The dynamic strain aging (DSA) mechanism proposed by Cottrell in 1953. This theory explains, when the diffusion velocity of solute atoms becomes equal to the dislocation mobility, the solute atoms can diffuse through the lattice and even to the pin dislocations. With increasing stress, mobile dislocations get rid of the solute atoms resulting in terminating the pinning effect. The serrated flow in stress-strain curve is presented due to the repeated dynamic pinning and unpinning effects.
On the other hand, as an efficient barrier, precipitates contribute significantly to hindering dislocation motion and enhancing the strength of materials. Some researchers thought that the precipitates that can be sheared by dislocation may promote the serrated flow. since GP zones precipitates are unresolved in TEM and having very small size (in angstrom), can it promote serrations in CuCrZr alloy?
I am not 100% Sure though, but the type of serration in ferrous alloy caused by solute atoms rushing to dislocation strain field to pin it down and dislocation then tearing free of pinning cannot occur for GP zones- diffusing along with a whole bulk of atoms as an indivisible unit (be it tens or twenties or even more atoms) is extremely difficult. But if the atoms concentrating in GP zones are same atoms that do the dislocation pinning, and Dislocation stain field can dissolve GP zones, tunnel atoms one by one and then redeposit GP zone on dislocation strain fields, I cannot tell. But if kinetics allow, this can happen, especailly if deformation is slow. Whether the strain energy of dislocation can precipite GP zones at its core would depend on many factor- one of the prime factor is whether the consequental stage of GP zones (new phases) are more voluminous/less dense than the parent phase.
However, if the GP zones are like little strong nano-islands in a soft-ductile matrix, then like nanocomposite (hard fiber breaking before soft matrix fails), there are chances of serrations (follow any composite stress-strain diagram with reinforcing phase more rigid and stronger than matrix phase)
as for the CuCrZr alloy (according to the study https://doi.org/10.1016/j.prostr.2019.08.222)
CuCrZr alloy is a PH copper alloy (heat-treatable alloy). Cr content must be lower than 1.5wt% to avoid the formation of coarse Cr particles. Zr, whose concentration is lower than 0.25wt%, increases the alloy hardness due to formation of precipitates and increases the alloy ductility avoiding intergranular fracture.
As a treatment increase both hardness and ductility of precipitation-hardened phase, this might add complexity to whole of the process. Better comments are possible studying phase diagrams and precipitate chemistry as well as alloying nature study of this particular alloy.
Best of Luck with your research!
Yes, GP zone (Grain boundary Precipitate) precipitates with small size, even if they are unresolved in TEM, can still contribute to serrations in a CuCrZr alloy. The size of the precipitates is not the only factor that affects their ability to promote serrated flow. Other factors, such as their distribution and orientation within the material, can also play a role.
GP zone precipitates are known to act as obstacles that impede the motion of dislocations, and their presence can lead to dynamic strain aging (DSA) and serrated flow. The small size of the precipitates does not necessarily prevent them from having an effect, as long as they are able to interact with dislocations and impede their motion.
While the small size of GP zone precipitates in a CuCrZr alloy may make them difficult to observe in TEM, they can still play a role in promoting serrated flow through their interaction with dislocations.
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