Ali Moshiri - Academia.edu (original) (raw)
Papers by Ali Moshiri
Journal of Materials Research and Technology, 2023
The present work deals with the cyclic deformation behavior of AlSi10Mg alloy fabricated through ... more The present work deals with the cyclic deformation behavior of AlSi10Mg alloy fabricated through selective laser melting. Toward this end, the printed material was heat treated and was tested through strain-controlled push–pull fatigue under different strain amplitudes. The highest strengths were recorded for the direct aged, as-built and solutionized microstructures, respectively. The directly aged microstructure was characterized by the transformation of the columnar solidified structure into the equiaxed one and formation of the nano-Si precipitates. This was led to the best fatigue performance where an outstanding balance between the fatigue life and strength level was recorded. The low aspect ratio of the melt pools intensified the Marangoni effect, therefore, caused concentration of the material flow on the wetting side. This led to crack initiation and propagation at the end of the melt pools and formation of balling defects. Balling defect was characterized as the initiation site in the case of as-built and directly aged specimens, the cone-like geometry of which resulted in crack path deflection and a better fatigue performance. For solution treated microstructure, the melt pools were dissolved and the lack of fusion holding a critical size and located close to the surface, was characterized as the main crack initiation site.
Journal of Materials Research and Technology, 2023
The present work demonstrates a novel interpretation of the effect of well-known heat treatments ... more The present work demonstrates a novel interpretation of the effect of well-known heat treatments of solutionizing (ST) and solutionizing plus aging (T6) along with a newly-developed direct aging (DA), on the microstructural evolution and corresponding deformation behavior of selectively laser-melted AlSi10Mg alloy. To this end, different heat treatments were employed to not only modify the microstructure but also adjust the defect structure. Furthermore, the monotonically deformed microstructures and the corresponding fractured surface at temperatures of 25 and 200 °C was studied to address the effect of post-processes on the damage mechanism. Surprisingly, it has been understood that the flow responses of the treated microstructures haven't improved as much as it was expected. That is attributed to the deteriorating effect of dissolving the cellular structure along with its considerable impact on trapped gas defect. Furthermore, the melt pool boundaries (MPB) found to be prone to crack nucleation and growth owing to the high connectivity of Si-network and strain localization in heat-treated specimens as well as in As-built ones. Small precipitates from the inner part of the melt pool were likely to agglomerate in the heat-affected zone (HAZ) under the Ostwald ripening mechanism where these primary coarse Si precipitates had existed.
Journal of Materials Research and Technology, 2022
The origin of cyclic hardening under low strain amplitude (with N ¼ 25284 cycles to failure) foll... more The origin of cyclic hardening under low strain amplitude (with N ¼ 25284 cycles to failure) followed by pseudo-plateau response under high strain amplitude (with N ¼ 2671 cycles to failure) during fully reversal (R ¼ À1) strain-controlled pullepush fatigue of Mg-8.2Gd-3.6Y-1.6Zn-0.5Zr (wt.%) at room temperature condition was explored. The (i) dislocations trapping between LPSO (long period stacking order) lamellas, (ii) substructure development, and (iii) deformation twinning and tangling/rearrangement of partials within twin band were known as the main factors contributing to the room temperature cyclic hardening response. The pseudo-plateau behavior and cyclic stabilization were also attributed to the co-formation of the veins structure in the vicinity of 18R LPSO and reversion of 14H LPSO at higher strain amplitudes.
Journal of Materials Research and Technology, 2023
This study aims to investigate the deformation mechanisms of an austenite-based duplex Fe–Mn–Al–C... more This study aims to investigate the deformation mechanisms of an austenite-based duplex Fe–Mn–Al–C steel at room-temperature through uniaxial tensile tests, strain rate sensitivity and stress relaxation analysis. Through numerical analysis and microstructural studies, this investigation reveals that increasing strain leads to the formation of low-angle boundaries (LABs) at the vicinity of grain boundaries. Consequently, these LABs play a facilitating role in the stress-assisted diffusion of carbon atoms, thereby triggering the dynamic strain aging (DSA) phenomenon. The evidence for this is substantiated by the strain rate sensitivity coefficient and stress relaxation results obtained from numerical analysis during uniaxial tensile tests. As deformation progresses, the misorientation of LABs increases, influencing the strain hardening behavior. The intensified DSA contributes to enhanced work hardening, while substructure development results in softening, creating a trade-off between these contrasting effects.
