抄録
Age-hardening of some high purity Cu–Be binary alloys has been studied and the hardening curves were classified into three distinct types: Type-1, Type-2 and Type-3. As the low temperature ageing process can be clearly distinguished from the high temperature ageing process in such binary alloys, two C curves are obtained corresponding to the respective processes.
Complete reversion of hardness was found to occur, if the hardening process prior to the reversion treatment remains within the zone formation stage. The reversion temperature corresponds to the lower temperature limit, above which the Type-3 ageing, i.e. purely high temperature ageing, will occur, as shown in Al–Cu alloys by Beton and Rollason. This occurrence of reversion was confirmed by means of transmission electron microscopy and a selected-area diffraction technique.
The reversion temperature of the G. P. zone determined from this experiment is found to be raised with increase in solute concentration than that in the case of Al–Cu alloys (430°∼450°C for 1.91 wt% Be and, 330°∼380°C for 1.64 wt%Be alloy).
Reageing after reversion was also investigated which occurs at a much slower rate within the zone formation stage (Type-1 and the early stage of Type-2) because of the remarkable decrease in the number of quenched-in vacancies, but the reduction in rate was found to be much less in the stage of high temperature ageing (Stage-2).
The effect of Fe, Al, Si and Co has also been studied. Among these, Co was found to be most effective in retarding the zone formation. This seems to be the cause of the difference between the ageing behaviours of those binary alloys and commercial beryllium copper.
