A γ titanium aluminide alloy produced by a powder-metal (PM) process, and techniques for fabricating sheets and sheet-metal components from the alloy, have been developed. The alloy and techniques, used together, are expected to satisfy a need for relatively economical manufacture of lightweight, high-temperature-resistant components of propulsion systems, control surfaces, and general structures of advanced aircraft and spacecraft. The specific strength of the alloy is similar to the specific strengths of superalloys, while its specific stiffness is greater and its density is smaller. For applications in the temperature range of 500 to 800 °C, this alloy can be used in place of superalloys, thereby making it possible to reduce weights of components by as much as 50 percent.
The composition of the alloy is Ti- 46.5Al-4(Cr-Nb-Ta)-0.1B. This is the same composition as that of an ingot-metal (IM) alloy used previously in a forging process. The manufacture of parts by the prior IM-based forging process was inhibited by (1) limitations, inherent in the process, on the sizes (including thicknesses) of sheets; (2) inconsistency of properties among sheets; and (3) high cost — ≈$104/lb (≈$2.2 × 104/kg) [prices as of year 2000]. In contrast, it has been estimated that it will soon cost only ≈$150/lb (≈$330/kg) to manufacture parts by use of this PM alloy and the associated fabrication techniques. Even in comparison with other titanium alloys, the weights of components made of this alloy can be 15 percent lower.
The PM-based process can be summarized as follows:
- A powder mixture of the required composition is consolidated into a pre-material blank. In the prior IMbased process, the consolidation step included hot isostatic forging and resulted in a 50-percent rejection rate. In contrast, the PM consolidation step results in a nearly zero rejection rate.
- The top and bottom of the blank are machined parallel.
- The blank is canned, rolled, and decanned.
- The blank is ground to final thickness.
One of the techniques developed in conjunction with this alloy and the aforementioned process is a sheet-rolling technique that makes it possible to produce sheets of the alloy at relatively low cost. Another technique is one of relatively-low-temperature hot forming that eliminates (relative to a prior hot-forming technique) the need for hot presses in environmental chambers. Also developed were innovative brazing (see figure), transient-liquid-phase bonding, and laser welding techniques. The combination of these developments makes it possible to fabricate components ranging from turbine blades 1 in. (≈2.5 cm) long to hot propulsion-system ducts as long as 30 ft (≈9 m).
This work was done by Paul Bartolotta of Glenn Research Center, Gopal Das of Pratt & Whitney, Heinrich Kestler of Plansee Aktiengesellschaft, and Rob LeHolm of B. F. Goodrich Co.
Inquiries concerning rights for the commercial use of this invention should be addressed to
NASA Glenn Research Center,
Commercial Technology Office,
Attn: Steve Fedor,
Mail Stop 4–8,
21000 Brookpark Road,
Cleveland, Ohio 44135.
Refer to LEW-17173.