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| AN INVESTIGATION OF THE DIRECTIONAL SOLIDIFICATION OF A NICKEL-BASE SUPERALLOY |
| Lin Dongliang;Lin Tung-liang;Yao Deliang Shanghai Jiaotong University |
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Cite this article:
Lin Dongliang;Lin Tung-liang;Yao Deliang Shanghai Jiaotong University. AN INVESTIGATION OF THE DIRECTIONAL SOLIDIFICATION OF A NICKEL-BASE SUPERALLOY. Acta Metall Sin, 1979, 15(2): 177-303.
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Abstract The structure and properties of a directionally solidified high strength castnickel-base superalloy have been studied. Directional solidification significantly in-creased the resistance to thermal-fatigue and intermediate temperature rupture lifeas well as the ductility and the tensile strength and high temperature rupture lifeof the alloy. The improvement of rupture life at certain intermediate temperature(about 760℃) was found to be due to an extension of the secondary stage ofcreep, whereas at a high temperature (about 980℃) the same improvementcame from an extension of the tertiary stage. The absence of grain boundaries inthe transverse direction gave rise to better mechanical properties, in particular, the<100> preferred orientation of the columnar grains played an important part inthe increased strength at elevated temperatures. The secondary creep rate was lowered and the second creep stage extendedafter high temperature solution treatment. This was found to be due to the solu-tioning of the coarse γ' phase on heating and the subsequent reprecipitation of auniformly dispersed fine γ' particles in the cast alloy after cooling. In the above directionally solidified alloy, primary MC carbides seem to serveas the sites for creep and thermal-fatigue crack initiation. This rather suggests thatthe high temperature mechanical properties of the alloy may possibly be furtherimproved if its carbon content is lowered.
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Received: 18 February 1979
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