Environmental damage of a cast nickel base superalloy |
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Authors: | D A Woodford |
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Affiliation: | (1) Corporate R & D, General Electric Company, 12301 Schenectady, NY |
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Abstract: | Exposure in air in the temperature range 900 to 1100 °C produces a major loss in stress rupture life and ductility of IN738.
The sensitivity to this environmental damage increases with decreasing test temperature in the range 1000 to 700 °C. Oxygen
is identified as the source of the damage for air exposure and indirect evidence supports grain boundary penetration of the
gas to considerable depth. It is argued that oxygen segregation can lead to grain boundary immobilization and unstable intergranular
fracture at intermediate temperatures. It is shown that compositional modifications, particularly boron and hafnium additions,
may reduce the oxygen damage susceptibility, and that a cobalt base coating effectively eliminates the susceptibility. The
relevance of these observations in understanding the effect of test environment on creep-rupture and fatigue crack propagation
is considered. |
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Keywords: | |
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