Creep of discontinuous aluminium alloy matrix composites produced by powder metallurgy route

摘要

Some recent results obtained investigating creepbehaviour of discontinuous aluminium and aluminium alloymatrix composites, i.e. aluminium and/or aluminium alloysreinforced by silicon carbide particulates or short fibres andprocessed by powder metallurgy are overviewed with the aim toget better understanding of some characteristic features of thisbehaviour. The creep behaviour of the composites underconsideration is primarily affected by fine alumina particlesgenerally present in the matrix of any aluminium and aluminiumalloy matrix composite processed by powder metallurgy. Theknown potential mechanisms of surpassing these fine incoherentparticles by dislocations are briefly discussed. The most likelymechanism involving athermal detachment of dislocations fromsuch particles is discussed with respect to the experimental factthat the true threshold stress decreases with increasing temperaturemore strongly than the shear modulus. In this context,disappearance of the true threshold stress at high creep testingtemperatures is illustrated by some experimental results andinterpreted in terms of a transition from the athermal to thethermally activated detachment of dislocations from interactingparticles. Further, such topics are discussed as the relation betweenthe true stress exponent and the true threshold stress, the role ofsimultaneously acting load transfer effect and the threshold effectand, especially, the possible origin of temperature dependence ofthe relaxation factor characterizing the strength of dislocation/finealumina particle interaction.