Plastic deformation behavior and strengthening mechanism induced by ultrasonic impact treatment in CoCrFeNiB0.15 high entropy alloy coatings

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The matching of strength and toughness of laser cladding coatings determines, to a certain extent, the practical applicability of the coatings. In this paper, ultrasonic impact treatment (UIT) was employed to optimize the microstructure and properties of the CoCrFeNiB 0.15 high entropy alloy coating. The microstructure evolution and performance modification of the coatings before and after UIT (referred to as B0.15 coating and UIT-B0.15 coating) were characterized and analyzed. The UIT resulted in a plastic deformation layer with a thickness of approximately 45.37 μm in the near surface. The plastic deformation mechanisms of the single-phase dendrites and the intergranular eutectic were deformation-twin-induced and dislocation-induced, respectively. Synergistic strengthening mechanisms, mainly including dislocation strengthening, deformation-twin strengthening, and fine-grain strengthening, increased the surface microhardness of the B0.15 coating by 46.2 %, from 281.1 HV0.2 to 410.8 HV0.2. Moreover, the gradient hardening layer with a depth of ~658 μm was formed, and the elastic modulus increased synchronously. After UIT, the residual compressive stress of the B0.15 coating increased from 222.8 ± 18.2 MPa to 1397.5 ± 117.3 MPa, the self-corrosion current density decreased from 1.08 × 10 −7 Amp/cm 2 to 3.39 × 10 −8 Amp/cm 2 , and the passivation potential range was further expanded. UIT can comprehensively improve the corrosion resistance of the B0.15 coating by refining grains, increasing the material density, and improving the surface stress state.