Twinning-induced Plasticity Effect Research Articles

Strength enhancement of a bi-lamellar PM Ti–6Al–4V alloy without sacrificing ductility by Al partitioning and twinning-induced plasticity effect

Ti–6Al–4V alloy samples with two bi-lamellar microstructures were prepared by cost-effective thermomechanical powder consolidation and two inter-critical annealing treatments; one comprising of annealing at 900 °C followed by air cooling (900-AC alloy) and the other comprising of annealing at 910 °C followed by water quenching and aging (910-Q&A alloy), respectively. Both bi-lamellar microstructures encompass lamellae of primary α phase and β transformed structure which consists of ultrathin secondary α lamellae and β thin layers. Thanks to the higher Al concentration in the primary α lamellae associated with the higher annealing temperature and finer scale of βt structure lamellae, the α and βt lamellae of the 910-Q&A alloy exhibit a higher nano-hardness than that of the 900-AC alloy (5.4 and 4.6 GPa vs. 4.5 and 4.3 GPa) as well as a larger difference in nano-hardness between the α and βt lamellae (0.8 vs. 0.2 GPa). These microstructural and nano-hardness differences lead to a significant enhancement of the yield strength of the 910-Q&A alloy by 200 MPa compared to the 900-AC alloy with almost no decrease of tensile ductility. Quantitative analysis indicates that the hardening of α and βt lamellae accounted for approximately 35% and 28% of the total strength increment, respectively, while the heterostructure induced hardening associated with the inhomogeneity between the α and βt lamellae accounts for approximately 37% of the strength increment. Interestingly, the significantly higher flow stress of the 910-Q&A alloy during tensile deformation induces a significant higher degree of trans-lamellar twinning which is believed to be responsible for mitigating the strain localization and maintaining the good tensile ductility despite of a higher flow stress.

Consequences of Deep Rolling at Elevated Temperature on Near-Surface and Fatigue Properties of High-Manganese TWIP Steel X40MnCrAl19-2

Due to pronounced work-hardening induced by the complex interplay of deformation mechanisms such as dislocation slip, twinning and/or martensitic phase transformation, high-manganese steels represent a class of materials well-suited for mechanical surface treatment. In the present study, the fatigue behavior of a high-mangsanese steel showing twinning-induced plasticity (TWIP) effect at room temperature (RT) was investigated after deep rolling at 550 °C. Results are compared to a former study discussing the behavior after RT deep rolling. Evolution of the near-surface microstructure was analyzed by scanning electron microscopy (SEM), microhardness measurements and residual stress depth profiles obtained by X-ray diffraction (XRD). Both uniaxial tensile tests and uniaxial tension-compression fatigue tests have been conducted in order to rationalize the macroscopic material behavior. Following deep rolling at 550 °C, SEM measurements employing electron backscatter diffraction (EBSD) revealed a heavily deformed surface layer as well as localized deformation twinning. Specimens showed inferior hardness and residual stress depth profiles when compared to RT deep rolled counterparts. Tensile tests indicated no difference between the conditions considered. Fatigue properties however were improved. Such behavior is rationalized by a more stable residual stress state induced by dynamic strain aging.

Facile route to implement transformation strengthening in titanium alloys

Developing lighter, stronger and more ductile aerospace metallic materials is in demand for energy efficiency strategies. Alloys with twinning-induced plasticity (TWIP) and/or transformation-induced plasticity (TRIP) effects have been exploited to defeat the conflict of strength versus ductility, yet very few if any physically informed methods exist to address the complex interactions between the transitions. Here we report a facile route to deploy transformation-mediated strengthening in Ti alloys, which particularly focuses on the supervised activation of TRIP and TWIP via a mechanism-driven modelling approach. New alloys were comparatively developed and presented notable resistances to strain localisation, but interestingly through distinct mechanical characteristics. Specifically, extraordinary strain-hardening rate (dσ/dε) with a peak value of 2.4 GPa was achieved in Ti-10Mo-5Nb (wt.%), resulting from the synergetic activation of hierarchical transformations. An efficient model integrating TRIP and TWIP was applied to understand the interplays of the transition mechanisms.

