Laser induced reaction synthesis of TiC+WC reinforced metal matrix composites coatings on Al 6061

Abstract

Most laser clad surface layers on aluminium alloys consist of a hard carbide phase and an aluminium alloy matrix phase. The distribution of the carbide phase and the strength of the matrix phase are not always satisfactory. The paper describes a method to fabricate a metal matrix composite layer on Al 6061 by adopting the laser induced reaction synthesis technique. Powder of pure titanium, pure carbon, pure tungsten or tungsten carbide are mixed at various proportions and then pasted on an Al 6061 surface. Laser cladding with Ni–Al powders delivered by a coaxial nozzle onto the above pasted surface using a 2 kW Nd:YAG laser was carried out. During laser cladding, exothermic reactions of Ti–C, W–C and Ni–Al expedite the melting and alloying of the coatings. X-Ray diffraction and scanning electronic microscopy results show that TiC and WC phases were in situ synthesized during the cladding process and they appear in a Ni–Al matrix. The microstructure, hardness and pin-on-disk wear of the coatings are investigated and discussed.