B2 Phase Research Articles

Microstructure, mechanical properties and corrosion resistance of direct energy deposited AlCu0.25CoCrFeNi2.1 high entropy alloy: Tailored by annealing heat treatment

In this study, a novel high entropy alloy AlCu0.25CoCrFeNi2.1 is additively manufactured by laser direct energy deposition process. The microstructure, mechanical properties and corrosion resistance of the prepared AlCu0.25CoCrFeNi2.1 high entropy alloy are investigated and tailored by annealing heat treatment. The results indicate the alloy exhibits a dual-phase microstructure with face-centered cubic (FCC) columnar dendrites and body-centered cubic (BCC) interdendritic structures. The annealing heat treatment facilitates the precipitation and coarsening of Cu-rich short rod-like B2 phase within the incipient FCC phase and the dissolution of incipient BCC phase, synergistically varying the proportion of FCC/BCC + B2 contents and tailoring the properties. The hardness of microstructure fluctuates under the coupling effect of precipitation strengthening and lattice distortion reduction and shows an overall downward trend with the increase of annealing time. The tensile properties are noteworthily improved within 6-h annealing and achieve a maximum ultimate tensile strength of 1156.4 MPa. After 8-h annealing, the ductility of the alloy obtains a maximum value of 30.3% with minor loss of ultimate tensile strength. The corrosion resistance is dramatically enhanced and obtains the best value after 2-h annealing, and then gradually deteriorates with the destroying of FCC matrix passive film phase by coarsened B2 phases. These results are of great importance in rapidly designing/manufacturing novel high entropy alloys by laser direct energy deposition process and tailoring microstructure, mechanical properties and corrosion resistance by annealing heat treatment.

A novel AlCo1.2Cr0.8FeNi2.1 eutectic high entropy alloy with excellent corrosion resistance

A novel AlCo1.2Cr0.8FeNi2.1 eutectic high entropy alloy (EHEA) was designed and prepared. The microstructure of the as-cast alloy was characterized that a fine lamellar structure composed of FCC (L12) phase and B2 phase. The mechanical of the EHEA was studies by the tensile tests, and the corrosion properties of the EHEA in 3.5 wt% NaCl solution at room temperature was investigated. The results shown that the alloy exhibits synergistic effect of strength- plasticity with a high tensile strength of 1048.42 MPa and an excellent elongation of 18.92%. Potentiodynamic polarization test and electrochemical impedance spectroscopy (EIS) indicated that the EHEA exhibits spontaneous passivation in 3.5 wt% NaCl solution, forming a protective passive film that exhibits p-type and n-type semiconductor properties, with the main components of Al2O3, CoO, Cr2O3, Fe(OH)3, and NiO. Furthermore, the corrosion mechanism of EHEA was discussed.

Severe plastic deformation of two-phase TiNiCuNb shape memory alloy

(Ti54Ni34Cu12)90Nb10 alloy with initial two-phase structure of B19 martensite and β-Nb phase was subjected to high-pressure torsion (HPT) process at room temperature. HPT leads to the formation of nanocrystalline bands of β-Nb phase alternating with amorphous matrix. Nanocrystalline debris of B2 phase was found to be embedded into the amorphous matrix. Refinement of β-Nb phase upon HPT is much greater compared to that for pure Nb alloy.

Microstructure and mechanical properties of high-entropy diboride-based ceramic assisted by Ti3AlC2 additive

Ti3AlC2 was used as the additive to fabricate a novel (Zr0·2Ta0·2Nb0.2Hf0.2Mo0.2)B2-based (HEBTAC) ceramic using spark plasma sintering at 1900 °C. The as-prepared HEBTAC ceramic sample consists of (Ti, Zr, Hf, Ta, Nb, Mo)B2, multiscale (Zr, Hf, Ta, Nb, Mo)C, and Al2O3 phases, which are produced by the decomposition of Ti3AlC2 and subsequent exchange reaction & solid solution reactions during the sintering process. The relative density, hardness, fracture toughness, and flexural strength of the HEBTAC ceramic sample are 99.43 %, 27.92 ± 1.87 GPa, 5.84 ± 0.14 MPa m1/2, and 629 ± 8.7 MPa, respectively, which are even better than the same class of high-entropy diboride ceramics previously published. Solid-solution strengthening, dislocation strengthening and nano-HEC strengthening existed in the ceramic sample contribute to its excellent mechanical properties. The in situ formed Al2O3 and (Zr, Hf, Ta, Nb, Mo)C effectively enhances the toughness of the HEBTAC ceramic sample through the synergistic effect of intrinsic and extrinsic toughening. This study presents a new approach for reactive sintering densification of high-entropy diborides with both high strength and high toughness.

