Twinning-induced Plasticity Research Articles

Simultaneous improvement of strength and plasticity: nano-twin construction for a novel high-nitrogen TWIP steel

For metallic materials, an increase in strength generally results in a decrease in plasticity, and the simultaneous improvement of strength and plasticity (SISP) has been a hot but difficult topic. In this study, through high-nitrogen (N) alloying, a novel high-N twinning-induced plasticity (HN-TWIP) steel was designed. It was surprisingly found that, with higher N content, the SISP was achieved successfully. Compared to 0.3N, the ultimate tensile strength and uniform elongation of 0.6N increased by 95 MPa and 5.6%, respectively. Systematic microstructural analyses indicated that more and thinner twins formed at higher N content during the deformation. Especially, different with conventional TWIP (CV-TWIP) steels, numerous ultrafine nano-twins (<15 nm) were detected in HN-TWIP steels. Combined with the flow stress analyses, their strengthening behavior was found to be attributed to both the N solid solution strengthening and nano-twin strengthening. More importantly, by promoting planar slip, the ultrafine nano-twins provided an additional work-hardening and delayed the necking appearance, which resulted in plasticity enhancement. In other words, the origin of the strength-ductility trade-off avoidance was the nano-twins/ultrafine nano-twins microstructure. Further studies revealed that, by breaking the conflict of low stacking fault energy (SFE) and excellent austenite stability, HN-TWIP steels obtained a breakthrough reduction in SFE. HN-TWIP steels with the extremely low SFE could acquire the special nano-twin microstructure and the SISP mechanical behavior. Accordingly, only by continuously reducing the SFE in the alloying design, the difficult SISP could be realized in TWIP steels. This is a novel and simple strategy for the modification of the metal mechanical properties, and it is meaningful for materials in engineering applications.

Achieving superior strength-ductility balance via heterogeneous structure and successive TWIP+TRIP effects in medium Mn steel

In the present work, the medium Mn steel with a strength - ductility product of 49.5 GPa·% was fabricated by a hot rolling, quenching and intercritical annealing process. The excellent mechanical property is attributed to the heterogeneous austenite morphologies, i.e., lath, granular and equiaxed austenite, and the successive TWIP + TRIP effects. The present work especially focus on two aspects: i) the evolution of micro-strain between different morphologies of austenite and ferrite during tensile deformation and its impact on the strain hardening caused by the transformation induced plasticity (TRIP) effect; and ii) the strengthening mechanisms of successive twin induced plasticity (TWIP) and TRIP effects in heterogeneous structures. Under different austenite/ferrite micro-strain interactions, the sequence of TRIP effect is in granular, lath and equiaxed austenite grains. Prior to this, the TWIP effect mainly enhance the strength of austenite, particularly equiaxed grains, which act as a high-strength skeleton structure, postponing the initiation of necking.

Effects of TRIP and TWIP mechanisms on improved Charpy impact energy of thick hot-rolled duplex lightweight steel plates

Charpy V-notch impact testing serves as a fundamental method for assessing the toughness of conventional steels, but its applicability becomes challenging for duplex (δ-ferrite + γ-austenite) lightweight steels due to their complex microstructures and varied deformation mechanisms. In this study, Charpy absorbed energies of hot-rolled duplex lightweight steel plates, incorporating both transformation-induced plasticity (TRIP) and twinning-induced plasticity (TWIP) mechanisms, were investigated to understand their fracture behavior comprehensively. The microstructural analysis revealed that the D4 (0.4C-15Mn-6Al (wt.%)) steel exhibited lower δ-ferrite volume fraction and superior Charpy absorbed energy than the D2 (0.2C-15Mn-6Al) steel, attributed to its dominance of TWIP mechanism. Conversely, the D2 steel, with many ferrite/austenite interfaces, showed lower strain hardening and absorbed energy. At lower temperatures, both TWIP and TRIP mechanisms operated, but dominant TRIP mechanism along with higher δ-ferrite volume fraction in the D2 steel accelerated crack propagation, further reducing absorbed energy. The superior toughness of the D4 steel, driven by the dominant TWIP mechanism at lower temperature, highlighted its potential for practical utilization of thick hot-rolled lightweight steel plates in automotive, shipbuilding, military, and construction industries.

