Abstract
Cold spray is a solid-state additive manufacturing process that has been increasingly used for restoration of damaged parts. Due to the nature of powder solid-state bonding, cold spray coatings usually possess pores in the microstructures. Heat treatment has been widely used as a post-processing method to reduce the porosity of cold sprayed coatings. However, it usually requires the whole component to be treated in the furnace and typically takes a few hours to finish the treatment. This study aims to develop a localized and rapid post-processing method for cold sprayed coatings. Multi-layer cold sprayed coatings of CoNiCrAlY on an Inconel 718 substrate were produced. Then the coatings were heat treated at 800 °C, 900 °C, 1000 °C and 1100 °C by rapid induction heating. The porosity level of the coatings reduced significantly after induction heating for a short period of merely 10 min. This is attributed to the preferential Joule heating at pore regions, which results in pore closures within the coatings. The potential application of induction heating as a rapid post-processing method for cold spray coatings has been demonstrated in this work.
Highlights
Cold spray is an effective solid-state additive manufacturing technique
After induction heating at 800 ◦ C, the porosity percentage was found to be reduced to 2.1%
For induction heating at 900 ◦ C, the porosity percentage was further reduced to 1.6%, which was almost half of the porosity in the as-sprayed coating
Summary
Cold spray is an effective solid-state additive manufacturing technique. During the cold spray process, the preheated feedstock particles are accelerated to supersonic speed to hit the substrate, and the particles would bond on the substrate with a fine microstructure through severe plastic deformation to form the coating [1,2]. Due to the advantages of the cold spray technique, it has been increasingly applied to repair damaged aerospace components. Inconel 718 is a nickel-based superalloy that has been extensively used to make aerospace components such as gas turbine blades due to its excellent mechanical performance [3]. To provide more reliable performance and durability of the nickel-based superalloy at high temperatures, an appropriate coating is usually required to avoid the component damage. MCrAlY (where M = Ni, Co, or both) alloy has been widely used in thermal barrier coatings (TBCs) as the bond coat layer to provide corrosion and oxidation protection for nickel-based superalloys in harsh environments [4]
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