Phase transformation behavior and mechanical properties of NiTi shape memory alloys fabricated by directed laser deposition

Directed laser deposition shows promise as a method for fabricating complex structure NiTi shape memory alloy parts in engineering, aerospace, automobile, and biomedical fields. The dislocation density has an impact on phase transformation behavior and mechanical properties of NiTi manufactured by directed laser deposition. In this work, NiTi samples were produced by directed laser deposition, and the mechanism of martensitic phase transformation and its interactions with dislocation density were revealed through molecular dynamics. Laser power and scanning speed are the main factors affecting dislocation density, the phase compositions of the samples are B2, B19′, and Ti2Ni phase, and the samples with dislocation density below 2 × 1015 m−2 show single-step B2–B19′ martensitic transformation, stress plateau and improved elongation, the samples with dislocation density above the value exhibit no significant transformation peak and no stress plateau. The movement of (100) twin planes and the growth of advantageous variants are observed in the simulation which can explain stress-induced martensitic reorientation and the stress plateau phenomenon. The bending test suggested that the sample under the optimal parameters has an 85 % recovery ratio within 8 % pre-strain.

Unraveling the role of the BCC-B2 transition and V occupancies in the contradictory magnetism-ductility relationship of FeCoV alloys

The contradictory relationship between magnetism and ductility restricts further applications of FeCoV alloys in high-performance electrical machines. The role of the BCC-B2 transition, accompanied by vanadium (V) site occupancies, in magnetic moments and ductility has been explored using first-principles calculations. The variations in magnetism and ductility of FeCoV alloys are attributed to the coupling of the BCC-B2 transition and V occupancies. When V replaces Fe atoms in the equiatomic B2-FeCo alloy, the superior magnetism observed in B2-Fe50-cCo50Vc alloys is a consequence of the enhanced local magnetic moment of Fe and the ferrimagnetic-ferromagnetic transition in the magnetic state. Moreover, due to the preferential V occupancy in the B2 phase, the B2-Fe46Co50V4 alloy exhibits comparable ductility to the BCC-Fe50Co46V4 alloy. The results indicate that the increased brittleness in the B2 phase arises from the raised Peierls stress and the enhanced covalent component in interatomic bonding, which is caused by the strong hybridization between Fe and Co atoms. Pearson correlation analysis illustrates that valence electron concentration (VEC) and V content are significant factors in the contradictory relationship between magnetization and ductility. The theoretical results demonstrate that tuning the V content and atomic occupancies is helpful to achieve a trade-off between magnetization and ductility in B2-FeCoV alloys.

Microstructure evolution and mechanical properties of β/γ-TiAl alloy during high-rate near-isothermal multidirectional forging

The microstructure of β/γ-TiAl alloy was characterized and analyzed in various deformation regions during a high-rate near-isothermal multidirectional forging (HR-NIMDF) process in this study. The results indicate that the localized precipitation of the B2 phase occurs within the large lamella microstructure through DRX and heterogeneous exsolution decomposition mechanism in the stagnant zone. The majority of mixed fine-grained microstructures (α2/γ/B2), with a grain diameter smaller than 1 μm, were formed under an appropriate stress-temperature coupling field. In the central region of the large deformation zone, a small twisted lamellar microstructure with low B2 phase content is observed, suggesting that HR-NIMDF can efficiently decompose the (α2/γ) lamellar structure and achieve refined grain microstructures. After undergoing HR-NIMDF, the β/γ-TiAl alloy exhibits a low tough-brittle transition temperature and an elongation of 7 % at 650 °C, with an ultimate tensile strength of 862.6 MPa. At 700 °C, the elongation increases to 55.4 %, while the ultimate tensile strength decreases to 653.8 MPa. Moreover, this study demonstrates that when the plastic deformation degree is insufficient and the adiabatic warming effect is relatively pronounced, significant precipitation of the B2 phase leads to a reduction in DRX extent within the material, ultimately resulting in the formation of large residual (α2/γ) lamellar microstructure. The unsynchronized thermal-force coupling relationship between the precipitation of the B2 phase and DRX holds significant implications for advancing and refining the thermoplastic deformation process of β/γ-TiAl alloy.

