Optimizing the microstructure and fretting tribo-corrosion resistance of Zr-4 alloy via laser shock peening

Zr-4 alloy, a critical material for reactor core components, operates long-term in a LiOH-containing corrosive coolant environment, where fretting tribo-corrosion is a primary failure mechanism. In this work, laser shock peening (LSP) was applied at varying laser power densities (0–6.6 GW/cm 2 ) to modify the alloy surface, with the aim of systematically evaluating its effect on fretting tribo-corrosion performance and elucidating the underlying strengthening mechanisms. Comprehensive characterization via XRD, EBSD, TEM, electrochemical tests, and fretting experiments shows that increasing power density shifts the dominant plastic deformation mechanism from dislocation slip (<2.6 GW/cm 2 ) to deformation twinning (≥2.6 GW/cm 2 ). This transition induces pronounced surface nano-crystallization and grain refinement, which collectively enhance corrosion resistance through a denser passive film and improve wear resistance via strengthened mechanical properties. Quantitative analysis confirms that LSP markedly suppresses the synergy between wear and corrosion, reduces material loss, and shifts the fretting regime from gross slip toward mixed or partial slip, accompanied by a transition in wear mechanism from severe abrasive wear accompanied by crevice corrosion (<2.6 GW/cm 2 ) to mild abrasive and adhesive wear (2.6∼4.0 GW/cm 2 ), and finally to oxidative wear (5.3∼6.6 GW/cm 2 ). The enhanced performance is attributed to accelerated re-passivation, inhibited micro-galvanic corrosion, and improved crack resistance resulting from grain refinement and residual compressive stress. These findings offer valuable guidance for surface engineering of Zr-4 alloys to extend their service life in nuclear applications.