Page 10 - НАЦІОНАЛЬНА АКАДЕМІЯ НАУК УКРАЇНИ

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values of this indicator, which will protect the coatings from cracking, correspond to

σres/σc ≤ 0.55.

The arc coatings from CWs sprayed onto an aluminum or steel base have the

same typical lamellar structure, where the lamellae are crystallized droplets of the CW

melt on a steel base. The structure of the coatings contains the pores and oxide

inclusions. It was established that the amount of the oxygen, and, accordingly, oxide

inclusions in the structure of the arc coatings, decreases with an increase of the Cr

content in the CW from 6 to 17 wt.%. In the process of spraying the coatings, the low-

melting components of the charge – Na 2B 4O 7 or B 2O 3 melt and form a protective film

around the ferrochrome particles (the main component of the CW charge) and, thus,

reduce the oxidation of Cr. When using the supersonic air flow, the arc coatings have a

more dispersed structure and a smaller number of pores than when using the subsonic

air flow, which leads to an increase of the cohesive strength (σc) and a decrease of the

residual tensile stresses of the first type (σres) in the coatings. The exothermic

reactions that occur between the components of the CW charge during the spraying of

the arc coatings and an increase of the kinetic energy of molten droplets in the

supersonic spraying mode cause an increase of their temperature by 300...500 °C, and

the formation of zones of fusion of the coating and the aluminum base, and as a result,

an increase of the adhesion strength of the coating to the base. It was found that the C

content in the coatings as a result of burnout decreased relative to its content in the

CW: in the subsonic mode to 0.71 wt.% and fluctuated within the range of 0.71…

0.80 wt.%, and in the supersonic mode – to 0.51 wt.% and fluctuated within the range

of 0.49…0.53 wt.%. Such fluctuations in its content were due to the heterogeneity of

the coatings, which caused the uneven distribution of C and Cr, Mn and Si within ±5%

in their lamellae.

To develop the charge of the CWs of the corrosion-resistant coatings, the

calculation formulas were used that allowed to determine the required Cr content in the

coating lamellae to ensure its concentration in them of at least 12 wt.%. The formulas
take into account the uneven distribution of Cr in different coating lamellae due to their

microheterogeneity, as well as the depletion of the solid solution inside the lamellae by