Enhanced twinning-induced plasticity effect by novel {315}α″/{332}β correlated deformation twins in a Ti-Nb alloy

This paper reports a new {315}α″ type deformation twinning system, in adition to {130}<310>α″ in a full α″ Ti-23Nb (at.%) alloy. The {315}α″ twins were identified by trace analyzes based on electron backscatter diffraction (EBSD) results, meanwhile ex-situ EBSD measurements showed that both {315}α″ and {130}α″ deformation twins transform into {332}β twins of the β parent phase after annealing at 573 K. The crystallographic correspondences between the α″ twinning systems and the {332}β twins have been analyzed theorectically, of which {315}α″/{332}β and {130}α″/{332}β correlated deformation twins were confirmed experimentally. The calculations of twinning shear, shuffle and Schmid factor were carried out to survey the priority of occurrence of these α″ twins. It is concluded that the remarkable work-hardening and enhanced plasticity arise from both {315}α″ and {130}α″ deformation twins in the present full α″ Ti-23Nb alloy.

Crystallographic orientation dependence of Charpy impact behaviours in stainless steel 316L fabricated by laser powder bed fusion

Despite the extensive research on the mechanical properties of stainless steel 316L (SS316L) produced by laser powder bed fusion (LPBF), only a handful of studies have investigated its impact performance even though it is critical for structural applications experiencing rapid loading. In this study, the crystallographic-orientation-dependent Charpy impact behaviours of LPBF-SS316L were systematically investigated. Samples with their longitudinal directions (LDs) along the 〈100〉, 〈110〉 and 〈111〉 crystallographic directions were tested at both room temperature (RT) and liquid nitrogen temperature (LNT). At RT, the 〈100〉 and 〈111〉 samples exhibited similar impact toughness, while that of the 〈110〉 samples was the lowest. At LNT, the absorbed energy of the 〈100〉 and 〈111〉 samples experienced varying decreases. However, the impact toughness of the 〈110〉 samples did not suffer from the cryogenic temperature, exhibiting the highest absorbed energy value at LNT. The percentage of the shear area on the fracture surface was well correlated with the impact toughness. EBSD analysis showed that all the samples fractured at RT contained deformation twins. The lower impact toughness of the 〈110〉 samples was attributed to the slow strain hardening recovery due to their moderate twinning-induced plasticity (TWIP) effect under tension. At LNT, deformation twinning still prevailed in the 〈100〉 samples, while the 〈110〉 and 〈111〉 samples favoured strain-induced martensite, featuring dispersed ε-martensite and a considerable amount of α'-martensite, which led to strong transformation-induced plasticity (TRIP) effect. In particular, the 〈110〉 samples were characterized by a more widespread strain-induced martensitic transformation, resulting in their highest impact toughness at LNT among the three orientations. This study provides valuable insights into the design of crystallographic texture of LPBF-SS316L towards better impact properties for future structural applications. • Impact behaviours along the 〈100〉, 〈110〉 and 〈111〉 directions of LPBF-SS316L. • Great impact toughness at room temperature and liquid nitrogen temperature (LNT). • No deterioration in impact toughness of the 〈110〉 samples at LNT. • ε-martensite in LPBF-SS316L after deformation. • Correlations between impact toughness and deformed microstructure.

Deformation Mechanism Investigation on Low Density 18Mn Steels under Different Solid Solution Treatments

To meet the demand of the 10% weight reduction goal for automotive steel, the microstructure and mechanical properties of Fe-18Mn-Al-C steel with different carbon and aluminum contents were investigated under different solid solution treatments, and the deformation mechanisms of the experimental steels were elucidated. Aided by thermodynamic calculation, transmission electron microscopy (TEM) and in situ scanning electron microscope (SEM) analysis, it was shown that for the 18Mn-1.5Al experimental steel with about 20 mJ/m2 stacking fault energy (SFE), the twinning-induced plasticity (TWIP) effect always dominated in this steel after different solid solution treatments under tensile deformation. With the 7 wt% aluminum addition, the SFE of austenite was affected by temperature and the range of SFE was between 60 and 65 mJ/m2. The existence of δ-ferrite obviously inhibited the TWIP effect. With the increase in the solution treatment temperature, δ-ferrite gradually transformed into the austenite, and the n-value remained low and stable in a large strain range, which were caused by the local hardening during the tensile deformation. Due to the difference in the deformability of the austenite and δ-ferrite structure as well as the inconsistent extension of the slip band, the micro-cracks were easily initiated in the 18Mn-7Al experimental steel; then, it exhibited lower plasticity.