Role of (Al, Ti) alloying and annealing temperature in precipitation, recrystallization, and mechanical properties of ferrous multi-component alloys

L12-precipitate-strengthened multi-component alloys (MCAs) possess exceptional combination of strength and ductility. However, the high production costs of L12-containing MCAs impede their industrial application. This study introduces a novel approach for designing cost-effective L12-containing MCAs by microalloying Al and Ti with a base composition of Fe50Ni30Cr20 (at%). Three types of MCAs were investigated in this study: Fe50.13Ni28.84Cr18.56Al1.39Ti1.08 (1Ti alloy), Fe46.53Ni27.32Cr19.91Al3.44Ti2.80 (3Ti alloy), and Fe48.51Ni25.93Cr15.75Al5.10Ti4.71 (5Ti alloy) (at%). An increase in the (Al, Ti) content from 1 to 3 at% accelerates the formation of L12 particles, whereas an increase in the (Al, Ti) content from 3 to 5 at% leads to the activation of the brittle B2 and D024 phases. The rapid co-precipitation of the L12, B2, and D024 phases in the 5Ti alloys substantially hinders recrystallization during annealing, whereas the 3Ti alloys exhibit the highest rate of recrystallization upon annealing at 600 and 700 °C, mainly due to the reduction in the stacking fault energy of the matrix. The 5Ti alloys exhibit the highest hardness and the lowest plasticity owing to the presence of brittle B2 and D024 precipitates. By contrast, the 3Ti alloy annealed at 600 °C, in which dense and relatively fine L12 particles precipitated, exhibits a superior combination of hardness and plasticity. This study provides insights into the composition and annealing condition-dependent precipitation, recrystallization, and mechanical properties of ferrous MCAs.

Electropulsing of low-density duplex steel for strengthening and ductilization by microstructural refinement

The present investigation finds the effect of electropulsing treatment on the mechanisms of refining and reprecipitation of ordered L20 structure (B2) and its impact on tensile properties of low-density duplex steel of Fe-18Mn-10.5Al-1 C-6Ni composition. The selected composition without manganese is melted at 1600°C by induction heating in a vacuum but Mn is added into the melt at 1560°C, in the argon atmosphere to reduce the loss. The melt is cast into a plate form in a copper mold. The cast steel is homogenized, hot rolled, and annealed (PD1-A sample) to get elongated bands, spheroids, and platelets of B2 phase with an austenitic matrix which results in a yield strength of 1015 MPa, and tensile strength of 1285 MPa with a plastic elongation of 16.3%. Electropulsing partially dissolves the B2 phase at a temperature much lower than the equilibrium solvus by reducing barrier energy because of electron wind. As a result, the sizes of bands and spheroids are reduced, and platelets are disintegrated. Electron wind force deforms coarse precipitates, and fragments as well as spheroidized it. Electropulsing of annealed steel (PD1-AE) mobilizes dislocations, and recovers it in B2, but induces localized recrystallization of austenite. At a later time of the signal, the temperature rapidly falls and the matrix becomes supersaturated but electropulsing accelerates low-temperature precipitation of the B2 phase. Therefore, electropulsing can be adopted as a fast manufacturing process to dissolve, deform, fragment, spheroidize and reprecipitate high temperature phase at much lower temperature by dominant athermal effect of electron wind energy over thermal effect. Electropulsing also induces recovery and recrystallization at a relatively low temperature and reduces defect density. Reduction in the overall size of B2 and its distribution towards better uniformity provided an increased yield strength of 1077 MPa, tensile strength of 1355 MPa, and a plastic elongation of 21.6%. The selected duplex low-density steel follows two-stage work hardening of Ludwigson model with an additional stage of dynamic recovery. Fractography analysis confirms that both samples show mixed modes of ductile and brittle fracture, with an increase in size and area percentage of dimples.

Synergistic effect of twin consumption within lamellae and slip system activation at grain boundary on the formation of nano-spherical B2 phase

In this study, the spheroidization behavior of the B2 phase in TiAl alloys under isothermal compression is revealed for the first time, reducing the cut apart trend on matrix. Results show that the deformation stored energy under the 1050 °C–40 %–0.01s−1 condition is insufficient so that most B2 phase bends and twists with the γ lamellae rather than being spheroidized. Under the 1000 °C–80 %–0.01s−1 condition, reduced temperature and increased strain further promote B2 phase spheroidization. The B2 phase nucleates and becomes spheroidized by twin boundary consumption within the γ lamellae. At the γ recrystallized grain boundary, the B2 phase grows into a spherical crown shape due to favorable slip tendency activation, multiple dislocation shear, and microslip bands coordination. This work offers a significant approach to improving the hot workability of TiAl alloys.

