Mathematical estimation of inhomogeneity of the cutting tool structure strengthened with CrN coating

Abstract

Problem. Nuts grinding in the processing industry is produced with steel disk knives which have an insufficient durability of 1-2 turns. In order to increase the cutting tool operational stability, the hardening implementation is reasonable. The conducted industrial tests show that the service life of the tool reinforced by different methods differs. Among the reasons for the different operational resistance there are structural heterogeneity and nonequilibrium state of the phases of the deposited film coatings. Goal of our study consists in application of a new mathematical approach to estimate the heterogeneity degree of various structural components of a hardened cutting tool CrN surface operating under the local influence of abrasive particles. Methodology. An estimation of the degree of the hardening coatings structural heterogeneity is carried out with an optical-mathematical method. Results. A comparative analysis of features of the hardened tool surface structure formation with the initial state of the knife is performed. The proposed method makes it possible to establish that the degree of structural heterogeneity is 47 % lower for a tool with 3 μm thick CrN coating. Originality. Influence of the technology of tool hardening on tools' structure formation is determined. It is shown that cyclic coating of the tool surface prevents the diffusion of chemical elements from the base of the knife and reduces structural changes as compared to the initial state. The proposed method for describing the prints formation in the nanoindentification of coatings allowes one to estimate the behavior of the hardened layer deformation, which is important in understanding the performance of coating during operation. Practical value. A detailed analysis of the structures formed in the deposited layer made via the optical-mathematical method makes it possible to predict the development of the damageability of a hardened tool with different thicknesses of CrN coating