New observations of the twinning effect and austenite stability in intercritical quenched and tempered steel with high strength

To optimize the formability and strength of hot-rolled Fe-10Mn-0.4C-2Al-0.6 V medium Mn steel, intercritical quenching and tempering processes were carried out. The strength of the steel was enhanced, and the Ludders platform was eliminated. The higher strength of the steel was attributed to the occurrence of a complex twinning effect, martensitic transformation and V-carbide precipitation during tensile deformation. In particular, the twin martensite structure retained after the quenching-tempering process served as another previous twin to accelerate the generation of nanomechanical twins in recrystallized austenite grain. The occurrence of transformation-induced plasticity (TRIP) of austenite with poor stability in non-recrystallized regions stimulated the TRIP and twinning-induced plasticity (TWIP) effects in austenite with high stability in recrystallized regions. Therefore, two pathways to improve the formability and optimize the mechanical properties of medium Mn steel by adjusting the quenching and tempering processes were proposed in this paper: (1) Manufacturing more martensite twin structures and (2) regulating the balance of austenite stability in both recrystallized and non-recrystallized regions.

Mechanical behaviour and microstructure of Fe-20/27Mn–4Al-0.3C low magnetic steel at room and cryogenic temperatures

The stress-strain curves and strain hardening rate curves of Fe–20Mn–4Al-0.3C (20Mn) and Fe–27Mn–4Al-0.3C (27Mn) steels were obtained by tensile tests at room and cryogenic temperatures. The yield strength, tensile strength, and elongation of 20Mn and 27Mn steels at −196 °C were significantly improved, and the product of strength and ductility reached 92.6 GPa·% and 80.1 GPa·%, respectively. There were a large number of deformation twins in 20Mn and 27Mn steels, and the deformation-induced martensite effect also occurred in 20Mn steel. The twinning-induced plasticity (TWIP) and transformation -induced plasticity (TRIP) at −196 °C significantly improved the strength and plasticity of the steels, but TRIP has a stronger effect. The work hardening rate of 20Mn steel was higher than that of 27Mn steel. The fracture mechanism of 20Mn and 27Mn steels at −196 °C was ductile fracture. Plastic deformation of 20Mn steel at low temperature can be divided into the dislocation slipping, twinning, and deformation-induced martensitic transformation stages, whereby a high elongation (77.4%) was obtained, which was also ascribed to the formation of microbands and dislocation cross slipping during the deformation process. The deformation mechanism of 27Mn steel was mainly the TWIP effect, in which the deformation-induced martensite did not form. Therefore, the work hardening rate of 27Mn steel was lower than that of 20Mn steel, and the elongation was relatively low (68.3%). Although 27Mn steel exhibited large plastic deformation during low temperature deformation, there was almost no martensite, which has a more stable austenitic structure and better low magnetic property.

Effects of temperature and loading rate on phase stability and deformation mechanism in metastable V10Cr10Co30FexNi50-x high entropy alloys

Room- and cryogenic-temperature compressive properties for the three V10Cr10Co30FexNi50-x (x = 40, 45, 50) high entropy alloys are investigated under quasi-static and dynamic loading conditions. The face-centered cubic (FCC) stability, which is estimated by the calculation of Gibbs free energy difference between FCC and body-centered cubic (BCC) phases, decreases in increasing order of Fe content. The 40Fe and 45Fe alloys consist of FCC single phase, whereas the 50Fe alloy is composed of a duplex structure with ~95 vol% of body-centered cubic (BCC) lath martensite. Under the quasi-static loading condition at room temperature, the dislocation slip prevails in the 40-at.%-Fe-containing alloy, while the twinning-induced plasticity (TWIP) and transformation-induced plasticity (TRIP) are activated in the other alloys. The decrease in testing temperature lowers the FCC stability, activating both TWIP and TRIP mode. Under the dynamic loading, the magnitude of TWIP effect enhances, but that of TRIP effect reduces in comparison to the quasi-static loading. The adiabatic heating induced from the dynamic loading increases the FCC stability, thereby resulting in the reduced TRIP effect. Despite the increased stability, the TWIP occurs more actively because the dynamic loading enables the increased flow stress to readily exceed the critical stress required for TWIP. These variations of deformation mechanisms according to the FCC stability, testing temperature, loading rate, adiabatic heating effect, and increased flow stress effect are systematically correlated by the shifting of stability on the slip-TWIP-TRIP mechanism band.

