Page 15 - НАЦІОНАЛЬНА АКАДЕМІЯ НАУК УКРАЇНИ

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and the size and depth of local defects significantly reduced. Obviously, after the

modification, another Al/Al 4SiC 4 galvanic pair appears and the corrosion failure

proceeds localized with the formation of a pitting in places where Al 4SiC 4 inclusions

are present.

By potentiodynamic studies, it was found that heating the substrate to 250°C is

less efficient than 100°C, due to the higher volume content of Al 4SiC 4 inclusions,

which are the cause of the corrosion destruction of the modified layer. It was revealed

that, although the modified layer is heterogeneous, its corrosion resistance increases

by 2-6 times depending on the medium.

The ambiguous influence of the sizes of vanadium carbide was established.

Micromechanical studies have found that in the presence of cobalt, the microhardness

of the coating, the elastic modulus and tensile stresses of the second kind are reduced,

and microplasticity is increased. Therefore, in friction tests with a rigidly fixed

abrasive, when wear occurs by excision the surface with abrasive particles, cobalt,

which reduces the microhardness and cutting force of the coating by abrasive

particles, also reduces its wear resistance.

However, when testing with a non-fixed abrasive, when wear occurs due to
rolling of the abrasive particles on the surface of the coating, the fatigue mechanism

of nucleation and propagation of microcracks is most often realized. In this case, with
the decreasing of tensile stresses of the second kind in the coating with cobalt and the

increasing of its microplasticity, its wear resistance increases.
Analyzing the results of potentiodynamic studies, it was found that the

corrosion resistance of the studied gas-thermal coatings determines their porosity,

which depends on the spraying methods. In lengthy tests, there is a risk of sub film

corrosion, which may contribute to delamination of the coating.

Therefore, for long-term operation in corrosive environments, products with

coatings applied by high-speed flame spraying should be impregnated with

substances that would protect the substrate from the penetration of corrosive

environments.