The PLC Effect in the Absence of Long-Range Cottrell Atmospheres in RR1000

The Portevin–Le Chatelier (PLC) effect is widely attributed to the partitioning of interstitial C atoms around dislocation cores in mild steels, to form Cottrell atmospheresCottrell atmosphere. However, limited empirical evidence exists to clarify how similar mechanisms extend to complex multicomponent alloy systems such as Ni-based superalloys. The presence of the PLC effect was demonstrated in coarse-grained RR1000 ranging 200–550 °C through digital image correlationDigital image correlations (DIC). The effect was also demonstrated in simple binary Ni-(20–25)Cr (wt.%) alloys, suggesting that the microstructural complexity of superalloysSuperalloys is not key to elucidating the atomistic origins. Probe-corrected scanning transmission electron microscopyTransmission electron microscopy (STEM)-energy dispersive X-ray spectroscopy and atom probe tomographyAtom probe tomography were performed on interrupted specimens displaying the PLC effect. No evidence of long-range solute enrichment was observed in the vicinity of dislocation cores. Hence, alternative origins for the effect were considered; evidence for short-range order was assessed in Ni–Cr powder through neutron diffraction. A preference was observed for particular local configurations of Ni and Cr atoms within a unit cell, resembling, but not identical to, those in long-range ordered Ni2Cr. High-resolution STEM imaging demonstrated the presence of nanodomains in Ni–Cr and RR1000 containing diffraction contrast effects resembling superlattice fringes. STEM image simulations based on refined unit cell structures demonstrated that such features may relate to the local lattice distortion in short-range ordered (SRO) domains. The results do not support the presence of long-range Cottrell atmospheresCottrell atmosphere within the temperature range of the PLC effect, but instead of SRO, an alternate hypothesised origin of the PLC effect.