Synthesis and characterization of Pulsed- Electrodeposited Cr and Cr-ZrO2 Coating

Abstract

In the present study (Cr) and (Cr-ZrO2) composite coatings were deposited on low carbon steel substrate by pulse electroplating (PED) technique to enhance tribology and mechanical properties of conventional chromium coating. Zeta potential of ZrO2 particles in electrolytes was investigated and from the Iso-electric point obtained, the bath pH was maintained at a fixed value. The effect of PED parameter such as frequency and duty cycle on the morphology of the coating was investigated. The structure and morphology of the coating were evaluated using (SEM) and (XRD). Microhardness tester and ball-on-plate type wear tester were used to access the microhardness and wear resistance of coatings. Finally along with the PED parameters the effect of dispersed ZrO2 particles on coating properties such as hardness, wear resistance were correlated and it was observed that the change in property was due to dispersion hardening and favourable crystallographic orientations. The crystallite size was averagely 30-50 nm and a strong (220) texture was obtained in composite coatings and in unreinforced Cr coatings a strong (210) texture was determined from the XRD data. The composition and surface morphology of coatings were studied by using EDS and SEM. Hardness and Wear resistance of the coatings were determined by using microhardness tester and ball on plate wear tester, improved hardness and wear resistance of composite coatings were observed compared to the unreinforced chromium coatings. The wear loss behaviour of the coatings developed at different frequency and duty cycle follows the general trend i.e wear loss decreases with increase in frequency and duty cycle. The microhardness values obtained for the composite coatings are higher than the pure Cr coating hardness, the improvement is attributed to dispersion strengthening caused by the embedded second phase particles, texture and modified microstructure of chromium matrix.