Adhesion and hardness of compositionally gradient TiO2/Ti/TiN, ZrO2/Zr/ZrN, and TiO2/Ti/Zr/ZrN coatings

A technique using compositionally gradient interlayers has been applied to TiO2/Ti/TiN, ZrO2/Zr/ZrN, and TiO2/Ti/Zr/ZrN multi-compositional coatings t o enhance the adhesion of hard coatings to substrate. The coatings were pre pared by de reactive magnetron sputtering using a combination of a Zr or a Ti metal target and a pure Ar, an Ar-O-2 mixture, or an Ar-N-2 mixture disc harge 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 s howed a very poor adhesion. By using glass/ZrO2/Zr or glass/TiO2/Ti composi tionally gradient interface layers, the adhesion strength of ZrN coatings w as enhanced to the adhesion strength almost equal to or higher than those o f TiO2 or ZrO2 single layer coatings. From the results of internal stress e valuation, 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 GP a and larger than those of coatings with a TiN overlayer. The increase in t he hardness by inserting a compositionally gradient interface was observed in ZrO2/Zr/ZrN and TiO2/Ti/Zr/ZrN systems. (C) 1998 Elsevier Science S.A. A ll rights reserved.