Further observations on the effect of repeated pressurization on yielding and brittleness

Abstract

The yield point in Armco iron and brittleness in chromium are removed by a hydrostatic pressure treatment at ∼ 10 kbars, but return after ageing at temperatures where solute can diffuse; a further treatment at the same pressure does not have the same effect as the initial pressurization (Bullen et al. 1964 a). Observations described herein support the previous interpretation that dislocations form at inclusions but do not all run back on removal of the pressure. Tests in which the ageing temperature between pressurizations is varied indicate that these dislocations are trapped by the friction stress. Re-pressurization at increased pressure after ageing has the same effect as the initial pressurization; the observations suggest that the number of particles which can generate dislocations increases rapidly with increasing pressure.