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4931 |
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Thursday, May 12, 2016, Yellow River Hall 2:40 PM Power Generation IV |
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Understanding of the mechanism of excellent thermal stability of single-phase b-(Ni,Pt)Al bond coat during cyclic oxidation by experimental and theoretical study |
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Hongfei Chen* / Shanghai University/School of Materials Science and Engineering, China Liya Ye / Shanghai University, China Guang Yang/ Shanghai University, China Yanfeng Gao/ Shanghai University, China Hongjie Luo/ Shanghai University, China Bin Liu/ Shanghai University, China |
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Single-phase beta-(Ni,Pt)Al and PtAl2+beta-(Ni,Pt)Al composite coats were fabricated on Ni substrates through electroplating a layer of platinum and followed by aluminization process. Microstructures and chemical compositions of these platinum aluminide coats were characterized before and after cyclic oxidation. Compared with the PtAl2+beta-(Ni,Pt)Al bond coat in which the crack appears, the single-phase bond coat exhibited super thermal stability. It is attributed to the lower growth rate of thermally grown oxide and less stress accumulation since the diffusion of Pt in the beta-(Ni,Pt)Al coat is slower than that in the PtAl2+beta-(Ni,Pt)Al coat during cyclic oxidation. Furthermore, structural interstices and phase formation enthalpy of platinum aluminides were calculated via first principles calculations and the thermodynamic approaches based on Miedemas model and Alonsos method. We found that, in the beta-(Ni,Pt)Al phase, Pt diffuses between high Pt-modified and low Pt-modified nickel aluminides at first and concentrates in the high Pt-modified regions finally. These results indicate that the diffusion behavior of Pt plays a key role on the degradation of bond coats. Controlling the Pt diffusion is expected to an effective way of structure and property optimization of the bond coats. |