Abstract
Strengthening due to the thermo-mechanical treatment (TMT) was examined in the polycrystalline Cu-7.5at%Ni-2.5at%Al alloy. Specimens were solution treated, aged, cold rolled and finally aged. It was found that their mechanical properties were much improved not only at room temperature but at high temperatures up to 500°C, comparing to those simply aged and mechanicothermal treated (MTT: solution treated, cold rolled and finally aged).
Precipitated particles with Ll2 type ordered structure grown during preageing, were sheared by cold rolling. High density of dislocations was introduced. However, sheared particles played an important role to strengthen the alloy. The first notable effect of TMT is to retard recovery of the cold rolled structure extremely in final ageing. In consequence, the deformed structure was kept after final ageing. The second is the growth of precipitated particles with smaller sized and higher density in final ageing, which were formed from sheared particles and nucleated in the matrix. Excess vacancies introduced by cold rolling would accelerate the growth of particles.
Strengthening in the TMT specimens is considered to be attributed to the random dispersion of a large number of small sized particles and the existence of high density of dislocations.
