within the α2-phase of lamellar (α2 +γ) colonies. We have characterized these changes by transmission electron microscopy and made a correlation to the elastic constants determined by resonant ultrasonic spectroscopy during in-situ annealing at the same temperature. The results show a continuous increase of the E-modulus. This can be attributed to elastic strains acting within α2 lamellae as a result of lattice transformations. After 5000 h, a thermodynamic equilibrium was established with equal fractions of α2-phase and O-phase that differ only in lattice symmetry and Nb content. Generally, the presence of O-phase should contribute to lower elastic moduli, however in the present case the evolving microstructural characteristics were responsible for the observed increase in the E-modulus.
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