Exploiting magnetic sediment co-electrodeposition mechanism in Ni-Al2O3 nanocomposite coatings

Abstract

• Magnetic sediment co-electrodeposition (MSCD) mechanism of Ni-Al 2 O 3 nanocomposites. • Coating morphology, crystal structucture, e, microhardness, nanoparticles loading and zeta potential were the main criteria. • Two phenomena control MSCD: (i) magnetohydrodynamic (MHD) and (ii) gravitational force. • MHD predominates for nano-sized particles (<100 nm) by reducing the thickness of the diffusion layer. • Gravitational force is dominant for agglomerated particles (>300 nm). Our focus in this work is to exploit a mechanistic view of magnetic sediment co-electrodeposition (MSCD). Ni-Al 2 O 3 nanocomposite coatings were electrodeposited in the presence and absence of an external magnetic field using sediment co-deposition (SCD) cell design. The dispersion, zeta potential, and size of Al 2 O 3 particles in solution were measured and interpreted for the MSCD mechanism. The effects‌ of magnetic field on morphology, crystallographic texture, microhardness, dispersion of Al 2 O 3 nanoparticles in Ni metal matrix were studied and a co-deposition kinetic model was accordingly postulated. Magnetic sediment co-electrodeposition not only changes the surface morphology of Ni-A 2 O 3 from pyramidal-shaped to spherical grains, but it also increases the microhardness (from 365 to 500 HV) by decreasing the crystallite size (from 130 to 110 nm). Calculations of relative texture coefficient (RTC) values and Rietveld analysis showed that the growth of texture (2 0 0) of Ni-Al 2 O 3 composite coatings is reinforced in the presence of a magnetic field. Based on our assumed model, two determining phenomena control the magnetic sediment co-deposition process: (i) magnetohydrodynamic (MHD) and (ii) gravitational force. MHD predominates for nano-sized particles (<100 nm) by reducing the thickness of the diffusion layer, whereas, the gravitational force is dominant for agglomerated particles (greater than300 nm).