Quasi-Static Tensile Behaviors, Mechanisms, and Constitutive Descriptions of Commercially Pure Titanium at Diverse Strain Rates in Ambient Air and Liquid Nitrogen

The quasi-static tensile behaviors, mechanisms and the constitutive descriptions of commercially pure titanium over a strain rate range of 10−4–10−1 s−1 at 77 and 293 K have been investigated and compared by means of OM, SEM, EBSD, and TEM. The results show that the strain hardening rate at all strain rates generally shows a falling-increasing-falling changing tendency at 77 K. Due to the small twin’s density at 293 K, strain hardening rate shows monotone decreasing tendency and generally has much lower values at all strain levels than that at 77 K. Serration behavior can be found in the strain hardening rate curves at low strain rates. The repeated pinning and depinning of dislocations with interstitial atoms could be responsible for this. The elongation at 293 K is proportional to the twin volume fraction in microstructure, which is attributed to the twinning-induced plasticity effect. However, it shows the reverse changing tendency at 77 K. This means that excessive twins may exert detrimental effect on the plasticity of CP Ti. Based on the EBSD and TEM results at the uniformly deformed part of the tensile specimens, it is proved that excessive twins in microstructure could act as obstacles to the movement of dislocations. Won model has been used to describe the constitutive curves under different conditions. It shows good prediction accuracy at 293 K. By contrast, due to the lack of specific consideration of the twinning effect in Won model, its prediction performance at 77 K is ordinary.

Facile Route to Implement Transformation Strengthening in Lightweight Alloys

Developing lighter, stronger and more ductile aerospace metallic materials is in demand for energy efficiency strategies. Alloys with twinning-induced plasticity (TWIP) and/or transformation-induced plasticity (TRIP) effects have been exploited to defeat the conflict of strength versus ductility, yet very few if any physically informed methods exist to address the complex interactions between transitions. Here we report a facile route to deploy transformation-mediated strengthening in lightweight Ti alloys, which particularly focuses on the controlled activation of TRIP and TWIP via a mechanism-driven modelling approach. New alloys were comparatively developed and presented notable resistances to strain localisation, but interestingly through distinct mechanical characteristics. Specifically, extraordinary strain-hardening rate with a peak value of 2.4 GPa was achieved in Ti-10Mo-5Nb (wt.%), resulting from the synergetic activation of hierarchical transformations. A model integrating TRIP and TWIP was applied to understand the interplays between the transition mechanisms that individually contribute to strength and uniform elongation.

Improved strength of a medium-Mn steel by V addition without sacrificing ductility

Here, we investigated the effects of adding a micro-alloying element to medium-Mn steel and explored why a resulting sample containing precipitates exhibited higher strength than one without precipitates, without sacrificing ductility. The model alloys comprised steels of Fe–8Mn-0.2C–3Al-(0, 0.2)V (wt.%); they were cold-rolled and intercritically annealed at identical temperatures between 670 and 730 °C for 30 min. These annealed steels exhibited two-phase microstructures consisting of ferrite (α) and retained austenite (γ R ), with a nanoscale globular morphology. Smaller grain sizes and lower volume fractions of γ R were observed in the V-containing specimen, relative to the V-free specimen, owing to the formation of VC precipitates. The latter were mostly formed in the α phase, rather than in the γ R phase. These VC precipitates meant that the V-containing steel showed a lower C concentration in γ R and a higher C concentration in α than the V-free steel. We propose that such phase compositions enhanced the strain hardening rate during the later stage of mechanical loading due to more active twinning-induced plasticity and dynamic strain aging. These effects resulted in the observed higher tensile strength in the V-containing steel, without sacrificing ductility. • V-added steel shows a better combination of stregnth-ductility than V-free steel. • More active twinning-induced plasticity (TWIP) was observed in V-added steel. • More active dynamic strain aging (DSA) was observed in V-added steel. • Tuned chemical contents by VC help to activate TWIP and DSA effects.

Microstructure and deformation behavior of two TWIP/TRIP high entropy alloys upon grain refinement

Twinning induced plasticity (TWIP) and phase transformation induced plasticity (TRIP) are two effective mechanisms for achieving good combination of strength and ductility in metallic materials, such as steels and high entropy alloys (HEAs). A further enhancement of the strength-ductility combination can be achieved by grain refinement owing to the grain boundary strengthening effect. In this work, we investigated the microstructure and mechanical properties of a TRIP HEA (Cr20Mn24Fe30Co20Ni6, at.%) and a TWIP HEA (Cr20Mn15Fe34Co20Ni11, at.%) after grain refinement by cold-rolling and short-time annealing. The results show a simultaneous increase of strength and ductility for the Cr20Mn15Fe34Co20Ni11 alloy after grain refinement, maintaining the TWIP effect. However, the Cr20Mn24Fe30Co20Ni6 alloy displays a significant enhancement of strength accompanied by a loss of ductility. Detailed microstructure analysis shows that nano-sized σ precipitates are formed in the Cr20Mn24Fe30Co20Ni6 alloy during the grain refinement process. While the nano-precipitates contributes significantly to the strength, they also lead to a spread of micro-voids and early fracture upon deformation. Our work provides some insights in balancing different strengthening mechanisms in alloy design and microstructural manipulation.

