Influence of the current density on CaP coating growth during the US-assisted micro-arc oxidation

Regularities of the CaP coatings’ thickness and roughness growth with the changing current density during micro-arc oxidation (MAO) process under the external ultrasound (US) were studied. A high-level negative correlation between the thickness or roughness and the current density was observed. This was due to the fact that the current density decreased with time by hyperbolic law and both the thickness and roughness oppositely increased by logarithmic law with time. For the growth rates of the coatings’ thickness and roughness, the direct linear dependencies on the current density were revealed. The decreasing current density with time more affected the increasing coatings’ thickness or roughness and the decreasing growth rates for the control MAO coating thickness and roughness than for the US-assisted MAO coatings.