A Comparative study of Al-Al2O3 Micro- and Nanocomposites Prepared by Powder Metallurgy Route

Abstract

Metal matrix composites (MMCs) are new generation materials which combine both metallic properties (ductility and toughness) and ceramic characteristics (high strength and modulus), leading to greater strength in shear and compression and to higher service temperature capabilities. Aluminum matrix composites find wide range of applications like aerospace, automobile industries due to high strength to weight ratio, high toughness and good corrosion resistance. Addition of ceramic particles improves wear resistance, hardness and corrosion resistance to the aluminum matrix. The advent of nanostructured material production techniques have led to an unprecedented growth in the area of metal matrix composites with extraordinary superior strengths. The surplus strength entitled to the material has to be compromised with the loss in ductility.

In the present investigation, Al-Al2O3 MMNCs were fabricated by reinforcing 1, 5 and 7 vol. % of alumina powder (average particle size <50 nm) into aluminum (average particle size ~ 23 nm) and subsequently consolidated by using spark plasma sintering (SPS) technique. Another composition containing 1, 5 and 20 vol. % of alumina (average size~10µm) was reinforced into aluminum and MMC had been fabricated by SPS to compare the physical as well as mechanical attributes of the microcomposite and nanocomposites. In both cases SPS was conducted at a temperature of 500C for 5 minutes with a pressure of 50 MPa. The microstructural characterization of composites was carried out by optical microscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The microstructures of Al-Al2O3 nanocomposites reveal remarkable intermixing and embedment of alumina nanoparticles in the matrix as compared to microcomposite. The SEM micrographs show good compatibility between alumina nanoparticles and aluminium matrix. SEM micrograph also reveals the presence of large amount of pores in micorcomposite than nanocomposites. TEM micrographs represent almost uniform distribution of alumina nanoparticles in aluminum. A maximum hardness value of 0.5 GPa and 0.3 GPa were achieved for micro and nano composites respectively. However, a higher nano indentation hardness value of 0.8 GPa was obtained for Al-7 vol. % Al2O3 nanocomposite. A density value of more than 90% of theoretical density was obtained for both the composites. It has been found that wear resistance of micro-composites are higher than nano-composites and it increases with increasing alumina content. Plastic shear flow, cracking and de-lamination are predominant wear mechanisms for Al-Al2O3 micro and nano-composites.