Microband-induced Plasticity Research Articles

Dynamic Compression and Constitutive Model in Fe-27Mn-10Al-1C Duplex Lightweight Steel

Fe-Mn-Al-C lightweight steels have been of significant interest due to their excellent mechanical properties and unique microstructures. However, there has been limited focus on the dynamic deformation. Here, we systematically investigate the mechanical responses over various strain rates and corresponding microstructure evolution in quasi-static and dynamic compression to reveal the transition of deformation mechanisms. The present lightweight steel exhibits a significant strain rate effect, with the yield strength increasing from 735.8 to 1149.5 MPa when the strain rate increases from 10−3 to 3144 s−1. The deformation in ferrite under high-strain-rate loading is dominated by wave slip, forming a cellular structure (cell block). Meanwhile, the deformation in austenite is dominated by planar slip, forming dislocation substructures such as high-density dislocation walls and microbands. In addition, the deformation twinning (including secondary twinning)- and microband-induced plasticity effects are responsible for the excellent dynamic compression properties. This alloy delays damage location while maintaining high strength, making it ideal for shock loading and high-strain-rate applications. The Johnson–Cook (J–C) constitutive model is used to predict the deformation behavior of lightweight steel under dynamic conditions, and the J–C model agrees well with the experimental results.

A dual-precipitation strategy for simultaneously enhancing the strength and ductility of cost-effective medium Mn steels at low temperatures

A dual-precipitation strategy has been utilized to simultaneously improve the strength and ductility of the cost-effective medium Mn steels for cryogenic applications. When the temperature decreases from room temperature (RT) to liquid nitrogen temperature (LNT), the dual-precipitation state, including NiAl and Cu-rich intermetallics in ferrite and austenite respectively, exhibits a simultaneous increase in the yield strength (YS, to ∼1160 MPa) and tensile elongation (TEL, to ∼40 %), and a significantly higher secondary strain hardening. On the one hand, the NiAl precipitates can strengthen the ferrite matrix and provide dislocation storage capacity for strain accommodation. On the other hand, the Cu-rich precipitates can stabilize the austenite matrix, activate the formation of microbands (MBs) and delay the transformation-induced plasticity (TRIP) effect until large strains. Therefore, multistage cooperative precipitation hardening, microband-induced plasticity (MBIP) and TRIP give rise to comprehensive strength-ductility interactions, which are comparable to those of the best-performing expensive cryogenic materials.

Effect of deformation temperature on strain localization phenomena in an austenitic Fe-30Mn-6.5Al-0.3C low-density steel

We have investigated the influence of the deformation temperature from 25 °C (RT) to -196 °C on the dislocation structures associated with strain localization phenomena in an austenitic Fe-30Mn-6.5Al-0.3C (wt.%) low-density steel by electron channeling contrast imaging (ECCI), electron backscatter diffraction (EBSD), and bright-field transmitted forescattered electron imaging ((BF) t-FSEI) techniques. The characteristics of the dislocation structures were evaluated on the main texture components, i.e. <111>//tensile axis, <112>//tensile axis, and <001>//tensile axis directions. The inhomogeneous character of the plastic behavior is promoted upon cryogenic deformation due to the formation of dislocation structures associated with strain localization, namely microbands (MBs) and deformation bands (DBs). ECCI analysis of the dislocation structure reveals that the deformation temperature has a strong influence on the thermal-assisted dislocation processes controlling the dislocation configurations and MB formation mechanisms. The MB nucleation mechanism evolves from a cross-slip-assisted mechanism at RT deformation conditions to a slip band-assisted mechanism at cryogenic deformation temperatures. This effect has a profound effect on the grain orientation dependence of the MB structure but not on its crystallographic alignment. On the other hand, cryogenic deformation temperatures (-196 °C) enhance the material's mechanical strength and ductility due to the activation of deformation twinning, which is associated with the reduction of the stacking fault energy. We find that MBs have a small contribution to strain-hardening and ductility due to the small mechanical resistance of these dislocation structures against the advance of deformation twins and dense dislocation layers, and the comparatively small plastic strain accommodated by them, respectively. These findings provide new insights into the microband-induced plasticity (MBIP) effect.

