Massive Transformation in High Niobium Containing TiAl-Alloys

Abstract

Massive transformation in high Nb bearing γ-TiAl-based alloys, Ti-45Al-7.5Nb and Ti-46A1-9Nb (at.%), and the thermal stability of the resulting microstructure were investigated. Using a quenching dilatometer, a nearly complete massive transformation in Ti-45Al-7.5Nb was found at about 1050°C after annealing at 1305°C for 10min and subsequent cooling with a rate of 55K/s. Higher starting temperatures and higher cooling rates lead to incomplete massive transformation and small transformed areas situated at the grain-boundary triple points of the parent α-grains are observed. By means of EBSD only in one case the same orientation of the close-packed planes of parent α-grains and of massively transformed γM-areas was observed.

The thermal stability of the microstructure of massively transformed Ti-46Al-9Nb sheet material was tested by annealing samples for 1 hour between 400 and 1200°C. Above 800°C a drop of hardness was measured and X-ray diffraction patterns show an increasing separation of (200)γ and (002)γ reflections as expected from a tetragonal γ-TiAl lattice. After annealing at 1100°C α2-phase segregates at grain boundaries and after 1200°C α2-lamellae appear insides the γM-grains parallel to all four {111}γ-planes.

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Correspondence to A. Bartels.

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Bartels, A., Bystrzanowski, S., Chladil, H. et al. Massive Transformation in High Niobium Containing TiAl-Alloys. MRS Online Proceedings Library 842, 31–36 (2004). https://doi.org/10.1557/PROC-842-S5.48

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