Microstructure and sliding wear resistance of an Al-12Â wt.% Si/TiC laser clad coating

Metal matrix composite coatings consisting of an Al-12 wt.% Si-alloy matrix reinforced with TiC were prepared by laser cladding from mixtures of Al-12 wt.% Si alloy and TiC powders. For the processing parameters used (power density 200 MW/m2 and interaction time 0.3 s), a small proportion of TiC dissolves in the melt, resulting in a microstructure composed of 34 vol.% of TiC and 3 vol.% of Ti3SiC2 particles dispersed in a matrix consisting of proeutectic α-Al dendrites and α-Al + Si eutectic. The coating material presents a hardness of 165 HV and a wear coefficient of 2.24 × 10−5 mm3/(N m) in ball-on-plate dry sliding wear tests, using quenched and tempered AISI 440C martensitic stainless steel as the counterbody material. Analysis of the worn surfaces showed that the sliding motion of the contacting bodies leads to the formation of a tribolayer consisting of Fe oxides, as well as metallic phases. On the basis of theoretical calculations it is suggested that the primary material removal mechanism involves the propagation of cracks through the thickness of this tribolayer, followed by crack channeling and debonding of tribolayer fragments.