Excellent dynamic properties and corresponding deformation mechanisms in a microband-induced plasticity steel with dual-heterogeneous structure

A dual-heterogeneous structure with dual phases and heterogeneous grains was designed in a high Mn microband-induced-plasticity (MBIP) steel. The heterogeneous structured sample exhibits similar dynamic shear yield strength, while exhibiting enhanced dynamic uniform shear strain and dynamic shear toughness by 36 % and 47 %, respectively, as compared to the homogeneous structured sample. The strain hardening mechanisms contributing to the excellent dynamic shear properties in the heterogeneous structured sample have been revealed. Firstly, the superior hetero-deformation-induced hardening capability of the heterogeneous structured sample arises from a higher density of geometrically necessary dislocations induced in each phase. Secondly, a pronounced strain rate effect is observed in body-centered cubic (BCC) grains and face-centered cubic (FCC) ultra-fine grains, leading to an elevated level of strain rate sensitivity. Finally, the MBIP effect is also observed in FCC coarse grains under dynamic loading. Moreover, the MBIP effect in FCC ultra-fine grains is more likely to occur at high strain rates due to the emergence of single-wall domain boundaries, which is not observed during quasi-static tensile testing. The present results provide new routes for designing impact-tolerant structures in advanced metals and alloys.

Influence of Thermo-Mechanical Process and Nb-V Microalloying on Microstructure and Mechanical Properties of Fe–Mn–Al–C Austenitic Steel

In present study, a novel Nb-V microalloyed Fe–Mn–Al–C steel and a non-microalloyed Fe–Mn–Al–C austenitic steel were treated with different thermo-mechanical processes. The microstructure of the test steels was observed by scanning electron microscope, transmission electron microscope, electron probe micro-analyzer, and X-ray diffractometer. A tensile test was conducted to estimate the mechanical properties of the test steels. Results show that the equiaxed austenitic grains are obtained in both test steels, while hot rolling reduces the grain size significantly. The grain size of the Fe–Mn–Al–C steel decreases by 40%–55% after the addition of Nb-V due to the precipitation of nanoscale (Nb,V)C particles within the austenite matrix. Compared with the solid solution treated specimens, the strength of the hot-rolled or aged specimens is improved. Meanwhile, the strength of the Fe–Mn–Al–C steel with Nb-V microalloying is also increased by 55 MPa due to the precipitation strengthening and fine grain strengthening, while the elongation is decreased. The Nb-V microalloyed Fe–Mn–Al–C steel, after hot rolling + aging treatment, obtains the maximum strength, with the yield and tensile strength of 669 MPa and 1001 MPa, respectively. The strengthening mechanisms that contribute significantly to the yield strength are solid solution strengthening and dislocation strengthening. They are 185 MPa and 211 MPa, respectively, for the Nb-V microalloyed Fe–Mn–Al–C steel at hot rolling + aging conditions. Meanwhile, the segregation of carbon atoms after aging treatment also improves the yield strength significantly.

Effect of Al content on the low-stress abrasive wear behaviour of Fe-18Mn-xAl-0.7C alloys

The low-stress ASTM-G65 abrasive wear behaviour was studied in a system of high manganese steels Fe-18Mn-xAl-0.7C with aluminium contents of 0%, 3%, 6% and 9.5% by weight and the results were compared with those of AISI D2 and AISI 9260 steels. By a completely randomized design (CRD), it was determined that the highest wear resistance corresponds to AISI D2 steel, followed by Fe18Mn0Al, Fe18Mn3Al, Fe18Mn9Al, Fe18Mn6Al and AISI 9260 steel. Using micro hardness tests, surface analysis and staking fault energy calculations it was possible to establish a relationship between wear resistance and the strain hardening mechanisms such as transformation induced plasticity (TRIP), twinning induced plasticity (TWIP) and microband induced plasticity (MBIP) for the Fe-Mn-Al-C steels under study.

