Developing ultrafine-grained structure with balanced α/γ fraction via underwater friction stir processing enables enhanced wear and corrosion resistance of duplex stainless steel.

Further improving the wear and corrosion resistance of duplex stainless steel (DSS) without disrupting the balanced ferrite (α)/austenite (γ) ratio is worth exploring, but very challenging. Here, we explored the feasibility of utilizing solid-state friction stir processing in air (AFSP) and underwater (UFSP) to realize surface modification of DSS. Notably, we successfully developed an ultrafine-grained (UFG) structure with balanced α/γ ratio on the DSS by UFSP, which imparts both enhanced wear and corrosion resistance to the sample surface. Further, the associated microstructure evolution mechanism during FSP of DSS in both environments is systematically elucidated. The simultaneous improvement in both wear and corrosion resistance is well correlated with the resulting microstructure characteristics. This work provides a simple and cost effective pathway to achieve a synergistic increase in the wear and corrosion resistance of DSS. We anticipate that the UFSP should be applicable to many dual-phase metallic systems. • Surface ultrafine-grained, γ/α balanced duplex stainless steel was developed by underwater friction stir processing. • The associated formation mechanism of ultrafine-grained duplex structure was systematically elucidated. • The concurrently enhanced wear and corrosion resistance was well correlated with the resulting microstructures. [ABSTRACT FROM AUTHOR]