P/M Al-8 mass%Fe合金の応力緩和と高温変形機構

Abstract

Stress relaxation tests were carried out for a P/M Al-8 mass%Fe alloy using a lever type creep machine at temperatures from 573 to 673 K. The way to estimate the strain rate just after the start of stress relaxation, \dotεr0, was discussed. The values of \dotεr0 were compared with the strain rate just before the relaxation test(steady-state creep rate), \dotεs, and the work hardening rate, h, and the recovery rate, r, were determined.The relation between the strain rate, \dotεr, and the actual stress of the specimen, (σ−σr), during the stress relaxation test, was almostly linear in a log-log plot except the early stage after the start of stress relaxation. The \dotεr0 was estimated by extrapolating the linear relation to the initial creep stress. The \dotεr0 was usually smaller than the \dotεs, which showed that the contribution of the effective stress to high temperature deformation could be neglected in the present alloy. The h did not depend on temperature and slightly or scarcely decreased with the increase in stress, while it tended to decrease rapidly in the high stress range above a critical stress, that is the Orowan stress. The r, on the other hand, largely depended on stress and temperature, and the activation energy for it was close to that determined from the temperature dependence of the steady state creep rate, \dotεs.Relation between \dotεr and actual stress (σ−σr) during the relaxation tests in the low stress region below the critical stress was very close to one between steady-state creep rate \dotεs and creep stress σc obtained by creep tests at each temperature. It is thought that the internal structure during the stress relaxation is close to one in the steady state creep deformation.