# Comprehensive Study of the Mechanical and Tribological Properties of NiCr-Al Detonation Coatings
## 2 Materials and Methods  
For the deposition of NiCr-Al coatings, 14 MoV6-3 low-alloy steel was selected as a substrate (according to ISO 4955) [44]. For substrate preparation, 14 MoV6-3 steel was cut into discs with a diameter of 50 mm and a thickness of 3 mm. Prior to coating deposition, the surface of the substrate samples was ground using abrasive papers up to grit size 1000, followed by sandblasting to enhance the mechanical interlocking and adhesion strength of the coating. Polishing up to grit size 2000 was applied to the cross-sectional samples prepared for microstructural analysis. To prepare the composite powders, Ni75 Cr25 powder and Al powder with a purity of 99.99% were used. A BML-6 ball mill was used for mixing the powder blend and performing mechanical activation. The mechanical activation was carried out for 2 h at a vibration frequency of 30 Hz. Figure 1 shows the morphology and particle size distribution of the NiCr-Al (20 wt.%) composite powder obtained by scanning electron microscopy (SEM) (TESCAN MIRA3 LMH (TESCAN, Brno, Czech Republic). The particle size of the powder was determined from the SEM images using ImageJ software (version 1.54). The measurements were conducted on three SEM images taken at 100\(\times\) magnification. The average particle size and standard deviation were calculated based on the measurements of individual particles. The NiCr-Al coating was applied using a CCDS2000 detonation spraying system (LIH SB RAS, Novosibirsk, Russia), with the process being computer-controlled (Figure 2). The schematic diagram of the coating process using the CCDS2000 detonation system is shown in Figure 3. The detonation spraying process is carried out in the following sequence:combustible gases (acetylene, oxygen, and inert gases) are supplied and mixed in the combustion chamber (3) through the valve block (9; 2); the gas mixture in the combustion chamber is ignited by the ignition device (4), resulting in the formation of a detonation wave that propagates at high speed through the barrel (14); simultaneously, powder is fed under pressure from the feeder (11) into the barrel space (10); during the detonation explosion, the powder particles melt and accelerate under the influence of the shock wave, impacting the surface of the substrate (12) to form a coating layer. The detonation spraying process is controlled via the control unit (1), and during spraying, the movement of the sample is regulated using a 3D manipulator (13). Figure 1: Morphology (**a**) and particle size distribution (**b**) of the NiCr-Al (20%) composite powder. Figure 3: Schematic diagram of the coating deposition process using the CCDS2000 detonation system [45]. 1—control computer; 2—gas distributor, 3—mixing and ignition chamber, 4—igniter, 5—inlet valve, 6—fuel line, 7—oxygen line, 8—gas valves, 9—gas supply unit, 10—barrel bore section, 11—powder feeder (dispenser), 12—workpiece; 13—manipulator, 14—barrel muzzle section. Figure 2: CCDS2000 detonation spraying system. To deposit the NiCr-Al coating, an oxygen-acetylene (O\({}_{2}\)/C\({}_{2}\)H\({}_{2}\)) mixture was used as the explosive gas, which is the most commonly used fuel in detonation spraying of powder materials. Depending on the composition and ratio of the O\({}_{2}\)/C\({}_{2}\)H\({}_{2}\) explosive mixture, chemical interactions may occur between individual phases of the composite particles [45]. The spraying process was carried out with the explosive gas mixture at a ratio of O\({}_{2}\)/C\({}_{2}\)H\({}_{2}\) = 1.856. Nitrogen was used as the carrier gas. The distance between the substrate and the detonation barrel was 150 mm. This distance allows the impact energy of the particles on the surface to be maintained at an optimal level, resulting in the formation of a coating with high adhesion. The diameter of the barrel was 20 mm. The barrel diameter regulates the flow of the sprayed particles and ensures their uniform distribution.