PtAl 2 modified (Ni, Pt)Al coatings with varying PtAl 2 contents were prepared by means of depositing Pt layers of 2, 5, and 8 μm in thickness, followed by an aluminizing process. Single-phase (Ni,Pt)Al coating (designated 2-Pt) was obtained with 2 μm Pt layer, while dual-phase coatings with PtAl 2 dispersion in (Ni, Pt)Al matrix (designated 5-Pt and 8-Pt) were formed with 5 and 8 μm Pt layers, respectively. Cyclic oxidation behavior of the three coatings were characterized at 1150°C. Results reveal that PtAl 2 accelerates nucleation of α -Al 2 O 3 , yet paradoxically delays θ -to- α -Al 2 O 3 transformation. It leads to enhanced coating structural stability but degraded oxide scale adhesion. Density functional theory calculations unveil that it was attributed to a lower work of separation at PtAl 2 /Al 2 O 3 interface than that at (Ni,Pt)Al/Al 2 O 3 interface. Notably, 5-Pt coating exhibits the highest cyclic oxidation resistance, benefited from a balanced PtAl 2 content that optimizes both structural stability and oxide adhesion.
Yang et al. (Fri,) studied this question.