The role of grain boundary migration during low-cycle fatigue of α-iron at 450° to 700°C
Low-cycle fatigue tests have been carried out on α-iron over the temperature range 450° to 700°C. With increasing temperature, the number of cycles to failure decreased and the fracture changed from mixed transgranular/intergranular to almost entirely intergranular. At 650° to 700°C, there was a marked tendency for grain boundaries to migrate and become aligned preferentially at 45 deg to the stress axis. The rate of migration was shown to be mainly dependent on the strain amplitude. Interrupted tests at 700°C showed that failure was due to nucleation, growth, and linkage of intergranular cavities. The onset of cavitation was delayed until grain boundaries had stabilized at 45 deg to the stress axis.
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