Coupling Effect of Disconnected Pores and Grain Morphology on the Corrosion Tolerance of Laser-Clad 316L Coating

The corrosion resistance of 316L cladding layers was addressed via the electrochemical test, to illustrate the coupling effect of the disconnected pores and grain morphology on the corrosion tolerance of 316L cladding layers. Scanning electron microscopy (SEM), X-ray diffraction (XRD), and electrochemical testing were employed to characterize the microstructure, elemental distribution, phase composition, and corrosion resistance of the cladding layers. The results indicate that the disconnected porosity in the surface of the cladding layer decreased from 0.79% to 0.48% and the grain morphology underwent a transformation from equiaxed crystals to columnar and lath crystals, with the increasing scanning speed. The primary phase in the cladding layer was gamma-Fe. Under the dual effect of a low disconnected porosity and grain morphology, the corrosion potential of the cladding layer became more electropositive from -568 mVSCE to -307 mVSCE, and the corrosion current density reduced from 4.664 mu A center dot cm-2 to 1.645 mu A center dot cm-2. The pitting potential improved from 0.005 VSCE to 0.575 VSCE as the scanning speed increased. Thus, the non-connected pores in the 316L cladding layer also affected the corrosion resistance, especially the pitting resistance. The corrosion resistance of the cladding layer can be significantly enhanced via the control of the disconnected pores and grain morphology.