Abstract
Multilayer hard coatings remain among the most effective engineering solutions for reducing friction and wear and for extending the service life of components operating under high contact loads. However, their practical performance is governed not by multilayering per se, but by the extent to which the selected deposition technology enables reproducible control over three key parameters: layer density and defectiveness, adhesion to the substrate and/or interlayers, and architectural tunability through interface quality. This mini-review systematizes deposition approaches relevant to tribological applications and proposes a generalized classification comprising chemical processes (sol–gel, chemical vapor deposition (CVD), atomic layer deposition (ALD), hydrothermal synthesis, electrodeposition, anodization, and electroless coatings), physical vacuum techniques of the PVD family (magnetron sputtering, cathodic arc deposition, hollow cathode discharge (HCD) ion plating, ion beam assisted deposition (IBAD), among others), as well as hybrid and functional solutions (PVD+CVD, composite, self-lubricating, and nanocomposite systems). It is demonstrated that the selection of a deposition process for multilayer architectures must be based on technological constraints that directly affect interface stability and coating durability, including the deposition temperature window and conformality, interfacial diffusion-induced boundary blurring, residual stresses, and critical defects such as porosity, macroparticles, and growth-related imperfections. Practical guidelines are formulated for correlating “architecture–deposition regime–microstructure–tribological behavior,” and key directions for future research are identified, including interface and defect engineering, targeted hybridization of deposition processes to compensate for intrinsic limitations (conformality, density, adhesion, and interface stability), and the use of predictive modeling validated by comparable tribological testing.