Search

The paper proposes methods to predict the reliability of a multilayered coating based on a model with independently (sequentially) degrading layers. For the mathematical description of the process of crack penetration into the depth of a layered solid body from the free surface with certain roughness, the propagation of a crack tip into a layer adjacent to the free boundary of the coating is considered. This stochastic process is described through the specification of all multipoint probability distributions (densities), and it represents a Markov process. A mathematical model, described by equations of the parabolic type, is proposed to describe the above-mentioned process. Based on the above model, graphs are constructed to describe the change in the time of the crack propagation through a layer depending on the surface roughness and the ultimate strength (ductility) of the coating. The crack growth rate will be in the range from 10-6 mm/s (when the surface roughness is low) to 10-4 mm/s (when the surface roughness is high).

The article proposes a model of the ultimate stress state of the material of the coated tool cutter. It is found that with an increase in the fracture toughness of a tool in connection with the material ductility the machining accuracy deteriorates due to arising elastic-plastic vibrations of the tool cutter. In case when no ultimate stress state is reached, that is, a tool operates in the elastic region, then an alternating stress distribution diagram is realized for the tool cutter at the beam approximation. Therefore, in addition to the frictional vibrations, arising from the interaction between the tool cutter and a workpiece, the elastic vibrations can arise, which affects the machining accuracy and the service life of the coated tool cutter. The use of coatings makes it possible not only to increase the wear resistance of cutting tools, but also to transform the stress distribution diagrams of the normal σN and tangential τγ contact stresses acting on the rake face of the cutting tool. In particular, it is possible to control the length of the total contact area between the chips and the tool rake face.

The article deals with the problems of cracking in the structure of multilayered coatings under the conditions of stochastic loading process. A mathematical model has been proposed in order to predict the crack propagation velocity in the coating while taking the influence of interlayer interfaces into account. A technique for calculating the probability density distribution of the coating fracture (failure rate) has been developed. The probability of a change in the crack growth direction is compared with the experimental data that were obtained as a result of the studies focused on the pattern of cracking in the Zr,Nb-(Zr,Nb)N-(Zr,Nb,Al)N and Ti-TiN-(Ti,Cr,Al)N coatings under the conditions of the real stochastic loading of cutting tools during the turning. The influence of the crystalline structure of the coating on the cracking pattern has been studied. The investigation has found the significant effect of the crystalline structure of the coating layers on the cracking pattern. [ABSTRACT FROM AUTHOR]

The study proposes a model for the deposition of coatings, which takes into account the stochastic nature of the deposition process and is built considering the influence of the parallel convection and diffusion processes. The investigation has found that the dispersion of the motion direction of deposited particles in front of a substrate increases, which indicates a growth of the randomness in the trajectories of the particles being deposited. The obtained formulas indicate the fractal nature of the deposition process. During the formation of the multilayer coating structure, mismatched fractal structures of the layers overlap each other and thus the clustering effect is largely leveled out. The value of the nanolayer λ period has a significant influence on the fractal structure of the coating and the formation of feather-like hierarchical structures in it. [ABSTRACT FROM AUTHOR]

The article discusses the influence of the thickness of the wear-resistant layer of the Zr-ZrN-(Zr,Al,Si)N nanolayer composite coating on the values of residual stress and the nature of coating wear. The study focused on coatings with wear-resistant layer thicknesses of 2.0, 4.3, 5.9, and 8.5 µm, deposited using filtered cathodic vacuum arc deposition (FCVAD) technology. The X-ray diffraction (XRD) method based on the anisotropy of the elasticity modulus was used to find the values of the residual stress. The nature of the formation of interlayer delamination under the influence of residual compressive stress was studied using a scanning electron microscope (SEM). When the wear-resistant layers had a thickness of 2.0–5.9 μm, tensile stress formed, which decreased with an increase in the thickness of the coating. When the thickness of a wear-resistant layer was 8.5 μm, compressive stress formed. Under the action of compressive stress, periodic interlayer delamination formed, with a pitch of about 10 binary nanolayers. A mathematical model is proposed to describe the nature of the formation of interlayer delamination under the influence of compressive residual stress, including in the presence of a microdroplet embedded in the coating structure. [ABSTRACT FROM AUTHOR]