Preparation of Al2O3 coating on Nb fiber and the effect on interfacial microstructure of Nbf/TiAl composite

Abstract

Continuous Nb fiber-reinforced TiAl-matrix composites are a potential structural material to satisfy the service requirements in space industry. However, the premature cracking failure is resulted from the brittle reaction products formed at the interface between Nb fiber and TiAl matrix, which accelerates the structural failure of Nb f /TiAl composite. Fortunately, Al 2 O 3 coating could be introduced on the surface of Nb fiber to tackle the problem. In this study, Al 2 O 3 coating was prepared on the surface of Nb fiber by the cathodic plasma electrolytic deposition (CPED) technology, and then the Al 2 O 3 -coated Nb fibers were used to reinforce TiAl alloy by using vacuum hot-pressing sintering. Furthermore, the influence of the Al 2 O 3 coating on the interfacial microstructure of Nb f /TiAl composite after hot-pressing sintering and thermal exposure was studied. The results show that deposition voltage plays a key role in the microstructure of Al 2 O 3 coating on the Nb fiber. As the voltage increases from 200 V to 400 V, the thickness, density and Al 2 O 3 content of the coating increase. Meanwhile, the bonding between Nb fiber and Al 2 O 3 coating is better when the deposition voltage exceeds 350 V, and the components of Al 2 O 3 -coated Nb fibers prepared from fiber to coating are as follows: Nb/Nb 2 O 5 /Nb 2 O 5 + Al 2 O 3 /Al 2 O 3 . The Al 2 O 3 coating can restrain the formation of the interfacial brittle phases including σ-Nb 2 Al and α 2 -Ti 3 Al during hot-pressing sintering process of Nb f /TiAl composite. In addition, the introduction of Al 2 O 3 coating can reduce the defects in interface, as well as avoid the formation of the crisscrossed and deleterious oxides, which improves interfacial oxidation resistance of the Nb f /TiAl composite. • A uniform and dense Al 2 O 3 coating with a thickness of 4–6 μm can be obtained on Nb fiber surface by CPED technology. • Al 2 O 3 coating can prevent the formation of interfacial brittle phases during the preparation of Nb f /TiAl composite. • Al 2 O 3 coating with excellent thermal stability can avoid the formation of crisscross harmful oxides.