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.
