Hardness analysis of duplex coating

The combined processes of plasma nitriding and cathodic arc ion plating were applied to high-speed steel substrates. The cross-sectional hardness of the diffusion zone increased proportionally with nitrogen concentration in the case. The composite hardness of the resulting duplex coatings layer were measured by a micro-Vickers tester as a function of indentation size. On the basis of the volume law of mixtures, the composite hardness of the duplex coatings was calculated using the film hardness and the cross-sectional hardness of nitrided layer. The calculated composite hardness showed good agreement with the measured composite hardness of the duplex coatings.