Ti基複合材料ブレードの開発

Abstract

The high specific strength and stiffness of titanium alloy matrix composites (TMCs) with continuous fiber reinforcement are attractive for aerospace structural applications. However, the enormous production cost of TMCs is a serious impediment to their practical applications. One promising approach to reduce the production cost is the application of a superplastic forming technique to TMC parts manufacturing. A series of superplastic-formable TMC sheets, SiC/Ti-4.5Al-3V-2Mo-2Fe (SCS-6/SP-700) composites, were developed, and both their superplastic deformation and the defects generated during this deformation were investigated. The diaphragm-forming method (DFM) was adopted of a superplastic forming technique to reduce the tensile flow stress generated in the TMC sheet during deformation, and using this technique blade-shaped models were successfully fabricated without any observable defects in the fiber/matrix interface. In this study, TMC blades for an aerospace engine have been developed using DFM, and their burst strength was evaluated by a spin test. TMC sheets with 39-ply SCS-6 were formed by DFM and isothermal forging. Two SP-700 root blocks were attached to the deformed TMC by means of vacuum hot pressing. This near-net-shaped composite was machined to the final configuration. While no defects were observed by optical microscopy in the TMC blades, several un-bonded areas were found in the diffusion-bonded interfaces. The configuration of these interfaces was complex, and the plastic deformation of the matrices did not confer sufficient contact between the mating surfaces due to one-directional loading of the pressing. As the result of the spin test, the TMC blades burst at a tip speed of 782 m/s, which was 11% lower than the expected speed based on the material data. The break originated in an un-bonded area.