Effect of surface contamination on electrochemical corrosion behavior of ultrasonic shot peened TA2 alloy

Abstract

Ultrasonic shot peening (USSP) is a technique to tune the performance of metallic materials by generating gradient nanocrystalline structure (GNS) as well as residual compressive stress. However, surface contamination can also be introduced during USSP. The nature of this surface contamination layer and how it influences the corrosion behavior of alloy require further investigation. In this work, we found that a Fe-rich oxide layer with a thickness of around 50 nm, mainly in an amorphous state, was introduced on the topmost surface layer of TA2 alloy during USSP treatment. Electrochemical corrosion results indicate that this Fe-rich oxide significantly decreases the corrosion resistance of TA2 alloy. By polishing off this surface contamination layer, the corrosion resistance of the peened sample becomes superior compared to the untreated counterpart, indicating that the introduction of the Fe-rich oxide layer conceals the beneficial effect of GNS caused by USSP. Additionally, the corrosion resistance of TA2 alloy after USSP treatment exhibits a downward trend with the increasing repeated use of steel shots. The corrosion mechanism and potential use of this surface contamination layer are also briefly discussed.