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

• Published in: Corrosion science Vol. 111; pp. 162 - 174
• Main Authors: Yang, Y.F., Jiang, C.Y., Yao, H.R., Bao, Z.B., Zhu, S.L., Wang, F.H.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.10.2016
• Subjects: A. Metal coatings; A. Platinum; B. SEM; B. TEM; C. Oxidation; B. SEM; A. Metal coatings; C. Oxidation; A. Platinum; B. TEM
• ISSN: 0010-938X; 1879-0496
• DOI: 10.1016/j.corsci.2016.05.011

A dual-layered alumina scale consisting of upper equiaxed and inner columnar grains was observed on the β-(Ni,Pt)Al coating specimen with 5μm 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. [Display omitted] ⿢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 5μm 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 8μm 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.