Journal of Materials Research and Technology, 2022
The present work deals with the short-time thermal phase-stability of the as-cast eutectic AlCoCr... more The present work deals with the short-time thermal phase-stability of the as-cast eutectic AlCoCrFeNi2.1 high entropy alloy. Toward this end, the effect of different temperatures (800–1000 °C) and soaking times (15–60 min) on the stability of primary dendritic regions and formation of the ordered phases was explored. Microstructural characterization was supported by thermodynamic calculations and assessment of the subsequent mechanical properties. Upon the increase in annealing temperature and soaking time, the primary FCC dendritic areas grown and destabilized owing to elemental partitioning. This was followed by dendrite fragmentation and formation of needle shape B2 ordered phases within the primary FCC regions. Despite the unstable nature of the primary constituent phases, the material hardness increased considerably to a peak point corresponding to the moderate soaking time of 45 min. The variation of the subsequent mechanical properties was discussed relying on the characteristics of the ordered and primary phases.
Advanced Engineering Materials, 2023
Herein, the occurrence ofa B2-phase separation and formation of Cr-rich nanoprecipitates during t... more Herein, the occurrence ofa B2-phase separation and formation of Cr-rich nanoprecipitates during the solidification process of AlCoCrFeNi2.1 eutectic highentropy alloy is addressed. Toward this end, various advanced characterizations, including high-resolution transmission electron microscopy and atom probe tomography combined with thermodynamic calculations, are employed. The as-solidified microstructure is composed of face-centered cubic (FCC) dendrites and interdendritic regions consisting of a eutectic mixture of FCC and bodycentered cubic (BCC) phases. The presence ofuniformly distributed Cr-rich nanoprecipitates is traced through the BCC B2 phase in the interdendritic area. Regarding the occurrence of upward diffusion and Gibbs free energy variation, the formation of Cr-rich nano-precipitates is attributed to the spinodal decomposition where the critical temperature of 800 °C is passed behind during the solidification process. The formation of dense dislocation array in the interdendritic region due to thermal stress induced during solidification is introduced as a pathway for diffusion of alloying elements in the course of cooling stage.
Journal of Materials Research and Technology, 2022
The present work deals with the short-time thermal phase-stability of the as-cast eutecticAlCoCrF... more The present work deals with the short-time thermal phase-stability of the as-cast eutecticAlCoCrFeNi2.1 high entropy alloy. Toward this end, the effect of different temperatures (800e1000 C) and soaking times (15e60 min) on the stability of primary dendritic regions andformation of the ordered phases was explored. Microstructural characterization was sup-ported by thermodynamic calculations and assessment of the subsequent mechanicalproperties. Upon the increase in annealing temperature and soaking time, the primary FCCdendritic areas grown and destabilized owing to elemental partitioning. This was followedby dendrite fragmentation and formation of needle shape B2 ordered phases within theprimary FCC regions. Despite the unstable nature of the primary constituent phases, thematerial hardness increased considerably to a peak point corresponding to the moderatesoaking time of 45 min. The variation of the subsequent mechanical properties was dis-cussed relying on the characteristics of the ordered and primary phases.
Journal of Materials Research and Technology, 2022
The present research clarifies the texture and microstructure evolution of a rare earth (RE) cont... more The present research clarifies the texture and microstructure evolution of a rare earth (RE) containing magnesium composite reinforced by SiC particles (Mg-RE/SiC) during friction stir processing. Rotating tool induced mechanical stirring and frictional heat lead to occurrence of dynamic recrystallization (DRX) and development of the strong basal texture component. The presence of second phase particles in the matrix could stimulate the occurrence of continuous dynamic recrystallization (CDRX) and particle stimulated nucleation (PSN) and postpone discontinuous dynamic recrystallization (DDRX). The presentation of crystallographic orientations in an appropriate reference frame indicated formation of a new rare earth texture (RE-texture) component, near the <11-24>//shear plane normal (SPN) and <20-21>-<11-21>//shear direction (SD) orientations. This texture component was developed through simultaneous activity of basal and non-basal slip systems during dynamic recrystallization.
