Creep of a nickel-based single-crystal superalloy during very high-temperature jumps followed by synchrotron X-ray diffraction

Investigating the Dislocation-Driven Micro-mechanical Response Under Non-isothermal Creep Conditions in Single-Crystal Superalloys

“…To the best knowledge of the authors, dislocation structures originating from non-isothermal cyclic creep have to date only been studied by Viguier and Hantcherli et al [7,41] Their test series on the superalloy MC2 exposed the material to a peak temperature of 1150°C for 30 minutes and cooled the sample down to room temperature in 25 minutes. In other studies of high-temperature (heating to 1050°C and more) thermal creep cycling, [2,22,41] the c¢-dissolution was equally large, resulting in a much larger movement of the interface between its peak and base temperature position than in the current study. This greater disruption to the interface is thought to be the reason why paired dislocation networks have not been observed in the cited studies.…”

“…Le Graverend et al showed that similarly high misfit magnitudes could be achieved during short high-temperature excursions. [22,44] The same study verified in-situ that an increase in misfit magnitude was directly related to an addition in strain accumulation from added dislocation motion. The high-temperature excursions thus require additional interfacial dislocations, while simultaneously decreasing the Orowan glide resistance in the c-matrix (see Figure 6(c)) thereby allowing the dislocations to reach their required target quicker.…”

“…The primary driving forces for the added dislocation activity during thermal cycling are the continuously changing misfit stresses. [22,42]…”

“…The phase fraction variation does not precisely track the temperature profile due to the different diffusivities of the alloying elements. [20,21] Instead, as seen in-situ using synchrotron X-ray radiation, [22] the c¢-dissolution lags behind the temperature profiles depending on exposed temperature and thermal gradient.…”

High-Temperature Dislocation Climb in the γ′ Rafts of Single-Crystal Superalloys: The Hypothesis of a Control by Dislocation Entry into the Rafts

“…As shown in [3], while the plastic strain of the γ channels stops immediately, it carries on for a while at a reduced rate within the γ' rafts in direction As pointed in [25], the density of dislocations climbing within a raft before the jump move afterwards on an average distance 2 ⁄ before reaching its end and annihilating. The residual plastic strain for population 2 is then also:…”