The microstructure characteristics and mechanical properties of Al2O3 coated TiNb fibers reinforced TiAl matrix composites

The Al2O3 coating on continuous TiNb fiber can effectively suppress the interfacial reaction in TiNbf/TiAl composites. Some phase transitions in fiber have been founded and their formation reason was analyzed. The micromechanical properties of each phase and macroscopic mechanical properties of the composites were also systematically studied. The α+β duplex structure exhibiting texture feature was found in the most regions of TiNb fiber. Meanwhile α+δ layer, σ layer, outer α layer, and β layer would be formed respectively within 10 μm of the fiber surface whose formation reasons were explained from thermodynamics dominated by Al element. Nanoindentation tests indicated the deformation capacity of each phase satisfied: β>δ>σ>α (outer)>α (inner)>Al2O3 coating. The composite with coated fibers has excellent fracture strength of 498 MPa and the fracture toughness of 18.72 MPa m, which was benefited from the fine grain strengthening and precipitation strengthening mechanisms. The Al2O3 coating can significantly improve the thermal stability of the composites during thermal exposure below 1250 °C, and keep the mechanical properties from degradation. This work is of great significance for understanding the phase transformation and deformation process of innovative Al2O3 coated TiNb fiber reinforced TiAl matrix composites.