The role of interatomic interactions in the tribooxidation and wear of the multilayer Ti0.2Al0.55Cr0.2Si0.03Y0.02N/Ti0.25Al0.65Cr0.1N coating at severe cutting conditions

Abstract

Tribooxidation is the main mechanism to adapt the cutting tool to extreme mechanical and thermal loads during high-speed cutting. Wear and tribooxidation processes in the single layer TiAlCrSiYN and multilayer TiAlCrSiYN/TiAlCrN non-stoichiometric coatings on cutting tools after dry cutting with speed of 500 m/min on the running-in and steady wear stages were studied by the set of modern surface analysis methods. The reasonable preference of the multilayer coating comparing to the single layer one was demonstrated. It was established that oxide films with an amorphous-nanocrystalline structure are formed on the surface of the wear hole. Their composition is close to k Cr₂O₃, TiO₂, Al₂O₃ (sapphire) and Al₂O₃ · 2(SiO₂) (Mullite 1:2). Prospects of yttrium addition in the complex nitride were estimated by quantum chemical calculations, which has shown that such polyvalent metals as Ti⁺⁴, Cr^+5,6, Y⁺⁴, Al⁺³ in a multicomponent nitride form a very complex spatially organized electronic structure of double and triple bonds with unoccupied π*-orbitals of nitrogen atoms. Quantum-chemical calculations of the oxidation susceptibility of these coatings with Y microadditions confirmed that this element is more inert than chromium and it is predominantly involved in the formation of interatomic bonds with Al, Ti, Cr affecting the mechanical properties of nitride coatings.