Ensuring the strength and ductility synergy in an austenitic stainless steel: single- or multi-phase hetero-structures design

Heterogeneous microstructures have been proposed to optimize the mechanical properties in the respect of strength and ductility synergy in many alloy systems. In this work, the multi-phase hetero-structured microstructure consisting of fine grains and coarse grains where the ferrite is embedded in the vicinity of the nano-grains was obtained by regulating the thermomechanical processing parameters. A yield strength of 1.2 GPa which is more than two times higher than the coarse grained counterpart with less uniform elongation loss is achieved in the multi-phase hetero-structured steel. The microscopic load transfer in this complex microstructure is investigated by the in situ high energy synchrotron X-ray diffraction. The persistent strain hardening is ascribed to the hetero-deformation induced stress associated with the joint activation of transformation-induced plasticity (TRIP) and twinning-induced plasticity (TWIP) effects. As a comparison, the single-phase hetero-structured steel exhibits little lower strength but higher uniform ductility.

A TWIP-TRIP quinary high-entropy alloy: Tuning phase stability and microstructure for enhanced mechanical properties

To understand the relations among phase stability, microstructure and deformation behavior of a non-equiatomic quinary Fe40Mn10Co20Cr20Ni10 (at.%) high-entropy alloy (HEA) with both transformation- and twinning-induced plasticity (TRIP & TWIP) effects, we systematically investigated the microstructural changes under different processing conditions and the corresponding tensile properties. The HEA has a single face-centered cubic (FCC) structure after thermomechanical processing. Inclusions enriched with Mn are rarely presented due to the relatively low Mn content compared to that in the reference equiatomic HEA. The HEA shows higher yield strength (375 MPa), ultimate tensile strength (785 MPa) and total elongation (77.5%) compared to the reference equiatomic HEA (349 MPa, 657 MPa and 59.9%, respectively) at a similar grain size of ~4.5 μm, which was also accompanied by the simultaneous increase of lattice friction stress and Hall-Petch coefficient. Further, introducing non-recrystallized zones of ~8 vol% significantly increases the yield strength (589 MPa) and ultimate tensile strength (865 MPa), at a high elongation (69.1%). Multiple strengthening mechanisms were activated upon deformation, including dislocation slip, nano-twining, and phase transformation, which explains the rationale behand the excellent strength-ductility synergy. The work further broadens the window for achieving a wide spectrum of mechanical properties of HEAs by phase stability-oriented alloy design and microstructure tuning.

Effect of hot/warm rolling on the microstructures and mechanical properties of medium-Mn steels

This study provides processing strategies for the Fe-0.20C-11.0Mn-4.0Al steel to meet the requirements of different automobile parts by using hot rolling + intercritical hardening + tempering (HR) and warm rolling + tempering (WR). The mechanical properties and microstructure evolution were investigated. Due to a mild transformation-induced plasticity (TRIP) effect, twinning-induced plasticity (TWIP) effect and strain anisotropy during deformation, the HR sample showed the best product of tensile strength and elongation, which was above 70 GPa·% (strength: 889 MPa, total elongation: 79.6%); such a steel can be used in manufacturing complex-shaped automotive components such as anti-collision beams, C pillars and bumpers and even for cold working. The WR sample also achieved excellent mechanical properties, with a product of tensile strength and elongation of 45.8 GPa·% (strength: 1171.5 MPa, total elongation: 39.1%). Furthermore, the WR sample exhibited an increased dislocation density, fresh martensite formation and reduced high temperature ferrite phase, leading to a high yield strength of 938.7 MPa, which can be used in B pillars and floors for the prevention of intrusion in case of car collision.

