Modified NiCr20Ti PVD-coating of Liquid Rocket Engines Combustion Chambers

The equipment and technology for applying heat-resistant coatings to the working surface of the liquid-propellant rocket engine (LPRE) combustion chamber are presented. The application of experimental coatings was carried out by the vacuum-arc method in a deep vacuum and in a vacuum in a nitrogen atmosphere for coating modification. The coatings were applied to the inner surface of a copper simulator of the LPRE combustion chamber. The coating material was NiCr20Ti alloy. The structure, phase composition, atomic-crystalline structure and hardness of the obtained coatings were investigated. The coating consists of two main structural components: a condensed matrix and a droplet phase of the cathode material. Nitriding helps to reduce the content of the droplet component. The coating is a Ni-Cr solid solution, which has a face-centered cubic lattice. Nitriding leads to the appearance of additional phases CrN, Cr ₂ N in an amount of up to 10% and the formation of a finer crystalline structure. The coherent scattering regions (CSR) for coatings obtained without nitriding are symmetrical in crystallographic directions and have dimensions of ~ 250 Å. Nitriding leads to a slight decrease in the CSR size to 200–210 Å and their asymmetry. The coatings contain residual tensile stresses ranging from 100–250 MPa with relative strain values ​​ε = - (0.06–0.14) %. Nitriding increased the hardness of the coatings from 383–414 HV to 544–615 HV. The created protective coatings will ensure an increase in the operational characteristics and service life of engines, which is important with the transition of space technology to reusable systems.