Recent advances in laser-cladding of metal alloys for protective coating and additive manufacturing

Abstract Material degradation of metal alloys usually starts from the surface induced by tribological systems along with extremities including elevated temperatures, irradiations, erosion, corrosion, etc. Surface engineering, e.g. cold-working, carbonization, nitridation, etc., and coating are distinct routes that have been developed to protect the surface of metallic components. Laser cladding is an advanced method to produce metal alloys and build them up layer-by-layer, which has the advantage of being feasible in digitalizing the materials engineering via mixing and/or switching amongst individual feedstocks. It is compatible with many other robots- and CNC (computer numerical control)-based processes, such as machining, peening, rolling, burnishing, etc., for advanced remanufacturing. Recent studies on elemental and microstructural evolutions, as well as their response to external fields, e.g. ultrasonic vibrations or magnetic fields, during the solidification of the melt pools, provide new insights into laser cladding of metal alloys. Here, we present a special review on laser cladding of metal alloys with the focus placed on recent advances in technical variants towards high-quality protective coatings. Existing issues and their potential solutions will be discussed in tandem with material characterizations and performance evaluations. Through discussing the process-structure-performance relationships as well as their evaluations assisted by in-situ data collection and machine learning, we present the readers with a perspective on recent advances and provide an outlook on future developments of laser cladding for protective coatings and additive manufacturing.