Page 14 - НАЦІОНАЛЬНА АКАДЕМІЯ НАУК УКРАЇНИ

14

2...5 microns of a round shape were found in the coating structure. The porosity of

the coatings was in the range of 2...5%.

Coatings obtained by PSCDV also have a lamellar structure. However, unlike

HVOF coatings, most of the droplets are practically fused to each other, and the

lamellas are strongly deformed, which indicates that the droplets at the moment of

impact on the sprayed surface were completely melted. VC carbides, extremely small

in size (<500 nm), were found in the coating structure. The porosity of the coatings

did not exceed 0.5%. Such a difference in their structure is caused by a higher

temperature of the plasma (15000°C) than gas-flame jet (2600...2800°C).

The addition of Co powder to the FeCr-VC powder spraying mixture did not

affect the size of VC carbides, but they turned out to be irregular shape. It was found

that the sizes of carbides in the coating structure depend on the chosen spraying

method, which provides a certain temperature to the molten drops. The higher the

temperature of the sprayed droplets the smaller VC carbides are formed in the

coating. Small VC carbides were obtained using the PSCDV method when the

temperature of the droplets was higher than the melting temperature of VC carbides.

So, since the structural phase composition of the formed coatings is the same,
the main factors that affect on their properties are the size of the carbide inclusions

and porosity.
It was found that during friction with a rigidly fixed abrasive, the wear

resistance of coatings increases with the size of VC inclusions. If Co is present in
them, the trend is similar, but wear is greater. Since cobalt does not form carbides,

ductile inclusions based on it are formed in the structure of such a coating.

When tested with non-fixed abrasive, the wear resistance of the coatings

increases with decreasing VC sizes. It was further enhanced with the addition of Co

to the spray powder composition.

By metallographic analysis of the corroded surface, it was found that, unlike an

unmodified alloy, in which, under the corrosive medium influence, sections enriched

in MgZn 2 (Al/MgZn 2 galvanic couple) are dissolved, the modification by SiC

particles of B95 alloy inhibits their dissolution, slowing down corrosion processes,