B2 Particles Research Articles

Tailored precipitation assisted by laser-induced cellular dislocation network structures in Al0.3CoCrFeNi high entropy alloy

Cellular dislocation network structures play a critical role in strengthening metals, while their ability to tailor the precipitation of second-phase particles has long been overlooked. Herein, a novel strategy combining laser surface treatment and two-steps annealing is proposed to produce B2 network structures in the as-cast Al0.3CoCrFeNi high-entropy alloy. Cellular dislocation network structures are first introduced in the plates by the laser surface treatment on both sides, then the L12 phase is precipitated on the wall of the dislocation networks by annealing at 700 °C. During second annealing at 800 °C, previously precipitated L12 precursors provide kinetically preferred sites and element segregation for the precipitation of the B2 phase, finally forming dense B2 network structures within the defect-scarce matrix. Dislocations can easily move inside the network structures, and they are blocked by the B2 particles in the wall areas, thus presenting a superior strength-ductility synergy.

On the microstructural evolution and mechanical property development of additively manufactured AlCoCrFeNi2.1 eutectic high-entropy alloy with aging temperature

In this study, the microstructure and mechanical properties of a laser powder bed fusion processed eutectic high-entropy alloy, AlCoCrFeNi2.1, and the influence of aging temperature have been investigated. The as-printed material consists of a hierarchical cellular eutectic microstructure with γ cells and a B2 network along the cell boundaries. The γ matrix contains homogeneously distributed Al2O3 nanoparticles and sporadically distributed L12 long-range ordered (LRO) domains. Some B2 grains contain ultrafine body-centred cubic Cr-rich precipitates. Aging at 500–700 °C leads to disruption of the B2 network and coarsening of the B2 grains at the intersections of several cells and thinning of the rest of the regions. At 800 °C, the B2 cellular network completely disappears and turns into large isolated spherical or near-spherical B2 particles with the original γ cells being fully integrated. At 600 °C, numerous ultrafine γ′ nanoparticles form from the γ matrix and turn into elongated γ′ at 700 °C but completely disappear at 800 °C due to the formation of thermally more stable B2 precipitates. The as-printed samples show a high yield strength (YS∼ 1050 MPa) and good ductility (elongation ∼ 20 %) due to the strengthening effects from the LRO domains and the less deformable B2 and Al2O3 particles. Aging at 600–700 °C leads to significant strength improvement mainly owing to the γ′ particles. Aging at 800 °C results in a considerable decrease in YS but improves the ductility due to the disappearance of γ′ precipitates and the B2 cellular network.

Achieving an ultrahigh yield strength of 1.5 GPa in warm-rolled lightweight steel via synergistic multiplication of precipitation and dislocations

The microstructural evolution and tensile property of a Fe-18Mn-8Al-1C-5Ni (wt%) lightweight steel subjected to warm-rolling and subsequent aging treatment have been investigated. During the warm rolling process, dislocations-induced precipitates further hinders movement of dislocations, resulting in the synergistic multiplication of dislocations and B2 particles. Additionally, shear bands observed within the grains also induce the formation of B2 particles. Subsequent aging facilitates the precipitation of coherent κ-carbides within the matrix, with their its size and volume fraction increasing as dislocation density rises. The newly designed warm-rolled and aged steel exhibits a remarkable ultrahigh strength (yield strength of 1537 MPa and tensile strength of 1632 MPa) and a total elongation of 11.29%. Such superior tensile property not only surpass those of other hot rolled lightweight steels strengthened by B2 and/or κ-carbides but also exceed those of the steels subjected to additional cold rolling. This advancement is expected to expand the applications of B2-strengthened steels in response to an increasing demand for lightweight constructions.

