MCrAlY bond coat alloys, where M represents Ni, Co, or their combination, are widely used as bond coat materials for turbine blades in modern aero engines. They play a crucial role in enhancing the bonding strength between the ceramic top coat and the superalloy substrate, as well as in improving high-temperature oxidation and corrosion resistance. During high-temperature service, a thermally grown oxide layer, mainly composed of α-Al2O3, forms between the bond coat and the ceramic layer, providing protection and preventing further oxidation of the bond coat. To further improve the high-temperature microstructural stability and oxidation resistance of NiCoCrAlY bond coat alloys, the work aims to investigate the effect of low Ru content on the high-temperature oxidation performance of NiCoCrAlYHfReRu alloys based on an Hf-Re co-modified NiCoCrAlY system.
The phase compositions of the bond coat alloys and oxide scales were analyzed through X-ray diffraction (XRD, Rigaku SmartLab-9 kW) with a working voltage of 45 kV and a current of 20 mA. A Cu target was used, with a scanning range of 20°-90° and a scanning rate of 5 (°)/min. The room-temperature microstructure of the alloys, the surface morphology and cross-sectional morphology of the oxide scales, and the elemental compositions were characterized by field-emission scanning electron microscopy (FESEM, Zeiss Sigma 300) and electron probe microanalysis (EPMA, JXA-iHP200F). The working voltages of FESEM and EPMA were 20 kV and 15 kV, respectively. During the cross-sectional analysis of the oxide scales, chromium plating was performed by physical vapor deposition prior to sample preparation to prevent damage or spallation of the oxide scales.
The phase composition analysis showed that the theoretical equilibrium phases of the bond coat alloys containing 0.25wt.% and 0.5wt.% Ru were β-NiAl, γ′-Ni3Al, σ-CoCr, α-Cr, and Ni5Y. Under non-equilibrium conditions, the room-temperature microstructure was observed to consist ofβ-NiAl, γ′-Ni3Al, α-Cr, and Ni5Y intermetallic compounds. When the Ru content increased from 0.25wt.% to 0.5wt.%, the β-NiAl phase fraction in the 0.5wt.% Ru alloy was higher than that in the 0.25wt.% Ru alloy within the temperature range of 1 000-1 250 ℃. After isothermal oxidation at 1 100 ℃ for 200 h, the oxidation behavior of both the 0.25wt.% Ru and 0.5wt.% Ru alloys followed Wagner's parabolic oxidation law. The average mass gains per unit area increased from 8.486 g/m2 and 7.582 g/m2 to 29.789 g/m2 and 28.562 g/m2, respectively, while the average oxidation rates decreased from 0.339 g/(m2·h) and 0.303 g/(m2·h) to 0.149 g/(m2·h) and 0.143 g/(m2·h), respectively. With the increasing Ru content, the average oxidation rate of the bond coat alloy decreased. The oxide scale thicknesses of the 0.25wt.% Ru and 0.5wt.% Ru alloys were 5.25 μm and 4.98 μm, respectively. Meanwhile, surface oxide spallation and internal oxidation were both alleviated.
Based on the phase constitution and oxidation behavior, Ru content may regulate the solid-solution behavior and diffusion process of Al in the β-NiAl phase, thereby reducing Al consumption and interdiffusion loss. This contributes to maintaining the stability of the β-NiAl phase and promotes the formation of a more continuous, dense, and stable protective oxide scale. As the Ru content increases from 0.25wt.% to 0.5wt.%, the high-temperature oxidation resistance of the NiCoCrAlYHfReRu alloy is further improved.
Key words
bond coat alloy /
phase composition /
high-temperature oxidation resistance /
NiCoCrAlYHfReRu /
Ru modification
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Funding
National Natural Science Foundation of China (52664048); Program for Young Talents of Science and Technology in Universities of Inner Mongolia Autonomous Region (NJYT24070); Metallurgical Engineering First-Class Discipline Scientific Research Special Project of the Department of Education of Inner Mongolia Autonomous Region (YLXKZX-NKD-050); AECC Beijing Institute of Aeronautical Materials Institutional Fund (KJ42250521); Key Research and Achievement Transformation Program of Inner Mongolia Autonomous Region (2026YFHH0117); Postgraduate Research Innovation Project of Inner Mongolia Autonomous Region (KC2025065S); Baotou Lucheng Talent Individual Project; Stable Support Program Funding (KZ0C240599)
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