Single cycle plasma nitriding and hard coating deposition in a cathodic arc evaporation device

Abstract

The duplex treatment of alloy steel (nitriding + hard coating) has been studied for a few years now. It is an interesting method not only for increasing fatigue strength and tempering resistance but also for improving corrosion and wear behaviours, particularly under high loads. Such treatments are used for dieing or hot-working applications and are often performed with a discontinuous combination of nitriding and hard coating. This solution has some disadvantages with regards to intermediate external steps prior to coating/polishing and grinding. The aim of this work is to investigate the possibilities and interests of performing duplex treatment during a single cycle within an industrial cathodic arc evaporation PVD device. Two types of plasma nitriding were tested: ‘conventional’ plasma nitriding in N 2 + H 2 mixtures and low-pressure enhanced plasma nitriding assisted by an electron beam produced by a new arc evaporation source. Hard coatings (TiN or CrN) with good adhesion can be deposited on nitrided high-alloy steels if nitriding, ion cleaning and coating parameters are adjusted. A smooth surface on the bright nitrided substrate (without compound layer) prior to the coating stage must be achieved in order to reach the best mechanical properties of the composite. This technology, which does not require additional polishing steps before completion, can result not only in lower production costs but in high continuity between the two stages of duplex treatment.