Structure, mechanical properties and thermal stability of CrAlN/ZrO2 nanomultilayers deposited by magnetron sputtering

New types of CrAlN/ZrO2 nanomultilayers with different ZrO2 layer thickness were synthesized by reactive magnetron sputtering. The structure, mechanical properties and thermal stability were investigated by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HRTEM) and nano-indentation techniques. The results indicated that, when ZrO2 layer thickness was less than 1.0 nm, tetragonal-structured ZrO2 layers were forced to transform to pseudomorphic fcc structure under the template effect of CrAlN layers and grew epitaxially with CrAlN layers, resulting in abnormal enhancement of mechanical properties. The maximum hardness and elastic modulus could respectively reach 47.2 GPa and 538.9 GPa when ZrO2 layer thickness was 1.0 nm. With further increase of ZrO2 layer thickness, ZrO2 layers could not keep fcc structure and broke epitaxial growth structure, leading to the decrease of mechanical properties. High-temperature annealing revealed that hardness and elastic modulus decreased slightly when heated at a temperature below 900 °C for 30 min, while dropped significantly as annealing temperature raised to 1000 °C. However, even after annealing at 1000 °C for 30 min, the nanomultilayers still retained hardness and elastic modulus as high as 36.8 GPa and 465.7 GPa, showing the excellent mechanical properties at elevated temperatures.

► The novel CrAlN/ZrO2 nanomultilayers were produced by reactive magnetron sputtering. ► The ZrO2 layers were forced to transform to fcc structure by CrAlN layers. ► The maximum hardness and elastic modulus reached 47.2 GPa and 538.9 GPa. ► The high hardness of 36.8 GPa was retained after annealing at 1000 °C for 30 min.