Digital Repository, ICF12, Ottawa 2009

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Isothermal and Thermomechanical Fatigue Behaviour of IN738LC
S. Yandt, D.Y. Seo, P. Au, J. Beddoes

Last modified: 2013-05-03


The isothermal low-cycle fatigue (IT-LCF) and the in-phase (IP) and out-of-phase
(OP) thermomechanical fatigue (TMF) life of IN738LC nickel-base superalloy
was investigated in the temperature range of 750ºC to 950ºC. The experimental
results indicate that fatigue life depends on strain-temperature phasing and
mechanical strain range. In-phase TMF tests exhibited lives that were similar to
the strain-life data obtained from IT-LCF tests conducted at 950°C. A crossover
of IP and OP-TMF strain-life curves, where OP-TMF resulted in the longest life
at high-strain ranges and shortest life at low-strain ranges, was also observed.
Under all test conditions fatigue cracks nucleated at surface connected grain
boundaries and propagated along grain boundaries. Extensive creep cavitation
and intergranular damage were observed in IP-TMF test specimens. A higher
density of surface-connected fatigue cracks was observed for IT-LCF and IP-TMF
loading conditions than for OP-TMF.

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