Microstructure, mechanical and tribological performances of a directionally solidified γ-TiAl alloy

Abstract

In the present study, Ti-47Al-2Nb-2Cr-2Mn directionally solidified by electromagnetic cold crucible was mainly composed of alternatively arranged (α 2 + γ) lamellae, and exhibited a room-temperature tensile ductility of 1.55%, and an ultimate strength of 587 MPa. At 800 °C ultimate strength remained high at 512 MPa, with 4.33% ductility. The crack propagated around B2 phase at room temperature, but cut though B2 phase at elevated temperature. Both dislocation slip and twinning governed the room-temperature plastic deformation, and the twin boundary acted as the obstacle to dislocation slip. The friction coefficient of the N-orientation (70°-90°) TiAl sample was the highest, followed by the I-orientation (35°-50°) and P-orientation (0°-15°) samples, while their wear rates presented an opposite trend. The P-orientation sample was more liable to form the tribo-oxide layer. Moreover, the local plastic deformation during dry sliding resulted in pile-ups along the edge of wear tracks. • Cracks bypass (room temperature) and cut through (elevated temperature) B2 phase. • Dislocation- and twinning-controlled deformation mechanisms at room temperature. • Lowest friction coefficient and highest wear rate for P-orientation sample. • Tribo-oxide layer preferentially formed in P-orientation sample.