Enhancement on mechanical properties via phase separation induced by Cu-added high-entropy alloy fillers in metastable ferrous medium-entropy alloy welds

This study evaluated the weldability of metastable ferrous medium-entropy alloys using high-entropy alloy fillers with various Cu contents and elucidated the strengthening mechanisms at room and cryogenic temperatures by focusing on the formation of a Cu-rich phase (FCC2) in the weld metal (WM). The WM with higher Cu content exhibited more dual face-centered cubic (FCC) phases with dendrite-shaped compositional heterogeneity due to phase separation driven by higher mixing enthalpy. The FCC2 induced greater lattice distortion, resulting in higher nano-hardness and stronger solid-solution hardening. In addition, the increased presence of FCC2 in the WM promoted grain refinement and the formation of additional grain boundaries within individual grains. After cryogenic deformation, the base metal and heat-affected zone in transverse welds underwent martensitic transformation from metastable FCC (transformation-induced plasticity), while the diluted WMs exhibited twinning-induced plasticity because of their higher stacking fault energy (SFE) compared to the base metal. The combination of these deformation mechanisms enhanced the cryogenic tensile properties without compromising ductility. Furthermore, the cryogenic tensile properties of weld with higher Cu content were further improved due to the increased formation of deformation twins in the WM. The consumption of solute Cu to form more Cu-rich FCC2 resulted in compositional variations in the matrix (FCC1), leading to a further reduction in the SFE of FCC1 and the activation of additional twin formation. Additionally, FCC2 with a relatively higher SFE refined secondary twins as well as contributed to further dislocation accumulation. This study suggests that the formation of Cu-rich phase in the WM can enhance mechanical properties at both room and cryogenic temperatures and provides a valuable approach for the future development of welding materials to improve the mechanical properties of FCC-based welded structures.

Effect of Plastic Deformation on Thermal Properties in Twinning-Induced Plasticity Steel.

The effect of plastic deformation induced by wire drawing on thermal properties in twinning-induced plasticity (TWIP) steel has been investigated. The investigation on the relationship between thermal conductivity (k) and the microstructure in the drawn TWIP steel wire was systematically performed to accurately understand the behavior of the k of a metal during wire drawing. The yield and tensile strengths linearly increased with drawing strain owing to the deformation twins and dislocations that were generated during wire drawing. However, the total elongation sharply decreased with drawing strain. The linear thermal expansion coefficient of the TWIP steel exhibited a similar value regardless of drawing strain. The density decreased linearly with temperature, and it was independent of the drawing strain. k increased initially and then decreased after reaching its maximum value with increasing drawing strains. At a nominal drawing strain of 0.26, k increased compared with the state of hot rolling because the increase in k due to grain elongation was greater than the decrease in k due to dislocations generated during wire drawing. However, as the amount of drawing step increased further, the influence of dislocations on k increased more than that of grain elongation, causing k to decrease.

Effect of Rapid Cooling on Microstructure and Mechanical Properties in Friction Stir Welded Twin-Induced Plasticity Steel

Effect of Rapid Cooling on Microstructure and Mechanical Properties in Friction Stir Welded Twin-Induced Plasticity Steel

Sintering densification mechanism of binder jet 3D printing 316L stainless steel parts via dimensional compensation technology

The dimensional compensation technology can achieve high dense metal parts with precise dimensions for binder jet 3D printing (BJ3DP). In this study, two models (cuboid and gear) of BJ3DP 316L stainless steel (BJ3DP316LSS) parts were established. Numerical simulation and experimental volume shrinkage of the BJ3DP316LSS sintered parts via dimensional compensations technology were investigated. When the dimensional compensation coefficient was set as 1.25, the BJ3DP316LSS cuboids and gears exhibited high densification as 99.6% and 99.4%, respectively. The experimental dimension deviation rates of cuboid and gear parts after dimensional compensations ranged from −3.56% to −0.15% and from 0.89% to 3.42%, respectively. Due to twinning-induced plasticity mechanism, the BJ3DP316LSS sintered gear part via dimensional compensation technology exhibited high hardness (∼139 HV), high yield strength (∼249 MPa), high ultimate tensile strength (∼546 MPa) and excellent elongation (∼62%), which are higher than those of the reported 316LSS samples.

