The analysis of nickel-obsidian composite formation on mild steel surface through electrocodeposition process

Composite, the engineering material consisting of two different macroscopic phases, can be synthesized through electro co-deposition reaction by adding particles into the solution of the electroplating process. The obsidian powder as dispersed particles and the nickel-metal as the matrix are the materials that can be synthesized using that technique. The hardness of obsidian is in the range of 650-900 HV, whereas nickel is 380 HV. We have investigated the formation mechanism of the coated composite layer made via electrocodeposition reaction. The electrocodeposition of the obsidian particle was controlled by kinetic, electrophoretic, and gravity forces that act on the particles. The resultant of these forces determines the direction of particles. The experimental result shows that increasing particle concentration from 0 to 25 g/L increased the hardness of the coated layer from 380 to 504 HV. The kinetic force can keep the particles suspended in solution at this concentration range. However, a further increase in particle concentration to 50 g/L decreases the kinetic energy of particles significantly, causing the particles to fall without depositing at the cathode and reducing the hardness down to 430 HV. Meanwhile, increasing current density increase the rapidness of the electro co-deposition reaction. At the increasing current density at a range of 3.3-10 Ampere/dm², the hardness of the coated layer is at the range of 420-540 HV. Coated layer thickness decreases slightly as particle concentration increases but increases significantly as current density increases. The highest hardness of the coated layer, 540 HV, was obtained at a particle concentration of 25 g/L and a current density of 10 A/dm².