Effect of thermo-reactive diffusion coatings on microstructure and wear behavior of powder metallurgy steel cutting inserts

Abstract

In this study, powder metallurgy-produced 1.337 steel (PMS 1.3377) was subjected to boronizing, titanizing, and vanadinizing processes at 950 °C for 2 hours. The influence of boride and carbide coatings formed on the surface of PMS 1.3377 on the microstructure of these steels and their wear behaviors at room temperature and 500 °C were investigated. Characterization of the formed coating layers was carried out through Scanning Electron Microscopy (SEM-EDS), X-ray Diffraction (XRD), microhardness, and wear testing. Wear tests considering the cutting tool turning, milling, and drilling applications of PMS 1.3377 were conducted at room temperature and 500 °C in ambient air with a 10 N load and a 250 m sliding distance against an Al2O3 ball. Metallographic studies showed that coating layers with thicknesses of 98±2.1, 11±0.5, 13.5±0.6 µm and hardness of 2566±125 HV0.1, 2037±104 HV0.1, and 1800±197 were obtained by boronizing, titanizing and vanadinizing processes, respectively. The dominant phase structures in the obtained coatings were determined to be FeB, TiC, and VC for boronizing, titanizing, and vanadinizing, respectively. Due to the high hardness of boride and carbide phases and their ability to form more stable oxide layers during wear, the coated samples exhibited lower friction coefficients and lower wear volume losses. While untreated PMS 1.3377 experienced delamination and oxidation wear mechanisms at room temperature, the wear mechanism at 500 °C transformed into adhesive and oxidation wear. On the other hand, in the coated samples, the wear mechanism was found to occur as adhesive, oxidative, and delamination at both room temperature and 500 °C.