Niobium Carbide Coatings Grown on Cold Work Tool Steel AISI D3 by Thermomechanical Processing: Characterization, Wear and Corrosion Behaviors

In this study, niobium carbide (NbC) coatings were grown on AISI D3 cold work tool steel via thermoreactive diffusion (TRD) at 900, 1000 and 1100 degrees C for 2, 4, and 6 h. The microstructures and phase formed, the surface roughnesses, the microhardness and fracture toughness values, and the wear and electrochemical corrosion behavior of the NbC coatings were investigated. Compact, smooth and crack-free NbC layers with 8.75-17.10 mu m thickness and 1558-2286 HV0.1 hardness were obtained on the surface of the AISI D3 steel. Depending on the TRD temperature and duration, the NbC coatings improved the wear resistance by up to 5 times and corrosion resistance up to 14 times compared to the untreated alloy. With increasing temperature and duration, the thickness and microhardness values of NbC coatings increased. However, significant changes in wear and corrosion resistance was observed depending on Nb, C, O and Fe contents of NbC coatings rather than thickness and microhardness. The wear resistance was found to depend on fracture toughness as well as hardness. Corrosion resistance depended mostly on the surface roughness and the defects (especially microcracks) present on the surface.