Abstract
Some recent results obtained investigating creep behaviour of discontinuous aluminium and aluminium alloy matrix composites, i.e. aluminium and/or aluminium alloys reinforced by silicon carbide particulates or short fibres and processed by powder metallurgy are overviewed with the aim to get better understanding of some characteristic features of this behaviour. The creep behaviour of the composites under consideration is primarily affected by fine alumina particles generally present in the matrix of any aluminium and aluminium alloy matrix composite processed by powder metallurgy. The known potential mechanisms of surpassing these fine incoherent particles by dislocations are briefly discussed. The most likely mechanism involving athermal detachment of dislocations from such particles is discussed with respect to the experimental fact that the true threshold stress decreases with increasing temperature more strongly than the shear modulus. In this context, disappearance of the true threshold stress at high creep testing temperatures is illustrated by some experimental results and interpreted in terms of a transition from the athermal to the thermally activated detachment of dislocations from interacting particles. Further, such topics are discussed as the relation between the true stress exponent and the true threshold stress, the role of simultaneously acting load transfer effect and the threshold effect and, especially, the possible origin of temperature dependence of the relaxation factor characterizing the strength of dislocation/fine alumina particle interaction.

Key words
discontinuous composites, aluminium matrix, fine alumina particles, creep behaviour, threshold stress, load transfer effect

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