Journal of Materials Research and Technology, 2022
The microstructure and microtexture of an extruded and annealed GWZ (Mg-8.2Gd-3.6Y-1.6Zn-0.5Zr, w... more The microstructure and microtexture of an extruded and annealed GWZ (Mg-8.2Gd-3.6Y-1.6Zn-0.5Zr, wt.%) magnesium alloy was recorded strain by strain in the course of thermomechanical processing. The specimens were compressed down to various interruption strains of 0.1, 0.3, and 0.5 under the strain rate of 0.001s-1 at 400°C, the temperature at which the material was capable to be recrystallized extensively. Appreciable refinement was recognized even at low imposed compressive strain of 0.1, and the recrystallization process was completed at true strain 0.3 where the mean grain size of 4.3μm was attained. The LPSO stimulated nucleation (LSN) and conventional continuous dynamic recrystallization (CDRX) mechanism were contributed in grain refinement. Consequently, the initial basal texture was considerably weakened which was mainly ascribed to the formation of RE-texture components. At higher imposed strain of 0.5, the majority of grains were found in deformed states, the capability of strain softening was decreased and the microtexture only changed in respect of intensity compared with true strain of 0.3. These indicated that the imposed strain was mainly accommodated through dislocation multiplication and tangling within the previously recrystallized grains. Complementary, the slip / twin activity, and the sequence of strain accommodation was investigated through Schmid analysis of the various systems.
Journal of Materials Research and Technology, Jan 29, 2022
The present study deals with the extraordinary twin formation during compressive deformation of a... more The present study deals with the extraordinary twin formation during compressive deformation of a Fe-37.55Mn-8.5Al-0.6C (wt.%) low-density steel at warm temperature regime (200-600°C). Despite the conventional opinion regarding the restrictive effect of increasing temperature on the occurrence of deformation twinning, not only the twin boundary fraction did not decrease, but also twinning was encouraged at 400°C and even 600°C. This was discussed relying on the occurrence of dynamic strain aging phenomenon, which caused a bump in corresponding hardening rate curves. The medium entropy of the alloy, which made short-range diffusion of solute atoms feasible and facilitated local pinning of the mobile dislocations, provided a proper condition for the occurrence of high temperature strain ageing. Finally, the unbalanced pinning of trailing and leading dislocations influenced on their velocity and caused widening the stacking faults which in-turn could significantly assist deformation twinning at such high deformation temperatures.
The present work deals with the effect of friction stir processing on the stability of the austen... more The present work deals with the effect of friction stir processing on the stability of the austenite during quenching and also its mechanical stability in the course of subsequent room temperature straining in a duplex ferritic lightweight steel. Interestingly, it was found that the austenite fraction increased owing to the dynamic phase transformation of ferrite to the austenite and enhancement in austenite stability. In this regard, the influence of dislocation density variations, partitioning in solute elements (Mn and C) and grain refinement on austenite stability was discussed in details. The optimum austenite stability during quenching was achieved in the case of processed microstructure holding finer grain size, and higher dislocation density. These provided fast track diffusion for austenite stabilizer elements, which decreased the thermally activated martensite starting temperature and finally led to stabilization of austenite. These factors have directly influenced the mechanical stability of the austenite during subsequent deformation and increased the strain range for the occurrence of strain induced martensitic transformation which led to a significant strength/elongation balance. The capability of transformation induced plasticity (TRIP) effect was deteriorated in the case of microstructures with lower austenite stability. Surprisingly, despite the appreciable decrease in grain size the yield strengths of the processed specimens were not influenced significantly. The deviation was justified considering the fact that the critical stress of TRIP effect was lower than of predicted through Hall-Petch relationship.
A novel method is offered with the task of unveiling the underlying micro-mechanisms of cyclic de... more A novel method is offered with the task of unveiling the underlying micro-mechanisms of cyclic deformation. This method by merging of dwell-fatigue and stress relaxation concept provides the capability of assessment of the dislocation response to cyclic deformation and subsequently the differences between tensile and compressive half-cycles behavior. Interestingly, the apparent activation volume and mobile dislocation density have been successfully calculated in the course of cyclic loading. Noteworthily, room-temperature dynamic strain aging is firmly proved through these novel findings in a cyclically-loaded lightweight steel. This promises to be a breakthrough in deep understanding the behavior of materials under cyclic loading.
The present work deals with revealing the fatigue and dwell-fatigue behavior and correlated damag... more The present work deals with revealing the fatigue and dwell-fatigue behavior and correlated damage mechanisms of Fe-Mn-Al-C lightweight steel. Surprisingly, alteration in loading mode from monotonic to cyclic induces reversible dislocation movement and facilitates the occurrence of dynamic strain aging. Additionally, applying dwell time by an acceleration of strain aging intensified stress asymmetry during dwell fatigue. The occurrence of strain aging has a bilateral effect on the crack initiation and growth. On one hand, strain aging stimulates twin formation and retards fatigue crack initiation, however, on the other hand, reduces hardening capacity, restricts the plastic deformation and facilitates crack propagation.
