Titanium alloys and titanium aluminides are being considered as key materials for the manufacture of lightweight compressors and turbines in modern aircraft and rocket engines. The joining technology that provides reliable work above 930°F (500°C) is needed to fabricate functional turbine components. Only then, the full high-temperature strength capabilities of TiAl alloys and titanium matrix composites can be exploited. Two filler metals were tested for brazing heat-resistant joints at 2156-2190°F (1180-1200°C): TiBraze 1200 (Ni-27Ti-10Al) and TiBraze 375 (Ti-37.5Zr-15Cu-10Ni) in the form of transfer tape. Microstructure and shear strength of the brazed joints were studied at 1000, 1200, and 1470°F (540-800°C). Brazing at the temperature substantially above the liquidus of the filler metals resulted in a noticeable gain of both the high temperature and room temperature strengths. Joints of hot-pressed titanium aluminide brazed by Ti- 37.5Zr-15Cu-10Ni filler metal exhibited shear strength at 1470°F (800°C) as high as 41.6- 47.3 ksi (287-326 MPa) and 63-68 ksi (435-469 MPa) at 1200°F (650°C). Some other methods for improving hot strength of titanium-based alloys are also discussed, particularly: (a) application of composite filler metals and (b) pre-coating of surfaces to be brazed to prevent early oxidation and promote wetting.
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