ULTRAHARD COATINGS FROM TI-BN MULTILAYERS AND BY COSPUTTERING

Two new techniques for the preparation of very hard Ti-B-N coatings are presented. The first method is accomplished in two steps: (i) the deposition of a multilayer coating of the sequence Ti-BN by reactive or non-reactive sputtering from a titanium and a hexagonal BN target respectively; (ii) a subsequent thermal treatment of the multilayer to induce a diffusion-activated mixing process between the titanium and BN layers with consequent phase transformations. The coatings were characterized with respect to stoichiometry by X-ray photoelectron spectroscopy with respect to structure by glancing angle X-ray diffractometry and with respect to hardness and residual stress by micro-indentation and the substrate-bending method respectively. Hardness values up to 6000 HV were observed at a concentration ratio [Ti]:[B]:[N] = 1:0.5:0.4. The coating with this compositional ratio is assumed to comprise a mixture of two solid solutions of the type Ti(Bx,Ny) and TiN1-x(By). This new technique has the advantage that almost stress-free coatings with good adhesion to metallic and non-metallic substrates are obtained. The second method is a co-sputtering process from a titanium and BN target. With this method coatings of considerable compressive stress are obtained.