Laser heat treatment for improved cold sprayed copper coating ductility

As cold spray technology transitions to an additive manufacturing process, optimizing the mechanical properties of cold-sprayed coatings has become increasingly critical. The inherent brittleness of as-sprayed coatings is often mitigated through post-heat treatment. Localized laser heat treatments are proposed as an effective method to enhance the ductility of cold-sprayed coatings on large components without compromising the base metal. However, adapting furnace heat treatment procedures to laser heat treatment presents significant challenges. In this study, a 4kW YAG laser was employed to heat treat 4-5 mm thick cold-sprayed copper coatings. Surface temperatures were monitored during the heat treatment using an infrared camera or surface thermocouples. The heat-treated coatings were characterized through hardness measurements, tensile testing, and microstructural examinations. Preliminary trials on small coupons and larger parts indicated a reduction in hardness throughout the thickness, but only minor improvements in ductility. Challenges related to laser absorption, temperature control and coating debonding are discussed. The influence of laser heat treatment duration on annealing and sintering phenomena, and the resulting impact on coating ductility, is also examined. Additional laser heat treatment trials on a large component using optimised conditions achieved a deposit ductility of 11%, a value approaching that attainable with furnace heat treatment.