Fabrication of Al-CNTs MMC by induction melting with improved Dispersion and wetting of CNTs in Al Matrix using a multifunctional flux

Abstract

Aluminum/carbon nanotubes (Al-CNTs) composite is an encouraging candidate material for aerospace applications due to its expected high strength-to-weight ratio. Carbon nanotubes (CNTs) offer remarkable reinforcements owing to their high specific strength and specific modulus. However, uniform dispersion and wetting of the CNTs is extremely difficult in molten aluminum, due to large difference in surface tension forces of the two components. In present work, the dispersion issue was improved using induction melting technique, where innate stirring action of induction melting dispersed the nanotubes in molten aluminum. The wetting was improved using a multifunction flux (titanate of potassium), which, when was incorporated in molten mixture of aluminum and CNTs having, instigated in-situ reactions to form titanium carbides on the surface of the nanotubes causing increased wetting of CNTs by molten aluminum. The composites were characterized using scanning electron microscopy, x-ray diffraction, transmission electron microscopy and mechanical testing. Refinement in crystallite size was achieved down to ~150 nm and a corresponding increase in lattice strain up to ~3.46x10-3 was observed in the composites. A simultaneous increase in v i yield strength ~208 %, tensile strength ~218 %, and hardness ~100 % was observed. However, the decrease in the ductility of the composite associated with the strengthening of the matrix was <25 %. Additionally, stress relaxation behavior of the annealed composite was improved by ~30 % compared with pure aluminum. Consequently, the stress relaxation rate of the composite was decreased even beyond the yield strength of the annealed pure aluminum. Therefore, induction melting and usage of the flux for improvement in the dispersion and wetting of the nanotubes, respectively, appeared to be a potential method to fabricate Al-CNTs composites.