Dynamic recrystallization during microindentation: A site-specific study of indents using a novel LaserFIB method
Bibliographic record
Abstract
Grain-refinement by continuous dynamic recrystallization (cDRX) is generally known to require extreme deformation conditions—high strain/strain rates—like those observed in extreme deformation processes, e.g., microparticle impact and high-energy ball milling. It is not clear whether cDRX steps can be interrupted to circumvent the requirement for such extreme conditions; a phenomenon we term two-step cDRX or interrupted cDRX (icDRX). We hypothesized that simple microindentation of a predeformed metal could result in grain refinement by icDRX mechanism without the need for post-process heat treatment, as conventionally done. Microindention of friction stir processed (FSP) aluminum is conducted to test this hypothesis. To circumvent the limitations involved in the characterization of a large indent size and the problem with conventional focused ion beam (FIB) methods of accessing deep regions of interest such as the apex of an indent, we use a custom FIB lift-out grid and LaserFIB-method to extract a large TEM lamella from microindents for scanning/transmission electron microscopy (S/TEM). The results show an unusually high hardness value for aluminum that is explained by the transformation of prior dislocation cells to bonafide cDRXed ultrafine grains during microindentation to establish an icDRX grain refinement mechanism: prior dislocation cells develop into partitioned elongated subgrains at the upper corner of the indent ; evidence of ultrafine near-equiaxed grains that indicates the onset of cDRX emerges midway down the indent ; and complete grain refinement by icDRX occur at the indent apex . Conclusively, the microstructural observations are also consistent with the deformation map for aluminum, while the hardness/yield strength is reasonably modeled. These findings are particularly interesting for metal additive manufacturing (and allied) processes that develop dislocation cell structures; an additional simple plastic deformation step on these manufactured parts can drive the dislocation cells to completely refined grains by icDRX , thereby improving materials’ mechanical properties.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".