Study on behavior of NiAl coating with different Ni/Al ratios

β-NiAl coatings with different Ni/Al ratios were deposited on K403 superalloy substrates via magnetron sputtering. The phase transformation and diffusion phenomenon of the NiAl/Ni-based superalloy system after vacuum annealing at 900 and 1000 °C were analyzed using X-Ray diffraction (XRD), field emission scanning electron microscope (FE-SEM) and energy dispersive X-ray spectrometry (EDS). The effect of coating concentrations on the outward diffusion behavior of substrate elements was discussed. The high Cr concentrations in the Al-rich NiAl coatings were caused by the intense interdiffusion between Al and Cr. The Ti, W and Mo partitioned to γ′-Ni3Al in the coatings. Several possible reasons for the formation of γ′-Ni3Al at the surface of Ni-rich NiAl coating were identified, including: diffusion behavior of W and Mo in β-NiAl, destabilizing effect of substrate elements on β-NiAl, and diffusion rates of Ni and Al in β-NiAl. The volume change in β ⇛ γ′ transformation process shows Ni uphill diffused to the γ′-Ni3Al islands at the surface of Ni-rich NiAl coatings. The IDZ (interdiffusion zone) thickness and precipitates in IDZ were related to the Al initial concentrations in the coatings.

► The effect of different Ni/Al ratios on behavior of β-NiAl coatings was studied.
► The reason why γ′-Ni3Al formed at the surface of Ni-rich NiAl coatings was discussed.
► The diffusion behavior of substrate elements as a function of coating compositions.
► The IDZ thickness was related to the Al initial concentrations in the coatings.