Morphological Changes During Annealing of Electrodeposited Ni-Cr Coating on Steel and Their Effect on Corrosion in 3% of NaCl Solution

Steel containing carbon of 0.2% was coated with Ni and Cr through electrodeposition, and subsequently annealed at 400 and 600 degrees C for 5 min, 30 min, 1 h and 2 h. During annealing at 400 degrees C, the formation and growth of oxides occurred in the form of petals along with voids, cracks and porosities. However, at 600 degrees C, the nucleation and growth of chromium oxide whiskers produced a surface almost free from crack, porosity and void for 1 h and 2 h of holding. In accordance with the surface morphology, the bare steel, as-deposited steel, all specimens deposited and annealed at 400 degrees C, and specimens deposited and annealed at 600 degrees C for 5 and 30 min exhibited continuous corrosion in 3% of NaCl solution. However, the specimens deposited and annealed at 600 degrees C for 1 and 2 h exhibited an improved corrosion resistance in 3% of NaCl solution with high pitting potential due to presence of a dense passive oxide film almost free from voids at the surface.