Achieving excellent strength–ductility combination of Al-aided Mg–Gd–Al–Zr–Zn alloys fabricated by cold metal transfer-based wire-arc directed energy deposition via uniform equiaxed grains and multiple precipitates

Limited ductility consistently poses a challenge for high-strength Mg–RE (rare earth) structures prepared by additive manufacturing. Particularly following heat treatment, while the strength of the Mg–RE alloy experiences a substantial increase, there is a noteworthy decrease in its ductility. Herein, a novel Mg–Gd–Al–Zr–Zn thin wall was successfully fabricated by cold metal transfer-based wire-arc directed energy deposition (CMT-WA-DED) and Al alloying. The microstructural evolution and mechanical properties of deposited and heat-treatment alloys were elucidated systematically. By adding Al element, Al2Gd and Al–Zr phases with thermal stability were precipitated in the deposited alloy. During the solidification or heat treatment stage, Al2Gd and Al–Zr phases could pin grain boundaries to restrict grain growth. The as-deposited alloys exhibited fully equiaxed grains at different heights and orientations. Thus, the thin wall exhibited good isotropic performance. After the heat treatment, the grain size only slightly grew and no abnormal grain growth was observed. Various morphologies of β precipitation phases were discovered along grain boundaries and within the grains. Additionally, a high density of β' and β1 phases within the grains and β phases along the grain boundary played pivotal roles in enhancing the mechanical strength of the Mg–Gd–Al–Zr–Zn alloy. The alloys exhibited an excellent combination of strength and ductility with ultimate tensile strength of 340 ± 7 MPa, yield strength of 212 ± 5 MPa, and elongation of 12.7 ± 0.9 %. This work provides theoretical and practical reference value for the Mg–RE structures obtaining an excellent combination of strength and ductility prepared by additive manufacturing.

Designing the heat treatment process for Mg-10Gd-4Y-xZn-0.6Zr (wt.%) alloy: A study on the transformation of microstructure and properties

Heat treatment of Mg10Gd-4Y-xZn-0.6Zr (x = 0, 1, 2 wt%) alloys has been optimized based on thermodynamic calculations and experiments. The phase transformations during the heat treatment and their effect on the mechanical properties of the alloys were discussed. Using thermodynamic calculations, three solution treatment temperatures of 475 °C, 500 °C, and 525 °C were determined, and the phase transformation under these temperatures were calculated and characterized, the results aligned well with experimental results. The optimal solution treatment technology was determined to be 500 °C for 18 h. After solution treatment, experimental alloys were subject to isothermal aging at 225 °C, the peak aging time for the experimental alloys was established. The microstructure under peak-aged state of the alloy was characterized, revealing a co-existed β’ and β1 phases. The GWZ1041K alloy, after peak aging treatment, exhibited optimal mechanical properties, with a tensile strength, yield strength, and elongation of 392.3 MPa, 249.3 MPa, and 5.7%, respectively. The study further analyzed the reasons for the microstructure transformation during the heat treatment and their influence on mechanical properties.

Hot pack rolling the Ti2AlNb alloy prepared by SPS: Testing of the high-temperature properties of the alloy directly without the prior heat treatment

Ti2AlNb alloy holds large research significance as a lightweight material for high-temperature structural applications in the next generation of aero-engines. In this work, pre-alloyed Ti2AlNb powders were spark plasma sintered to fabricate the raw compact, which was then hot rolled at different phase fields to fabricate sheets. The high-temperature properties of the sheets were tested directly without the prior heat treatment. Results show that the Ti2AlNb sheets have good high-temperature strengths even without the heat treatment prior to testing. For the sheet rolled at the single B2 phase region, the maximum tensile strength was up to 931.4 MPa at 650 °C. The sheet mainly shows intergranular fracture mode due to the weak bonding at grain boundaries. The sheets rolled at the O + B2 phase region have low tensile strengths at different testing temperatures. For the sheet rolled at α2+O + B2 phase region, the tensile strength gains its maximum strength of 956.6 MPa at 650 °C, and the sheet shows transcrystalline fracture mode. The fracture mechanisms of the sheets rolled at different phase regions are analyzed in detail and proved by experiment. This work shows the potential of fabricating Ti2AlNb sheet by using the spark plasma sintered compact.

