Mechanisms of stress generation and relaxation in thin films and coatings

The failure modes of thin metal films and ceramic coatings induced by both intrinsic (growth) stresses and external effects (uniaxial tension, alternating bending, thermal treatment) were studied. Stress relaxation that causes soft films and hard coatings to fail was demonstrated to be governed by essentially the same mechanisms. The primary factor governing the reliability of thin-film structures was shown to be the strength of the film/substrate interface

Effect of a hard sublayer on contact interaction and wear behavior of electrodeposited gold-based coatings

The mechanical properties and wear of electroplated Au–Ni coatings deposited on beryllium bronze substrates with Ni or Ni–B intermediate layers were investigated. It was revealed that the sublayer material has no significant effect on the hardness and the elastic modulus of the coatings. At the same time, the harder sublayer favors localization of plastic deformation and, thus, strain hardening of coatings in the course of tribological tests. The Ni–B sublayer was shown to provide significant wear reduction of Au–Ni coatings as compared with the Ni sublayer

Effect of a hard sublayer on contact interaction and wear behavior of electrodeposited gold-based coatings

The mechanical properties and wear of electroplated Au–Ni coatings deposited on beryllium bronze substrates with Ni or Ni–B intermediate layers were investigated. It was revealed that the sublayer material has no significant effect on the hardness and the elastic modulus of the coatings. At the same time, the harder sublayer favors localization of plastic deformation and, thus, strain hardening of coatings in the course of tribological tests. The Ni–B sublayer was shown to provide significant wear reduction of Au–Ni coatings as compared with the Ni sublayer

Estimating degradation of strength of neat PEEK and PEEK-CF laminates under cyclic loading by mechanical hysteresis loops

A method for assessing the degradation of mechanical properties of neat polyetheretherketone and its laminated composite reinforced with unidirectional carbon fibers is proposed. It is based on the calculation of the maximum and minimum strains in a cycle, as well as both dynamic and secant moduli estimated from mechanical hysteresis loops. These parameters reflect the material damage degree, enabling to predict its current mechanical state

Improvement of Thermal Cycling Resistance of AlxSi1−xN Coatings on Cu Substrates by Optimizing Al/Si Ratio

The effect of the elemental composition of AlxSi1−xN coatings deposited on Cu substrates by magnetron sputtering on their structure, mechanical properties and thermal cycling performance is studied. The coatings with Al-Si-N solid solution, two-phase (AlxSi1−xN nanocrystallites embedded in the SixNy tissue phase) and amorphous structure were obtained by varying Al/Si ratio. It is shown that polycrystalline coatings with a low Si content (Al0.88Si0.12N) are characterized by the highest thermal cycling resistance. While the coatings with a high and intermediate Si content (Al0.11Si0.89N and Al0.74Si0.26N) were subjected to cracking and spallation after the first cycle of annealing at a temperature of 1000 ◦C, delamination of the Al0.88Si0.12N coating was observed after 25 annealing cycles. The Al0.88Si0.12N coating also exhibited the best barrier performance against copper diffusion from the substrate. The effect of thermal stresses on the diffusion barrier performance of the coatings against copper diffusion is discussed

NUMERICAL STUDY OF STRESS-STRAIN LOCALIZATION IN THE TITANIUM SURFACE MODIFIED BY AN ELECTRON BEAM TREATMENT

Numerical simulation is performed to investigate the mesoscale stress-strain localization in a surface-modified commercial titanium alloy. The calculated crystalline microstructure corresponds to that observed in experiments and is accounted for in an explicit way as initial conditions of a dynamic boundary-value problem. The latter is stated in terms of plane strain developing in microstructure subjected to tension and is solved numerically by the finite-difference method. Elastic-plastic constitutive models were built to describe the experimental mechanical response both of the substrate and of the modified layer. Plastic strain localization is found to depend on the grain yield strength

Estimating degradation of strength of neat PEEK and PEEK-CF laminates under cyclic loading by mechanical hysteresis loops

A method for assessing the degradation of mechanical properties of neat polyetheretherketone and its laminated composite reinforced with unidirectional carbon fibers is proposed. It is based on the calculation of the maximum and minimum strains in a cycle, as well as both dynamic and secant moduli estimated from mechanical hysteresis loops. These parameters reflect the material damage degree, enabling to predict its current mechanical state

Continuous Electron Beam Post-Treatment of EBF3-Fabricated Ti-6Al-4V Parts

In the present study, the methods of optical, scanning electron, and transmission electron microscopy as well as X-ray diffraction analysis gained insights into the mechanisms of surface finish and microstructure formation of Ti-6Al-4V parts during an EBF3-process. It was found that the slip band propagation within the outermost surface layer provided dissipation of the stored strain energy associated with martensitic transformations. The latter caused the lath fragmentation as well as precipitation of nanosized β grains and an orthorhombic martensite α″ phase at the secondary α lath boundaries of as-built Ti-6Al-4V parts. The effect of continuous electron beam post-treatment on the surface finish, microstructure, and mechanical properties of EBF3-fabricated Ti-6Al-4V parts was revealed. The brittle outermost surface layer of the EBF3-fabricated samples was melted upon the treatment, resulting in the formation of equiaxial prior β grains of 20 to 30 μm in size with the fragmented acicular α′ phase. Electron-beam irradiation induced transformations within the 70 μm thick molten surface layer and 500 μm thick heat affected zone significantly increased the Vickers microhardness and tensile strength of the EBF3-fabricated Ti-6Al-4V samples