High-Temperature Creep Behavior of a Columbium Alloy, FS-85
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION CLEVELAND OH LEWIS RESEARCH CENTER
Pagination or Media Count:
Creep tests of 1000 hours duration and greater were conducted in the temperature range 20000 to 22000 F on a commercially available columbium alloy FS-85 in vacuum units designed and built to achieve ultimate pressures of 10 torr. At a stress level of 10 000 pounds per square inch, FS-85 exhibited moderate creep resistance at 2000 F, 1-percent strain being achieved in 775 hours. At 21000 and 22000 F and the same stress level, the alloy was much weaker, 1-percent strain being achieved in 355 and 50 hours, respectively. The Manson-Haferd linear time-temperature parameter proved moderately successful in predicting the long-time creep lives from relatively short-time creep data, the maximum error between predicted and experimental lives being a factor of 1. 7 and the average error being a factor of 1. 3. The agreement is considered good in view of the large scatter generally observed in long-time high-temperature creep tests. In all cases, however, the observed experimental life was shorter than the predicted life. The nonconservative nature of these predictions may be due in part to the fact that the predictions were based on data obtained at a pressure level of approximately to 10 -6 torr, but the long-time tests to which the predictions are compared were made at a lower pressure level, 10 -8 to 10 -9 torr. Creep tests conducted in the conventional-vacuum units 10 -6 torr and the ultrahigh- vacuum units under the same conditions of temperature and stress yielded creep curves that are virtually identical for the first few hundred hours but that deviate with increasing test time. The conventional-vacuum tests then showed a reduced creep rate compared with that of the ultrahigh-vacuum tests.
- Properties of Metals and Alloys