Research On Microstructure And Properties For Laser Remelting Al₂O₃-TiO₂ Coating

In this paper, nano-aggregates Al₂O₃-13% TiO₂（mass fraction） ceramic powder used was as raw material, nanostructured ceramic coatings have been successfully fabricated on the surface of titanium by plasma spraying, and the ceramic coatings were treated with laser remelting process, The research on microstructure and properties of coating by laser remelting treatment were carried out. Revealing the changes of microstructure and properties of coating in laser remelting treatment.Scanning electron microscopy（SEM） was used to observe the morphology of the coating, energy dispersive spectroscopy（EDS） was used to analysis the component of the coating, X-ray diffraction（XRD） was carried out to analysis the phase in the coating,microhardness of remelted layer was measured by microhardness tester, crack propagation resistance of remelted layer was tested with the indentation hardness testing method,bond strength of coating and the substrate was tested by Automatic scratch adhesion machine.After the test results show that the laser remelting spray coating with the defect layer（lamellar structure, porosity and micro cracks） will be eliminated, and then into a densification, homogenization of microstructure of remelting layer, and consists of sheets of original structure all into the equiaxial crystal and columnar crystal. After laser remelting, γ-Al₂O₃ of the as-sprayed coating is transformed into α-Al₂O₃, and Al₂ TiO₅ are also formed in the LRm C. Grain in coating are refinement homogenization and densification.The average hardness values in Vickers of plasma spray coating is about 2 3 times that of the substrate, and it has been found that the microhardness of the remelted layer are higher than that of the plasma spraying coating.which is 3⁴ times that of the substrate. In the laser remelted coating, the densification and homogenization microstructure play an important role in improving the microhardness of the coating. The reasons of enhancement of crack propagation resistance after laser remelted a re that spray coating of state organizations have been densification, improved uniformity, eliminate some will crackperformance against defects have a greater impact, such as: the pores and microcracks;another effect of crack propagation resistance because of unmelted particles in the remelted coating evenly distributed. The bond strength of Laser remelting Al₂O₃-13 wt.% TiO₂ coating is about 2 3 times than plasma spraying state Al₂O₃-13 wt.% TiO₂ coating. There are two explanations for the enhanced bond strength after laser remelting, one is due to changes in the binding mode, the state sprayed coating and the substrate binding into mechanical metallurgical bonding after remelting coating and substrate. The other maybe that the grain refinement of the coating.