Thermal fatigue behaviour of a 2014/Al2O3-SiO2 (Saffil (R) fibers) composite processed by squeeze casting

Thermal fatigue behaviour of a 2014/Saffil composite has been investigated. This composite was produced by infiltration of preforms of Saffil fibers ( Al2O3-SiO2 fibers) with a 2014 aluminium alloy (Al-4.7Cu-1.0Si-0.6 Mg). The composite samples, containing 13 vol.% of fibers, were sectioned and their microstructure was investigated by optical microscopy, scanning electron m icroscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and X-ray diffr action (XRD). Tensile tests, hardness and microhardness measurements were c arried out. The fracture surfaces were examined by SEM. Dilatometry was use d in order to measure the thermal expansion coefficient (CTE) and to evalua te the strength of matrix/fiber bonds. Thermal cycling tests were performed on specimens (either as fabricated or in the T6 temper) in the temperature range between 25 and 220 degrees C. Af ter 1000 cycles both the microstructure and the mechanical characteristics of the composite samples were investigated. The thermal fatigue resulted in a damage of the composite because of the partial fragmentation of the fibe rs. in addition, other phenomena involving the modification of composite ma trix microstructure, such as over-aging of T6 treated samples and precipita tion of strengthening phases within the matrix of as-cast samples, were obs erved. Thermal cycling also resulted in interfacial matrix/fiber reaction, which probably strengthened the composite and caused a CTE decrease. All th ese phenomena concurred to change both tensile behaviour and material hardn ess. (C) 2000 Elsevier Science S.A. All rights reserved.