Ultrasonic impact treatment on residual stress and substructure evolution in laser-DED manufactured CrCoNi alloy : Mechanisms and implications for corrosion performance

Bi, X. and Shao, D. and Yuan, Y. and Wang, C. and Hong, M. and Huang, Y. and Li, R. (2025) Ultrasonic impact treatment on residual stress and substructure evolution in laser-DED manufactured CrCoNi alloy : Mechanisms and implications for corrosion performance. Surface and Coatings Technology, 517: 132791. ISSN 0257-8972

Abstract

This study investigates the effects of ultrasonic impact treatment (UIT) on residual stress distribution and microstructural evolution in CrCoNi medium-entropy alloy coatings fabricated by laser-directed energy deposition (L-DED). Combining finite element simulation and experimental analysis revealed that: (i) UIT effectively transforms detrimental surface tensile stress (~400 MPa) into compressive stress (~300 MPa), thereby reducing the susceptibility to crack initiation caused by residual stress accumulation during the rapid solidification of the L-DED process; (ii) surface microhardness increases by 82.6 %, from 230 HV to 420 HV, with an affected depth of approximately 600 μm, attributed to increased dislocation density and grain boundary strengthening induced by UIT; (iii) microstructural characterization reveals that UIT induces severe plastic deformation in the deposited layer, increasing the fraction of low-angle grain boundaries from 30.8 % to 77.8 %, while simultaneously inhibiting recrystallization. The validated numerical model elucidates the interaction between the thermo-mechanical coupling in L-DED and the dynamic plastic deformation mechanisms activated by UIT, providing critical insights into stress redistribution and microstructural refinement. Further, electrochemical tests demonstrate that UIT-treated coatings exhibit enhanced corrosion resistance, as evidenced by increased corrosion potential, decreased corrosion current density, and reduced localized pitting. These mechanisms provide a basis for developing predictive frameworks for UIT-aided L-DED processing of CrCoNi alloy for high-performance coatings in extreme environments.