Dislocation Substructure Evolution and Damage Accumulation in Large-Grained Homogenized and Fine-Grained Hot-Rolled Superni 625 During LCF at 298 K and 973 K.
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| Title: | Dislocation Substructure Evolution and Damage Accumulation in Large-Grained Homogenized and Fine-Grained Hot-Rolled Superni 625 During LCF at 298 K and 973 K. |
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| Authors: | Godasu, Ashwin Kumar1 (AUTHOR), Chahar, Sonika1 (AUTHOR), Kumar, Atul2 (AUTHOR), Prakash, Ujjwal1 (AUTHOR), Mula, Suhrit1 (AUTHOR) suhrit.mula@mt.iitr.ac.in |
| Source: | Metallurgical & Materials Transactions. Part A. Aug2025, Vol. 56 Issue 8, p2834-2852. 19p. |
| Subjects: | Strains & stresses (Mechanics), Dislocation nucleation, Fatigue cracks, Fatigue life, Alloy fatigue |
| Abstract: | The present study investigates synergistic role of grain size and deformation temperature on slip activity and dislocation substructure evolution during low-cycle fatigue (LCF) of concentrated solid solution alloy Superni 625. Total strain-controlled isothermal LCF tests were conducted at 298 K and 973 K by applying various strain amplitudes. It is revealed that the large initial mean free path of dislocations associated with a large grain size (LGS) material causes delayed slip transition from single → duplex/multiple slips during LCF. This in turn manifests in two-stage cyclic hardening regimes: weak primary hardening in initial cycles followed by a steep secondary hardening. In contrast, in a fine grain size (FGS) material, fast slip transition rate arises to attain grain compatibility near grain boundary regions and evidences a single continuous strong cyclic hardening. Further, irrespective of the grain size, formation of dislocation walls and nucleation of persistent slip bands (PSBs) are found to be limited at room temperature (RT) deformation and almost always resulted in a cyclic saturation and/or softening in later stage. However, at 973 K, the cyclic deformation is observed to be less localized compared to the RT deformation and there is a concomitant rise in the concentration of dense dislocation tangles, which avoided the onset of cyclic softening. The change in the deformation micromechanisms at 973 K is attributed to the occurrence of thermally assisted deformation micromechanisms like dynamic strain aging and dynamic precipitation. Finally, the role of annealing twins on fatigue damage accumulation is studied and revealed that annealing twins could resist intergranular crack nucleation and propagation in concentrated solid solution alloys such as Superni 625, thereby significantly enhancing the fatigue life. [ABSTRACT FROM AUTHOR] |
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| Database: | Engineering Source |
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| Abstract: | The present study investigates synergistic role of grain size and deformation temperature on slip activity and dislocation substructure evolution during low-cycle fatigue (LCF) of concentrated solid solution alloy Superni 625. Total strain-controlled isothermal LCF tests were conducted at 298 K and 973 K by applying various strain amplitudes. It is revealed that the large initial mean free path of dislocations associated with a large grain size (LGS) material causes delayed slip transition from single → duplex/multiple slips during LCF. This in turn manifests in two-stage cyclic hardening regimes: weak primary hardening in initial cycles followed by a steep secondary hardening. In contrast, in a fine grain size (FGS) material, fast slip transition rate arises to attain grain compatibility near grain boundary regions and evidences a single continuous strong cyclic hardening. Further, irrespective of the grain size, formation of dislocation walls and nucleation of persistent slip bands (PSBs) are found to be limited at room temperature (RT) deformation and almost always resulted in a cyclic saturation and/or softening in later stage. However, at 973 K, the cyclic deformation is observed to be less localized compared to the RT deformation and there is a concomitant rise in the concentration of dense dislocation tangles, which avoided the onset of cyclic softening. The change in the deformation micromechanisms at 973 K is attributed to the occurrence of thermally assisted deformation micromechanisms like dynamic strain aging and dynamic precipitation. Finally, the role of annealing twins on fatigue damage accumulation is studied and revealed that annealing twins could resist intergranular crack nucleation and propagation in concentrated solid solution alloys such as Superni 625, thereby significantly enhancing the fatigue life. [ABSTRACT FROM AUTHOR] |
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| ISSN: | 10735623 |
| DOI: | 10.1007/s11661-025-07824-2 |
