Effect of interfacial coatings on mechanical properties of 2.5D Nextel™ 720 fiber toughened zirconia-mullite matrix composites

In this study, 2.5D bent shallow cross-linked structure NextelTM 720 (N720) fiber-reinforced yttria-stabilized zirconia-mullite composites with pyrolytic carbon (PyC) and fugitive pyrolytic carbon (FC) interfacial coatings were prepared by using a precursor infiltration and pyrolysis approach (called as N720f/PyC/YSZ-Mu and N720f/ FC/YSZ-Mu, respectively). The effects of PyC and FC coatings on the failure mechanisms and mechanical properties of the composites were investigated. The N720f/PyC/YSZ-Mu composite shows ductile fracture behavior while the N720f/FC/YSZ-Mu composite shows brittle fracture behavior. The fracture toughness and flexural strength of the N720f/PyC/YSZ-Mu composite reach -7.00 MPa center dot m1/2 and - 120.79 MPa, respectively. In contrast, the corresponding properties of the N720f/FC/YSZ-Mu composite are -3.66 MPa center dot m1/2 and - 59.02 MPa, respectively. Microstructure analysis indicates that the weak PyC interfacial layer contributes to toughening by promoting fiber pull-out and debonding, thus enhancing the mechanical properties of the N720f/PyC/ YSZ-Mu composite. The retrogression of the mechanical properties of the N720f/FC/YSZ-Mu composite originates from the damage to N720 fibers during the preparation procedure. This paper provides a new idea for the development of high-performance oxide CMCs with a 2.5D structure.