Kinetics of V(N,C) and Nb(N,C) coatings produced by V–Nb–RE deposition technique

Abstract

A duplex surface treatment on AISI H13 steel has been developed involving nitrocarburizing and followed by vanadium niobium and rare earths (V–Nb–RE) thermo-reactive deposition (TRD) techniques. The TRD process was performed in molten borax salt bath at 1223, 1283 and 1343K for 1–4h, respectively. The process formed a thickness of 6 to 35μm of vanadium carbonitride and niobium carbonitride coatings on a hardened diffusion zone. Characterization of the coatings by means of scanning electron microscopy (SEM) and X-ray diffraction analysis (XRD) indicates that the compact and dense coatings mainly consist of V8C7, NbC, NbN and VN phases. The value of Vickers hardness of the coatings was up to 1350 HV0.1 after tempering at 848K for 2h. All the growth processes of the vanadium carbonitride and niobium carbonitride coatings obtained by V–Nb–RE deposition technique followed a parabolic kinetics. Activation energy (Q) for the process was estimated to be 215.68kJ/mol of vanadium carbonitride coating, and 134.32kJ/mol of niobium carbonitride coating. Under certain conditions, the values of Q were greater than single vanadizing and deposition niobium. However, growth rate constant (K) was very similar among pairs of them.