Abstract Investigations have been carried out to study the process of strain ageing caused byoxygen in molybdenum by measuring the variation of the height of the internal frictionpeak with ageing-time. It was found that the peak height decreascs gradually and even-tually disappears with ageing-time both in quench-aged and in strain-aged specimens. Ifthe fully aged specimens were re-strained, the peak reappears immediately and its heightis higher than that of the quenched specimen. These processes may be repcatcd if thespecimens were further aged and strained. Systematic studies have been made on the kinetics of strain ageing and on the effectof deformation on the peak height. The results show that (1) the kinetics of strainageing follows Cottrell-Bilby's t~(2/3) relation; (2) the peak height increases with deforma-tion up to about 2.5％, and then decreases; (3) the decrease of the peak height cor-responds to an increase of yield stress. According to the above experimental results, it is believed that the decrease of thepeak height is associated with the segregation of oxygen atoms to dislocations duringageing. On the basis of this assumption, the dislocation density and the atmosphere con-centration were estimated.
