A Study on the Orientation Relationship and Interface Structure of the α2 (Ti3Al) and B2 Phases in the TiAl-Nb Sheets After Heat Treatment

In this paper, TiAl-Nb sheets were fabricated via elemental foil metallurgy using Ti, Al, and Nb foils. The microstructure of the TiAl-Nb sheet was regulated by a two-step heat treatment process, which involved short-time holding at 1410 °C, 1430 °C and 1450 °C, followed by long-time holding at 1150 °C. Subsequently, the microstructure of the sheet was analyzed, emphasizing the orientation relationship and interface structure between the B2/β phase, Ti3Al phase, and the TiAl matrix. The results indicated that, subsequent to diverse heat treatment processes, the TiAl-Nb sheet comprised α2(Ti3Al) and B2/β phases at the grain boundaries and within the grains, whereas the matrix structure was γ(TiAl). After TiAl-Nb sheets were heat-treated at 1410 °C for 3 min and then at 1150 °C for 2 h, the microstructure of the sheets was observed to be composed of relatively fine lamellar structures. The TiAl phase, Ti3Al phase and B2/β phase existed in the form of coherent interfaces with extremely small misfit degrees. The interfacial energy between phases was small, making it easier to obtain an alloy microstructure with a higher content of the γ(TiAl) phase. To further provide a basis for the selection of heat treatment processes, the matrix method analysis indicated that, after holding at 1410 °C for 3 min and subsequently at 1150 °C for 2 h, the TiAl phase and Ti3Al phase in the sheet structure exhibited obvious preferred orientations. A short β-phase holding (3 min) followed by a long α + γ two-phase holding was an effective process route for obtaining a fine lamellar structure.