Abstract

The wear and failure mechanism for multilayered nanostructured coatings has a number of significant differences from the one typical for monolithic single-layered coatings. In particular, while the strength of adhesion bonds at the “substrate-coating” boundary is important for monolithic coatings, then for multilayered nanostructured coatings, the strength of adhesion and cohesion bonds at interlayer boundaries and boundaries of separate nano-sublayers becomes of significant significance. Meanwhile, the delamination arising in the structure of multilayered nanostructured coatings can have both negative (leading to loss of coating uniformity and subsequent failure of coating) and positive influences (due to decrease of internal stresses and inhibition of transverse cracking). Various mechanisms of formation of longitudinal cracks and delaminations in coatings on rake tool faces, which vary based on the compositions and architectures of the coatings, are studied. In addition, the influence of internal defects, including embedded microdrops and pores, on the formation of cracks and delaminations and the failure of coatings is discussed. The importance of ensuring a balance of the basic properties of coatings to achieve high wear resistance and maximum tool life of coated metal-cutting tools is shown. The properties of coatings and the natures of their failures, as investigated during scratch testing and dry turning of steel C45, are provided.

Highlights

  • The obtained curves were used to determine two parameters: the first critical load LC1, at which first cracks appeared in nanoscale multilayered composite coatings (NMCC), and the second critical load LC2, which caused the total failure of NMCC

  • Numerous research efforts and the experience of the authors of this paper show that a scratch test does not have a unique correlation with the tool life of a coated tool [1]; the test allows only “rejecting” coatings with insufficient strength of adhesion bonds

  • This test enables a study of the nature of the coating failure, from the point of view of delaminations that occur in its structure

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Summary

Introduction

One way to improve the performance characteristics of tool materials is to enhance their surface properties by applying modified coatings [1]. The use of a multilayered architecture of coatings and the use of nanostructured technology can significantly improve the performance characteristics of a new generation of coatings. If in some slip plane dislocations stop before a sufficiently powerful obstacle, a cluster of dislocations is formed, and it causes a high concentration of stresses at the obstacle This concentration of stresses results in formation of a dislocation microcrack. It should be noted that the problems of crack formation and delamination in the structures of multilayered coatings have not been studied as thoroughly as have other aspects of operation and wear of such coatings

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