PERITECTIC OSCILLATIONS IN DIRECTIONALLY SOLIDIFIED Ti-52at%Al

This study investigates the phenomenon of peritectic oscillations in a Ti-52at%Al alloy, which exhibited banded segregation perpendicular to the growth direction during directional solidification under planar interface conditions. The primary objective was to elucidate the mechanisms responsible for the observed microstructural features, which were characterized by alternating solid phases of a and y, indicating cellular instability. A combination of arc melting for alloy formation and advanced directional solidification techniques, including containerless levitated zone melting, were employed to achieve high purity and controlled conditions. Analysis revealed that the microstructure's banding resulted from oscillatory variations in composition throughout the solidification process, signifying a peritectic transformation from a + L to y. Results demonstrate that the 52at%Al composition was hypoperitectic, suggesting critical insights into the high temperature phase relationships of near equiatomic Ti-Al alloys. The findings from this investigation enhance the understanding of alloy behavior during solidification, with implications for the production of high-performance TiAl single crystals.