A comparative investigation on microstructure evolution and wear resistance of in situ synthesized NbC, WC, TaC reinforced Mo2FeB2 coatings by laser cladding

Abstract

To improve the microhardness and wear resistance of Mo2FeB2 coatings, composite coatings were prepared by laser cladding using in situ synthesized NbC, WC, and TaC. The influence of different carbides on the morphology, microstructure, microhardness, residual stress, and tribological properties of the composite coatings was investigated. The results showed various microstructural morphologies in different composite coatings. Apparent herringbone structures were observed in most coatings except for the Mo2FeB2/TaC composite coating and a eutectic structure was formed in the Mo2FeB2/WC composite coating. In addition, the heat-affected zone was typically composed of acicular martensite and lath martensite. The microhardness of the Mo2FeB2/WC composite coating increased to 1543.6 HV0.5 compared with 985.7 HV0.5 observed for the Mo2FeB2 coating. Tensile stress existed in the coating, bonding zone, and heat-affected zone, whereas the substrate exhibited compressive stress. The Mo2FeB2/WC composite coating exhibited the lowest tensile stress (298 MPa). The Mo2FeB2/WC composite coating containing WC and the W2C phase had the lowest coefficient of friction (0.38) and wear rate (3.90 × 10−5 mm3/Nm), indicating its excellent tribological properties. Moreover, the wear mechanism of the Mo2FeB2 coating is severe adhesive and abrasive wear. The adhesive wear mechanism was mitigated by the formation of in situ synthesized NbC, WC, and TaC. The wear mechanism of the Mo2FeB2/WC composite coating was only a slight abrasive wear.