EFFECTIVE REDUCTION OF CYCLIC STRESSES IN COATED SAMPLES

Abstract

The effect of two variants of condensed electron-beam titanium coatings on energy dissipation and fatigue resistance of the substrate material (Ti−6Al−4V) and the Cu-coating substrate, as well as the Hf/Ag/Ni/Cr microlayers coating, under nondestructive and destructive cyclic stresses was studied. This coating is peculiar in that a material with a higher elastic modulus is used in each subsequent layer (from the substrate to the outer layer) and the coating layers have a columnar microstructure and the binder layer has submicron twins peculiar to electron-beam evaporation and condensation in vacuum. With the layered macro- and microstructure, the energy of vibrations is absorbed by the coating material through both internal friction (between the coating layers and between the coating and the substrate) and dissipation of vibration energy on numerous defects of the columnar structure (intercolumnar porosity). For this purpose, resonant oscillations of the cantilevered samples on the first and second forms were excited to determine the dependence of the vibration decrement on the maximum stresses in the samples and the destructive fatigue stresses on the number of load cycles. In addition, the vibration transmission coefficients for cyclic stresses and vibration energy of fluctuations were experimentally defined and justified for use. One coefficient is equal to the ratio of the difference in stresses between the uncoated and coated samples to stresses in the uncoated sample at the same relative installation power in various tests. The other coefficient is equal to the difference in energy between the uncoated sample and coated sample to the energy of vibrations in the uncoated sample at the same relative installation power in various tests. The Hf/Ag/Ni/Cr coating is shown to provide greater energy dissipation but lower fatigue properties than the Cu coating and substrate. The vibration transmission coefficients are more sensitive to energy dissipation than the vibration decrement.