Investigation of formability, wear and corrosion behaviors of niobium carbide coatings on AISI D3 cold work tool steel

Corrosion and wear damages cause high costs to industrial economies every year. Because wear and corrosion damages are mainly related to surface and near-surface layers properties of materials, it is an essential solution to form a hard coating or thin film on the surface to avoid these damages and extend the service life by improving the performance of materials. Therefore, the field of surface engineering and technology has been developed to preserve the chemical and physical composition of the material and modify its surface properties. In this study, a Niobium carbide (NbC) coating layer was formed on the surface of AISI D3 steel using the Thermo-reactive diffusion method (TRD) at 900, 1000 and 1100°C with 2,4,6 hours parameters. Characterization of the formed NbC coating layer was determined by Scanning Electron Microscopy (SEM-EDS), X-ray Diffractometer (XRD), microhardness, nano indentation, Vickers adhesion test, abrasion test and electrochemical corrosion test. Corrosion tests were performed electrochemically at room temperature in a 3.5% NaCl solution.Wear tests were carried out at room temperature under a 10N load at a sliding distance of 100-250 m against a 6.3 mm diameter Al2O3 ball with a diameter of 8.00 mm and a velocity of 200 mm/s. As a result of the TRD process, compact, smooth and crack-free NbC type layer with excellent adhesion with the substrate in the range of 8.75-17.10 µm thickness and 1558-2286 HV0.025 hardness, was obtained. Depending on the TRD temperature and time, the NbC coatings improved wear resistance by up to 5 times and corrosion resistance by up to 14 times compared to the un-treated AISI D3. The thickness and microhardness values of NbC coatings increased with increasing temperature and time, showing significant changes in wear and corrosion resistance properties. The surface morphologies of the worn samples revealed that the wear mechanism was abrasive in the untreated sample. In contrast, oxidative-supported adhesive wear was the dominant wear mechanism in the NbC-coated samples. In addition, it has been determined that corrosion resistance mostly depends on surface roughness and surface defects (especially microcracks).