Thermally enhanced mechanical properties of arc evaporated Ti0.34Al0.66N/TiN multilayer coatings

Abstract

Cubic metastable Ti0.34Al0.66N/TiN multilayer coatings of three different periods, 25+50, 12+25, and 6+12 nm, and monoliths of Ti0.34Al0.66N and TiN where grown by reactive arc evaporation. Differential scanning calorimetry reveals that the isostructural spinodal decomposition to AlN and TiN in the multilayers starts at a lower temperature compared to the monolithic TiAlN, while the subsequent transformation from c-AlN to h-AlN is delayed to higher temperatures. Mechanical testing by nanoindentation reveals that, despite the 60 vol % TiN, the as-deposited multilayers show similar or slightly higher hardness than the monolithic Ti0.34Al0.66N. In addition, the multilayers show a more pronounced age hardening compared to the monolith. The enhanced hardening phenomena and improved thermal stability of the multilayer coatings are discussed in terms of particle confinement and coherency stresses from the neighboring TiN-layers.