Effect of Al 2 Ti Phase on Plastic Behavior in Ti-62.5at%Al Single Crystals
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Effect of A12Ti Phase on Plastic Behavior in Ti-62.5at%Al Single Crystals Takayoshi Nakano, Koutarou Hayashi, Keishi Ashida and Yukichi Umakoshi Department of Materials Science and Engineering, Graduate School of Engineering, Osaka University, 2-1, Yamada-oka, Suita, Osaka 565-087 1, Japan ABSTRACT The microstructure and plastic deformation behavior in Ti-62.5at.%Al single crystals were investigated focusing on effect of the formation of h- and r-AI2Ti precipitates. Crystal structure, morphology and volume fraction of the precipitates depended strongly on the annealing temperature. The r-A12Ti phase precipitated as a plate in the Li 0 matrix containing A15Ti3 superstructure below 1200'C, while the h-Al 2Ti phase appeared at the higher temperature. The r-A12Ti had six-fold periodicity along the c-axis of the L10 structure and formed a semi-coherent boundary with the matrix maintaining an orientation relationship with {101)r.AM //{ 101)l0 . In contrast, small particles of h-A12Ti with three-fold periodicity along the baxis were homogeneously distributed in the matrix forming an obscure coherent phase boundary. Yield stress for specimens with a [201] loading axis anomaly increased showing a maximum peak around 800'C and then rapidly decreased. f111 }
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