Laser cladding of Cu-NbC nanocomposite coatings

Abstract

Cu-matrix composites are interesting materials to be used as coatings in applications where efficient heat transfer and good wear resistance are simultaneously necessary, like mould repair, electric sliding contacts, high temperature seals, etc.In this work, Cu-NbC nanocomposite powder was synthesized in-situ by mechanical alloying from elemental mixtures of Cu, Nb and graphite powders and used to produce Cu-10% NbC coatings on CK45 steel substrate by laser cladding. The coatings have an average thickness of 800 Pm and present some porosity due to the oxidation of the powder and consequent incorporation of oxygen in the coating. Their microstructure was characterized by SEM, EDS, XRD, and TEM analysis. It consists of very fine (submicron sized) NbC particles uniformly distributed in the Cu matrix.The coatings present an average microhardness of 180 HV. The wear behavior of the coatings was investigated through microscale wear tests performed under dry sliding conditions against a steel counterbody. The influence of load on the prevailing wear mechanisms was analyzed and related to the microstructure of the coatings. Two wear regimes were identified. At low loads the predominant wear mechanism is abrasion, while at high loads adhesion and material transfer are the main mechanisms. However, the wear coefficients are relatively low (10−13 m2/N) and wear remains in the moderate regime.Cu-matrix composites are interesting materials to be used as coatings in applications where efficient heat transfer and good wear resistance are simultaneously necessary, like mould repair, electric sliding contacts, high temperature seals, etc.In this work, Cu-NbC nanocomposite powder was synthesized in-situ by mechanical alloying from elemental mixtures of Cu, Nb and graphite powders and used to produce Cu-10% NbC coatings on CK45 steel substrate by laser cladding. The coatings have an average thickness of 800 Pm and present some porosity due to the oxidation of the powder and consequent incorporation of oxygen in the coating. Their microstructure was characterized by SEM, EDS, XRD, and TEM analysis. It consists of very fine (submicron sized) NbC particles uniformly distributed in the Cu matrix.The coatings present an average microhardness of 180 HV. The wear behavior of the coatings was investigated through microscale wear tests performed under dry sliding conditions against a steel counterbody. The in...