On the Variants of Thermal Process in Developing Strong and Ductile Medium Mn Steel

In this contribution, we investigate the influence of three heat treatments, including intercritical annealing (IA), quenching and partitioning (Q&P) and combination of IA and Q&P (IA-Q&P), on microstructure and mechanical properties of the medium Mn steel. The steel treated by IA process has largest volume fraction of austenite, which is responsible for the longest elongation and largest energy absoprtion with operation of both transformation-induced plasticity (TRIP) effect and twinning-induced plasticity (TWIP) effects. The medium Mn steel produced by IA-Q&P treatment has a mixture microstructure with retained austenite, ferrite and lath martensite. The existence of martensite in the IA-Q&P steel makes the higher yield strength than that of the IA steel. The better uniform elongation of the IA-Q&P steel than that of the Q&P steel is ascribed to the larger volume fraction of retained austenite and higher mechanical stability of austenite. The Q&P steel has highest yield stress due to its martensite matrix. It is expected that the tensile properties of medium Mn steel can be tuned by different thermal processes (IA, Q&P and IA-Q&P) to facilitate its broad automotive applications.

In situ investigation of the deformation behaviors of Fe20Co30Cr25Ni25 and Fe20Co30Cr30Ni20 high entropy alloys by high-energy X-ray diffraction

In situ synchrotron-based high-energy X-ray diffraction (HE-XRD) technique was employed to investigate the mechanical behaviors and microstructural evolution of face-centered cubic (FCC) Fe20Co30Cr25Ni25 and Fe20Co30Cr30Ni20 high entropy alloys (HEAs) during tensile deformation. Fe20Co30Cr30Ni20 HEA has a good combination of strength (ultimate tensile strength of 864 ± 35 MPa) and ductility (elongation of 0.627 ± 0.021). The HE-XRD investigation reveals that Fe20Co30Cr30Ni20 HEA has the transformation-induced plasticity (TRIP) effect, which starts at a critical stress of ~555 MPa. Transmission electron microscopy confirmed this deformation-induced new phase is hexagonal-close-packed structured ε-martensite, which follows an orientation relationship of {111}γ//(0001)ε, and ⟨110⟩γ//[112¯0]ε with the FCC γ matrix. The observation of deformation twins in the deformed samples of the two studied HEAs proves that twinning-induced plasticity (TWIP) effect occurs in both HEAs. The combination of TRIP and TWIP effects lead to the high strength, large ductility and improved strain hardening behavior of Fe20Co30Cr30Ni20 HEA.

Thermodynamic Stacking Fault Energy, Chemical Composition, and Microstructure Relationship in High-Manganese Steels

Stacking fault energy (SFE) is related to activating complex high strength and ductility mechanisms such as transformation-induced plasticity and twinning-induced plasticity effects. This type of energy can be estimated by many different methods and its importance is in its ability to predict microstructure and phase transformation behavior when the material is submitted to stress/strain. In order to study the SFE, chemical composition, and microstructure relationships, eleven different welding parameters were chosen to obtain a large range of dilution levels. A new tubular wire electrode of high-manganese steel (21 wt pct Mn) was used as the consumable and an SAE 1012 steel plate (0.6 wt pct Mn) as the base metal in a flux-cored arc welding process. These welding parameters were related to the phases formed and phase transformation behavior in the fusion zone. The SFE of the austenite phase was calculated using a thermodynamic model. The welding parameters produced SFE values in the range of − 5 to 7 mJ/m2. $$\epsilon $$ -martensite and austenite were observed in all samples, but $$\alpha $$ ′-martensite was only found in those that presented negative SFE values, i.e., those with lower Mn content. Chemical Gibbs Free energy was the component with the most influence on the SFE. Nanoindentation detected the phase transformations during hardness testing for the medium and low dilution levels used, while the high dilution levels presented the highest hardness and modulus of elasticity values, and the lowest elastic and plastic deformation values. The results provide an improved method to develop high-manganese steels with microstructure control through welding parameters.

Novel Co-free high performance TRIP and TWIP medium-entropy alloys at cryogenic temperatures

Recently, high- and medium-entropy alloys (HEAs and MEAs) have been found to exhibit excellent cryogenic mechanical properties, but most of them contain high-priced Co element. Therefore, developing HEAs or MEAs with high strength and ductility and relatively low cost is urgent. In this work, novel Co-free FexMn75-xNi10Cr15 (x = 50 and 55 at.%) MEAs were developed, which exhibit a good combination of low cost, high strength and ductility at cryogenic temperature. It was found that the Fe50Mn25Ni10Cr15 MEA exhibits a combination of cryogenic tensile strength of ∼ 0.98 GPa and ductility of ∼ 83 %. The excellent cryogenic mechanical properties were attributed to joint of twinning-induced plasticity (TWIP) and transformation-induced plasticity (TRIP) effects. The present study sheds light on developing low cost MEAs with high performance for cryogenic-temperature applications.