Microstructures and mechanical properties of a multi-phase β-solidifying TiAl alloy densified by spark plasma sintering

This work deals with the densification of TNM alloys by spark plasma sintering. Pre-alloyed powders with composition Ti–43.9Al–4Nb–0.95Mo–0.1B (at.%) were sintered between 1237 and 1429 °C, applying a pressure of 100 MPa. The microstructures of the alloys were studied by scanning electron microscopy and transmission electron microscopy. Tensile tests at room temperature and creep experiments at 700 °C and 300 MPa stress were performed. Post-mortem analyses of deformed samples were also carried out by transmission electron microscopy to explain the mechanical properties. Duplex, nearly lamellar and so-called β microstructures were obtained as a function of the sintering temperature. Attention is focused on the nearly lamellar microstructure. This type of microstructure is composed of small lamellar α2/γ-colonies, which are surrounded by γ + β0 intercolony borders. It exhibits very strong creep resistance associated with moderate ductility at room temperature. It is demonstrated that the use of β solidifying alloys during SPS is an efficient way to reduce the size of the lamellar microstructure. Finally, the mechanical properties obtained are explained in terms of the characteristics of this microstructure.

(a) Nearly lamellar microstructure formed by small lamellar grains surrounded by extended non-lamellar intercolony borders. (b): Creep curves at 700 °C and 300 MPa, showing exceptional low creep rate and long life time. (c): Deformation microstructure in a border after a tensile test performed at room temperature.Figure optionsDownload high-quality image (101 K)Download as PowerPoint slide