High Frequency Fatigue Properties of TZC and T-111 Alloys.

Abstract

High frequency fatigue tests were conducted in an ultrahigh vacuum environment on recrystallized mqlybdenum base alloy TZC and tantalum base alloy T-111 at temperatures between 1800' and 2200' F (982' and 1204' C). The results indicated that in this temperature range no well-defined endurance limit existed for either material. At A ratios of 0.45, fatigue strengths a t 2000' F (1093' C) and lo9 cycles were as low as 16 000 psi (1 1. 0~1 0~ N/m2) for the TZC and 34 000 psi (2 4. 8~1 0 N/m2) for the T-111. The application of a cyclic load to a staticallyloaded specimen produced a marked acceleration in the degree of specimen extension. In both the TZC and T-111 alloy the increase was characterized by a relatively rapid first stage creep extension (on the order of 1 to 10 percent) compared to the very small extensions (less than 0. 0 1 percent) observed at the same temperatures and peak stresses in the isostatic creep tests. In the TZC alloy the dynamic loading increased the steady state creep rate by approximately two orders of magnitude; however, this acceleration w a s not observed for the T-111 alloy. Possible reasons for this behavior a r e discussed in t e r m s of previous observations concerning the isostatic creep behavior of these materials.