THERMAL FATIGUE OF INTERPENETRATING C/AL COMPOSITES

摘要

We produced interpenetrating graphite/aluminium composites by pressure infiltration of aluminium-silicon alloys into microporous graphite preforms. Infiltration with the AlSi7Ba alloy significantly increases the flexural strength and fracture toughness of the composites, resulting in values of up to 120 MPa and 1.93 Mpam{sup}0.5, respectively. After thermal cycling, a slight reduction in the mechanical properties for graphite/AlSi7Ba composites is observed, mainly due to precipitation reactions and silicon phase coarsening. No deterioration of mechanical properties is measured for graphite/AlSi12 composites. Due to the large mismatch in the coefficients of thermal expansion of the constituent phases, stress relaxation processes in combination with an increase in the sample's length occurred after thermal cycling. We show that the electrical conductivity is highly sensitive to damage evolution within the metallic phase. Independent of the infiltrated alloy, void formation in the highly conducting metal phase causes electrical conductivity to deteriorate after thermal cycling.