Chromium and vanadium carbide and nitride coatings obtained by TRD techniques on UNI 42CrMoS4 (AISI 4140) steel

Different Thermo-Reactive Diffusion and Deposition (TRD) treatments have been analysed in the present work. The processes were carried out on UNI 42CrMoS4 (AISI 4140) steel both in the nitrided and bare state at temperatures of 825, 900 and 1000 degrees C, the samples being quenched in water afterwards. Hard, compact and adherent vanadium and chromium carbide and vanadium nitride coatings, mainly consisting of Cr7C3, V6C5 and VN, were obtained using different processing conditions. Biphasic layers composed by two different carbides were also obtained. The average micro-hardness of the coatings ranged from 1717 +/- 170 to 2451 +/- 236 HV0.02 whereas R-a values between 0.2 and 1.2 mu m were measured. The kinetics of the coating growth was also studied on the basis of SEM observations. It was demonstrated that the layer thickness is related to the time by a parabolic law and to the temperature by an Arrhenius-like behaviour. (C) 2015 Elsevier B.V. All rights reserved.