Microstructural characteristics and degradation mechanism of the NiCrAlY/CrN/DSM11 system during thermal exposure at 1100 °C

To limit the elemental interdiffusion, a CrN diffusion barrier was introduced into the interface of NiCrAlY overlayer and DSM11 substrate. During vacuum heat treatment and thermal exposure, the single and continuous CrN barrier layer was first changed to the multilayer structure and then to the Ti-rich interlayer. With the gradual loss of continuity in the diffusion barrier, the elemental interdiffusion was accelerated. Due to the interdiffusion, the transformation of β-NiAl → γ′-Ni3Al → γ-Ni and the low Al level occurred in the overlayer. The phase transformation of metastable θ-Al2O3 to stable α and the accelerated elemental interdiffusion affected the integrity of the surface scales. After 100 h exposure at 1100 °C, the Al element was insufficient and the duplex coatings were degraded.

Figure optionsDownload as PowerPoint slideResearch highlights▶ With the introduction of CrN diffusion barrier, the oxidation-resistance of the coating system was improved to some degree. ▶ The transformation of θ-Al2O3 to α-Al2O3 and the outward-diffusion of alloy elements affected the integrity of the surface scales. ▶ A series of phase transformation took place in the overlayer. ▶ 3β-NiAl → γ′-Ni3Al + 2[Al]. ▶ 2γ′-Ni3Al → 6γ-Ni + 2[Al].