Improvement of the Hardness of Bilayer Coatings Produced by Gas-Thermal Spraying

In this work, samples of 30KhGS steel coated by thermal spray were investigated. The coating procedure consisted of two stages. At the first stage, a powder mixture of Cu + Al (mass ratio 4:1) was deposited. At the second stage, under the same process parameters, TiC powder was applied. After each spraying stage, the structure, elemental composition and stress state of the coatings were examined. Following the second deposition, hardness and wear resistance of the sample were measured. The results showed that the hardness and wear resistance of the test specimen increased on average by 40% compared to the corresponding properties of 30KhGS steel subjected to quenching and tempering. The residual stress level in the first (lower) coating was higher than in the upper layer; this difference is related to the distinct mechanisms of layer formation. The lower layer forms through melting and subsequent solidification, whereas the top layer forms by liquid-phase sintering. The obtained results demonstrate the effectiveness of the two-layer coating for increasing the hardness and wear resistance of 30KhGS steel, which broadens the possibilities for surface restoration and repair of parts.