No abstract

No abstract

No abstract

SUMMARYSeveral Cb, Ta, Mo, and W base alloys have been creep tested with both constant and continuously increasing loads in a vacuum environment of < 1~1 0 -~ t o r r at temperatures and stresses chosen to provide between 1/2 and 1 percent creep i n times up to 20 000 hours. Isostatic design data a r e presented in the form of a.Larson-Miller plot for 1/2 o r 1 percent creep life for each of these refractory alloys. Elevated temperature tension test data from the tantalum base alloy T-111 showed a strain aging reaction in the 1400' to 2200' F (760' to 1204' C) range which produced an unusual transient creep behavior. Analysis of the isostatic steady state creep data for this material showed that the minimum creep rate can be described by the expression 5 of13. 17,-90 000/RT ?-in the temperature and stress ranges of 1600' to 2600' F (870' to 1427' C) and 500 to 45 000 psi ( 0 . 3 4~1 0~ to 31. OX107 N/m2). These values of activation energy and s t r e s s exponent suggest that the isostatic steady state creep of T-111 is governed by a diffusion controlled microcreep mechanism rather than by nonconservative dislocation motion. The creep tests which were run on T-111 alloy with continuously increasing loads provided continuously increasing creep rates which were comparable to the isostatic steady state creep rates at equivalent s t r e s s levels.Methods have been developed for prediction of the 1 percent creep life under varying s t r e s s conditions from isostatic creep test data, and comparison of these predictions with the experimental results shows the dependence of analytical techniques on the character of the isostatic creep curves.Based on work done under NASA contracts NAS 3-2545 and NAS 3-9439.

No abstract