Abstract
Influence of microtwins (MTs) on Portevin-Le Châtelier (PLC) effect of a Ni-Co-based superalloy was investigated by tensile tests and transmission electron microscopy. Two groups of samples were pre-strained at 725 °C to produce MTs. Existence of MTs improved the alloy's yield strength, but it changed the PLC effect from type-B to type-C, and increased the serration amplitudes by ∼6 times, during tensile deformation at 400 °C. Microstructural characterizations indicate that dislocation-MT interactions lead to break of MTs in both γ matrix and γ′ precipitates, creating soft channels for dislocation glide. The high serration amplitudes were rationalized on the basis of sudden plastic flow along those soft channels and subsequently strain hardening due to dislocation multiplication. These results demonstrate that MTs influence the PLC effect much more significantly, compared with traditionally accepted dislocation-solute interactions.
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