Microstructural Characterization of Ti-44Al-11Nb in the Chill-Cast and Directionally Solidified Configurations
NAVAL POSTGRADUATE SCHOOL MONTEREY CA DEPT OF MECHANICAL ENGINEERING
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The microstructural evolution in chill-cast and directionally solidified Ti-44Al-11Nb at. was studied by x-ray diffraction XRD, scanning electron microscopy SEM, and transmission electron microscopy TEM methods. From this data, the microstructural distribution and formation sequences of various phases like Al3Ti, TiAl, and Ti3Al were established. The elemental and phase distributions were determined by TEM with energy dispersive x-ray spectroscopy EDX and spectrum imaging. Both casting techniques produced the same phases, Al3Ti, TiAl, and Ti3Al with some Nb in solid solution, but the microstructural distribution was markedly different. The chill-casting technique resulted in a coarser microstructure, with large gamma crystals and duplex regions of either gamma alpha2 or gamma Al3Ti interspersed throughout the alloy. The directional solidification technique resulted in a much more uniform microstructure with fine lamellar grains in a dendritic macrostructure. Both casting techniques showed enrichment of niobium in interdendritic regions.
- Metallurgy and Metallography