Engineering, Energy, Transport AIC

Ihor BABYN – Candidate of Technical Sciences, Associate Professor of the Department of machinery and equipment for agricultural production of Vinnytsia National Agrarian University (St. Soniachna, 3, Vinnytsia, Ukraine, 21008, e-mail: ihorbabyn@gmail.com, https://orcid.org/0000-0002-7070-4957).
Pavlo LUTS – Candidate of Technical Sciences, Senior Lecturer of Department of machines and equipment of agricultural production of Vinnytsia National Agrarian University (St. Soniachna, 3, Vinnytsia, Ukraine, 21008, e-mail: luts@vsau.vin.ua, https://orcid.org/0000-0002-3776-8940).

Gas-thermal plasma spraying is one of the leading methods for forming protective ceramic coatings for parts operating in extreme conditions of high temperatures, abrasive wear and aggressive environments. The properties of such coatings (microhardness, bond strength, crack resistance, wear resistance) are extremely sensitive to the technological parameters of the process due to their lamellar structure and the presence of defects (pores, microcracks, incompletely melted particles).
The work systematically investigated the influence of key parameters of atmospheric plasma spraying (APS) on the microstructure and mechanical properties of ceramic coatings based on aluminum oxides (Al₂ O₃) and yttrium-stabilized zirconium (YSZ). The arc current (400 – 600 A), the ratio of plasma-forming gases Ar /H₂ (40/5 – 40/15 l/min ), the spraying distance (80 – 120 mm), and the torch travel speed (200 – 400 mm/s) were varied. The critical plasma spraying parameter (CPSP) served as an integral indicator of the energy load of the process.
The results showed that increasing CPSP from 0.8 to 1.2 kW/l contributes to better particle melting, a decrease in porosity from 15 – 20% to 5 – 8%, thinning of lamellae (from 2 – 3 μm to 1 – 2 μm) and improvement of interlamellar adhesion (the adhesion index increases to 0.85). This leads to an increase in microhardness by 20 – 40% (up to 1200 – 1400 HV), adhesion strength to 70 – 90 MPa and wear resistance by 1.5 – 2 times (according to the ASTM G65 test). Optimization of the hydrogen content in the plasma-forming mixture increases the particle velocity to 500 – 600 m/s, which further reduces porosity to 4 – 6%. At the same time, an excessive increase in CPSP causes an increase in residual stresses (up to 500 MPa tensile) and vertical cracks, which worsens thermocyclic resistance (reduction in the number of cycles to failure at 1000°C from 500 to 200).
Reducing the spraying distance to 80 – 100 mm and the torch speed to 200 – 300 mm/s provides a more uniform dense structure with minimal defects and an increased elastic modulus of up to 200 GPa. Correlation analysis confirmed a strong negative dependence of microhardness on porosity (r = –0.92) and a positive dependence of adhesion strength on the adhesion index (r = 0.88).
Theoretical 2D models of the microstructure were used for visualization: at low CPSP – a loose porous structure with numerous horizontal cracks; at high CPSP – a compact lamellar structure with minimal cavities.
The obtained data allow us to develop recommendations for optimizing the sputtering regimes (CPSP ≈ 1.0 kW/l, Ar /H₂ = 40/10 l/ min, distance 100 mm) to achieve a balance between density, hardness and crack resistance. This opens up prospects for increasing the service life of coatings by 1.5 – 2 times for use in aircraft turbines, power equipment, the chemical industry and other high-tech industries where the reliability of protective layers is critical.

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