Comprehensive mapping of mechanical properties and martensitic transformation in Ti–Al–Mo standard ternary system: Integrating literature data and fabricating novel high-Al-content superelastic alloys

Titanium alloys are increasingly used as structural and functional materials owing to their exceptional properties. This study aimed to develop β-Ti shape memory alloys by creating a compositional map of the phase constitution and mechanical properties of the Ti–Al–Mo ternary system at room temperature, particularly near the α″+β phase region. Data for 95 alloy compositions were collected from the literature, and the composition region of Ti–(7–14) mol% Al–(3–7) mol% Mo, which has rarely been reported, was experimentally investigated. The phase constitution of Ti–Al–Mo alloys primarily depends on the Mo concentration; however, at Al concentrations of 10 mol% or higher, the β phase region expands. The yield stress was found to be minimal around 6 mol% Mo on the low-Al side, and this minimum shifted to lower Mo concentrations as the Al content increased, corresponding to the β/(α″+β) boundary. The ultimate tensile strength increased marginally in low-Mo compositions because of the twinning-induced plasticity effect, with the optimal composition near Ti–11 mol% Al–4 mol% Mo. Superelasticity was observed in high-Al regions, particularly in the Ti–11 mol% Al–6 mol% Mo alloy, which exhibited a superelastic recovery strain of 3.2 % and a total shape recovery strain of 6 %. These findings highlight the potential for developing new room temperature superelastic alloys in the Ti–(10–14) mol% [Al]eq–(5–6) mol% [Mo]eq composition region.

Improved yield strength-ductility synergy of a high Mn TWIP steel by grain refinement and partial recrystallization

The industrial application of high Mn twinning-induced plasticity (TWIP) steels is limited by their low yield strength (YS). In this work, a combination of grain refinement and partial recrystallization was applied to increase the YS of a high Mn TWIP steel to 1215 MPa, along with a total elongation (TE) of 16 %. The high YS of the partially recrystallized steel mainly originates from the combination effect of high dislocation density up to 8.3 × 1014 m−2, fine grain size of about 1 μm in recrystallized regions, and dense mechanical twins with a small spacing of about 20 nm in unrecrystallized regions. This work provides a potential way to improve the YS-ductility synergy and broaden the application of TWIP steels.

A novel high-Mn duplex twinning-induced plasticity lightweight steel with high yield strength and large ductility

In this study, we report a novel high-Mn Fe–21Mn–6Al–4Si–1C (wt.%) duplex lightweight steel with concurrent chemical ordering and twinning-induced plasticity effects. This steel is capable of achieving an exceptional combination of strength and ductility following either cold-rolling and annealing at 1000 °C or subsequent short-term aging at 550 °C. In its as-annealed state, this steel primarily consists of γ-austenite and α-ferrite, with α-ferrite appearing as dispersed particles within fully recrystallized γ grains. Furthermore, L′12- and D03-type ordered nanodomains exist within these two phases, respectively. The aging treatment negligibly affects the size and volume fraction of both the γ-austenite and α-ferrite, yet it enhances the degree of ordering as well as the size and volume fraction of their ordered nanodomains, leading to a rise in yield strength from ∼800 to ∼1062 MPa and a decline in total elongation from ∼60.4% to ∼44.4%. The high yield strength of this steel originates from multiple strengthening mechanisms involving dislocation interactions with solute atoms, ordered nanodomains, γ grain boundaries and γ/α phase boundaries. This steel plastically deforms via planar slip during the initial stages. The rather small γ grain size, coupled with the presence of hard α-ferrite particles, fosters the dynamic slip band refinement (DSBR) effect, thereby enhancing the flow stress sufficiently to trigger deformation twinning in the steel during the later stages. The DSBR effect, combined with the progressive formation of deformation twins, stacking faults and Lomer-Cottrell locks, imparts pronounced strain hardenability to this steel, leading to its outstanding ductility.

