Influence of the Morphology of the Interface between the Coating and the Substrate on the Distribution of Thermoelastic Stresses in High-Speed Steels

Finite element methods have solved the problem of the influence of the morphology of the interface between a coating made of high-speed steel S2-9-2 and a substrate made of structural steel 30HGSA on the distribution of thermoelastic stresses in the coating. It was solved in two stages. At the first stage, the behavior of stresses during cooling from a temperature of 1573 K to a temperature of 293 K was studied. At the second stage, after cooling, a static tensile load was applied to the coating surface. The morphology of the interface was determined using scanning electron microscopy data. It follows from them that the interface has a curved appearance and, in the first approximation, can be described by a harmonic function. It is shown that at the cooling stage the undulating interface between the coating and the substrate serves as the most effective barrier to crack formation, redistributing the areas of dangerous tensile forces into the substrate. The application of a tensile static load to the coating after cooling has shown that in the case of a rectilinear interface, when the value of the elastic modulus of the substrate (E_c) is an order of magnitude less than the elastic modulus of the coating (E_s), the coating separation from the substrate is observed. The plastic flow occurs mainly in the coating. The same situation is observed for a curved boundary with the only difference that it prevents separation. If E_s = 10E_c, then for a rectilinear boundary, plastic flow is observed both in the substrate and in the coating, and for a curved boundary, this process occurs mainly in the substrate.