Performance and Damage Evaluation of a Regeneratively Cooled Thrust Engine Coated with ZrO₂ / Ni Functionally Graded Materials : Evaluation Test Results of a Chamber Partially Coated with ZrO₂ / Ni FGM Made by the Electroforming Method

Abstract

A combustion chamber partially coated with ZrO₂ / Ni functionally graded materials (FGM) was cyclically tested, using a bipropellant of nitrogen tetroxide (NTO) / monomethyl hydrazine (MMH) at a chamber pressure (P_C) of 0.9 MPa, to show the effect of such coatings on the life span of the chamber. This thermal barrier coatings were applied using a process that employed the electroforming method. The C^* efficiency (ηC^*) for the durability tests of the partially ZrO₂ / Ni FGM-coated chamber was 97% at P_C=0.9 MPa and mixture ratio (MR) of NTO / MMH=1.65. At the cylindrical section of the chamber, the thermal barrier coating subsequent to composed of pure ZrO₂ remained partially intact. However, the inner surface coating of the chamber throat section suffered premature delamination. The typical damage mode observed in a carbon fiber-reinforced carbon matrix (C / C) chamber of a bipropellant engine in our previous study was also seen near the injector face. In the cycle durability tests, the damage to the coating was inspected by means of the Replica method. After a total of 260 firing tests, a profile of the coating damage was obtained by means of a computer-aided micro-analyzer (CMA) system.