Compactness of coatings treated by MAO and LSM on Ti alloy

Abstract

Microarc oxidation (MAO) coatings exhibit loose surfaces, big micropores and porosity that lead to shortcomings in mechanical properties. Three kinds of MAO coatings were prepared on TC4 alloys (Ti–6Al–4V) in electrolyte and treated by laser surface melting (LSM) with various power densities. Compactness of the coatings was analyzed based on the scanning electron microscope images. The results showed that the porosity and the average diameter of pores were decreased, and a compact remelting layer was formed in the MAO+LSM coatings. On the discontinuous smelting surface of MAO+LSM coating, pores were often found in the individual melting microarea. Most of molten pools were originated in the pore of MAO coating surface; as the laser energy was absorbed continually, discrete melted areas grew and finally expanded into continuous melted areas. The content of anatase increased after LSM treatment especially under low scanning speed of the laser beam. The average hardness of MAO+LSM coatings is almost twice the hardness of MAO coating, and the wear resistance is also excellent for compactness of LSM coating. Consequently, to improve the coating mechanical properties of TC4 treated by MAO, the secondary modification process of laser remelting plays a positive role.