Trivalent chromium electrodeposition bath is environmentally friendly choice to replace the conventional, highly toxic, and carcinogenic hexavalent chromium electrodeposition bath. In this study, Cr-Al₂O₃, Cr-SiC, and Cr-Al₂O₃-SiC nanocomposites coatings on copper substrate were prepared by electrodeposition from trivalent chromium bath containing dispersed nanoparticles of Al₂O₃ and SiC. Meanwhile, the crystalline structure, surface morphology, and composition of the deposits were analyzed using X-ray diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM), and Energy Dispersed X-ray Spectroscopy (EDX), respectively. The Vickers Microhardness test and Pin-on-Disc wear test (American Society for Testing and Materials, ASTM G99) were carried out to investigate the mechanical properties whereas the corrosion resistance test was done using electrochemical polarization method on nanocomposites coating samples.

The optimum conditions of the trivalent chromium electrodeposition were a current density of 20A/dm², a pH of 1.5, a temperature of 35 °C, and a deposition time of 60 minutes. The optimum conditions for the co-electrodeposition of Cr-Al₂O₃ nanocomposite coating were an agitation speed of 200 rpm, 40 g/L of Al₂O₃ nano-powder, a deposition of 60 minutes, and without the use of PEG additive. The optimum concentration of SiC of Cr-SiC nanocomposite coating was 10g/L. Furthermore, the optimum heating rate of heat was 2 °C/min.

The Cr-Al₂O₃, Cr-SiC, and Cr-Al₂O₃-SiC nanocomposites coatings revealed that the addition of Al₂O₃ and SiC nanoparticles had a positive effect on hardness, but a negative effect on corrosion resistance and wear resistance under a dry sliding test. The hardness of Cr, Cr-SiC, Cr-Al₂O₃, and Cr-Al₂O₃-SiC coatings increased in ascending order. The high microhardness is crucial to achieve performance enhancement upon the incorporation of nanoparticles with the chromium matrix. However, the corrosion resistance performance of Cr, Cr-SiC, Cr-Al₂O₃, and Cr-Al₂O₃-SiC coatings decreased sequentially due to the agglomeration of Al₂O₃ and SiC nanoparticles.

The heat treatment recrystallized the crystal structure of the coating from amorphous to nanocrystalline. After heat treatment, the chromium nanocomposites showed an impressive enhancement in hardness and corrosion resistance, but a deterioration in wear resistance. The mismatch of the coefficient of thermal expansion between the chromium coating and the copper substrate formed a crack network which reduce the wear resistance. Among these nanocomposite coatings, Cr-Al₂O₃-SiC nanocomposite coating has the best hardness and wear resistance. The hardness of Cr-Al₂O₃-SiC nanocomposite coating increased by 23.1% compared to the Cr coating. After heat treatment, the hardness of the coating was significantly improved by 159.4% compared to the Cr coating.

Figure 1: FESEM surface view of Cr-Al₂O₃-SiC nanocomposites coating before (a), (b), (c) and after (d), (e), (f) heat treatment at three different magnifications: 100x (a & d); 1,500x (b & e) and 10,000x (c & f).

Figure 2: FESEM cross-sectional view of (a) as-plated chromium and Cr-Al₂O₃-SiC nanocomposites coating (b) before and (c) after heat treatment.

Figure 3: Hardness of as-plated chromium and Cr-Al₂O₃-SiC nanocomposites coating before and after heat treatment.

*Abstract of the thesis (PhD) by Eydar Tey.

For further information, please contact:

Zulkarnain Zainal, PhD
zulkar@upm.edu.my

Date of Input: 30/10/2024 | Updated: 06/12/2024 | roslina_ar