Enhanced Mechanical Properties of Ceramic Rod-Reinforced TWIP Steel Composites: Fabrication, Microstructural Analysis, and Heat Treatment Evaluation

This study investigates the development and characterization of ceramic rod-reinforced TWIP (twinning-induced plasticity) steel matrix composites, produced using the lost foam casting technique. Mechanical tests revealed a substantial improvement in both flexural strength and ductility, with the composite demonstrating more than double the strength of unreinforced TWIP steel. Furthermore, a simple low-temperature heat treatment further enhanced these properties, increasing the flexural strength of the composite to 1023 MPa while also improving its ductility. The improvement in mechanical performance is attributed to the formation of additional twins in the TWIP steel matrix during deformation following heat treatment, which resulted in further strengthening of the matrix.

Improving ductility and strength of high-entropy alloy [formula omitted] via multi-directional forging and annealing

A dual-phase high-entropy alloy Fe50Mn30Co10Cr10 is treated via multi-directional forging (MDF) and subsequent annealing at 600°C–1000°C. Different microstructures with totally different grain sizes and phase ratios are obtained. The MDF increases yield strength and ultimate tensile strength at the expense of ductility. Via annealing the MDF-processed alloy at 1000°C, the full recrystallized sample yields a excellent combination of high strength and good ductility due to the grain boundary strengthening, transformation-induced plasticity and twinning-induced plasticity. The yield strength, ultimate tensile strength and elongation at failure are 16.2%, 14.2% and 35.3% than those of the as-cast sample. The postmortem characterizations of this annealed sample show strong 〈111〉 texture in the austenite phase along the loading direction and intense martensite transformation with the gradually disappearance of the annealing twins.

Effect of the strain rate on the deformation mechanisms of TWIP-type steel

This paper describes the influence of the strain rate on the microstructure of X55MnAl25-5 steel from the group of high-manganese steels exhibiting the twinning-induced plasticity effect. The tests were carried out at a wide range of strain rates, starting with static tensile tests where the appropriate strain rates were 0.005 s−1, and ending with tests using a flywheel machine at strain rates of 1830 s−1 and 4650 s−1. The increase in the applied strain rate on the example of the tested steel results in hardening. Evolutionary changes leading to the predominance of dislocation slipping over the twinning are observed in the microstructure under static deformation conditions. The increase in the intensity of twinning with the simultaneous decrease in the mobility of dislocations progresses as the strain rate increases. The microstructure evolution was characterized using light optical microscopy and scanning electron microscopy, including electron backscatter diffraction. The qualitative analysis of the deformation twins was performed. For the lowest strain rate, 5·10−4 s−1, deformation twins appear in a single twinning system, while increasing the strain rate leads to the activation of multiple twinning systems. Proceeding to the range of dynamic tests reveals an increase in the participation of the twinning mechanism in the deformation of the examined steel. With an increasing strain rate, the effect of texture on the twinning process activity decreases. Based on the obtained results, a diagram was elaborated that presents the microstructural changes which take place in X55MnAl25-5 steel after deformation under static and dynamic tensile conditions in graphical form.

Influence of Ceramic Size and Morphology on Interface Bonding Properties of TWIP Steel Matrix Composites Produced by Lost-Foam Casting

This study investigated the fabrication and characterization of large ceramic-reinforced TWIP (twinning-induced plasticity) steel matrix composites using the lost-foam casting technique. Various ceramic shapes and sizes, including blocky, flaky, rod-like, and granular forms, were evaluated for their suitability as reinforcement materials. The study found that rod-like and granular ceramics exhibited superior structural integrity and formed strong interfacial bonds with the TWIP steel matrix compared to blocky and flaky ceramics, which suffered from cracking and fragmentation. Detailed microstructural analysis using scanning electron microscopy (SEM) and industrial computed tomography (CT) revealed the mechanisms influencing the composite formation. The results demonstrated that rod-like and granular ceramics are better for reinforcing TWIP steel composites, providing excellent mechanical stability and enhanced performance. This work contributes to the development of advanced composite structures with potential applications in industries requiring high-strength and durable materials.

