Characterization of Coatings Obtained by Boriding Niobizing Treatment of an AISI H13 Steel

Abstract

Wear is responsible for numerous industrial problems leading to increased maintenance costs due to the necessity of replacing worn components or due to equipment failure and manufacturing process downtime. Surface treatments can improve performance because the component maintains its ductile interior but with significantly improved surface wear resistance while using a minimal amount of material. Niobizing the surface of tool steel leads to the formation of very hard coatings, in the range of 2300 HV, composed of niobium carbide but with limited thickness. Boriding also produces very hard coatings, on order of 2000 HV, but with a much thicker layer than attainable by the niobizing treatment. If both were applied to the same material they could potentially complement each other by forming a duplex coating with a thin, but very hard, surface coating supported by an inner layer with slightly lower hardness but substantially thicker. The objective of this work was to evaluate the wear resistance of a coating formed by the niobizing and boriding diffusion treatments. Boron and niobium coatings were prepared on AISI H13 tool steel by thermo-reactive diffusion treatment in molten borax with 10 wt% aluminum followed by the niobium carbide pack process. The boriding treatment was performed at 900°C for 2 h, followed by a pack process at 1000°C for 2, 4, and 6 h. Optical microscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, micro-adhesive wear test, and Vickers micro-hardness were used to analyze the samples. The boriding and niobium carbide pack process produced coatings with thicknesses above 45 and 4 μm, respectively.