Microstructure, mechanical properties and thermal stability of Cr/WC nano-multilayered coating synthesized by ion beam sputtering

Cr/WC nano-multilayered coatings with fixed period ratio (Cr:WC=1:2) were synthesized by using ion beam sputtering method. The microstructure, mechanical properties and the thermal stability of coatings were investigated by X-ray diffraction, Scanning Electron Microscopy, Transmission Electron Microscopy and nanoindentation. Well-defined laminar amorphous microstructure and uniform monolayers, which consists of amorphous WC1-x and Cr, can be found in the as-deposited nano-multilayered coatings with series modulation period. Although the hardness of Cr/WC nano-multilayered coating increases with the increasing of modulation period, it is still lower than the value predicted by Hill model. Almost all the toughness of Cr/WC nanomultilayered coatings are lower than that of monolayer Cr coating, however, they are higher than that of monolayer WC coating, indicating that the addition of Cr and nano-multilayered architecture can improve the toughness of monolayer WC coating. Both microstructure and mechanical properties of Cr/WC nanomultilayered coatings were stable when the vacuum heat treatment temperature was lower than 400 degrees C. As the heat treatment temperature was 600 degrees C, some nanocrystalline W2C, W and WC1-x were enclosed in the amorphous WC sublayer which is beneficial to its hardness enhancement while it is harmful to its toughness. As the heat treatment temperature was 800 degrees C, the nano-multilayered structure was destroyed completely and its mechanical properties were seriously degraded.