Fabrication and deformation behavior of a novel laminated TiAl matrix composite

Two-phase titanium aluminides are desirable for a wide range of high-temperature structural applications for their excellent thermo-physical properties. In this paper, a novel laminated TiAl matrix composite (LMC) consisting of alternating equiaxed grain layers (EGLs) and fully-lamellar grain layers (FGLs) has been fabricated successfully by hot-pressing and subsequent reaction annealing. After microstructure tailoring, the LMC exhibited a good combination of strength and ductility at 850 degrees C. Experiments demonstrated that the thermal residual stress induced by the fabrication process had a periodic distribution across the layers. The competition between residual stress and externally applied stress changed the stress state and accordingly the Ti3Al twining was activated, which benefited the accommodation of the incompatibility between alternating constituent layers. The crack tolerance was remarkably improved by layered structure in the LMC. Crack initiation occurred mainly in either the EGLs or the layer interface. However, they were constrained effectively by the laminated structure. Instead, these dense microcracks may relief the stress concentration and improve the deformation stability. This work is expected to enrich the current understanding on the stress-mediated deformation behavior of TiAl alloys, and provide guidance towards design of high-performance intermetallic laminated composites.

Automated summary

Two-phase titanium aluminides are favored for high-temperature structural applications due to their excellent thermo-physical properties. In this study, a novel laminated TiAl matrix composite (LMC) has been fabricated, exhibiting a good combination of strength and ductility at 850 degrees C. The thermal residual stress induced by the fabrication process has a periodic distribution across the layers, affecting the stress state and twining behavior of Ti3Al.