Journal of Materials Research and Technology, 2023
The present work deals with the cyclic deformation behavior of AlSi10Mg alloy fabricated through ... more The present work deals with the cyclic deformation behavior of AlSi10Mg alloy fabricated through selective laser melting. Toward this end, the printed material was heat treated and was tested through strain-controlled push–pull fatigue under different strain amplitudes. The highest strengths were recorded for the direct aged, as-built and solutionized microstructures, respectively. The directly aged microstructure was characterized by the transformation of the columnar solidified structure into the equiaxed one and formation of the nano-Si precipitates. This was led to the best fatigue performance where an outstanding balance between the fatigue life and strength level was recorded. The low aspect ratio of the melt pools intensified the Marangoni effect, therefore, caused concentration of the material flow on the wetting side. This led to crack initiation and propagation at the end of the melt pools and formation of balling defects. Balling defect was characterized as the initiation site in the case of as-built and directly aged specimens, the cone-like geometry of which resulted in crack path deflection and a better fatigue performance. For solution treated microstructure, the melt pools were dissolved and the lack of fusion holding a critical size and located close to the surface, was characterized as the main crack initiation site.
Journal of Materials Research and Technology, 2023
The present work demonstrates a novel interpretation of the effect of well-known heat treatments ... more The present work demonstrates a novel interpretation of the effect of well-known heat treatments of solutionizing (ST) and solutionizing plus aging (T6) along with a newly-developed direct aging (DA), on the microstructural evolution and corresponding deformation behavior of selectively laser-melted AlSi10Mg alloy. To this end, different heat treatments were employed to not only modify the microstructure but also adjust the defect structure. Furthermore, the monotonically deformed microstructures and the corresponding fractured surface at temperatures of 25 and 200 °C was studied to address the effect of post-processes on the damage mechanism. Surprisingly, it has been understood that the flow responses of the treated microstructures haven't improved as much as it was expected. That is attributed to the deteriorating effect of dissolving the cellular structure along with its considerable impact on trapped gas defect. Furthermore, the melt pool boundaries (MPB) found to be prone to crack nucleation and growth owing to the high connectivity of Si-network and strain localization in heat-treated specimens as well as in As-built ones. Small precipitates from the inner part of the melt pool were likely to agglomerate in the heat-affected zone (HAZ) under the Ostwald ripening mechanism where these primary coarse Si precipitates had existed.
Journal of Materials Research and Technology, 2022
The origin of cyclic hardening under low strain amplitude (with N ¼ 25284 cycles to failure) foll... more The origin of cyclic hardening under low strain amplitude (with N ¼ 25284 cycles to failure) followed by pseudo-plateau response under high strain amplitude (with N ¼ 2671 cycles to failure) during fully reversal (R ¼ À1) strain-controlled pullepush fatigue of Mg-8.2Gd-3.6Y-1.6Zn-0.5Zr (wt.%) at room temperature condition was explored. The (i) dislocations trapping between LPSO (long period stacking order) lamellas, (ii) substructure development, and (iii) deformation twinning and tangling/rearrangement of partials within twin band were known as the main factors contributing to the room temperature cyclic hardening response. The pseudo-plateau behavior and cyclic stabilization were also attributed to the co-formation of the veins structure in the vicinity of 18R LPSO and reversion of 14H LPSO at higher strain amplitudes.
Journal of Materials Research and Technology, 2023
This study aims to investigate the deformation mechanisms of an austenite-based duplex Fe–Mn–Al–C... more This study aims to investigate the deformation mechanisms of an austenite-based duplex Fe–Mn–Al–C steel at room-temperature through uniaxial tensile tests, strain rate sensitivity and stress relaxation analysis. Through numerical analysis and microstructural studies, this investigation reveals that increasing strain leads to the formation of low-angle boundaries (LABs) at the vicinity of grain boundaries. Consequently, these LABs play a facilitating role in the stress-assisted diffusion of carbon atoms, thereby triggering the dynamic strain aging (DSA) phenomenon. The evidence for this is substantiated by the strain rate sensitivity coefficient and stress relaxation results obtained from numerical analysis during uniaxial tensile tests. As deformation progresses, the misorientation of LABs increases, influencing the strain hardening behavior. The intensified DSA contributes to enhanced work hardening, while substructure development results in softening, creating a trade-off between these contrasting effects.