Overcoming the strength-ductility trade-off dilemma in austenitic lightweight steel via stepwise controllable intragranular dual nanoprecipitation

The strength-ductility trade-off is an inevitable scenario in precipitation-hardened austenitic lightweight steels. The reduction in ductility is due to the shearing of κ′-carbides by dislocations, resulting in limited work hardening capability. Conversely, non-shearable B2 particles can effectively improve the work hardening rate. However, these B2 particles tend to precipitate along grain boundaries and coarsen due to their incompatibility with the austenite matrix, resulting in negligible strengthening effect or even brittleness. We propose a stepwise controllable dual nanoprecipitation strategy to overcome the strength-ductility trade-off. To implement this strategy, we develop a manufacturing process that includes a high-temperature annealing treatment and a three-step aging process (700 °C/15min + 900 °C/15min + 450 °C/1 h). The higher annealing temperature increases the supersaturation of solute atoms in the austenite matrix, which improves the chemical driving force for the precipitation of intragranular B2 particles during aging at 900 °C. Additionally, the coarsened κ′-carbides (30–35 nm) formed during aging at 700 °C provide heterogeneous nucleation sites for the formation of intragranular B2 particles. Further aging at 450 °C promotes the precipitation of nano-sized κ′-carbides (5 nm) within the austenite matrix. The dual nanoparticles provide a significant precipitation strengthening contribution of 400 MPa without sacrificing ductility. The multiple deformation mechanisms of nanoscale “planar slip and Orowan bowing” provide an efficient source of work hardening capability. The present work aims to overcome the strength-ductility trade-off in austenitic lightweight steels by tailoring the precipitation process, which may provide insight into producing high-performance lightweight steels.

Mechanical, materials, and physicochemical effects on the high-temperature tribological behaviour of laser additive manufacturing AlCoCrFeNi2.1 eutectic high-entropy alloys

ABSTRACT The AlCoCrFeNi2.1 eutectic high-entropy alloys (EHEAs) were prepared using selective laser melting (SLM) to study the tribological properties at high temperatures, focusing on the complex mechanism of the friction process. The density of the SLM EHEAs is 99.70%. The lamellar and cellular structures are unevenly distributed at different locations. In situ XRD demonstrated the transition from BCC to FCC with increasing temperature. A large number of B2 particles are distributed in the BCC matrix. The fluctuation of the friction coefficient is closely related to the shape and size of the wear debris. The hardness of the alloy is ∼105 HV at 1000 °C. The wear rate first increases and then decreases with increasing temperature. The maximum thickness of the oxide film is 13.52 μm at 1000 °C and exhibits delamination. The combination of mechanical, materials and physicochemical effects during friction contributes to the excellent high temperature wear resistance.

Assessment of the potential structure and nucleation efficacy of multi-component heterogeneous substrate

In recent years, nucleation of multi-component heterogeneous interface structures has attracted increasing attention due to their excellent grain refinement and anti-poisoning capabilities in Al-Si alloy. In this research, a general methodology was proposed to predict the surface structure and meanwhile evaluate the grain refinement efficacy of the multi-component boride nucleants based on a comprehensive experimental and theoretical study of a novel Al-Si alloy refiner, i.e., Al-3.5 Nb-1 V-1B. By using high-resolution electron microscopy, the (Nb, V)B2 particle with a characteristic “core-shell” surface structure was observed, attributed to V adsorption driven by interfacial energy minimization, validated by ab initio calculations. A general interfacial energy-based model was then proposed which predicts the multi-component boride substrate structure, well consistent with the experimental findings. The nucleation potency of different substrates was analyzed in atomic scale and only if the interfacial atomic vibration was considered together with the nucleation-influencing factors (i.e., the lattice mismatch and the anti Si-poisoning effect), the predicted nucleation potency order can agree well with the experimental results. A thermodynamics-kinetics combined analytic model was summarized by coupling the lattice mismatch parameter, the interfacial Si adsorption energy and the interfacial atomic vibration amplitude, which accurately evaluates the multi-component boride grain refiners for the Al-Si alloys.

