| About this Abstract |
| Meeting |
2025 TMS Annual Meeting & Exhibition
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| Symposium
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Microstructural Evolution and Material Properties Due to Manufacturing Processes: A Symposium in Honor of Anthony Rollett
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| Presentation Title |
Dynamic Grain-Boundary Strengthening Contributes to Hardening During Microindentation |
| Author(s) |
Mina Dehghan, Ahmed Alade Tiamiyu |
| On-Site Speaker (Planned) |
Mina Dehghan |
| Abstract Scope |
Many previous works have conducted microindention of predeformed metals, but with no direct or site-specific evidence of how microstructure evolved. Hence, the typical microindentation process and associated hardening are attributed to circular dislocation loops beneath the indentation. Similarly, grain-refinement by continuous-dynamic recrystallization (cDRX) is known to occur mainly in metals under extreme deformation conditions—high strain/strain rates, and it is not observed in static-deformation like microindentation. Two limitations that may have obscured actual microstructural evolution could be due to the constraint in characterizing large indent sizes and the problem in the conventional focused-ion beam (FIB) method of accessing deep regions of interest. Using LaserFIB processes and custom FIB lift-out grids to overcome these constraints, we demonstrate for the first time that complete grain-refinement by cDRX occurs during microindentation of a predeformed dislocation cell-ladened metal, a phenomenon we term two-step-cDRX or interrupted-cDRX (icDRX). By gradual evaluation of a series of windows from the edge of the indent down to the apex, we track refined grain evolution using scanning/transmission electron microscopy: 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 occurs at the indent apex. This results in grain-boundary strengthening contribution that leads to an unusually high hardness value for aluminum during microindentation rather than the “pure” dislocation hardening that is long thought of. Convincingly, the microstructural observations are also consistent with the deformation map for aluminum, while the hardness/yield strength is reasonably modeled. These findings represent a significant advancement for the field for some reasons: they broaden the range of indentation hardening mechanisms that are currently understood; they highlight the possibility that cDRX steps can be interrupted to avoid the need for extreme deformation conditions; and they establish a mechanistic connection between the vast field of recrystallization and the even larger field of grain-refined metals. |
| Proceedings Inclusion? |
Planned: |
| Keywords |
Characterization, Mechanical Properties, Aluminum |