The Effect of Strain Rate on the Deformation Behavior of Fe-30Mn-8Al-1.0C Austenitic Low-Density Steel

Automotive steels suffer different strain rates during their processing and service. In this study, the effect of strain rates on the tensile properties of fully austenitic Fe-30Mn-8Al-1.0C (wt.%) steel was investigated, and the dominant deformation mechanism was clarified. Conventional and interrupted tension tests and various microscopic characterization methods were carried out in this study. The results indicate that the yield strength increases with the increasing strain rate in the range of 10−4–10−1 s−1, and a good strength–ductility combination was achieved in the sample deformed at 10−3 s−1. In the process of straining at 10−3 s−1, microbands and deformation twins were observed. Thus, the combination of microband induced plasticity (MBIP) together with twinning induced plasticity (TWIP) leads to a continuous strain hardening behavior, and consequently to superior mechanical properties. However, adiabatic heating that leads to the increase in stacking fault energy (SFE) and inhibits the TWIP effect, as well as thermal softening jointly induces an anomalous decrease in tensile strength at the high strain rate of 10−1 s−1.

Revealing effect of aluminum alloying on work hardening and impact behaviors of low-density Fe-18Mn-1.3C-2Cr-(4, 11)Al casting steel

The present study designed two kinds of Fe-18Mn-1.3C-2Cr-(4, 11)Al (wt.%) low-density steels. Tensile and impact tests were carried out to evaluate the work hardening and impact toughness properties via aluminum (Al) alloying control. Meanwhile, microstructure evolution and fracture morphology were investigated by X-ray diffraction (XRD), a scanning electron microscope (SEM) equipped with electron backscatter diffraction (EBSD), a transmission electron microscope (TEM), and a stereo-optical microscope (OM). It is found that the Al addition obviously promotes the dislocation planar slipping, resulting in cleavage and brittle impact fracture in 11wt.% Al steel. Besides, the microband-induced plasticity (MBIP) mechanism is found in 4wt.% Al containing steel, introducing considerable work hardening capacity and impact toughness of 156.8±17.4 J. The present study provides a direct illustration of the relationship between work hardening and impact toughness behaviors of these two low-density steels for potential application as impact-resistant components.

Simultaneous Twinning and Microband-Induced Plasticity of a Compositionally Complex Alloy with Interstitial Carbon at Cryogenic Temperatures

Intermediate to low stacking fault energy (SFE) high entropy alloys (HEA) have shown an excellent combination of strength and ductility as a result of deformation twinning and martensite transformation. However, even in the absence of these mechanisms HEA can show a good strength-ductility combination, as is the case with non-equiatomic (Fe40.4Ni11.3Mn34.8Al7.5Cr6)C1.1. The room temperature mechanical behavior of this alloy has been associated with Taylor lattice and microband formation. The current research focuses on tensile cryogenic deformation of this alloy and investigates if these features and/or alternate mechanisms like deformation twinning are obtained. Surprisingly, it is not one or the other but both deformation twinning and microband formation that are observed during cryogenic deformation. The activation of both deformation mechanisms is a combination that is not often reported as the former is generally associated with intermediate to low SFE alloys and the latter with intermediate to high SFE alloys. The activation of twinning in (Fe40.4Ni11.3Mn34.8Al7.5Cr6)C1.1 is attributed to the high yield stress-temperature variation, as a result of solid solution strengthening being far greater than in other commonly researched compositionally complex alloys. A ductility retention down to 4 K was observed, while simultaneously showing a significant increase in flow stress. Despite the intermediate to high SFE deformation behavior, (Fe40.4Ni11.3Mn34.8Al7.5Cr6)C1.1 exhibits excellent cryogenic strength-ductility combination.

Effect of Aluminum Content on the Dynamic Recrystallization of Fe18MnxAl0.74C Steels During Hot-Forging Treatments

In the present work, the dynamic recrystallization and microstructural evolution of the family of advanced high-strength steels Fe18MnxAl0.74C are studied, varying the aluminum content in 0, 3, 6, and 9 wt pct subjected to hot-forging treatments through three consecutive heating-deformation cycles. For characterization, X-ray diffraction (XRD), Mössbauer absorption spectroscopy (MAS), and electron backscattering diffraction (EBSD) were used. It was determined that for the steels under study, dynamic recrystallization occurs due to strain-induced boundary migration (SIBM) and is strongly influenced by the aluminum content of the alloy and its stacking failure energy (SFE), increasing that the aluminum content will generate greater nucleation sites, favoring the refinement of grains in the material and achieving a crystalline structure of random crystallographic orientation. The results are discussed throughout the article, allowing us to determine potential processing routes for advanced high-strength steels with predominantly plastic deformation mechanisms such as transformation-induced plasticity (TRIP), twinning-induced plasticity (TWIP), and microband-induced plasticity (MBIP).