High strength Al0.7CoCrFeNi2.4 hypereutectic high entropy alloy fabricated by laser powder bed fusion via triple-nanoprecipitation

Eutectic high-entropy alloys, composed of FCC/B2 phases with a narrow solidification interval and excellent fluidity, have become a new hotspot in additive manufacturing. Nevertheless, their microstructures exhibit significant sensitivity to processing parameters, feedstocks, and composition, ultimately limiting the alloys’ engineering applications. Here, a hypereutectic Al0.7CoCrFeNi2.4 alloy with a low cracking susceptibility index was designed by Thermo-Calc calculation and fabricated by laser powder bed fusion. Results show that the as-printed Al0.7CoCrFeNi2.4 alloy manifests a stable cellular structure, coupled with appreciable ultimate tensile strength (≥1200 MPa) and ductility (≥20%) over a wide range of processing parameters. After aging at 800 °C for 30 min, outstanding strength (1500 MPa) and elongation (15%) were obtained. Considerable mechanical properties after aging stem from a triple strengthening mechanism, i.e., L12 nanoprecipitates and rod-shaped B2 particles within the FCC matrix, along with Cr-enriched spherical nanoparticles in the B2 phase. Meanwhile, hierarchical structure, i.e., FCC dominated matrix, a discontinuous B2 phase, a precipitation-free zone in the B2 phase, and a K-S orientation relationship between FCC and B2, facilitate to maintain excellent plasticity. These results guide designing HEAs by AM with controllable microstructures and outstanding mechanical properties for industrial applications.

Enhanced thermal stability of pressureless liquid-phase sintered SiC ceramics via (Hf, Zr, Ta, Nb, Ti)B2 addition

High-temperature thermal stability plays a crucial role in the structural application of pressureless liquid-phase sintered SiC (PLS-SiC) ceramics. In this paper, a PLS-SiC ceramic processed with CeO2–Al2O3 as sintering additives with excellent high-temperature thermal stability was achieved by incorporating (Hf, Zr, Ta, Nb, Ti)B2 (HEB) particles. Results showed that PLS-SiC ceramics with HEB-free underwent a structural change from dense to porous microstructure after annealing at 1800 °C/1 h. Conversely, PLS-SiC ceramics with the addition of 10 vol% HEB exhibited excellent thermal stability, as evidenced by the retention of their dense microstructure after exposure to annealing at 1800 °C/1 h. The possible primary reasons for this significantly different response to the thermal stability could be probably attributed to fact that HEB reacted with CeAlO3 and SiC to form solid-phase products, subsequently inhibiting the formation of gas-phase products after decomposition of CeAlO3 alone in a high-temperature vacuum environment. In addition, the formation of a compact protective outer layer containing Hf–Ta containing diboride in PLS-SiC ceramics during the annealing process could effectively hinder the volatilization of volatile substances at a high temperature.

Effect of aging temperature on microstructure and mechanical properties of Fe–Ni–Cr–Al high entropy alloy

Investigating the strength–plasticity synergy of metal structural materials is a crucial scientific challenge. This study focuses on preparing high-entropy alloys (HEAs) comprising Fe–Ni–Cr–Al, which exhibit a heterostructural coexistence of several phases through cold rolling and aging (CRA). Above 600 °C CRA, the average grain size of the HEA was refined from 260 to 1.64 μm, and numerous annealing twins were formed. Concurrently, two forms of irregularly ordered body-centred cubic (B2) phases and nanoscale ordered face-centred cubic (L12) phases were precipitated. Large B2 particles precipitated along the grain boundary, whereas small B2 and L12 particles precipitated within the grains. The average sizes of the B2 and L12 particles were 510 and 2.21 nm, respectively. The fine grain and precipitation strengthening enhanced the HEA yield strength (from 254 to 710 MPa). The difference in plastic strain between the matrix and precipitate causes long-range back-stress strengthening and heterodeformation-induced hardening, enhancing the strain-hardening ability and maintaining the superior plasticity of the HEA. This study provides an effective approach for obtaining metal structural materials with strength–plasticity synergy.

