Crack-dominated failure of thrust chamber inner wall with multilayer metal coatings

Thrust chambers commonly reported in application features straight cooling channels and thin thermal barrier coatings. However, this design suffers from durability limitations due to high-temperature degradation, cyclic fatigue, and coating spalling. In this study, a different design incorporating electrodeposited multilayer metal coatings and spiral cooling channels is investigated. It reveals a progressive coating-to-inner wall cracking mode of the thrust chamber, distinct from the classical “doghouse failure” mechanism. Through multiscale characterization (macro to micro), multi-dimensional observation (3D to 2D), and fluid-thermal-structural coupling simulations, the crack behaviors in a tested thrust chamber segment after repeated hot firing tests are systematically analyzed. The results indicate that radial micro-cracks predominantly initiate near and above the Cr-Ni interface, exhibiting diversity in initiation location, morphology, and formation process. On a larger scale, the macro-cracks formed by micro-cracks growth and interaction are most likely to originate around the throat. Investigations on crack propagation demonstrate that the axial extension of macro-cracks along the thrust chamber is governed by localized influences from mud cracks within the Cr coating and global regulation through circumferential stresses. Nevertheless, their radial propagation is constrained by the thick coatings, leading to sequential fracture initiation across different metallic layers. In addition, distinct crack propagation mechanisms are identified: in the Cr coating, cracks propagate through leading crack formation at the tip; however, in the Ni coating, propagation occurs via nucleation, growth, and coalescence of voids near the crack tip, ultimately connecting with the tip. Based on these insights, several optimization strategies are proposed. This work can provide guidance for improving the reliability and longevity of reusable rocket engines with multilayer metal coatings and spiral cooling channels.