Dynamic Compressive Mechanical Behavior and Microstructure Evolution of Rolled Fe-28Mn-10Al-1.2C Low-Density Steel.

In this study, the quasi-static and dynamic compressive mechanical behavior of a rolled Fe-28Mn-10Al-1.2C steel (low-density) was investigated. X-ray diffraction, optical microscopy, electron backscattered diffraction and transmission electron microscopy were conducted to characterize the microstructure evolution. The results displayed that the steel has remarkable strain rate sensitivity and strong strain hardenability under high strain rate compression. Most specifically, the deformation behavior was changed with the increase in the strain rate. A feasible mathematical analysis for the calculation of stacking fault energies and the critical resolve shear stresses for twinning was employed and discussed the nucleation of the twinning. The microband-induced plasticity and twinning-induced plasticity controlled the deformation under high strain rate compression and provided a strong strain hardening effect. The higher mechanical response can increase the broad use of low-density steel in automobile applications.

Tensile Behaviors and Strain Hardening Mechanisms in a High-Mn Steel with Heterogeneous Microstructure.

Heterogeneous structures with both heterogeneous grain structure and dual phases have been designed and obtained in a high-Mn microband-induced plasticity (MBIP) steel. The heterogeneous structures show better synergy of strength and ductility as compared to the homogeneous structures. Higher contribution of hetero-deformation induced hardening to the overall strain hardening was observed and higher density of geometrically necessary dislocations were found to be induced at various domain boundaries in the heterogeneous structures, resulting in higher extra strain hardening for the observed better tensile properties as compared to the homogeneous structures. MBIP effect is found to be still effective in the coarse austenite grains of heterogeneous structures, while the typical Taylor lattice structure and the formation of microband are not observed in the ultra-fine austenite grains of heterogeneous structures, indicating that decreasing grain size might inhibit the occurrence of microbands. High density of dislocation is also observed in the interiors of BCC grains, indicating that both phases are deformable and can accommodate plastic deformation. It is interesting to note that the deformation mechanisms are highly dependent on the phase and grain size for the present MBIP steel with heterogeneous structures.

Differences in Deformation Behaviors Caused by Microband-Induced Plasticity of [0 0 1]- and [1 1 1]-Oriented Austenite Micro-Pillars

A uniaxial compression test and scanning/transmission electron microscopy observations were performed to investigate the differences in mechanical behavior and deformed microstructure between focused ion beam-manufactured [1 1 1]- and [0 0 1]-oriented austenite micro-pillars with 5 μm diameter from duplex stainless steel. After yielding, the strain hardening of two orientation micro-pillars increased sharply as a result of the formation of a microband, namely microband-induced plasticity, MBIP. The same phenomenon could be observed in a [0 0 1]-oriented pillar due to the activation of the secondary slip system, while slight strain hardening behavior was observed in the [1 1 1] orientation because of the refinement of the microband. Furthermore, the trend of the calculated strain hardening rates of both [1 1 1]- and [0 0 1]-oriented micro-pillars were in good agreement with the experimental data. This study proved that MBIP can be helpful for the mechanical property enhancement of steels.