The Effect of Nb/Mo on the Microstructures and Mechanical Properties of Fe–Mn–Al–Ni–C Austenitic Steels

The microstructures and mechanical properties of Fe–24Mn–10Al–6Ni–1C steels microalloyed by Nb, Mo, and Nb–Mo coaddition in both solid solution and aging states are evaluated. The results show that the addition of Nb, Mo, or Nb–Mo leads to a decrease in austenitic grain size and a suppression in κ‐carbides precipitation during aging. Besides, Mo slightly promotes precipitation of both B2 bands and particles as a ferrite stabilizer. However, Nb and Nb–Mo increase the volume fraction of B2 particles together with decreasing B2 bands due to the formation of NbC and (Nb, Mo)C. The strengths and ductility are improved simultaneously after adding microalloying elements. The coaddition of Nb–Mo achieves a best combination of strength and ductility. After aging, the precipitation of κ‐carbides and B2 leads to a further enhancement in yield strength but a reduction in plasticity for all the experimental steels. Additionally, the effect of Nb/Mo on the strain hardening behavior is also analyzed.

Variation of BCC/B2 coherent microstructure and resultant improvement in strength of Al0.7CrxFe3−xCoNi high-entropy alloys

The effects of Cr and Fe contents on the microstructure and mechanical properties of B2 nanoparticle-enhanced BCC-based Al0.7CrxFe3−xCoNi (x = 1.5–3.0) high-entropy alloys (HEAs) were studied. It was indicated that the addition of Cr and reduction of Fe in the alloys can increase the lattice misfits between the BCC and B2 phases, inducing the variations of BCC/B2 coherent microstructure and the significant improvements of the compressive yield strengths from ∼ 1485 MPa to ∼ 2252 MPa. The calculations of the yield strengths based on the microstructure of the alloys suggested that the improvements of the strengths were mainly due to the enhancements of the precipitation-strengthening effects. The interactions between dislocations and B2 particles with various shapes and sizes were also discussed on the basis of the calculations. It is demonstrated that adjusting the contents of Cr and Fe is an effective way to control BCC/B2 coherent microstructure and improve the mechanical properties of Al–Cr–Fe–Co–Ni HEAs.

Effect of microstructural evolution on corrosion behavior of Al0.7Cr2FeCoNi high-entropy alloy

In the present study, the influence of the microstructural evolution on the corrosion behavior of the B2 nanoprecipitation-strengthened BCC-based Al0.7Cr2FeCoNi high-entropy alloy (HEA) in a 3.5 mass% NaCl solution was studied. The alloys in the as-cast state and heat-treated at 673 K for 2 h consisted of the BCC matrix and the B2 nanoparticles, and the heat treatments at 873 K and 1073 K for 2 h induced the coarsening of the B2 particles and the precipitation of the σ phase. It was found that the alloys exhibited good corrosion resistance, as evidenced by the low corrosion rates of less than 10−3 mm/year and the spontaneous passivation due to the formation of the Cr-rich surface films. It is notable that the alloys in the as-cast state and heat-treated at 673 K showed the transpassive dissolution above ∼ 0.7 V vs. SCE, while the alloys heat-treated at 873 K and 1073 K suffered localized corrosion on the B2 phase at ∼ 0.40 V and ∼ 0.37 V during the anodic polarization, respectively. This deterioration in the corrosion resistance of the alloys heat-treated at the higher temperatures was attributed to the higher potential difference between the B2 and σ phases than that between the B2 and BCC phases, as well as the coarsening of the Cr-depleted B2 particles. It is demonstrated that the coarsening of the B2 particles and the precipitation of the σ phase should be suppressed to obtain the corrosion-resistant Al–Cr–Fe–Co–Ni HEAs.

