Electron beam hardening of PVD-coated steels: Improved load-supporting capacity for Ti1-xAlxN layers

This paper deals with the results of combining Ti1 − xAlxN coatings with a subsequent electron beam surface-hardening process. The coatings – differing in their chemical composition (Al = 17…30 at.%; Ti = 18…30 at.%) and thickness (1–6 μm) – were deposited by reactive magnetron sputtering onto the heat-treatable steel 51CrV4. During electron beam hardening (EBH), a special energy transfer field causes an isothermal surface temperature distribution. By varying energy input and interaction time, the resulting hardening depth could be adjusted in the range of 0.1 to 0.4 mm. The results are characterised by means of optical and scanning electron microscopy, hardness measurements and the evaluation of the chemical composition of the coatings by glow discharge optical spectroscopy. The load supporting capacity and the adhesion of the hard coatings was determined using scratch tests with increasing load. The chemical composition and thickness of the coatings applied by physical vapour deposition (PVD) significantly affected the results of subsequent EBH. Hardening depth increased with the increasing thickness and increasing Al content of the PVD layer. Furthermore, the coatings exhibited increasing resistance against thermal stress during EBH for decreasing layer thickness and increasing Ti content. Load support of the base material was improved by a factor of 2 to 3. Therefore, the duplex treatment PVD + EBH has a high potential for industrial application with respect to locally highly loaded components