Tribological performance of Ni-Cr-B-Si coatings deposited via laser cladding process

Abstract

Abstract Ni-Cr-B-Si alloy coatings deposited by the laser cladding process have high tribological resistance, good metallurgical bonding with the substrate, and an interesting set of mechanical properties. Aiming to correlate microstructure and the mechanical behavior of coatings in wear environments, three coatings were deposited over an ASTM A36 carbon steel substrate, them being C1 (1.05 kW–5 mm s−1), C2 (1.40 kW–21.7 mm s−1), and C3 (1.75 kW–30 mm s−1). The microstructure and microhardness of the coatings were analyzed, the former by using SEM and EDS. Ball-on-disk tests were performed to determine wear and friction coefficients. In order to evaluate the worn surfaces, SEM-EDS techniques were also employed. The different solidification rates affected the behavior of microstructure and microhardness. Coating C1, deposited with a lower cooling speed, provided a longer dwell time for the nucleation and growth of Cr-carbides (CrC) in the Ni-matrix, a factor that gave it a lower dilution, higher carbide concentration, and higher microhardness when compared to C2 and C3. In the ball-on-disk test, coatings with higher concentration and CrC size presented a higher variaton of their friction coefficient, but a lower volumetric loss and wear coefficient. Analysis of the worn surfaces showed that the CrC characteristics, deterioration of tribolayers, and coating material detachment close to the solidification cracks were the main features that change the coatings’ tribological performance.