Journal of Materials Research and Technology, 2022
The present work deals with the short-time thermal phase-stability of the as-cast eutectic AlCoCr... more The present work deals with the short-time thermal phase-stability of the as-cast eutectic AlCoCrFeNi2.1 high entropy alloy. Toward this end, the effect of different temperatures (800–1000 °C) and soaking times (15–60 min) on the stability of primary dendritic regions and formation of the ordered phases was explored. Microstructural characterization was supported by thermodynamic calculations and assessment of the subsequent mechanical properties. Upon the increase in annealing temperature and soaking time, the primary FCC dendritic areas grown and destabilized owing to elemental partitioning. This was followed by dendrite fragmentation and formation of needle shape B2 ordered phases within the primary FCC regions. Despite the unstable nature of the primary constituent phases, the material hardness increased considerably to a peak point corresponding to the moderate soaking time of 45 min. The variation of the subsequent mechanical properties was discussed relying on the characteristics of the ordered and primary phases.
Advanced Engineering Materials, 2023
Herein, the occurrence ofa B2-phase separation and formation of Cr-rich nanoprecipitates during t... more Herein, the occurrence ofa B2-phase separation and formation of Cr-rich nanoprecipitates during the solidification process of AlCoCrFeNi2.1 eutectic highentropy alloy is addressed. Toward this end, various advanced characterizations, including high-resolution transmission electron microscopy and atom probe tomography combined with thermodynamic calculations, are employed. The as-solidified microstructure is composed of face-centered cubic (FCC) dendrites and interdendritic regions consisting of a eutectic mixture of FCC and bodycentered cubic (BCC) phases. The presence ofuniformly distributed Cr-rich nanoprecipitates is traced through the BCC B2 phase in the interdendritic area. Regarding the occurrence of upward diffusion and Gibbs free energy variation, the formation of Cr-rich nano-precipitates is attributed to the spinodal decomposition where the critical temperature of 800 °C is passed behind during the solidification process. The formation of dense dislocation array in the interdendritic region due to thermal stress induced during solidification is introduced as a pathway for diffusion of alloying elements in the course of cooling stage.
Journal of Materials Research and Technology, 2022
The present work deals with the short-time thermal phase-stability of the as-cast eutecticAlCoCrF... more The present work deals with the short-time thermal phase-stability of the as-cast eutecticAlCoCrFeNi2.1 high entropy alloy. Toward this end, the effect of different temperatures (800e1000 C) and soaking times (15e60 min) on the stability of primary dendritic regions andformation of the ordered phases was explored. Microstructural characterization was sup-ported by thermodynamic calculations and assessment of the subsequent mechanicalproperties. Upon the increase in annealing temperature and soaking time, the primary FCCdendritic areas grown and destabilized owing to elemental partitioning. This was followedby dendrite fragmentation and formation of needle shape B2 ordered phases within theprimary FCC regions. Despite the unstable nature of the primary constituent phases, thematerial hardness increased considerably to a peak point corresponding to the moderatesoaking time of 45 min. The variation of the subsequent mechanical properties was dis-cussed relying on the characteristics of the ordered and primary phases.
Journal of Materials Research and Technology, 2022
The present research clarifies the texture and microstructure evolution of a rare earth (RE) cont... more The present research clarifies the texture and microstructure evolution of a rare earth (RE) containing magnesium composite reinforced by SiC particles (Mg-RE/SiC) during friction stir processing. Rotating tool induced mechanical stirring and frictional heat lead to occurrence of dynamic recrystallization (DRX) and development of the strong basal texture component. The presence of second phase particles in the matrix could stimulate the occurrence of continuous dynamic recrystallization (CDRX) and particle stimulated nucleation (PSN) and postpone discontinuous dynamic recrystallization (DDRX). The presentation of crystallographic orientations in an appropriate reference frame indicated formation of a new rare earth texture (RE-texture) component, near the <11-24>//shear plane normal (SPN) and <20-21>-<11-21>//shear direction (SD) orientations. This texture component was developed through simultaneous activity of basal and non-basal slip systems during dynamic recrystallization.
