Influence of CrxNy coatings deposited by magnetron sputtering on tool service life in wood processing

Cubic CrN(200) and a mixture of 25% CrN + 75% Cr2N(111) coatings were deposited by magnetron sputtering onto carbide tools and tested in wood machining. The composition of the layers was determined by X-ray photoelectron spectroscopy (XPS) analyses. Scanning electron microscopy (SEM) observations showed that Cr2N layers have a columnar structure while CrN layers seem to be featureless. Secondary ion mass spectroscopy (SIMS) profiles have shown a good homogeneity of the layers and no interdiffusion of the different species into the substrate. The mechanical properties of the chromium nitride coatings were characterized by residual stress measurement, hardness measurements and scratch adhesion tests. The layers have some compressive stresses in the range -1.7/-2.1 GPa and -0.4/-1 GPa for CrN and Cr2N, respectively. The more adherent layers are CrN ones which exhibit hardness up to 1900-2100 HV. Cr2N layers are harder (up to 1900-2100 HV) but less adherent. Machining tests were performed up to 5 and 10 km of cutting distance with industrial routers on Oriented Strand Board. Tool wear and service life were compared between the uncoated and coated tools. First, it has been observed that the edge wear is very high, just at the beginning of the routing process. The best result was shown by a carbide tool CrN coated on both faces; the service life of this tool is four times higher than the one of an uncoated tool. (C) 2001 Elsevier Science B.V. All rights reserved.