The thermal fatigue behavior of the tantalum alloys T-111 (Ta-8W-2Hf) and ASTAR 811C (Ta-8W-1Re-0.7Hf-0.025C) has been evaluated using completely reversed push-pull fatigue tests conducted in ultrahigh vacuum with independently programmed temperature and strain cycles. Test results showed that cycling of the test temperature simultaneously with the mechanical strain in most cases significantly reduced the cycles to failure of both alloys compared to isothermal testing. Notched specimens had reduced lives under isothermal conditions, but the presence of a notch or use of a 1-h holdtime provided only a small further decrease in life for the temperature cycled tests. Compressive stress at the maximum temperature produced longer lives than tensile stress. ASTAR 811C was more fatigue resistant than T-111 isothermally and did not have as great a decrease in life with thermal cycling. Results are analyzed by partition of plastic strains into creep and creep-independent components and considering where each component was active in the hysteresis cycle.

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.

A high-energy electron scattering study of the electronic structure and elemental composition of Oimplanted Ta films used for the fabrication of memristor devices J. Appl. Phys. 114, 073508 (2013); 10.1063/1.4818524 O K-energy loss near-edge structure change induced by tantalum impurity in monoclinic hafnium oxide

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