Reducing sulfur to improve thermal embrittlement in electrodeposited nickel using citric acid

Electrodeposited nickel usage has been limited owing to thermal embrittlement at high temperatures. Electrodeposited nickel generally contains sulfur, and the grain boundary segregation of sulfur leads to thermal embrittlement. As the main source of sulfur, saccharin (C7H5NO3S) has been suspected to primarily cause thermal embrittlement. In this study, electrodeposited nickel with improved ductility and high heat resistance was fabricated using citric acid instead of saccharin. Using citric acid, a strong (100) plane-preferred orientation parallel to a substrate was obtained over a wide current density range, similar to the case of using saccharin. Therefore, high ductility is expected in as-deposited electrodeposits obtained from electrolyte using citric acid over a wide current density range. The sulfur content in the samples significantly decreased from 0.025 to 0.007 wt% using citric acid instead of saccharin sodium. Specimens obtained from the electrolyte using citric acid achieved an elongation to failure of 7.4% even when annealed at 300 °C for 24 h, whereas specimens obtained from electrolyte using saccharin were brittle and exhibited no plastic deformation at an annealed state.