Abstract
This review presents a systematic analysis of recent studies (primarily, in 2019–2025, with reference to foundational earlier works) concerned with flame spraying of composite coatings, with an emphasis on the underlying physical mechanisms governing structure formation and service properties. Flame spraying is considered as complex multiphysics process involving coupled heat and mass transfer, gas dynamics, phase transformations, and mechanical deformation of particles during their interaction with the substrate. The analysis demonstrates that the physical state of particles, namely, temperature, velocity, and degree of melting, plays a decisive role in splat formation, development of interlamellar boundaries, and porosity evolution, which collectively determine the microstructure of flame-sprayed coatings. As shown, microstructure acts as a key link between process parameters and macroscopic properties, including adhesion strength, mechanical and tribological behaviour, damping capacity, and fatigue durability. Special attention is paid to the functional role of interlamellar boundaries and pores, which, beyond being structural defects, serve as dominant sources of internal friction and mechanical-energy dissipation under cyclic and dynamic loading. The review highlights the inherent trade-offs between hardness, wear resistance, adhesion reliability, residual stresses, and damping properties, emphasising the necessity of a physically grounded compromise-based design approach. The prospects for further development of flame-spraying technology are discussed in the context of in situ diagnostics, numerical modelling, multiscale analysis, and physics-based process control. These approaches enable the transition from empirical-parameter selection toward predictive design of composite and multilayer coatings with tailored and reproducible properties, expanding the application of flame-sprayed coatings in modern engineering systems from the physical-science perspective.