Crack formation and oxidation wear in (Cr,Y,Al)N and (Mo,Y,Al)N nanolayer coatings with high content of yttrium

The article considers the processes of cracking and oxidation in the nanolayer coatings of (Cr,Y,Al)N and (Mo,Y, Al)N with a high (about 50 at%) content of yttrium (Y). The studies were carried out during the turning of steel with subsequent investigation of the wear area using scanning (SEM) and transmission (TEM) microscopes. Although the main parameters (elemental composition and structure) are identical and the values of hardness and elastic modulus are close, tools with the coatings under consideration demonstrated noticeable difference in wear resistance. The (Mo,Y,Al)N coated tool had a wear resistance 45% higher than the (Cr,Y,Al)N coated tool and 30% higher than the (Ti,Cr,Al)N reference coated tool. Active formation of cracks is detected in the (Cr,Y,Al) N coating, while oxidation wear dominated in the (Mo,Y,Al)N coating. Therefore, coatings containing layers of materials characterized by an increased tendency to oxidize, but at the same time providing a favorable compositional effect, can be effectively used. This is possible provided that the oxidation-resistant layers protect the oxidation-prone layers from active contact with oxygen.