Hierarchically activated deformation mechanisms to form ultra-fine grain microstructure in carbon containing FeMnCoCr twinning induced plasticity high entropy alloy

Nanotructural evolution and grain refinement leading to heterogeneous bimodal structure were investigated during thermomechanical processing in carbon-containing FeMnCoCr twinning induced plasticity (TWIP) high-entropy alloy (HEA). The homogenized single-phase face-centered cubic alloy with the stacking fault energy of 19.4 ± 2 mJ m−2 was cold rolled up to thickness reduction of 84 % and annealed at 850 °C. Planar slip with profuse nanoscale deformation twinning was the dominant deformation feature at low rolling reduction (32 %). The heterogeneous structure could be obtained through subdivision of microstructure, continuous dynamic recrystallization and static recrystallization described as follows: (i) Hierarchical mechanical twinning, (ii) Interaction of twin-matrix (T/M) lamellae with shear-bands and (iii) Continuous dynamic recrystallization (CDRX) within the strain-induced boundaries (SIBs), (iv) Subsequent static recrystallization of the region with twin-matrix (T/M) lamellae and shear-bands. The strength and ductility enhancement during deformation was attributed to the hierarchy of microstructural evolution consisting of TWIP and microband-induced plasticity (MBIP). The heterogeneous bimodal structure composed of ultra-fine grains and larger grains with an average grain size of 0.5 μm and 3 μm respectively was achieved by post-rolling (84 %) annealing at 850 °C. Favorable strength-ductility combination with the ultimate tensile strength of 840 MPa and elongation of ~88 % was achieved by formation of heterogeneous bimodal microstructure through thermomechanical processing.

The impact-abrasive wear behavior of high wear resistance filling pipeline with explosion treatment

This work investigated the effect of explosion treatment on the wear resistance of Fe-31.6Mn-8.8Al-1.38C steel and the impact-abrasive wear behavior. The results show that under the different impact energy (1, 2 and 4 J), the wear resistance of the experimental steel after explosion treatment is improved by 1.32–1.40 times compared with that without explosion treatment, the hardness and the work hardening rate are also increased. The wear surface mainly consists of furrows and delaminated craters, as well as some cracks and press-in abrasives. With the decrease of impact energy, the furrows are deeper and longer gradually. The delaminated craters and press-in abrasives increase with the increase of cracks. During impact-abrasive wear, the work hardening occurs again on the surface with explosion treatment, and the work hardening of the wear surface is attributed to the generation of dislocations, mainly the microband induced plasticity (MBIP) effect, which improve the wear resistance.

Enhanced Mechanical Properties of Fe-Mn-Al-C Low Density Steel via Aging Treatment

This study investigated the tensile properties and deformation behavior of an aged Fe-26Mn-6Al-1C (mass%) alloy with a stacking fault energy of approximately 60 mJ·m−2. The results show that an ordered phase with a “short-range ordering” (SRO) structure formed after aging at 550°C for 10 h, further increasing the aging time to 48 h. Lamellar second-phase precipitates appeared at the austenitic grain boundaries. The aged sample at 550°C for 10 h exhibited an enhanced tensile strength (∼898 MPa) without notably sacrificing uniform elongation (∼46.3%), which was mainly attributed to the relatively high strain hardening in the entire plastic deformation due to the synergistic effects of planar slip, twinning-induced plasticity (TWIP), microband-induced plasticity (MBIP), and especially the formation of short-range ordering.

Mechanical properties and microstructure of the Al0.3CoCrFeNiTi0.3 high entropy alloy under dynamic compression

In this work, the mechanical properties and corresponding microstructural evolution of the as-cast Al0.3CoCrFeNiTi0.3 high-entropy alloy (HEA) under quasi-static and dynamic compressive loadings were investigated. The HEA consisted of FCC/L12 + BCC/B2 mixed solutions exhibited a good combination of high strength and large ductility upon quasi-static loading, which is mainly due to the strengthening effect of coherent L12-nanoparticles. The HEA exhibited a significant positive strain rate effect, and its yield strength rised from 810 to 1181 MPa when the strain rate increased from 10−3 to 4700 s−1. Compared with the quasi-static condition, the density of stacking fault (SF) networks and immobile Lomer–Cottrell (L-C) locks were greater under dynamic loading. Furthermore, the deformation mode of the HEA was dominated by planar glide under high strain rate loading, and the dislocation substructure showed Taylor lattice, high-density dislocation walls and intersected microbands with the increase of strain. The dynamic Hall–Petch and microband-induced plasticity effects could be responsible for the excellent dynamic compressive properties. Fractographic observations indicated that the fracture of the HEA is controlled by the mixed ductile-brittle mechanism under dynamic compressive loading. An improved Johnson-Cook (J-C) constitutive model considering adiabatic temperature rise was employed to predict the plastic flow behavior of the HEA under dynamic conditions and the improved J-C model was in good agreement with the experimental results.