Microstructural Dependence of the Impact Toughness of TP316H Stainless Steel Exposed to Thermal Aging and Room-Temperature Electrolytic Hydrogenation.

This work deals with the effects of two individual isothermal aging experiments (450 °C/5000 h and 700 °C/2500 h) and the subsequent room-temperature electrolytic hydrogen charging of TP316H stainless steel on its Charpy V-notch (CVN) impact toughness and fracture behavior at room temperature. Microstructural analyses revealed that aging at 700 °C resulted in the abundant precipitation of intermediary phases, namely, the Cr23C6-based carbide phase and Fe2Mo-based Laves phase, whereas aging at 450 °C resulted in much less pronounced precipitation of mostly intergranular Cr23C6-based carbides. The matrix phase of 700 °C-aged material was completely formed of austenitic solid solution with a face-centered cubic (FCC) crystal structure, whereas an additional formation of ferritic phase with a base-centered cubic (BCC) structure was detected in 450 °C-aged material. The performed microstructure observations correlated well with the obtained values of CVN impact toughness, i.e., a sharp drop in the impact toughness was observed in the material aged at 700 °C, whereas negligible property changes were observed in the material aged at 450 °C. The initial, solution-annealed (precipitation-free) TP316H material exhibited a notable hydrogen toughening effect after hydrogen charging, which has been attributed to the hydrogen-enhanced twinning-induced plasticity (TWIP) deformation mechanism of the austenitic solid solution. In contrast, both aging expositions resulted in significantly lowered hydrogen embrittlement resistance, which was likely caused by hydrogen trapping effects at the precipitate/matrix interfaces in thermally aged materials, leading to a reduced TWIP effect in the austenitic phase.

Simultaneously enhancing the strength and ductility of Fe–Mn–C twinning-induced plasticity steel via Cr/N alloying

The effect of Cr/N alloying on the tensile deformation behavior of Fe–Mn–C twinning-induced plasticity steel was investigated through monotonic tensile tests, X-ray diffraction, electron back-scattered diffraction, transmission electron microscopy, and digital image correlation technique. The results demonstrate that the addition of Cr/N significantly enhances both the strength and ductility of Fe–18Mn-0.6C steel while dynamic strain aging (DSA) behavior weakens or even disappears. Compared with that in the Fe–18Mn-0.6C steel, more densely-spaced, thinner deformation twins were formed in the Cr/N-alloyed steel. Moreover, the Cr/N additions promote deformation twins to form over a wider strain range. This unique twinning behavior leads to a sustained high strain-hardening rate at higher strains, thereby delaying plastic instability and concurrently enhancing strength and ductility.

Machine-Learning-Assisted Composition Design for High-Yield-Strength TWIP Steel

Twinning-induced plasticity (TWIP) steel is an ideal material for impact-resistant structures and energy absorption because of its high product of strength and elongation. However, compared with other advanced high-strength steels, the relatively low yield strength of TWIP steel is one of the important shortfalls that significantly limits its engineering applications. To enhance the comprehensive properties of TWIP steel, a machine learning design strategy that integrated comparative modelling, SHAP analysis, and multi-objective optimization were adopted in this study. Initially, various machine learning algorithms were compared for their predictive accuracy based on normalized data (273 entries) regarding the microstructure and properties of TWIP steel. Then, performance prediction models for yield strength, tensile strength, and elongation were established. SHAP analysis was subsequently employed to assess the significance and explicit laws of composition and microstructures in these three target properties, identifying key elements that enhance the overall performance. Furthermore, two new TWIP steels with high yield strengths and high products of strength and elongation were developed via multi-objective optimization. Under conventional hot forging + hot rolling + cold rolling + annealing processes, the two designed TWIP steels had yield strengths of 585 MPa and 560 MPa, tensile strengths of 1055 MPa and 1101 MPa, elongations of 55% and 58.5%, and products of strength and elongation of 58.0 GPa% and 66.4 GPa%, respectively. The yield strengths of the designed TWIP steels significantly improved while maintaining a reasonable product of strength and elongation. This work provides important references for the rational development of new TWIP steels.

