MECHANICAL-PROPERTIES OF CERAMIC MULTILAYERS - TIN CRN, TIN/ZRN, AND TIN/TAN/

Polycrystalline TiN/ZrN, TiN/CrN, and TiN/TaN multilayers were grown b y reactive magnetron sputtering on WC/Co sintered hard alloy substrate s. Hardness and elastic modulus were measured by nanoindentation testi ng. Hardness of TiN/ZrN multilayers decreased rapidly with increasing bilayer thickness (Lambda), peaking at hardness values = 30% lower tha n rule-of-mixtures values at Lambda = 30 Angstrom, and increased with further increases in Lambda. A comparison with other lattice mismatche d systems showed a similar hardness variation, but the sign was negati ve. The results suggest that coherency strains are responsible for the greater hardness change. Nanoindenter elastic modulus results showed the same behavior with hardness dependence on Lambda, i.e., elastic so ftening at Lambda = 30 Angstrom. TiN/CrN system showed no hardness and elastic anomalies. In TiN/TaN systems, hardness are lower than rule-o f-mixtures value of individual single layers for Lambda > 80 Angstrom, and increased rapidly with decreasing Lambda, peaking at Lambda = 43 Angstrom. As a result of analysis on the inclination of applied load f or indenter displacement (Delta P/Delta h), this paper demonstrates th at the enhancement of the resistance to dislocation motion and elastic anomaly due to coherency strains are responsible for the hardness cha nge.