The correlation of scratch adhesion with composite hardness for TiN coatings

The substrate hardness and coating thickness effects on the scratch adhesion of TiN coatings deposited on different substrates by arc evaporation and plasma assisted chemical vapor deposition are discussed from the point of view of the composite hardness. Experimental results show that the scratch hardness Ps of all samples may be expressed as a function of the Vickers composite hardness as Ps≒0.7 Hc for our condition. The critical loads Lc for coatings of different thickness on various substrate materials prepared by the same deposition method are observed to be aligned on the same straight line of the Lc–Hc plots. The critical load increases proportionally to the product of the scratch depth and the composite hardness at the critical load. From optical microscope observation of the scratch channels and from the analysis of the acoustic emission signals, the lower critical load of PCVD coatings compared with arc-evaporated ones may be ascribed to the weak cohesion strength of the coating.