Fabrication of carbon nanotube reinforced iron based magnetic alloy composites by spark plasma sintering

Near equiatomic Fe-Co composites containing up to 10 vol% of carbon nanotubes (CNTs) were prepared by spark plasma sintering at 900 C-degrees by applying a uniaxial pressure of 80 MPa for 2 min. The powder mixtures were blended by two methods: (a) ultrasonication in dimethylformamide, drying and dry ball milling; (b) dry ball milling. It is the first attempt to fabricate bulk CNT reinforced Fe based alloy composites by a sintering route. The CNTs helped to increase the volume fraction of the long range ordered structures in the matrix alloy. The former dispersion route helped to produce composites with better magnetic and mechanical properties than the latter one. Composites containing less than 1.5 vol% of CNTs showed an increase in saturation induction, mean bending strength, hardness in relation to the monolithic material due to the better densification produced by the addition of CNTs. A significant reduction in the coercivity was observed in all the composites with lower vol% of CNTs (< 2%) due to the increase in the compact density and the formation of nanocrystalline ordered crystallites with reduced dimensions, with respect to that of the monolithic material. Spark plasma sintering helped to retain the structural integrity of CNTs in all the Fe based composites fabricated. (C) 2014 Elsevier B.V. All rights reserved.