Interfacial structure, mechanical properties and thermal stability of CrAlSiN/CrAlN multilayer coatings

Incorporation of Si into CrAlN coatings has a positive effect on the mechanical and thermal properties, but promotes the wurtzite (w) AlN formation with decreased mechanical properties. In order to further optimize the properties of CrAlSiN coatings, multilayer architecture combining with single phase cubic (c) CrAlN layers and mixed cubic/wurtzite layers, where the CrAlSiN/CrAlN (ML) multilayer coatings with a similar modulation period and varied modulation ratios were prepared, is used to stabilize CrAlSiN sublayers in their metastable cubic structure by coherency to the CrAlN sublayer. The ML_1 coating with coherent growth between 1.4 nm CrAlSiN layer on the 2.9 nm cubic CrAlN layer exhibits large columnar grains extending over several layers. The increased thickness of CrAlSiN layer induces the coherency loss, and reveals a mixed c/w-ML_2 and _3 multilayer coatings. The ML_1 coating obtains the maximum hardness value of ~ 33.1 GPa due to the coherency strain and overall cubic formation, corresponding to ~ 31.2 and 31.6 GPa for ML_2 and _3, respectively. However, ML_1 coating presents an earlier w-AlN precipitation and N-loss than CrAlN and CrAlSiN monolithic coatings under thermal load.