Microstructural Evolution and Hot Deformation Behavior of Cu‐Containing Twinning‐Induced Plasticity Steel

High manganese twinning‐induced plasticity (TWIP) steels with excellent strength and plasticity have promising applications in automotive manufacturing, but limited corrosion resistance affects their further development. Alloying with Cu is a viable solution to improve corrosion resistance. However, there remains a paucity of research concerning the effect of Cu on the hot deformation behavior of TWIP steels. So, the investigation of the recrystallization behavior and microstructural evolution in Fe‐23Mn‐6Cr‐3Al‐0.2C‐xCu (x = 0, 2.5) TWIP steels has been conducted using uniaxial hot compression test. The results reveal that Cu alloying exerts minimal influence on the high‐temperatur flow behavior, with dynamic recrystallization emerging as the predominant softening mechanism in Cu‐containing TWIP steels. However, owing to the drag effect of solute atoms, Cu alloying increases the activation energy for hot deformation and marginally reduces hot workability. Fine recrystallized grains in Cu‐containing TWIP steels can be achieved by hot deformation at lower temperatures and strain rate regions. The recrystallization behavior of Cu‐containing TWIP steels hot deformed at low temperatures and high strain rates is obviously inhibited by the increase of the activation energy and stacking fault energy, coupled with the hindering effect of Cu solute atoms clustered at grain boundaries on grain boundary migration.

Influence of crystallographic textures on the hydrogen embrittlement resistance of austenitic stainless steel

Hydrogen embrittlement (HE) resistance is a significant concern in austenitic stainless steel (ASS) used for hydrogen transportation and storage. While microstructure-controlled methods to enhance HE resistance have been extensively studied in ferritic steels, comprehensive research on microstructure effects in ASS is lacking. In this study, two 316L ASSs with different microstructures were evaluated for HE resistance using electrochemical hydrogen charging. The steel with abundant in <111>+<110> orientations showed a significant elongation reduction after hydrogen charging. It revealed that, from the hydrogen permeation and thermal desorption analysis (TDA) results, effective diffusivity and activation energy of hydrogen were changed along the crystallographic orientation distributions. Also, transformation induced plasticity (TRIP) and twinning induced plasticity (TWIP) behavior affecting to the HE resistance preferentially formed in grains with <111> and <110> orientations rather than in those with <001> orientation during plastic deformation. Therefore, the study suggests that reinforcing the <001> microstructure is advantageous for improving HE resistance in 316L ASS.

Comparative study of tensile properties and impact toughness of duplex lightweight steel

Herein, a comparative study regarding the tensile properties and impact toughness of duplex lightweight steel and its deformation behavior was conducted to broaden its application from automotive steel sheets to thick-plate applications at various temperatures using Fe-0.2C–15Mn–6Al and Fe-0.4C–15Mn–6Al hot-rolled steels as model alloys. These steels revealed duplex microstructures with a large fraction of γ austenite (>0.7), featuring elongated δ ferrite grains aligned with the rolling direction and nearly globular γ grains. Both steels demonstrated an exceptional balance of tensile strength and ductility despite their low temperatures ranging from −20 °C to −100 °C, which was attributed to the active dynamic strengthening mechanisms, such as transformation-induced plasticity (TRIP) and twinning-induced plasticity (TWIP). However, contrary to the promising tensile test results, the steels demonstrated low values of the impact absorbed energy at temperatures ranging from −60 °C to −196 °C. This difference was likely owing to the rapid deformation rates in the Charpy impact tests compared to tensile tests, leading to the evolution of significant damage indicated by deep parallel cracks within the δ grains, without significantly activating the TRIP effect. Therefore, despite the impressive low-temperature tensile properties of the duplex lightweight steel, its suitability for cryogenic thick-plate applications must be approached with caution owing to the potential for compromised mechanical properties under sudden impact conditions.