7. The Nucleation and Development of Wear in Nanocomposite Coatings Under the Action of a Discrete Vapor-Droplet Flow

The analysis of the initial stage of wear initiation in crystalline materials with a heterogeneous structure under cyclic impact loading is conducted. Wear under these conditions begins with the formation of fatigue defects. Depending on the structure of the material and loading conditions, they are formed as cracks, pores or craters. A theoretical model is proposed for calculating the duration of their nucleation. The parameters of the model for its application in the conditions of droplet impingement erosion, in particular, under the influence of a discrete vapor-droplet flow, are considered and determined. The results of model calculations are presented in comparison with the experimental data of bench droplet tests for steel samples 20Cr13 with a sorbite structure and samples with a vacuum ion-plasma coating of the TiAlSi-system with a 3D-nanocomposite structure. It is shown that under conditions of contact cyclic loads, the wear resistance of materials and coatings is primarily determined by structural parameters. Based on the presented calculation results and experimental data, the use of the proposed model for the design of wear-resistant materials and coatings is recommended. Experimental data on the development of wear of the ion-plasma TiAlSi-coating upon droplet impingement action are also presented. Chipping of the coating occurs by the formation of fragmented porous cracks.