Fabrication of SiC Fiber Reinforced Titanium Matrix Composites Processed with Sprayed Preforms

A plasma-sprayed preform was newly developed to make the fiber distribution uniform and to improve the cavitation resistance of superplastic-formable titanium matrix composites (TMCs) sheets (SiC/Ti-4.5Al-3V-2Fe-2Mo mass%) during superplastic deformation. The microstructure and tensile strength of the TMCs processed with sprayed preforms (spray composites) were investigated. Sprayed preforms were manufactured by low-pressure-plasma-spraying under an Ar-gas pressure of 0.013 MPa using a matrix alloy powder with a particle diameter of less than 150 μm. The spray composites were fabricated through a foil/fiber/foil process using matrix sheets 0.15 mm in thickness and 4-ply sprayed preforms, and they were consolidated by hot isostatic pressing under an Ar-gas pressure of 150 MPa at 1023 K for 2 h. The sprayed area in the matrix of the sprayed composites consists of three typical structures resulting from the difference in diameter of the powder-particles, which can strongly affect the powder melting conditions. The tensile strength of the spray composite was less than that of TMCs processed with woven preforms (woven composite). This was due to hydrogen embrittlement of sprayed deposits in the spray composite, which had a hydrogen content of 0.0246 mass%. To reduce the hydrogen embrittlement, sprayed preforms were heat-treated in a vacuum at 873 K for 1 h before consolidation. As a result of this treatment, the hydrogen content of the sprayed deposit was reduced to 0.0007 mass%. The tensile strength of the spray composite was also improved, attaining the same strength as that of the woven composites. The tensile strength of the SiC fibers gradually decreased through spraying, heat treatment and consolidation. This, however, did not strongly affect the tensile strength of the spray composite.