Formation mechanism of Pt-modified aluminide coating structure by out-of-the-pack aluminizing

In this research, the formation mechanism of platinum-modified (Pt-modified) aluminide coating structure applied by out-of-the-pack aluminizing is investigated. For this purpose, the samples of superalloy were coated with 7.5 µm platinum prepared by electroplating. Then, they were heat-treated at 1080°C for 1 h in the vacuum (10−4 torr). The platinum-coated samples were aluminized using an out-of-the-pack single-step aluminizing process at 1050°C under different times and with fixed powder composition. Afterwards, the microstructures of the coatings were evaluated using scanning electron microscope (SEM), energy dispersive spectroscopy (EDS) and an X-ray diffraction (XRD). The results showed that Pt-modified aluminide coating was formed at first by the inward diffusion of Al and, then, by outward diffusion of Ni. The final coating microstructure consisted of three main layers. The outermost layer of PtAl2 precipitates in a β-Ni(Pt, Al) matrix, the middle layer of Ni-rich β-Ni(Pt, Al) and the innermost layer of interdiffusion zone.