Effect of thermo-chemical coatings on hardness and wear performance of TM-HSS steels

In this study, the effect of surface hardness enhancement by boronizing, titaniumizing, and vanadizing treatments at 950 °C for 2 hours on 1.3377 steel produced by powder metallurgy (PM) method, by forming boride or carbide phases on the surface, on the microstructure and wear behavior at room temperature and 500 °C of these PM steels was investigated. Characterization of the formed coating layers was carried out by Scanning Electron Microscope (SEM-EDS), X-Ray Diffraction (XRD), microhardness, and wear tests. Wear tests considering the areas of use as cutting edges in machining processes of 1.3377 PM steels were performed against Al2O3 balls at room temperature and 500 °C in open air environment with a load of 10 N and a sliding distance of 250m. Metallographic studies revealed that coating layers with thicknesses of 98±2.1, 11±0.5, and 13.5±0.6 µm and hardness values of 2566, 2037, and 1800 HV0.05, and modulus of elasticity values of 450-420-350 GPa, respectively, were obtained after boronizing, titaniumizing, and vanadizing processes. The dominant phase structures in the obtained coatings were determined as FeB, TiC, and VC for boronizing, titaniumizing, and vanadizing, respectively. Due to the high hardness of boride and carbide phases and the formation of more stable oxide layers during wear, the coated samples exhibited lower friction coefficients and lower wear volume losses. While the wear mechanism of PM 1.3377 steel involved delamination and oxidation at room temperature, it turned into adhesive and oxidative wear mechanisms at 500 °C. On the other hand, it was observed that the wear mechanism in the coated samples occurred as adhesive, oxidative, and delamination both at room temperature and 500 °C.