Effects of Fe on microstructure and mechanical properties of CoCrNiFeAl multi-principle elements alloys

Precipitation and twinning strengthening mechanisms have been extensively investigated to improve the yield strength and ductility of face-centered cubic (FCC) multi-principle elements alloys (MPEAs). Compared with well-studied Al0.3CoCrFeNi in CoCrFeNi system, the microstructure and mechanical properties of a new designed CoCrNiFe0.62Al0.38 MPEA with lower Fe content were evaluated by transmission electron microscopy and tensile tests, respectively. Higher volume fraction of B2 nanoprecipitates and early deformation twining within FCC matrix were proposed to play key roles in improving the synergy strength and ductility of the AlCoCrFeNi system. The experimental results presented herein not only provide insight into how transition metal element affect precipitation and twining process of B2 phase reinforced FCC MPEAs, but also demonstrate useful guidance for the development of precipitation hardened CoCrFeNi system other than adjusting conventional elements such as Al, Ti, Ta, etc.

Microstructure and mechanical properties of Ti-Nb alloys: comparing conventional powder metallurgy, mechanical alloying, and high power impulse magnetron sputtering processes for supporting materials screening

At the interface of thin film development and powder metallurgy technologies, this study aims to characterise the mechanical properties, lattice constants and phase formation of Ti-Nb alloys (8–30 at.%) produced by different manufacturing methods, including conventional powder metallurgy (PM), mechanical alloying (MA) and high power impulse magnetron sputtering (HiPIMS). A central aspect of this research was to investigate the different energy states achievable by each synthesis method. The findings revealed that as the Nb content increased, both the hardness and Young’s modulus of the PM samples decreased (from 4 to 1.5 and 125 to 85 GPa, respectively). For the MA alloys, the hardness and Young’s modulus varied between 3.2 and 3.9 and 100 to 116 GPa, respectively, with the lowest values recorded for 20% Nb (3.2 and 96 GPa). The Young’s modulus of the HiPIMS thin film samples did not follow a specific trend and varied between 110 and 138 GPa. However, an increase in hardness (from 3.6 to 4.8 GPa) coincided with an increase in the β2 phase contribution for films with the same chemical composition (23 at.% of Nb). This study highlights the potential of using HiPIMS gradient films for high throughput analysis for PM and MA techniques. This discovery is important as it provides a way to reduce the development time for complex alloy systems in biomaterials as well as other areas of materials engineering.Graphical abstract

Preparation of Zr-based metallic glasses gradient composites with designable amorphous fraction by laser powder bed fusion

Introducing ductile crystals in situ into the matrix is an efficient approach for enhancing the mechanical properties of bulk metallic glasses (BMGs). However, controlling the volume of the crystalline phase is challenging, and the introduction of crystals may be detrimental to its strength and ductility trade-off. In addition, BMGs prepared by conventional casting process suffers from the disadvantages of size limitation, inhomogeneous crystallization, and uncontrollable crystallization fraction. In this study, Zr48Cu47.5Al4Co0.5 amorphous powder with better forming ability was utilized as raw material and printed by selective laser melting (SLM) technique with high cooling rate. Through parameter adjustments and proactive design of amorphous fractions, gradient metallic glasses (GMGs) based on Zr has been successfully prepared. Micro-morphology, DSC tests, micro-area XRD, optical calculations and nanoindentation experiments all indicate the presence of gradient structures. The microstructure reveals that the crystalline phases in the heat affected zone (HAZ) are mainly B2 phase. In addition, the results of room temperature compression show that the yield strength (1.2 GPa) and plastic deformation (0.8 %) of the gradient structure are better than those of the samples prepared with a single parameter. The theme of amorphous fraction gradient structure design, realized by SLM technology, opens a new window for the large-scale development of high-performance BMGs.

Microstructure and mechanical properties of Al0.5CoCrFeNi HEA prepared via gas atomization and followed by hot-pressing sintering

Pre-alloyed Al0.5CoCrFeNi high-entropy alloy (HEA) powders were prepared via gas atomization and followed by hot-pressing sintering (HPS) at 1200 °C for 1 h to fabricate bulk materials. The phase stability, microstructure evolution and mechanical properties of Al0.5CoCrFeNi HEA were mainly investigated. Results indicated that the atomized powders exhibited a fine-grained FCC + dendritic-like ordered BCC (B2) dual-phase structure. Rapid solidification was favorable to the metastable B2 phase formation during gas-atomization. Partial of the dendritic-like B2 phase dissolved after annealing (>600 °C), resulted in a homogeneous dual-phase structure with irregular B2 phase dispersed in the FCC matrix. The homogeneous structure was “inherited” in the sintered bulks and coarsened after HPS. Tensile test results suggested that the sintered bulks possessed excellent comprehensive mechanical properties with yield strength, ultimate tensile strength and elongation of 587.3 ± 18.7 MPa, 960.2 ± 23.6 MPa and 32.6 ± 5.1%, respectively. The excellent mechanical response during deformation was mainly attributed to the synergistic deformation of the FCC/B2 phase and considerable back stress hardening mechanism.

