Search

Titanium nitride (TiN) coatings were obtained on the surface of 12Kh18N10T steel by air plasma spraying (APS) of TiN powders using an arc plasmatron made by the authors. The plasmatron has a node of circular input and gas-dynamic focusing of the powder and the output apertures of the nozzle-anode are made in the form of rectangular narrowing-expanding channels (No.34334 RK: IPC H05H 1/42). A study of operation modes of a plasmatron for spraying of powder coatings was carried out. The structural-phase state, microhardness and wear resistance of TiN coatings were systematically investigated. The optimum APS operating mode for deposition of TiN powder was determined: current 250 A, voltage 68 V, argon gas flow 34 L/min, spraying distance 150 mm. To reduce the oxidation of TiN powder in the APS process, a method of creating a nitrogen environment at the outlet of the anode nozzle, nitrogen flow rate 2.3 bar was used. The results of structural analysis showed that TiN is the main phase of the coating. The mechanism of formation of TiN structures was characterized by analyzing SEM results of TiN coating surface morphology and TiN droplets sprayed on the surface of the sample. The results showed that the TiN(1) coating has better wear resistance than the TiN(2) and TiN(3) coatings. The cross-sectional and longitudinal microhardness of the TiN coating was investigated. The highest cross-sectional hardness of TiN coating is 1250 HV0.1, which is in accordance with mode 1.

Ceramic coatings are used to protect against high-temperature oxidation of metal products. The efficiency of the technology of detonation spraying of two-layer coatings of aluminum oxide ( Al2O3 ) and a heat-resistant alloy (CoCrAlY) on the surface of a sample made of steel 12X18H10T was studied. A multi-chamber detonation unit was used in the work, providing high speed (up to 1000 m/s) and a 60–80% utilization rate of the sprayed material. We used an oxygen-neutral combustible mixture based on propane-butane. The coating material has a smooth gradient of properties from ceramic to sample substrate The complex of the obtained structural and physical-mechanical properties of the coating material makes it possible to predict its high performance under conditions of high-temperature oxidation.

In this study, the research results of the influence of pulsed plasma treatment on phase composition, hardness, and roughness of Cr3C2 -NiCr coatings are presented. The Cr3C2 -NiCr coating was applied to substrate 12Kh18N10T stainless steel by detonation spraying method. To change the physical and mechanical properties of sprayed coating’s surface layers, subsequent pulse-plasma treatment was used. The pulse-plasma treatment leads to changing the roughness of Cr3C2 -NiCr coating. The results of mechanical tests showed that after pulsed plasma treatment, the hardness of Cr3C2 -NiCr coating is increased. Based on X-ray diffraction analysis, it was found that the hardness increasing of coating is associated with phase transformations on the surface layer, in particular, the formation of the oxide phase and an increase in the number of carbide particles.

The article presents the study results of detonation spraying parameters on the phase composition and tribological properties of NiCr-Al2O3 powder coatings. The spraying was carried out at a ratio of the acetylene-oxygen mixture O2/C2H2=1.856. The detonation barrel filling volume with an explosive gas mixture varied from 30% to 68%. It is determined that the phase composition of the NiCr-Al2O3 coatings varies depending on the degree of detonation barrel filling. With an increase in the detonation barrel’s filling volume, the intensity of the NiCr diffraction peaks is decreased, and the intensity of the α -Al2O3 reflexes is increased, which indicates an increase in the content of the Al2O3 phase. When low filling volume, there is determined a low coating density and uneven roughness. The tribological test results showed that with an increase in the detonation barrel filling volume, there is a decrease in the wear volume, which confirms the increase in the coatings wear resistance. Determined that the lowest friction coefficient was recorded in the sample obtained at the barrel filling volume 68%. The coatings’ high wear resistance is associated with an increase in the alpha phase volume fraction of α -Al2O3 and coatings density.

As result of plasma-electrolytic nitrocarburizing 30CrMnSiA carbon steel (ferrite-perlite grade), there was a change in the elemental and phase composition, as well as the surface layer microstructure (40 ÷ 45 microns thick from the surface). A formation of Me23(CN)6 carbonitrides, FeN nitrides, Fe3C - (Fe,Cr)3C carbides and an increase in dislocation density within α–phase (tempered martensite crystallites), high-temperature lamellar martensite were observed. As a result of PEN / C exposure for 7 min. at 750 °C there is a reduction of friction coefficient and wear rate, what is connected with finely dispersed secondary phases FeN, (Fe, Cr)3C, Me23(C, N)6 formation. Thus there is an 2,5 ÷ 3,3 times increase in hardness of 30CrMnSiA carbon steel samples. Keywords: Carbonitrides, Microstructure, Electrolytic plasma processing, Wear rate, Hardness, Mild-Carbon steel