Effect of laser remelting on microstructure and fretting wear properties of APS Al2O3/Y2O3 composite coatings on TC6 titanium alloy

To enhance the fretting wear resistance of TC6 titanium alloy, an Al2O3/Y2O3 (81.5 mol.%: 18.5 mol.%) composite coating was prepared on the TC6 substrate using the APS process, followed by laser remelting. The microstructure and fretting wear behavior of the coatings were investigated. The results indicate that laser remelting transformed the main phases from Al2O3 and Y2O3 to an Al2O3/YAG (Y3Al5O12) eutectic structure. At the same time, the surface roughness decreased from Ra ≈9.8 ± 0.9 μm to Ra ≈3.1 ± 0.2 μm, the porosity dropped from 18.6 ± 2.7 % to 2.3 ± 0.1 %, and the hardness increased from 10.6 ± 0.2 GPa to 27.0 ± 1.1 GPa. The volumetric wear rate was reduced from 1.80 × 10−5 ± 0.13 × 10−5 mm3/(N·m) to 2.93 × 10−6 ± 0.01 × 10−6 mm3/(N·m), representing an approximately 71.6 % decrease compared with the TC6 substrate (1.03 × 10−5 ± 0.03 × 10−5 mm3/(N·m)). Under test conditions of 50 Hz, 60 N, and 105 cycles, laser remelting did not alter the dominant fretting wear mechanisms, which remained adhesive wear, abrasive wear, and brittle cracking, but it significantly improved the coatings resistance to fretting wear.