Damage mechanisms of single and polycrystalline nickel base superalloys SC16 and IN738LC under high temperature LCF loading

The mechanical behaviour of polycrystalline and single crystal nickel base superalloys, IN738LC and SC16, respectively, has been investigated under strain controlled LCF loading at 1223K. The alloys showed a very similar stress response: a long stable stress amplitude period preceded by either cyclic hardening at higher strain amplitudes or by cyclic softening at lower strain amplitudes. The fatigue life of the single crystal alloy was, however, measured to be about 10 times higher than that of the polycrystalline variant. This can be attributed to the differences in deformation and damage processes observed in the two alloys.