Abstract
In this paper the creep behavior and the microstructural stability of Ti-46Al-9Nb (in at.%) sheet material were investigated in the temperature range of 700°C to 815°C. The study involves three different types of microstructure, namely fully lamellar with narrow lamellar spacing, duplex and massively transformed. Short-term creep experiments conducted at 700°C and 225 MPa confirmed that the lamellar microstructure with narrow lamellar spacing exhibits a much higher creep resistance when compared to the massively transformed and duplex ones. During long-term creep tests up to 1500 hours stress exponents (in the range of 4.4 to 5.8) and apparent activation energies (of about 4 eV) have been estimated by means of load and temperature changes, respectively. Both, stress exponents and activation energies suggest that under the applied conditions diffusion-assisted climb of dislocations is the dominant creep mechanism. The thermal stability of the different microstructures under various creep conditions has been analyzed by electron microscopy and X-ray diffraction. Our investigations revealed considerable stress and temperature induced microstructural changes which are reflected in the dissolution of the α2 phase accompanied by precipitation of a Ti/Nb - rich phase situated at grain boundaries. This phase was identified as a co-related phase with B82-type structure. It was shown, that in particular the duplex microstructure is prone to such microstructural instabilities.
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Acknowledgments
The authors thank Dr. H. Kestler, Plansee AG, Austria, for supplying the sheet material.
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Bystrzanowski, S., Bartels, A., Clemens, H. et al. Creep Behavior and Microstructural Stability of Ti-46Al-9Nb with Different Microstructures. MRS Online Proceedings Library 842, 477–482 (2004). https://doi.org/10.1557/PROC-842-S7.12
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DOI: https://doi.org/10.1557/PROC-842-S7.12