Heterogeneity of microstructures in a Cu–Zr based amorphous alloy composite reinforced by crystalline phases

Amorphous alloy composites (AACs) comprising reinforcing crystalline phases exhibit far better mechanical properties than their base amorphous alloy counterparts, and Cu–Zr based alloys consisting of B2 phase particles embedded in an amorphous matrix are well-researched AACs in this respect. Traditionally, the B2 particles in Cu–Zr based AACs may appear to be homogeneously crystalline (without any amorphous phase inside), the glassy matrix homogeneously amorphous, and their interfaces atomically sharp. Yet, such a picture would pose difficulties in understanding how crystallization can happen in the glassy matrix, since the crystallized product is denser than but iso-stoichiometric with the matrix. The present work provides insights into this puzzle, by using electron microscopy, nanoindentation and molecular dynamics (MD) simulations to investigate the structures and mechanical properties of the crystalline and amorphous phases, and their interfaces in a Cu62Zr34.5Al3Nb0.5 AAC. Surprisingly, in this AAC, the superficially crystalline particles with tens to hundreds of microns large are found to be heterogeneous at the sub-micron scale, comprising nano-crystallites embedded in a glassy matrix, and the amorphous phase outside also exhibits a gradient in free volume content towards the interface. Smaller particles containing only B2 nano-crystallites are found to be softer than the amorphous matrix, while larger particles are harder than the amorphous phase due to martensitic transformation into the B19’ phase. MD simulations indicate that the B2 phase is marginally more stable than the glassy state, and on crystallization the densification leads to free-volume generation in the surrounding glassy matrix as observed experimentally. Mechanics analysis indicates that the strain energy in the glassy matrix associated with free-volume generation scales with the volume of the crystallization, as would be the crystallization energy itself. Hence, crystallization in the AAC leading to a two-phase structure is a spontaneous but kinetically limiting process arising from the net energy difference between the crystallization energy and free-volume energy produced in the glassy matrix. This work provides a detailed understanding of the heterogeneity in the microstructures in Cu–Zr based AACs, to shed light on the crystallization of the iso-stoichiometric B2 phase from the amorphous phase.

Precipitation transformation pathway and mechanical behavior of nanoprecipitation strengthened Fe–Mn–Al–C–Ni austenitic low-density steel

Precipitation strengthening has been widely adopted in austenitic low-density steel owing to excellent hardened effects. This approach generally employs the coherent κ′-carbides and non-coherent B2 particles. Revealing the precipitation transformation pathway is decisive for further optimizing the microstructures under specific engineering applications. Herein, the detailed precipitation sequence of Fe–28Mn–11Al–1C–5Ni (wt%) austenitic low-density steel as well as its influence on mechanical properties during aging process is systematically investigated. Our results reveal that nano-sized κ′-carbides domains (2 nm) exist in the solution-treated specimen. During aging at 500 °C for 1 h, the cuboidal κ′-carbides (15–20 nm) uniformly disperse in austenite matrix. However, after aging at 700 °C for 15 min, the coarsen κ′-carbides (30–35 nm) inhomogeneously distribute and align preferentially along the 〈1 0 0〉 directions. Further, extending the aging time to 60 min, the needle-type B2 particles replace the κ′-carbides due to the enrichment of Ni elements at the phase boundaries among the austenite and κ′-carbides. After aging at 900 °C, κ′-carbides entirely dissolve into the austenite matrix, and the intragranular B2 particles are the sole precipitates in the austenite matrix and follow the K-S orientation relationship with austenite. The work hardening capability seriously deteriorates due to the shearing of κ′-carbides by gliding dislocations. While the intragranular B2 particles preserve excellent work hardening rate by dislocations bow-out mechanism. The present work is meaningful for guiding the design of new generation dual-nano precipitation austenitic lightweight steel.

