The tensile creep-rupture properties of commercial pure copper were studied in vacuum of 760torr, 660torr, 470torr, 0.3torr and 9×10-3torr at 320°C. The following conclusions were obtained.
(1) The creep-rupture times in both vacuums of 0.3torr and of 9×10-3torr were five and two times larger than that in air, respectively. Therefore, the existence of the effect of vacuum environment was confirmed.
(2) With the decrease from 9×10-3torr to 0.3torr, the coherent oxide film Cu2O was observed on the surface of crept specimen. Besides, the exfoliating film of CuO was observed preferentially with the decrease from 0.3torr to 760torr.
(3) The creep test was interrupted at the time when the total strain reached 7 percent under σn=6.0kg/mm2 in both 9×10-3torr and 0.3torr. It was considered that the remarkable incease of the steady state creep rate in vacuum of 9×10-3torr resulted from the increase of dislocation density or the associated lattice strain on the basis of the measurement of micro strain by the X-ray diffraction technique.