Impact of Pt/Al ratios on the cyclic oxidation and TCP precipitation of β-(Ni, Pt)Al coated superalloy at 1150 °C

Abstract

The cyclic oxidation and topologically close-packed (TCP) phase precipitation behaviors of β-(Ni, Pt)Al coatings with different Pt/Al ratios at 1150 °C were investigated. In the initial oxidation stage, coatings with different Pt/Al ratios exhibited comparable high-temperature oxidation resistance, likely due to a similar level of Al absorption. Subsequently, oxide spallation was common for coatings with lower Pt/Al ratios due to the formation of fine-grained alumina and a “sandwich” structure (a multilayer porous structure) oxide scale. For coatings with higher Pt/Al ratios, severe rumpling occurred, and numerous cracks formed in the oxide scale. However, sufficient Al concentration in the outer zone and the improved deformation tolerance of the oxide scale enhanced the spallation resistance of the thermally grown oxide (TGO). Furthermore, a higher Pt/Al ratio promotes uphill diffusion of Al, which reduces its migration into the substrate, thereby diminishing TCP precipitation. Coatings with the same Pt/Al ratios but higher Pt and Al contents further reduced TCP precipitation after oxidation. This improvement is attributed to the initially lower Al concentration in these coatings' secondary reaction zone (SRZ) and their greater thickness.

Keywords

• β-(Ni
• Pt)Al coating
• Pt/Al ratio
• Oxidation resistance
• Coating rumpling
• TCP precipitation