Microstructural Studies of Al‐Al2O3 Nanocomposites Prepared by Powder Metallurgy Route

Abstract

Metal matrix nanocomposites (MMNCs) 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. The strengthening due to grain refinement can be delegated to a number of theories such as the Hall-Patch relation, Orowan bowing mechanism, Taylor relationship and several other models. Aluminum matrix composites circumscribe applications like aerospace, military and car industries due to low density, high toughness and good corrosion resistance. Addition of ceramic particles infers wear resistance, hardness and corrosion resistance to the aluminum matrix. Spark plasma sintering is a process in which the material gets consolidated effectively in lesser time rendering stunted grain growth which facilitates the dislocation impediment. In the present investigation, Al-Al2O3 MMNCs were fabricated by reinforcing 1, 5 and 7 vol. % alumina powder (average particle size<50 nm) into aluminum (average particle size ~ 22.87 μm) and subsequently consolidated by using spark plasma sintering (SPS). SPS was conducted at a temperature of 500°C for 5 minutes with a pressure of 50 MPa. The microstructural characterization of nanocomposites were carried out by optical microscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The microhardness and wear properties of the nanocomposites have also been studied. The microstructures of Al-Al2O3 nanocomposites reveal remarkable intermixing and embedment of alumina nanoparticles in the matrix. The SEM micrographs show good compatibility between alumina nanoparticles and aluminium matrix. TEM micrographs represent the uniform distribution of alumina nanoparticles in aluminum. Maximum hardness value of 61.5 HV was recorded for Al-5 vol. % reinforced Al2O3 nanocomposites. The mechanism of SPS is yet to be understood in the consolidation of nanocomposite materials and the detailed evolution of microstructure needs to be unraveled to get a blueprint of the all the events taking place in SPS.