Investigation of interfacial thermal stabilities of Nbf/TiAl composites with and without Al2O3 coating in interface

Abstract

Continuous Nb fiber-reinforced TiAl-matrix composites have tremendous potential for replacing brittle TiAl alloy. However, at elevated temperature, interfacial reaction between fiber and matrix is aggravated, causing instability of the interfacial microstructure and mechanical property of Nbf/TiAl composite. Fortunately, the problem could be solved by introducing fiber coating. Consequently, in this study, Al2O3 coating was prepared on Nb fiber by cathodic plasma electrolytic deposition (CPED) technique. Concurrently, interfacial microstructure changes of the composites were explored during thermal treatment at 1100 and 1200 °C. The results show that, during heat treatment at 1100 °C for up to 100 h, for the composite without Al2O3 coating, the interfacial microstructure changes are as follows: Nb/σ/α2/TiAl→Nb/σ/B2/α2/TiAl→Nb/σ/TiAl, which leads to serious thermal residual stress and cracks in interface. Inversely, the introduction of Al2O3 coating can prevent the formation of brittle σ phase during preparation and the 1100 °C heat treatment. However, under 1200 °C heat treatment, the Al2O3 coating gradually fads away and be replaced by α2-Ti3Al phase. Finally, the interfacial phases including σ and α2 are formed. The existence of the Al2O3 coating can delay the formations of the brittle phases and avoid cracks for a long time, which greatly improves interfacial thermal stability of the Nbf/TiAl composite.