Pre-treatment of Remelting Recovery: Ultrasonic Cleaning Mechanism of Non-metallic Layers from Superalloy Scrap Under Based on Hydrochloric Acid and Potassium Iodide Solution System

Superalloy scraps contain a large number of strategic metals such as nickel, cobalt, aluminum, chromium, tungsten and molybdenum, and the non-metallic layers on the surface should be cleaned before remelting recovery to ensure the material properties of superalloys after remelting. The non-metallic layers on the surface of superalloy scraps were cleaned with hydrochloric acid and potassium iodide solution as the cleaning solution. The removal rules of the concentration of hydrochloric acid, ultrasonic powers and ultrasonic time on the non-metallic layers on the surface of superalloy scraps were investigated, and the strengthening mechanisms of ultrasonic field on the cleaning of non-metallic layers on the surface of superalloy scraps were elucidated. The results show that with the increase of ultrasonic power, the increase of hydroxyl radical concentration and the generation of hydriodic acid in the cleaning solution are the important factors to promote the dissolution of non-metallic layers. When the concentration of hydrochloric acid was 12mol/L, the ultrasonic power was 600W and the ultrasonic time was 30 min, the removal rates of oxygen, nitrogen and sulfur on the surface of superalloy scraps were 91.2%, 70.0% and 73.6%. The enhancement mechanisms of ultrasonic cleaning of superalloy scraps were explained from the physical and chemical effects induced by ultrasonic field respectively. This cleaning process not only improves the corrosion of the cleaning solution, but also avoids the drawback of easy decomposition of HI, which provides an environmentally friendly method for the pretreatment of superalloy scraps before remelting recovery.