Abstract
Hardened and tempered low alloy steels were duplex treated by nitriding and TiNx coating by hollow cathode discharge. The influence of the composition and structure of the nitrided case, the mechanical treatment of the nitrided case before deposition (grinding, polishing), and the deposition parameters (sputter cleaning, nitrogen input, bias voltage) on the properties of the coating–nitrided steel composite have been investigated. It was found that the outermost nitride layer and a porous zone in the compound layer of the nitrided steel had negative effects on the adhesion,hardness, and wear behaviour of the composite. The outer compound layer can be denitrided by prolonged strong sputter cleaning. An intermediate titanium layer improved the resistance of the hard coating to adhesive failure. Higher nitrogen levels in the deposition atmosphere made it possible to form stoichiometric TiN with good mechanical properties. Best results in the scratch test, and the finest columnar structure, were achieved for coatings produced with a continuous increase of nitrogen input during deposition. Only a small loss of hardness occurred in comparison with stoichiometric TiN.
Get full access to this article
View all access options for this article.