A gradient B2-BCT transition introduced by deformation in eutectic high-entropy alloy

Eutectic high-entropy alloys (EHEAs) exhibit promising characteristics for achieving both high strength and good ductility owing to their diverse deformation mechanisms. In this study, a gradient B2-body-centerd tetragonal (BCT) phase transformation was observed in a deformed Al19Fe20Co20Ni41 (at. %) EHEA. The X-ray diffraction patterns indicate a gradual transformation from the B2 phase to the BCT phase, a process significantly influenced by the applied strain during tensile testing. The gradient transition region between B2 phase and BCT phase occurs within a single grain, where the lattice constant changes step by step. Such a mechanism holds huge potential for enhancing the mechanical properties of EHEAs.

A novel cast Co68Al18.2Fe6.5V4.75Cr2.55 dual-phase medium entropy alloy with superior high-temperature performance

A newly-designed Co68Al18.2Fe6.5V4.75Cr2.55 medium entropy alloy (MEA) with FCC + B2 structure exhibits not only an excellent strength-ductility combination at room temperature, but also an outstanding high-temperature mechanical properties in particular. The phase formation, microstructure and deformation mechanism of this designed dual-phase MEA at room and high temperatures were investigated and discussed in detail. Based on experimental results (XRD, SEM and TEM) and theoretical analysis (calculated diagram and empirical thermodynamic parameters), it is demonstrated that this newly-designed MEA consists of a dual-phase structure of a face-centered-cubic (FCC) phase (70.3 vol %) plus chemically ordered body-centered cubic phase (B2) (29.7 vol %). Meanwhile, the FCC phase is enriched with Co, Fe and Cr elements, while the B2 phase is enriched with Al and Co elements. Furthermore, compared with some HEAs/MEAs and commercial alloys, this newly-designed dual-phase MEA exhibits excellent strength-ductility combination with a high compressive yield strength of ∼1254 MPa, a fracture strength of ∼2657 MPa and a large compressive plasticity of ∼34.6 % at room temperature. In particular, the studied MEA also shows an outstanding high-temperature performance with an ultrahigh yield strength of ∼1213 MPa at 600 °C and ∼626 MPa at 800 °C, respectively. The excellent comprehensive mechanical properties of this designed dual-phase MEA at both room and temperatures mainly originate from synergy effect of alternate FCC + B2 structure and strengthening contributions of B2 phase. These important findings not only reveal the deformation and strengthening mechanisms of the newly-designed dual-phase MEA, but also provides an effective alloy design strategy for developing advanced structural materials serving as a wide range of temperature.

Synergistic Effect of Al and Ni on Microstructure Evolutions and Mechanical Properties of Fe-Mn-Al-C Low-Density Steels

In this study, the synergistic behavior of Ni and Al in two low-density steels (Fe-26Mn-10.2Al-0.98C-0.15V (wt. %) and Fe-29Mn-5Al-1C-12Ni (wt. %)) and their influence on microstructures and mechanical properties were investigated. The chemical composition of κ-carbides and B2 precipitated particles as a function of annealing and aging temperature and the matrix within which they formed were elucidated. The microstructures and deformation mechanisms of both steels were studied based on their strengthening contribution. The Fe-26Mn-10.2Al-0.98C-0.15V steel mainly realized precipitation strengthening through κ-carbides and grain boundary strengthening due to full recrystallization. The strengthening caused by Fe-29Mn-5Al-1C-12Ni steel was mainly due to the presence of the B2 phase in the matrix, which was non-coherent with FCC. This led to the Orowan bypass mechanism, which made precipitation strengthening the main strengthening contribution. The synergistic effect led to the shear or bypass mechanism of both steels when plane dislocation slip occurred. In addition, it also had an influence on the work-hardening capability during plastic deformation. This study provides a promising way to further enhance the yield strength of low-density austenitic steels through the synergistic effect of Ni and Al.