A novel surface restoration method for hydropower steel components: Plasma gouging and inconel cold spray coating for material repair

A novel surface restoration approach combining plasma gouging with subsequent cold spray deposition is demonstrated in this study. Plasma gouging removes damaged material from steel surface, preparing it for the following build-back process. The plasma gouging leaves a slightly grooved surface and forms a plasma gouging affected layer up to ∼300 μm thick. Within this layer, a hardened martensitic microstructure with a peak hardness of ∼370 HV—almost twice that of the base substrate (∼200 HV)—is produced. Cold spray deposition is then applied to restore the surface, leveraging its known capability to produce coatings with excellent cavitation resistance. Experimental results reveal that cold spray coatings deposited at low energy suffer from delamination, whereas high energy cold spray deposits yield a well-bonded coating. Microstructural analysis further shows that the martensitic layer formed by plasma gouging undergoes dynamic recrystallization during cold spray, reducing the hardness to 317 HV. Overall, this study demonstrates the feasibility and effectiveness of the combined plasma gouging and cold spray process for restoring damaged steel component surfaces.