EFFECT OF OXYGEN ON CREEP-RUPTURE OF NIOBIUM.
NAVAL RESEARCH LAB WASHINGTON D C
Pagination or Media Count:
The creep-rupture properties of electron-beam-melted niobium with additions of oxygen up to 0.35 weight-percent were determined at 1900F 1038C, 2300F 1260C, and 2600F 1427C at vacuums of 1 x .00001 torr or better. Rupture life generally increased and minimum creep rate decreased as the level of oxygen was raised. There was no deleterious effect on ductility even with the high oxygen additions. Increases in hardness as a function of cold work and oxygen content were obtained. Activation energies for high-temperature creep were determined which showed good agreement with the reported experimental activation energies for self-diffusion. At 1900F, but not at 2300 and 2600F, an anomalous behavior occurred which was manifested by a rapid acceleration followed by a deceleration in the flow process. The irregularity, which is represented as a step in the creep curve, occurs only under certain combinations of temperature, stress, and oxygen content. It appears to be related to substructure formation, and not to recrystallization or grain growth. Author