The effect of grain boundary orientation on creep and rupture of IN-738 and nichrome |
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Authors: | D A Woodford J J Frawley |
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Affiliation: | (1) General Electric Company, 12345 Schenectady, N. Y. |
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Abstract: | Creep rupture specimens taken from directionally solidified ingots of IN-738 and Nichrome in which the grain boundaries were
oriented longitudinally, transversely, and 45 deg to the stress axis have been tested over a range of temperature and stress.
For both alloys, the ductility was appreciably higher in the longitudinal orientation; but in IN-738, the creep strength was
higher in the other two orientations. The net effect on rupture life was small for the superalloy. The nichrome showed much
greater scatter which was due partly to inhomogeneous deformation and local recrystallization at the higher temperatures.
Because of the recrystallization, even the longitudinal specimens showed intergranular failure for nichrome. The microstructural
features of intergranular cracking both internally and on the surface are documented. It is suggested that surface cracking
may be an important contributory factor in leading to reduced life with decreased section size which is commonly observed
in conventionally cast superalloys. |
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