Journal of Materials Research and Technology, 2022
The microstructure and microtexture of an extruded and annealed GWZ (Mg-8.2Gd-3.6Y-1.6Zn-0.5Zr, w... more The microstructure and microtexture of an extruded and annealed GWZ (Mg-8.2Gd-3.6Y-1.6Zn-0.5Zr, wt.%) magnesium alloy was recorded strain by strain in the course of thermomechanical processing. The specimens were compressed down to various interruption strains of 0.1, 0.3, and 0.5 under the strain rate of 0.001s-1 at 400°C, the temperature at which the material was capable to be recrystallized extensively. Appreciable refinement was recognized even at low imposed compressive strain of 0.1, and the recrystallization process was completed at true strain 0.3 where the mean grain size of 4.3μm was attained. The LPSO stimulated nucleation (LSN) and conventional continuous dynamic recrystallization (CDRX) mechanism were contributed in grain refinement. Consequently, the initial basal texture was considerably weakened which was mainly ascribed to the formation of RE-texture components. At higher imposed strain of 0.5, the majority of grains were found in deformed states, the capability of strain softening was decreased and the microtexture only changed in respect of intensity compared with true strain of 0.3. These indicated that the imposed strain was mainly accommodated through dislocation multiplication and tangling within the previously recrystallized grains. Complementary, the slip / twin activity, and the sequence of strain accommodation was investigated through Schmid analysis of the various systems.
Journal of Materials Research and Technology, Jan 29, 2022
The present study deals with the extraordinary twin formation during compressive deformation of a... more The present study deals with the extraordinary twin formation during compressive deformation of a Fe-37.55Mn-8.5Al-0.6C (wt.%) low-density steel at warm temperature regime (200-600°C). Despite the conventional opinion regarding the restrictive effect of increasing temperature on the occurrence of deformation twinning, not only the twin boundary fraction did not decrease, but also twinning was encouraged at 400°C and even 600°C. This was discussed relying on the occurrence of dynamic strain aging phenomenon, which caused a bump in corresponding hardening rate curves. The medium entropy of the alloy, which made short-range diffusion of solute atoms feasible and facilitated local pinning of the mobile dislocations, provided a proper condition for the occurrence of high temperature strain ageing. Finally, the unbalanced pinning of trailing and leading dislocations influenced on their velocity and caused widening the stacking faults which in-turn could significantly assist deformation twinning at such high deformation temperatures.
The present work deals with the effect of friction stir processing on the stability of the austen... more The present work deals with the effect of friction stir processing on the stability of the austenite during quenching and also its mechanical stability in the course of subsequent room temperature straining in a duplex ferritic lightweight steel. Interestingly, it was found that the austenite fraction increased owing to the dynamic phase transformation of ferrite to the austenite and enhancement in austenite stability. In this regard, the influence of dislocation density variations, partitioning in solute elements (Mn and C) and grain refinement on austenite stability was discussed in details. The optimum austenite stability during quenching was achieved in the case of processed microstructure holding finer grain size, and higher dislocation density. These provided fast track diffusion for austenite stabilizer elements, which decreased the thermally activated martensite starting temperature and finally led to stabilization of austenite. These factors have directly influenced the mechanical stability of the austenite during subsequent deformation and increased the strain range for the occurrence of strain induced martensitic transformation which led to a significant strength/elongation balance. The capability of transformation induced plasticity (TRIP) effect was deteriorated in the case of microstructures with lower austenite stability. Surprisingly, despite the appreciable decrease in grain size the yield strengths of the processed specimens were not influenced significantly. The deviation was justified considering the fact that the critical stress of TRIP effect was lower than of predicted through Hall-Petch relationship.
A novel method is offered with the task of unveiling the underlying micro-mechanisms of cyclic de... more A novel method is offered with the task of unveiling the underlying micro-mechanisms of cyclic deformation. This method by merging of dwell-fatigue and stress relaxation concept provides the capability of assessment of the dislocation response to cyclic deformation and subsequently the differences between tensile and compressive half-cycles behavior. Interestingly, the apparent activation volume and mobile dislocation density have been successfully calculated in the course of cyclic loading. Noteworthily, room-temperature dynamic strain aging is firmly proved through these novel findings in a cyclically-loaded lightweight steel. This promises to be a breakthrough in deep understanding the behavior of materials under cyclic loading.
The present work deals with revealing the fatigue and dwell-fatigue behavior and correlated damag... more The present work deals with revealing the fatigue and dwell-fatigue behavior and correlated damage mechanisms of Fe-Mn-Al-C lightweight steel. Surprisingly, alteration in loading mode from monotonic to cyclic induces reversible dislocation movement and facilitates the occurrence of dynamic strain aging. Additionally, applying dwell time by an acceleration of strain aging intensified stress asymmetry during dwell fatigue. The occurrence of strain aging has a bilateral effect on the crack initiation and growth. On one hand, strain aging stimulates twin formation and retards fatigue crack initiation, however, on the other hand, reduces hardening capacity, restricts the plastic deformation and facilitates crack propagation.