Modulating heat input to optimize corrosion and synergistic cavitation erosion-corrosion behavior of Ni201 cladding layer by cold metal transfer

The effects of heat input (HI) on the microstructure, microhardness, corrosion resistance and cavitation erosion resistance of cold metal transfer (CMT) Ni201 cladding layers were studied. The Ni201 cladding layers present a γ single-phase austenite structure, which exhibit a columnar to equiaxed transition (CET) transformation along the temperature gradient direction of approximately parallel energy input. As HI increases, the microstructure tends to become coarsen and the dilution rate increases, resulting in lattice distortion of γ phase. The Ni201 cladding layer has a strong γ-fiber texture in the 〈100〉 orientation as indicated by the EBSD analysis. With the increase of HI, the grain size and Schmidt factor increase, while the average misorientation angle decreases. The microhardness of Ni201 cladding layer exhibits a general downward trend from 198.3 HV to 171.7 HV with the increase of HI, while the abnormal increase of the microhardness of S3 sample is caused by solution strengthening and precipitation strengthening. In addition, the coarsening microstructure and diffusion of elements such as Fe intensifies the galvanic corrosion reaction, leading to a downward trend in the corrosion resistance of cladding layers. Synergistic cavitation erosion-corrosion is used to detect the self-repair and re-passivation behavior of the passivation film during the cavitation erosion process of the Ni201 cladding layers. Increasing the HI leads to an increase in the mean depth of erosion rate (MDER) of Ni201 cladding layers from 3.6 μm·h−1 to 5.5 μm·h−1, which is attributed to deterioration of the passivation film quality and the reduction of the mechanical property. Finally, the synergistic cavitation erosion-corrosion mechanism of Ni201 cladding layers is proposed according to the analysis results. The CMT Ni201 cladding layers fabricated in this paper exhibit a great potential for anti-corrosion application in ocean engineering.