Cyclic oxidation and rumpling behaviour of single phase β-(Ni,Pt)Al coatings with different thickness of initial Pt plating

• Dual-layered α-Al2O3 scale was formed on (Ni,Pt)Al coating after oxidation.
• Pt-rich precipitates were observed in columnar grains of Al2O3 scale.
• Higher Pt content in (Ni,Pt)Al coating results in lower Young’s modulus and hardness.
• Besides phase transformation, coating deformability was important to affect rumpling.
• Al depletion rate was accelerated in turn by severer morphology rumpling.

Cyclic oxidation behaviour of single phase β-(Ni,Pt)Al coatings with different thickness of initial Pt plating was evaluated at 1100 °C in air. The coating sample of 5 μm Pt showed the best oxidation resistance, and after oxidation a dual-layered structure of alumina scale was formed on this coating with precipitation of Pt-rich particles at both boundary and interior of columnar α-Al2O3 grains. Comparatively, the coating sample with 8 μm Pt was prone to rumpling due to its lower hardness and Young’s modulus, while the severer rumpling behaviour in turn increased the scale spallation tendency and Al depletion rate.

A dual-layered alumina scale consisting of upper equiaxed and inner columnar grains was observed on the β-(Ni,Pt)Al coating specimen with 5 μm Pt after cyclic oxidation at 1100 °C for 200 cycles. The corresponding SAED patterns (b and c) confirm hexagonal crystal structures for the equiaxed and columnar α-Al2O3 grains, respectively. This unique structure of dual-layer was beneficial for the decreased oxidation rate, and the precipitation of Pt-rich particles along columnar alumina grain boundary may assist to block the outward transportation of Al cations.Figure optionsDownload as PowerPoint slide