Suppressing formation of spinel mixed oxides on HVOF MCrAlY bond coat via a low-power pulsed-laser remelting treatment

• A low-power pulsed-laser remelting technique is proposed to remove the splashed particles on HVOF MCrAlY bond coat. • Splashed particles are completely eliminated while the surface roughness of the bond coat is not affected after remelting. • Even after isothermal oxidation at 1000 °C for 400 h, only preferable α -Al₂O₃ is detected without any spinel mixed oxides. • This work provides a feasible solution to suppress the formation of mixed oxides for thermally sprayed MCrAlY bond coat. Controlling thermally grown oxide (TGO) on the surface of bond coat is crucial in determining lifetime of thermal barrier coatings (TBCs) used in gas turbines. For thermally sprayed MCrAlY bond coats, weakly bonded splashed particles inevitably form on coating surface, which leads to rapid growth of mixed oxides rather than preferred α -Al 2 O 3 during high-temperature exposure and thus shortens the lifetime of thermally sprayed TBCs. In the present work, high velocity oxygen fuel (HVOF) sprayed CoNiCrAlY and NiCoCrAlY coatings are taken as model materials. A novel low-power pulsed laser remelting technique is proposed to eliminate weakly bonded splashed particles. Effects of remelting treatment on surface morphology, microstructure and oxidation behavior are examined. Results show that at the optimal conditions with a melting depth of 2–3 μm, weakly bonded splashed particles are completely eliminated, and a decrement in surface roughness is avoided, which enables solid bond quality to the ceramic top coat. After the treatment, only a dense and conformal α -Al 2 O 3 layer forms on the bond coat surface after the high temperature exposure at 1000°C for 400 h for CoNiCrAlY bond coat and at 1100°C for 200 h for NiCoCrAlY bond coat. TGO formation mechanisms for both as-sprayed and remelted MCrAlY coating are discussed. The present work provides a feasible solution to suppress the formation of mixed oxides on thermally sprayed MCrAlY coatings during high temperature exposure and thus contributes to the longer lifetime of TBCs.