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| INVESTIGATION OF SURFACE GRAIN REFINEMENT OF SUPERALLOY CASTINGS |
| Fang Jian (Beijing Institute of Aeronautics and Astronautics); Yu Bin (Dong An Machine Works; Harbin) |
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Cite this article:
Fang Jian (Beijing Institute of Aeronautics and Astronautics); Yu Bin (Dong An Machine Works; Harbin). INVESTIGATION OF SURFACE GRAIN REFINEMENT OF SUPERALLOY CASTINGS. Acta Metall Sin, 1982, 18(3): 255-263.
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Abstract The mechanism of the surface grain refinement for superalloy castings has been investigated by examination of some recent allied approaches and by observations on the investment molds of various effectiveness using X-ray diffraction, microscopy and EPMA. It was identified that the grain refinement of the castings is dependent upon the decomposition of cobalt aluminate and the active alloying elements contained in the alloy. After the alloy casted, the isolated particles of high temperature type cobalt were found on the surfaces of the investment mold and the castings, as well as the products of the mixture of cobalt aluminate together with different active elements heated under vacuum. Both the vacuum DTA of cobalt aluminate mixed with Al powder and the thermodynamical estimation of the reaction may confirm that the formation of Co particles did not accompany with an endothermic peak as formerly expected, but, in fact, a small exothermie effect was observed. It seems that the surface grain refinement of the castings is mainly due to the nucleation of the cobalt particles produced during casting. Thus, a rationalized process proposed has already been put into industrial practice with remarkable results.
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Received: 18 March 1982
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1 Restall, J. E.; Toulson, E. C., Met. Mater., 7 (1973) , 187．
2 #12
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5 Feagin, R. C., U. S. Pat. 3 259 948, 1966．
6 Navrotsky, A.; Kleppa, O. J., J. Inorg. Nucl. Chem., 30 (1968) , 479． |
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