Effect of diffusion annealing on duplex coated pure titanium produced by hot-dip aluminizing and micro-arc oxidation

Abstract

In the present study, an Al2O3 ceramic coating was formed on a pure titanium surface with the application of the duplex coating technology produced by combining hot-dip aluminizing (HDA) and micro-arc oxidation (MAO) processes. Due to the porous nature of MAO coating with the structural and mechanical differences between the MAO (Al2O3) and HDA layers (Al, Al3Ti), diffusion annealing treatment was applied to duplex coated (HDA + MAO) titanium samples. With the diffusion annealing treatment, a composite layer with a thickness of about 125 mu m was formed beneath the modified MAO coating, which showed a denser structure by penetrating TiO2 into the MAO. MAO coatings with and without diffusion annealing exhibited compressive residual stresses with values of-1530 and-850 MPa, respectively. Microhardness and elastic modulus of the diffusion annealing-treated MAO coating reached 1230.1 HV and 241.3 GPa, respectively. The diffusion annealing-treated MAO coating provided-29% less coefficient of friction and-8.4 times greater relative wear resistance than that of MAO coating without diffusion annealing.