Development of Superplastic-Formable Titanium Matrix Composites

In development of continuous fiber reinforced titanium alloy matrix composites (TMCs) for practical applications there are some difficulties due to the enormous production cost resulting from preliminary forming and elaborate tooling for consolidation. One of the promising approaches to reducing the production cost is to apply a superplastic forming technique in manufacturing TMC parts. In the present study, superplastic-formable TMC sheets, SiC/Ti-4.5Al-3V-2Mo-2Fe (SCS-6/SP-700) composites, were newly developed, and their consolidation conditions, deformation characteristics and cavitation behavior were investigated. The TMCs were fabricated by foil/fiber/foil lamination using SP-700 sheets 0.12 mm in thickness and 4-ply SCS-6 preforms; they were consolidated by hot isostatic pressing under an Ar-gas pressure of 150 MPa at 973 to 1073 K for 2 h. In the case of the TMCs consolidated at a temperature above 1023 K, foil/foil and foil/fiber interfaces were successfully bonded, and their tensile strength at room temperature showed better reproducibility than that in the case of the TMCs consolidated at a temperature below 998 K. In preliminary tensile tests in the direction perpendicular to the fiber orientation at 1048 K, the TMCs consolidated at 1023 K showed a maximum true strain exceeding 69%. Thus, 1023 K was selected as the consolidation temperature. Deformation properties were tested by tensile tests in the direction perpendicular to the fiber orientation under a constant strain of 5×10−5 to 1×10−3 s−1 at temperatures in the range of 1023 to 1073 K. The TMC showed superplasticity with the maximum m-value of 0.58 at 1048 K. A maximum true strain exceeding 69% was achieved under a constant strain of 5×10−5 s−1 at 1048 K. Cavitations observed in specimens after deformation were classified into three types; one of these strongly depends on the forming conditions, but the other two do not. SCS-6/SP-700 composites were successfully bent both in the longitudinal direction and in the transverse direction at 1048 K.