[Isothermal ordering process and order-hardening in CuPd alloys (author's transl)].

Abstract

The isothermal ordering process in CuPd alloys containing 34.74 approximately 50.22 at % Pd was investigated by means of electrical resistivity measurements, X-ray diffraction, metallographic observations and hardness tests. The ordering mechanism and the order-hardening mechanism were discussed. Ordering in the alloys which are in the region of beta (ordered) single phase in equilibrium phase diagram, apparently occurred through single process, and the ordering rate was very high. On the other hand, ordering occurred through two processes (stage I and II) in the case of the alloys in which ordered and disordered phases, i.e. beta and alpha phases coexist, and the ordering rate was low. Ordering was attained by discontinuous ordering mechanism in both regions. Considering the value of activation energy for ordering and results of metallographic observations, it is suggested that the ordering is attained by grain boundary diffusion both in the beta single phase region and in stage II of the (alpha + beta) two phased region. It can be also interpreted that the order-hardening in these alloys is attributed to the increase of volume fraction of beta phase in both regions.