PhD Thesis Colloquium: Mr. Sunando Banerjee (07/09/26)
Thesis title:
Effect of Microstructural Evolution on Corrosion and Hydrogen Permeation Behavior of Electrodeposited Ni-Based Coatings
Faculty advisor(s):
Prof. Chandan Srivastava.
When?
07th September, 2026 (Monday), 03:00 PM (India Standard Time)
Where
Microsoft Teams Join: https://teams.microsoft.com/meet/43449397562564?p=TPt1z2mPNahRvb1E6q
Meeting ID: 434 493 975 625 64
Passcode: e5UK9WT2
Abstract
Electrodeposited Ni coatings are widely used in automotive, aerospace, oil & gas and marine applications because of their good mechanical and corrosion-resistant properties. Their performance, however, deteriorates in aggressive environments, particularly in the presence of Cl- ions, which destabilize and break down the passive film, leading to pitting corrosion. Furthermore, hydrogen embrittlement remains a critical challenge as absorbed atomic hydrogen leads to catastrophic failure of structural components. The present work systematically investigates the influence of deposition parameters and alloying additions in engineering the microstructure of electrodeposited Ni coatings and its consequential effects on corrosion and hydrogen permeation resistance.
First part of the study investigates the influence of deposition current density (20–120 mA/cm²) on microstructural evolution and electrochemical corrosion behavior of Ni coatings. Corrosion resistance initially decreased for coatings deposited at 20 to 50 mA/cm², then increased progressively for coatings deposited at 100 mA/cm², and finally decreased, with the lowest corrosion resistance observed at 120 mA/cm². EBSD analysis of the coatings deposited at 50 and 100 mA/cm² exhibited near- random texture. The highest corrosion resistance at 100 mA/cm² was due to a higher fraction of coincident site lattice (CSL) boundaries and a lower fraction of high-angle grain boundaries, whereas the lowest corrosion resistance at 120 mA/cm² was attributed to a weak (101) higher-energy texture coupled with a higher fraction of high-angle grain boundaries.
The second part examines the effect of pulse electrodeposition parameters, notably duty cycle and frequency, on the microstructure and corrosion behavior of Ni coatings. Although EBSD revealed no significant change in surface texture, significant variations in coating strain and grain boundary constitution were observed. The coating deposited at 80% duty cycle and 75 Hz exhibited the highest corrosion resistance, with a ~57% decrease in corrosion current density (jcorr) as compared with the lowest corrosion- resistant coating obtained at the 80% duty cycle and 150 Hz. The enhanced corrosion resistance was due to a higher fraction of CSL, low-angle grain boundaries and a lower coating strain, whereas higher fractions of high-angle grain boundaries and strain resulted in a lower value of the corrosion resistance.
The third part investigates the corrosion and hydrogen permeation behavior of Ni-xMo (x = 2, 4, 8 and 11 wt%) alloy coatings deposited by pulsed plating. Corrosion behavior was non-monotonic, with Ni-4 wt% Mo and Ni-11 wt% Mo showing the highest and lowest corrosion resistance, respectively. All the alloy compositions outperformed Ni in terms of corrosion resistance. The superior corrosion resistance of Ni-4 wt% Mo was attributed to lower-energy (001) and (111) textures, favorable grain boundary constitution, a stable Mo(VI) oxide within the passive film and a lower coating strain. The lowered corrosion resistance of Ni-11 wt% Mo was due to higher energy grain boundaries and a higher strain. Atom probe tomography analysis revealed the presence of Mo-enriched Ni-Mo nanoclusters, which increased hydrogen diffusion path tortuosity and enhanced resistance to hydrogen permeation. Conversely, a higher fraction of high-angle grain boundaries promoted hydrogen diffusion, resulting in similar saturation hydrogen permeation currents for Ni-4 wt% Mo and pure Ni coatings.
The fourth part elucidates the effect of compositional heterogeneity on the corrosion and hydrogen permeation behavior of pulse electrodeposited Ni-xW alloy coatings (x = 1.5, 3.5, 5.5 and 8 wt%). Corrosion rate decreased up to Ni-3.5 wt% W and increased thereafter, indicating non-monotonic behavior. The highest corrosion resistance of Ni-3.5 wt% W was due to a nearly homogeneous Ni-W solid solution and protective W(VI) oxide-containing surface film. The lowest corrosion resistance of Ni-8 wt% W was attributed to pronounced heterogeneity in W distribution, forming W-rich and W-poor regions that promoted micro-galvanic coupling. Experimental hydrogen diffusivity values derived from hydrogen permeation measurements (Devanathan-Stachurski cell) exhibited a nearly identical range across all the coatings. Density functional theory (DFT) first-principles calculations revealed that W incorporation promotes interstitial diffusion of hydrogen; however, this enhancement is counteracted by concurrent grain refinement observed microscopically, which introduces a high density of grain boundary trapping sites retarding the hydrogen transport and thereby, resulting in a similar values of effective hydrogen diffusivity obtained across all the compositions.