Interfacial optimization by CPED coating for improving mechanical properties of Nbf/TiAl composite

Abstract

Continuous Nb fiber-reinforced TiAl-matrix (Nbf/TiAl) composites with low density and excellent high temperature performance has been considered as a potential structural material to satisfy the service requirements in space industry. However, premature cracking failure caused by serious interfacial reaction (forming brittle phases and micro-crack) in the interface accelerates the failure of the composite. Depositing the inert coating on the Nb fiber surface could reduce and even prevent the interfacial reaction, improving the interfacial structure between Nb fiber and TiAl matrix. In this work, an efficient coating technology, cathodic plasma electrolytic deposition (CPED), was utilized to deposit Al2O3 coating on the Nb fiber surface, which successfully prevented the brittle phases formation at the interface between Nb fibers and TiAl matrix. The reliable and simple interface composed of Nb/Al2O3/TiAl was prepared through the careful adjustment of CPED parameters. The high-strength interface ameliorated the stress distribution, especially increasing the stress borne of Nb fibers by 40 % during the loading process. As a result, the optimized interface avoided premature cracking in interfacial region at initial loading stage and promoted the crack deflection and bifurcation at the overall deformation. Finally, the fracture toughness of the composite after interfacial optimization is increased by 30 % than that of without coating and 70 % than that of TiAl matrix. The above findings validate the feasibility of CPED technology in regulating the interface structure of composite materials, and provide a new method for interface structure design.