VACUUM ARC COATINGS FOR COMBUSTION CHAMBERS OF ROCKET ENGINES

An investigation was done for heat-resistant coatings from Ni-Cr and Fe-Ni-Cr alloys, produced by vacuum arc deposition with cathodes from nichrome alloy ХН78Т and steel 12Х18Н10Т. The microstructural analysis of the studied coatings applied by vacuum arc deposition with different amounts of reactive gas (nitrogen) in a deposition chamber showed the presence of two phases: a matrix and the distributed particles of liquid phase of various sizes and shapes. Vacuum arc deposition at a cathode arc current of 55 A for Ni-Cr and 82 A for Fe-Ni-Cr coatings, a cathode arc voltage of 28 to 32 V, an underlayer temperature of 490±30 оС, and no nitrogen in the chamber gives coatings with no apparent orientation of crystallites and a microhardness reaching 330 to 374 HV. The diffusion mobility of atoms decreases at a higher nitrogen pressure, which results in a coarse-crystal, porous-columnar structure of coatings with high porosity, a varying volume, and a rough surface. The influence of nitrogen pressure in a chamber on the strength of coatings was evaluated by their microhardness. A nitrogen pressure gain up to 0.13 Pa results in the increased microhardness of both coating systems, and the further growth in pressure has almost no effect on microhardness. It was discovered that a nitrogen pressure of 0.13 Pa gives the optimum combination of a coating’s strength and continuous structure with no pores and apparent columnar crystallites. Alloys from Ni-Cr with 80 % Ni are among the most heat-resistant industrial materials with a maximum operating temperature of up to 1200 оС. However, they are expensive, which makes Fe-Ni-Cr alloys more attractive, providing their heat resistance is sufficient for the operating temperature range. Therefore, it is reasonable to conduct further research on both Ni-Cr and Fe-Ni-Cr coatings to develop a deposition technology that can provide the required performance parameters. Controlling nitrogen pressure makes it possible to adjust the structure and properties of the coating during deposition.