Abstract
Fatigue tests, using both stress and strain control, have been performed on alloyed Ni3Al (γ′-phase). The fatigue life in stress controlled tests is independent of temperature below 800°C, which correlates with the temperature independent microyield strength of the γ′ phase. On the other hand, the fatigue life in strain controlled tests decreases with increasing temperature, correlating with a marked increase in the 0.2 pet offset yield strength of γ′ with temperature. This difference in behavior is attributed to a temperature dependent differential dislocation mobility. Thus, a temperature independent mobility for edge dislocations is considered to be responsible for the fatigue behavior under stress cycling, whereas it is proposed that a strongly temperature dependent mobility for screw dislocations (due to pinning by cross slip from octahedral planes into cube planes) controls the fatigue behavior under strain cycling. A comparison is made of the fatigue properties of alloyed γ′ and a typical γ′ precipitation hardened alloy, showing that the relative fatigue strength (endurance limit/yield strength) of the γ + γ′ superalloy is superior to that of single phase alloyed γ′ at elevated temperatures.
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Doherty, J.E., Giamei, A.F. & Kear, B.H. Influence of differential dislocation mobility on the fatigue behavior of alloyed. Metall Trans A 6, 2195 (1975). https://doi.org/10.1007/BF02818643
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DOI: https://doi.org/10.1007/BF02818643