Processing and characterization of laser clad NiCrBSi/WC composite coatings — Influence of microstructure on hardness and wear

NiCrBSi/WC composite coatings containing various amounts of WC/W2C particles were laser cladded on low carbon steel substrate S235JR. Coatings were processed using two different laser systems, a 1kW Nd:YAG and a 3.8kW high power diode laser (HPDL). Coatings obtained with the Nd:YAG source demonstrate significant changes in the matrix microstructure with WC/W2C particle addition. Specific analysis shows the formation of new carbides (W,Cr)xCy and boride phases (W,Cr)xBy resulting from a partial dissolution of the WC/W2C particles within the metal matrix. The Brinell macrohardness of the coatings reveals surprisingly low values for coatings containing 10vol.% and 20vol.% WC/W2C. Through nanoindentation measurements, it is suggested that the low hardness of these new carbide and boride phases most likely counteracts the WC/W2C addition and may explain this unexpected behavior. On the contrary, the same coatings deposited using the HPDL source exhibits no change in the microstructure of the NiCrBSi matrix and display an expected monotonic increase of composite hardness with WC/W2C amount. It is suggested that the microstructural appearance of new carbide and boride phases may not be related to the type of laser used but to the specific laser energy during the coating process. Contrarily to hardness, measurements show that the erosive wear is marginally affected by the microstructural differences of the coatings. These results demonstrate that evaluating the quality of laser cladded coatings by simply assessing their density and the absence of a crack (as usually done) is insufficient as it does not automatically guarantee reaching optimal mechanical performance. [Display omitted] •Metal matrix composite NiCrBSi/WC coatings were deposited by laser cladding.•Laser parameters have a significant effect on the coatings' microstructure.•Diffusion of W from the grains causes a reaction with chromium carbides and borides.•Nanohardness on newly formed phases was performed to explain macrohardness decrease.•The reaction between W and Cr phases does not impact wear resistance behavior.