A study on thermal shock response of Al-Al2O3 micro- and nanocomposites

Abstract

Metal matrix composites (MMCs) combine metallic properties (ductility and toughness) with ceramic properties (high strength and modulus) leading to greater strength in shear and compression and to high service temperature capabilities. The supercritical applications of these metal matrix nanocomposites necessitates their study with respect to service conditions. The service exposures of structural components encompass thermal as well as humid conditions. Aluminum-alumina system has extensive applications in aerospace and automobile industries. A significant thermal expansion mismatch may result in de-cohesion at the particle/matrix interface and/or a possible matrix cracking, particle fragmentation due to thermal stress. The as-received aluminium (Loba Chemie, purity > 99.7%, average size~22.09μm) and alumina (Sigma Aldrich, average size~10μm and <50 nm) powders were blended separately. Two sets of nanocomposites and microcomposites containing 1, 3, 5 and 7 vol. % of Al2O3 (average size<50nm) and 5, 10, 15, 20 vol. % of Al2O3 reinforced in aluminium were fabricated by conventional sintering at 600°C for duration of 60 minutes under argon atmosphere. The micro- and nano-composites were subjected to thermal shock. For one batch of specimens the treatment started from +80˚C temperature (60 minutes) to -80˚C temperature (60 minutes) (down thermal shock) and for the other batch the treatment was done in the reverse order (up thermal shock). After the thermal shock test mechanical and physical property determination was carried out i.e. hardness, and wear test followed by characterization under scanning electron microscopy for both micro- and nano-composites. The microstructural evolution during different thermal conditions would project an idea about the interfacial interaction at those conditions.