Steadyhyphen;state flow stress of dense (99percnt; of theoretical) polycrystalline YBa2Cu3O7minus;dgr;has been measured in direct compression at temperatures between 870 and 980thinsp;deg;C in oxygen partial pressures of 0.03, 0.18, and 1.0times;105Pa for strain rates between 5times;10minus;6and 4times;10minus;5sminus;1. The stress exponent was close to one, indicating that diffusional flow was the dominant deformation mechanism. The flow stress decreased with decreasing oxygen partial pressure, obeying a power law with an exponent of approximately 1/2 . The activation energy was about 800 kJ/mol at an oxygen partial pressure 1times;105Pa, but decreased to 600 kJ/mol at a pressure of 3times;103Pa.
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