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Abstract
Polycrystalline TiN/ZrN, TiN/CrN and TiN/TaN multilayers were grown by reactive magnetron sputtering on WC/Co sintered hard alloy substrates. Hardness and elastic modulus were measured by nanoindentation testing. Hardness of TiN/ZrN multilayers decreased rapidly with increasing bilayer thickness (Λ), peaking at hardness values ≍ 30% lower than the rule-of-mixtures value at Λ = 30 Å, and increased with further increases in Λ. A comparison with other lattice mismatched systems showed a similar hardness variation, but the sign was negative. The results suggest that coherency strains are responsible for the larger hardness change. Nanoindenter elastic modulus results showed the same behavior with hardness dependence on Λ, i.e., elastic softening at Λ = 30 Å. TiN/CrN system showed no hardness and elastic anomalies. In TiN/TaN systems, hardness was lower than the rule-of-mixtures value of individual single layers for Λ > 80 Å, and increased rapidly with decreasing Λ, peaking at Λ = 43 Å. As a result of analysis on the inclination of applied load for indenter displacement (δP/δh), this paper exhibits that the enhancement of the resistance to dislocation motion and elastic anomaly due to the change of lattice spacing are responsible for the hardness change.