P/M Al-8 mass%Fe合金のクリープ変形機構

Abstract

High temperature tensile tests and creep tests were carried out for two kinds of P/M Al-8 mass%Fe alloy specimens with different grain sizes. The stress and temperature dependences of minimum creep rate and the effect of grain size on them were examined, and the creep curves were analyzed by using the θ-projection method.The minimum creep rate increased rapidly with stress in the high stress range above a critical stress. The critical stress did not depend on the test temperature and depended on the heat treatment of specimen. It was nearly equal to the room temperature yield stress of the specimen which was taken to correspond to the Orowan stress. The activation energy of the minimum creep rate was nearly equal to that of the self diffusion of Al, Qd, in the high stress range above the critical stress. It was, however, higher than the Qd in the lower stress range than the critical stress, showing that the creep deformation in the low stress range was affected by the diffusion creep or grain boundary sliding mechanism while the dislocation creep was still dominant.The creep curves were well described by the θ-projection method. The θ parameters characterizing each creep curve showed generally different stress and temperature dependences below and above the critical stress. For example, strain parameter θ1 for primary creep was nearly constant independent of the temperature and stress below the critical stress, while it increased with stress above the critical stress. The activation energy of rate parameter θ2 for primary creep was about equal to that of the self diffusion of Al, Qd, above the critical stress, while it was lower than the Qd and rather closer to that of the grain boundary diffusion below the critical stress.