Page 9 - НАЦІОНАЛЬНА АКАДЕМІЯ НАУК УКРАЇНИ

9

to 4 MPa. At a counterbody hardness of 300-1000 HV0.3, the wear occurred due to

repeated elastic or elastic-plastic deformation of the counterbody surface. Such a

friction pair is a suitable for the use at the specific loads up to 10 MPa.

The method of the supersonic spraying of the wear-resistant reduction coatings

from cored wires (CW) of the Fe-Cr-Si-Mn-B-C alloying system was developed. The

supersonic air flow with a Mach number of 2 was obtained by increasing the air flow

pressure from 0.6 to 1.2 MPa, which resulted in an increase in its speed by 2 times

from 300 to 600 m/s, the molten droplets from 120 - 150 m/s to 280 - 300 m/s, while

the hardness of the coatings increased from 600 to 900 HV0.3, the abrasive wear

resistance by 1.4...1.7 times, and the level of the residual tensile stresses of the first

type in the coating decreased by 2 times.

The CWs of the Fe-Cr-Si-Mn-B-C alloying system were developed for the arc

spraying of the wear-resistant coatings with an exothermic charge based on the

powders of boron, chromium, titanium and iron carbides. The nano-sized (50...150 nm)

precipitates of the borides of titanium, chromium and iron were formed in the structure

of the coatings, which ensured an increase of the physical and mechanical

characteristics of the coatings. The complete fusion of the components of the charge

and the shell was achieved by adding 1 wt.% of a mixture of low-melting powders of

eutectic composition (FeSi + FeMn + B 2O 3) to the CW charge, which ensured the

production of homogeneous coatings with a predetermined structural and phase

composition. The wear resistance of the coatings sprayed in the supersonic mode twice

exceeded this indicator for U12 steel with a hardness of 840 HV0.3.

The indicator practically suitable for the certification of coatings for their

susceptibility to cracking was proposed and substantiated, which was defined as the

ratio of the residual tensile stresses of the first type in coatings σres to their cohesive

strength σc (σres/σc). Based on the analysis of the susceptibility to cracking of the

obtained coatings, the key values of the introduced indicator for practical use were

substantiated: σres/σc > 0.75 – corresponds to the beginning of the formation of single
cracks in the coatings, which makes the coatings unsuitable for operation. The optimal