Surface Engineering and Coating Technologies: A Systematic Review was Conducted on the Use of Metallic Components

The current systematic review critically summarizes the latest advances in surface engineering and advanced coating technologies for metallic components, based on more than 90 publications from the last eight years (from 2018 to 2026), that are published in peer-reviewed journals. The processing–structure–property relationships of multi-principal element alloy coatings, high-entropy ceramic systems, functionally graded materials (FGMs) and their derivatives in various applications such as aerospace, biomedical, and energy fields are discussed. Each of the physical vapour deposition (PVD), chemical vapour deposition (CVD), thermal spray processes (APS, HVOF, PS-PVD), electrochemical deposition and laser cladding are discussed with regard to microstructural control, adhesion, tribological properties and corrosion resistance. The importance of configurational entropy, sluggish diffusion and lattice distortion in achieving improved mechanical and thermal stability is highlighted. In addition to computational modelling, characterisation techniques such as nanoindentation, electrochemical impedance spectroscopy (EIS), pin-on-disk tribometry, X-ray computed tomography (XCT) and Raman spectroscopy are discussed. Graded systems are shown to be better than multilayer architectures for the capability to withstand thermal cycling and mitigate biomedical stresses, through a comparative analysis. The review ends with a summary of the current gaps or research challenges such as the development of multiscale predictive models, scalable green manufacturing processes, and stimuli-responsive multifunctional coating systems that can modulate the immune microenvironment in clinical implant applications.