Abstract
A technique using compositionally gradient interlayers has been applied to TiO2/Ti/TiN, ZrO2/Zr/ZrN, and TiO2/Ti/Zr/ZrN multi-compositional coatings to enhance the adhesion of hard coatings to substrate. The coatings were prepared by dc reactive magnetron sputtering using a combination of a Zr or a Ti metal target and a pure Ar, an Ar-O2 mixture, or an Ar-N2 mixture discharge gas, onto a borosilicate glass substrate. Adhesion of coatings to the substrate was estimated by a scratch method. The hardness of coatings was measured by a nano-indentation method. Without an interface, ZrN coatings showed a very poor adhesion. By using glass/ZrO2/Zr or glass/TiO2/Ti compositionally gradient interface layers, the adhesion strength of ZrN coatings was enhanced to the adhesion strength almost equal to or higher than those of TiO2 or ZrO2 single layer coatings. From the results of internal stress evaluation, it was found that a high internal stress causes a poor adhesion of ZrN coatings. Hardness of coatings with a ZrN overlayer were 20 to 35 GPa and larger than those of coatings with a TiN overlayer. The increase in the hardness by inserting a compositionally gradient interface was observed in ZrO2/Zr/ZrN and TiO2/Ti/Zr/ZrN systems.
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