ANOMALOUS HIGH TEMPERATURE CREEP BEHAVIOUR OF AN Al-8.5Fe-1.3V-1.7Si (8009Al TYPE) ALLOY REINFORCED WITH ALUMINA SHORT FIBRES

摘要

Creep in an Al-8.5Fe-1.3V-1.7Si (8009A1 type) alloy dispersion strengthened with fine Al_(12)(Fe,V)_3Si phase particles (Alloy in the following) at temperatures 798-848 K is not associated with a true threshold and the same holds for the Alloy reinforced with alumina short fibres (Composite in the following). While the true activation energy of creep in the Alloy is higher than the activation enthalpy of lattice self-diffusion in aluminium due to the energy of athermal detachment of dislocations from dispersed particles, this is not the case of the Composite. The true activation energy of creep in the latter is anomalously low and the creep behaviour cannot be described by the creep equation that holds for the Alloy, but contains the factor by which the flow stress in the dispersion strengthened matrix is reduced due to load transfer. Nevertheless, the creep strength of the Composite is, at the certain conditions at least, by a factor up to six orders of magnitude higher than that of the Alloy. This creep strength increment due to alumina short fibre reinforcement is accounted for in terms of the load transfer effect.