Effect of temperature on crystallite size and residual stress of nano-nickel coatings
Abstract
Nanocrystalline nickel coatings were prepared from a Watts bath using pulse current (PC) condition. To investigate the temperature effect on the crystallite size and residual stress of the nano-nickel coatings, The temperature of the electroplating bath was maintained at 35 °C, 40 °C, 50 °C, 55 °C, and 60 °C respectively. X-ray diffraction (XRD) analysis was performed to determine the crystallite size, relative texture coefficient, and residual stress of the studied coatings. The experimental results show that with increasing temperature of the Watts bath, the average crystallite size, relative texture coefficient of crystallographic plane (200) (same direction as (100)), and compressive residual stress of nanocrystalline nickel coatings increase. It is concluded that moderately increasing the temperature (up to about 60 °C) in the process of nanocrystalline nickel coating production will promote the preferred orientation of crystallographic plane (100) and the compressive residual stress, which enhances nickel crystal compaction, coating adhesion, and coating integrity.
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Introduction
The production and characterization of nanocrystalline coatings have been the subjects of intensive research by both the scientific and industrial communities in recent years due to their unique properties conferred by ultrafine crystallite size (typically smaller than 100 nm). There are serveral ways to produce nanocrystalline coatings. Among them, electrodeposition has received considerable attention as a feasible and economically viable technique [1-11] . Research has showed it is important to optimize the electrodeposition conditions of the nanocrystalline nickel coating such as bath temperature, which plays an important role for crystallite size of the electrodeposited coating sample [12-13] . However, very few experiments have been done on the effect of bath temperature on the crystallite size of nickel deposits. In some cases, the reported data are inconsistent or even different. For example, A. M. Rashidi et al [12] explored bath temperature from 45 °C to 65 °C and found that the crystallite size of deposits reduces as the plating temperature increases up to 55 °C and then increases by further increase in the bath temperature. According to Dini [14], it is generally expected that the crystallite size of the deposits increases by increasing the bath temperature and has been experimentally observed for some nanocrystalline deposits. The objective of the present investigation is to further evaluate the influence of bath temperature on the crystallite size, texture, and residual stress of nanocrystalline nickel coatings.
Conclusion
Based on the experimental results, it is found that with increasing temperature, the average crystallite size, relative texture coefficient of crystallographic plane (200) (same direction as (100)), and compressive residual stress increase. Therefore, it can be concluded that moderately increasing the temperature (up to about 60 °C) in the process of nanocrystalline nickel coating production will promote the preferred orientation of crystallographic plane (100) and the compressive residual stress, which enhances nickel crystal compaction, coating adhesion, and coating integrity.