Deformation mechanism and mechanical properties of TiN/ZrN nanolaminates by nanoindentation: effect of layer thickness and temperature

Mechanical performance of ceramic/ceramic nanolaminates at elevated temperatures is a main concern when they are applied as protective coatings on compressed blades of aeroengines. In this work, the deformation mechanism and mechanical properties of physical vapor deposited TiN/ZrN nanolaminates are studied by instrumented nanoindentation at 25-450 degrees C. The effects of layer thickness and temperature are highlighted, with the help of detailed microstructural characterizations. The results show a cracking activity of individual layers for nanolaminates with 50 nm thick layers at 25 degrees C, which is detrimental to the mechanical performance and arises a strong indentation size effect. In addition, due to nanocrystalline structures of both TiN and ZrN layers, reduction of layer thickness is not effective to strengthen the nanolaminate. As a result, 'the thinner, the stronger' rule that works for most nanolaminates does not hold for the specific TiN/ZrN system. The indentation cracking activity is prohibited at elevated temperature due to thermally activated plasticity of both layers. An approximate linear softening in modulus and hardness, as determined by nanoindentation, is observed. Based on the high temperature data, 'apparent' activation energy for TiN/ZrN nanolaminate is finally quantified. The work may forward the advance of novel ceramic/ceramic nanolaminates in hot-section components of aeroengines.