Effect of the macro-segregation on corrosion behavior of CrMnFeCoNi coating prepared by arc cladding

Abstract

The CrMnFeCoNi coatings were prepared by the tungsten arc cladding process on a substrate of X65 steel. A macroscopic scale solute segregation within the coated layer can be recognized, which is analyzed by coupling the fluid mechanics and calculation of phase diagram technique (CALPHAD). According to the no-slip boundary condition, a zero-velocity laminar fluid layer appears at the fusion pool boundary, which forms the macro-segregation zone. Energy dispersive spectroscopy (EDS) results demonstrated the macro-segregation zone possess higher Fe element portion (X65 steel enriched zone) compare to the other region in the coating layer. Electron backscattered diffraction (EBSD) and X-ray diffraction (XRD) results indicated that the macro-segregated regions exhibited body-centered cubic structure that possess high-density dislocations, which proves that martensite transformation occurs within the X65 steel enriched macro-segregated regions. Potentiodynamic polarization curves indicated that CrMnFeCoNi coated samples experienced three stages including active, passive and transpassive dissolution. In active stage, preferential dissolution occurred on macro-segregated regions, which can be attributed to two factors: phase portion factor and alloying component factor. In the passive stage, the CrMnFeCoNi coating formed passive film while the macro-segregated zones exhibited active dissolution, resulting in forming deep crevices. Once macro-segregation zones formed deep crevices, the crevice corrosion mechanism would be dominant. As a result, some deeper and wider crevices were formed. In transpassive region, the passive film dissolved, which aggravates the corrosion of the sample.