Micro-arc oxidation (MAO) coatings were produced on commercially pure titanium Grade 2 using a composite electrolyte containing sodium phosphate (Na₃PO₄) and sodium silicate (Na₂SiO₃), while varying the applied voltage. The surface morphology, phase composition, and structural features of the coatings were examined using scanning electron microscopy (SEM) and X-ray diffraction (XRD). The coatings exhibited a characteristic crater-like microporous surface morphology associated with the micro-arc discharge process. XRD analysis confirmed the formation of mixed TiO₂ phases in the anatase and rutile modifications, with higher voltages promoting the growth of the thermodynamically stable rutile phase. Corrosion and tribological properties were evaluated in a 3.5 wt.% NaCl solution using potentiodynamic polarization and a ball-on-disc test configuration, respectively. The results revealed a substantial improvement in both corrosion resistance and wear performance compared with bare titanium. The coating formed at 300 V demonstrated the highest wear resistance due to its denser microstructure, whereas the coating produced at 350 V exhibited the lowest friction coefficient and the greatest corrosion resistance, attributed to the increased rutile content. Overall, MAO coatings fabricated in the phosphate–silicate electrolyte effectively enhance the combined operational properties of titanium and can be recommended for applications requiring improved wear and corrosion resistance.

This study presents a systematic investigation of laser surface hardening of 9CrSi tool steel with the aim of establishing the relationships between processing parameters, microstructural evolution, and resulting mechanical and tribological properties under the applied laser conditions. The influence of laser power, modulation frequency, and scanning speed on the hardened layer depth, microstructure, and surface properties was analyzed. Laser treatment produced a martensitic surface layer with varying fractions of retained austenite, while the transition zone consisted of martensite, granular pearlite, and carbide particles. X-ray diffraction identified the presence of α′-Fe, γ-Fe, and Fe₃C phases, with peak broadening associated with increased lattice microstrain induced by rapid self-quenching. The surface microhardness increased from approximately 220 HV_0.1 in the untreated state to 950–1000 HV_0.1 after laser hardening, with hardened layer thicknesses ranging from about 500 to 750 µm depending on the processing regime. Instrumented indentation showed higher elastic modulus values for all hardened conditions. Tribological tests under dry sliding conditions revealed reduced coefficients of friction and more than an order-of-magnitude decrease in wear rate compared with untreated steel. The results provide a parameter–microstructure–performance map for laser-hardened 9CrSi steel, demonstrating how variations in laser processing conditions affect hardened layer characteristics and functional performance.

This study investigates the influence of detonation spraying parameters on the microstructure, mechanical properties and tribological performance of self-fluxing Ni–Cr–Fe–Si–B–C coatings deposited on AISI 321 stainless steel substrates. The effects of the barrel filling ratio (48–68%), the oxygen-to-fuel molar ratio (O/C = 1.026–1.856), and the delay time between detonation shots (0–1 s) were systematically evaluated. The coatings were characterized using scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), X-ray diffraction (XRD), microhardness measurements, instrumented indentation, and ball-on-disk tribological testing. Microstructural investigations revealed that the spraying parameters significantly influence coating thickness, porosity and defect formation. The lowest porosity (0.306 per cent) and the most homogeneous microstructure were obtained at a barrel filling ratio of 48 per cent, an O/C ratio of 1.026 and a shot delay of 1 s. XRD analysis identified a multiphase structure consisting of a Ni₃Fe matrix reinforced by Cr₇C₃ carbides, Ni₃B and CrB borides, and Ni₃₁Si₁₂ silicides. Tribological tests demonstrated that increasing the delay between shots significantly improved wear resistance, reducing the wear rate to 1.89 × 10⁻⁴ mm³/(N × m). The optimised coating exhibited an average coefficient of friction of 0.578 ± 0.093 and a wear rate of 1.03 × 10⁻⁴ mm³/(N × m). Instrumented indentation revealed a hardness of 1049.1 ± 43.4 HV and a Young’s modulus of 215.9 ± 8.5 GPa. The wear mechanism was predominantly abrasive–adhesive, whilst the wear rate of the 100Cr6 counter-body remained low at 1.20 × 10⁻⁵ mm³/(N × m). The results obtained demonstrate that appropriate optimisation of detonation spraying parameters enables the formation of dense Ni–Cr–Fe–B–Si–C coatings with superior mechanical and tribological properties, making them promising candidates for wear-resistant engineering applications.

Laser hardening is normally applied in the solid-state regime, and the behaviour of chromium steels treated at a line energy high enough to melt the surface is far less documented. Here 40Cr steel (AISI 5140) was laser hardened at 3000 W and 5 mm/s (600 J/mm) with one, two and three passes and compared with the untreated state by roughness measurement, microhardness profiling, quantitative porosity analysis, X-ray diffraction, dry ball-on-disc sliding against a 100Cr6 ball (6 N, 3 cm/s, 200 m, n = 3) and abrasive testing to GOST 23.208-79. One pass produced a hard (530–590 HV) but porous remelted layer, with 6–9% porosity in the top 300 µm and a dislocation density of 1.6 × 10¹⁵ m⁻². Repeated remelting reduced the porosity to below 1%, while the near-surface hardness fell to 280–310 HV, the dislocation density decreased four- to five-fold, and the hardened region extended to about 1300 µm, indicating tempering of the previously hardened material. After grinding and polishing, the specific wear rate of the steel in sliding fell significantly (p < 0.001) from 6.5 × 10⁻⁵ to 2.9, 4.3 and 1.7 × 10⁻⁵ mm³/(N·m), i.e., by 54, 34 and 74%, whereas the friction coefficient, 0.62–0.66, did not differ between the states. Under loose abrasive, the mass loss fell by 8.4, 25.5 and 14.3%. Three passes are recommended for sliding contacts and two passes for abrasive conditions; a single pass is not recommended because of the porosity of its remelted layer.