Recent Trends in Laser Cladding for Advanced Surface Engineering: A state-of-the-art review

Laser cladding has emerged as a transformative surface engineering technology capable of depositing metallurgically bonded coatings with tailored microstructures and enhanced functional performance. This comprehensive review synthesizes to establish systematic correlations between laser processing parameters, melt-pool dynamics, solidification behavior, microstructural evolution, and the resultant mechanical, corrosion, and hydrogen embrittlement properties of clad coatings. The review critically examines how key parameters, namely, laser power, scanning speed, beam diameter, powder/wire feed rate, dilution, and overlap ratio, govern grain morphology, phase constitution, defect density, and residual stress states across Ni-based, Fe-based, Co-based, high-entropy alloy (HEA), and ceramic-reinforced composite systems. Optimized processing conditions consistently yield refined cellular or equiaxed microstructures with enhanced hardness, wear resistance, and corrosion performance. At the same time, excessive heat input promotes grain coarsening, dilution-induced phase destabilization, and increased defect susceptibility. Particular emphasis is placed on hydrogen embrittlement mechanisms in laser-clad layers, revealing a multiscale interplay between hydrogen diffusion, microstructural trapping sites (grain boundaries, dislocations, phase interfaces), residual stress fields, and micro-porosity. The review demonstrates that FCC-dominated Ni/Co-based and HEA coatings exhibit superior hydrogen resistance due to stable passive films, low hydrogen diffusivity, and efficient trapping. In contrast, Fe-based systems require stringent parameter control to limit martensitic transformation and crack propagation. Current challenges and future directions are outlined, including AI-driven process optimization, in-situ monitoring, functionally graded multi-material designs, and hydrogen-safe coating development for emerging energy infrastructures. This review provides an integrated framework for designing next-generation laser-clad coatings with optimized performance in corrosive, wear-intensive, and hydrogen-containing environments.