A Mathematical interpretation model of Ti alloy micro-arc oxidation (MAO) process and its experimental study

Abstract

A mathematical interpretation model of micro-arc oxidation process parameters and ceramic coating properties in Ca/P electrolyte system was attempted to establish. The model includes micro-arc oxidation process parameters (power supply voltage Um, current density J, duty ratio ŋ, electrolyte conductivity and dielectric constant of anodic oxide gas), and the properties of ceramic coating (surface morphology, thickness, pores density, porosity, the average size of pores). The response of current during the process was studied. The properties of ceramic coating (morphologies, thickness and surface statistics) were measured by scanning electron microscopy (SEM), 3-D HIROX video microscope, TT230 coating and layer thickness measuring instrument and image analysis software ImageJx2.0. The current was measured by AC galvanometer GPM-8212. The molar conductivity of NaOH is the highest among the four electrolyte system components, and its concentration has the greatest impact on ceramic coating surface morphology. The analysis agrees with the experimental results in lower concentration (under 0.30 mol/L) extremely. However, there is a discrepancy at higher concentration (0.40 mol/L) since the much more molten metal during the reaction of MAO in higher conductivity electrolyte. Pores density is the major factor in determining the porosity. Current results show that ceramic coating had been generated at 40 s under the constant voltage system. The model provides a theoretical base for the interpretation of Ti alloy MAO process and determining the appropriate concentration of NaOH in Ca/P electrolyte system.