Effects of Diamond Nanoparticles on the Microstructure, Hardness and Corrosion Resistance of Chromium Coatings

Vladimir Petkov,Radoslav Valov

doi:10.11648/j.ajche.20200806.11

Abstract

Electrodeposited coatings of chromium and diamond nanoparticles on steel were obtained. The chromium is plated directly on the steel matrix without any intermediate layers. The influence of the electrodeposition current density, the electrodeposition time and the concentration of diamond nanoparticles in the chromium-plating electrolyte on the microstructure, the phase composition, the microhardness and the corrosion resistance of the chromium coatings were investigated. The phase and chemical compositions of the composite coating (chromium and diamond nanoparticles) were examined using X-ray Diffraction (XRD) and Scanning Electron Microscopy - Energy-Dispersive X-ray Spectroscopy (SEM-EDS) techniques. The microstructure and microhardness were examined with a metallographic microscope and a microhardness tester. The corrosion resistance was investigated in 3.5 wt % NaCl solution using the gravimetric method. The bond between the chromium coating and the steel matrix has diffusion character. A sublayer of separate irregular shape formations appears at concentration of diamond nanoparticles 25 g/l and more. The formation of these structures depends only on the concentration of diamond nanoparticles and is not influenced by the other electrodeposition parameters. With the increase of the concentration of diamond nanoparticles in the electrolyte the rate of chromium coating deposition increases and respectively the thickness of the coating increases also. This increase is more than twice the thickness of chromium coating without nanodiamonds. The microhardness of the composite coatings rises also compared to unmodified chromium coating. With the increase of the concentration of the diamond nanoparticles 2 times greater microhardness is achieved and up to 5 times greater corrosion resistance compared to monochromium coating. The values of the other electroplating parameters are constant.

Highlights

Alloying steels with Cr, Ni and other transition metals like Mo, Ti, W and V improves their chemical and mechanical properties such as hardness and corrosion resistance in aggressive environment
Still more important for the properties of the surface is the application of composite coating of chromium and diamond nanoparticles (ND) on unalloyed low and medium carbon steel
The optimum value of the yield is reached for values of the current density in the range from 40 to 80 A/dm2, which was the range for our study

Summary

Introduction

Alloying steels with Cr, Ni and other transition metals like Mo, Ti, W and V improves their chemical and mechanical properties such as hardness and corrosion resistance in aggressive environment. Some coatings obtained by sol-gel technology provide enhanced corrosion resistance [1]. They are very thin less than 1 μm, and cannot be applied on items exposed to abrasion and wear conditions. Surface treatment of plain, unalloyed steels with hard and corrosion resistant metals is economically advantageous and has a high technological effect. Still more important for the properties of the surface is the application of composite coating of chromium and diamond nanoparticles (ND) on unalloyed low and medium carbon steel.

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Results

Conclusion