Mechanism of twinning induced plasticity in austenitic lightweight steel driven by compositional complexity

The current work investigated the mechanical behaviors of a novel austenitic lightweight Fe-Mn-Al-Si-C steel that combined the characteristics of lightweight steel and TWIP steel, due to compositional complexity. The critical design principle lay in the synergetic addition of Al and Si to obtain simultaneously a stacking fault energy of 49.5 mJ/m2, short-range ordering, and density reduction. The initial strain hardening in this steel proceeded by microband-induced plasticity slip featuring the substructure of Taylor lattices due to planar-slip dislocations. It contributed to a high Hall-Petch coefficient of 673 MPa·μm0.5. In the latter stage of deformation, even though the stacking fault energy was not low, stacking faults and deformation twins were triggered when the critical stress was achieved. This transition behavior was first observed in lightweight steel and the overall effects led to an outstanding work hardening rate of about 2.4 GPa. This lightweight TWIP steel with a density of 6.98 g/cm3 possessed ultimate tensile strength of 800-950 MPa and total elongation of 67-77%. This study focused on its mechanical behaviors and developed a confined dislocation model to clarify the transition from dislocation glide to mechanical twinning.

Microband-Induced Plasticity in a Nb Content Fe–28Mn–10Al–C Low Density Steel

Novel Fe–28Mn–10Al–C–0.5Nb low-density steel was developed and the room temperature tensile behavior in the solid solution state and the microstructure evolution process during plastic deformation were studied, aiming to clarify the dominant deformation mechanisms. The results show that the developed steel was fully austenitic with a low density of 6.63 g/cm3 and fairly high stacking fault energy of 84 MJ/m2. The present fully austenitic Fe–28Mn–10Al–C–0.5Nb low-density steel exhibited an excellent ultimate tensile strength of 1084 MPa and elongation of 37.5%; in addition, the steel exhibited an excellent combination of strength and ductility (i.e., the product of strength and ductility (PSE) could reach as high as 40.65 GPa%). In spite of the high stacking fault energy, deformed microstructures exhibited planar glide characteristics, seemingly due to the glide plane softening effect. The excellent combination of strength and ductility is attributed to plasticity induced by microbands and leads to the continuous strain hardening during deformation at room temperature. Moreover, the addition of Nb does not change the deformation mechanism and strengthening mechanism of Fe–Mn–Al–C low-density steel, and can optimize the mechanical properties of the steel.

Corrosion Behavior of High-Mn Austenitic Fe-Mn-Al-Cr-C Steels in NaCl and NaOH Solutions.

The corrosion behavior of austenitic Fe–Mn–Al–Cr–C twinning-induced plasticity (TWIP) and microband-induced plasticity (MBIP) steels with different alloying elements ranging from 22.6–30 wt.% Mn, 5.2–8.5 wt.% Al, 3.1–5.1 wt.% Cr, to 0.68–1.0 wt.% C was studied in 3.5 wt.% NaCl (pH 7) and 10 wt.% NaOH (pH 14) solutions. The results obtained using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques, alongside optical microscopy analysis, revealed pitting as the dominant corrosion mechanism in high-Mn TWIP steels. An X-ray diffraction analysis of the surface revealed that the main corrosion products were hematite (Fe2O3), braunite (Mn2O3), and hausmannite (Mn3O4), and binary oxide spinels were also identified, such as galaxite (MnAl2O4) and jacobsite (MnFe2O4). This is due to the higher dissolution rate of Fe and Mn, which present a more active redox potential. In addition, a protective Al2O3 passive film was also revealed, showing enhanced corrosion protection. The highest corrosion susceptibility in both electrolytes was exhibited by the MBIP steel (30 wt.% Mn). Pitting corrosion was observed in both chloride and alkaline solutions.