Design of novel NiSiAlY alloys in marine salt-spray environment: Part I. Al-Si-Y and Ni-Si-Y subsystems

Abstract

MCrAlY (M=Ni, Co, NiCo) alloys have been widely used as a bond layer for thermal barrier coatings (TBCs). However, oxides form discontinuously on MCrAlY surface in the marine environment since Cr2O3 can react with NaCl and H2O at temperatures above 500 ℃. Replacing Cr with other alloying elements (such as Si) might prevent severe salt-spray corrosion effectively. To save time and efforts in materials design of the Ni-Si-Al-Y system, we obtained the thermodynamic descriptions of the ternary compounds by coupling the CALPHAD (CALculation of PHAse Diagrams) approach and first-principles calculations. Seven and eighteen ternary compounds were evaluated and calculated in the Al-Si-Y and Ni-Si-Y systems, respectively. Phase diagrams of the two systems were depicted after a series of experimental Al/Ni-Si-RE (RE denotes rare earth elements, including La, Ce, Pr, Nd, Sm, Gd, Dy, Ho, and Er) systems being analyzed. It is found that the RE elements with the same reference states tend to form ternary compounds with the same crystal structures. The model-based descriptions are the basis for the research and development of novel NiSiAlY alloys in resisting high-temperature corrosion.