A modified alloy, known as Modified PWA1484, is a single-crystal nickel-base superalloy, developed under a NASA Marshall Space Flight Center contract for use as a turbine blade and vane alloy for the space-shuttle main engine(SSME). This alloy is a modified PWA 1484 composition that uses innovative thermal-process techniques to generate a microstructure specifically tailored for SSME application. The superalloy exhibits significantly better fatigue and crack-growth resistance than previous turbine-blade alloys (such as PWA1480), particularly under severe hydrogen-embrittling conditions.

When compared to the conventional alloy PWA1480, Modified PWA1484 had a high cycle fatigue life that is 100 times greater than PWA1480. Fatigue strength for the new single-crystal nickel-base superalloy was approximately 30 ksi (207 MPa) higher than the previous turbine-blade material.

Modified PWA1484 has significantly better fatigue resistance in the critical near-threshold region of the fatigue-crack-growth curve than conventionally used material.

In other tests, the smooth low cycle fatigue life for PWA1480 was compared to the Modified PWA1484. Fatigue life for the superalloy was more than an order of magnitude greater than PWA1480.

Additionally, this single-crystal nickel-base superalloy was compared against PWA1480 in notched low cycle fatigue. Modified PWA 1484 proved to be 3 to 10 times greater than PWA1480 in notched low cycle fatigue.

When tested for fracture resistance, the Modified PWA 1484 was significantly better in the critical near-threshold region of the fatigue-crack-growth curve than PWA1480. (The results of this test can be seen in the illustration.)

These comparisons show that alloys, such as this single-crystal nickel-base superalloys, will provide better turbine blades and vanes for space-shuttle components, such as high-pressure fuel and oxidizer turbopumps.

This work was done by Daniel P. DeLuca, Charles M. Biondo, and Barrie J. Peters of United Technologies Pratt & Whitney for Marshall Space Flight Center. MFS-31203


NASA Tech Briefs Magazine

This article first appeared in the June, 1998 issue of NASA Tech Briefs Magazine.

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