Effect of WC and B4C reinforcement on microstructure, mechanical and wear properties of metal-based composite coatings in laser cladding process

Laser cladding, a prominent surface modification technique developed in recent years, is widely preferred due to its advantages such as high energy density, low heat input, superior coating-substrate strength, and controlled microstructure formation. Metal-matrix composite coatings are attracting particular attention in this field for providing resistance to harsh service conditions such as wear, oxidation, and high temperatures. These coatings offer significant improvements in properties such as hardness, wear resistance, and thermal stability thanks to the addition of ceramic reinforcements to the matrix phase. In this thesis, WC and B4C reinforced coatings were applied to low-carbon St37 steel in a FeCr-based matrix by laser cladding. Five different coating compositions were prepared, with WC contents of 0, 10, 20, 30, and 40%. In the laser cladding process, the powder mixtures were applied to the substrate surface in a gel-form consistency and then the coating process was carried out using fixed laser parameters. This aimed to increase wear resistance and surface hardness. The microstructural, mechanical, and tribological properties of the coatings were investigated in detail using different analysis and testing methods. Microstructural investigations revealed that the phase diversity in the microstructure increased with increasing WC addition. However, it was determined that structural continuity was partially disrupted at reinforcement ratios above 30% due to undissolved WC particles and phase separation. EDS analyses showed that Cr, W, and C elements concentrated around the precipitates, while XRD analyses showed the formation of carbide phases such as WC, W2C, M7C3, and M23C6 in the coating region. Microhardness measurements showed significant increases in hardness. While the average hardness was 353.2 HV in the N0 sample, this value reached 790.6 HV in the N40 sample. Wear tests and surface morphology analyses revealed intense plastic deformation traces, oxidation, and deep wear grooves in the uncoated K sample. These effects gradually diminished with the addition of WC, and surface deformations were largely suppressed in the N40 sample. Wear volume and coefficient of friction data also supported these findings, with the N40 sample achieving the lowest wear volume and average coefficient of friction values among all samples.