Enhanced strength-ductility balance of the (CoCrFeNiMn)95.2Al3.2Ti1.6 high-entropy alloy by co-precipitation of the B2 and sigma phases

The present work investigated the effect of the co-precipitation of the B2 and σ phases on the mechanical properties of the (CoCrFeNiMn)95.2Al3.2Ti1.6 high entropy alloy subjected to two-step annealing. The single-step annealed sample at 900 °C only showed B2 precipitates. Further annealing at 650 and 750 °C led to the co-precipitation of σ and B2 particles. The sizes and fractions of σ and B2 particles increased with increasing annealing temperature. The sample subjected to the second annealing at 750 °C, with large sizes and fractions of co-precipitated σ and B2 particles, exhibited high strength with maintaining moderate ductility (YS: 561 MPa, UTS: 1005 MPa, TE: 26%). The superior mechanical properties of the sample subjected to the second annealing at 750 °C could be owing to the co-precipitation hardening, back stress strengthening, joint activation of dislocation plasticity and deformation twinning. The present work offers a novel microstructure design to optimize the strength–ductility balance of high-entropy alloys via the co-precipitation of σ and B2 particles.

Understanding the microstructure evolution characteristics and mechanical properties of an AlCoCrFeNi2.1 high entropy alloy fabricated by laser energy deposition

In the present work, an AlCoCrFeNi2.1 high entropy alloy is fabricated by laser energy deposition. Specimens are heated to 700 °C (2#), 850 °C (3#) and 1000 °C (4#), respectively, held for 1 h and cooled in water to investigate the effect of heat-treating conditions on microstructure evolution and mechanical properties of the alloys. FCC(L12) + B2 dual-phase microstructure is acquired from all the four deposits. Ordered FCC (L12) disappears and transforms into B2 particles in 3# and 4#. Original B2 phase and newly formed B2 particles show K–S orientation relationship (OR) with adjacent FCC grains. Nano-sized phase m particles, which contain monoclinic lattice structure and have a composition similar with FCC phase, exist on FCC-BCC phase boundary in all the four deposits. FCC-m phase boundary is coherent. Existence of phase m in 4# indicates that it is stable at temperatures as high as 1000 °C. Precipitate hardening plays an important role in strengthening the materials, while the coarsening of precipitate particles weakens their strengthening effect. The high strength of this alloy group is also attributed to the two-phase interface strengthening effect. Possible reasons for the formation of m particles and their effect on the strength of the material are analyzed.

Balanced mechanical properties of Al0.3CoCrFeNiTix high-entropy alloys by tailoring Ti content and heat treatment

Al0.3CoCrFeNiTix (x = 0.025, 0.075, 0.15) high-entropy alloys (HEAs) were designed to investigate the impacts of Ti addition and the aging temperature (700–900 °C) on the mechanical properties of the alloys. The alloy aged at 700 °C with x = 0.15 yielded the highest ultimate tensile strength (UTS) and large fracture elongation at both room temperature and 700 °C. The UTS is 1299 MPa with fracture elongation up to 31.6% at room temperature, and 769 MPa with 32.5% at 700 °C. The product of strength and elongation of Al0·3CoCrFeNiTi0.15 is higher than the reported value of other similar FCC HEAs at elevated temperature. The reason for the outstanding balanced mechanical properties of the alloy is the uniformly distributed L12 and B2 particles. Ti promotes the precipitation of L12 phase and the precipitation temperature increased from 770 to 890 °C as Ti content increased. The amount of B2 phase reached a maximum at 900 °C with x = 0.15. The B2 particles at grain boundaries render the different variation tendency of ductility at 700 °C from that at room temperature.

Systematic study of the effect of Cr on the microstructure, phase content and hardness of the AlCrxFeCoNi alloys

Microstructure, phase content and hardness of homogenized multicomponent AlCrxFeCoNi (where x = 0, 0.2, 0.5, 1 and 1.8) alloys was studied systematically using light, electron microscopies and microhardness methods. The goal of this research was to understand the effect of Cr on the microstructure and the reason for the variations in mechanical properties, such as hardness, as a function of Cr concentration. Quaternary AlCoFeNi alloy (i.e., x = 0) was found to be single phase B2 (CsCl structure type) with elongated grains. Alloys containing Cr, solidified in dendritic regime. Phase content has also changed. Addition of Cr promoted the formation of the Body Centered Cubic (BCC) phase at the expense of the B2 and coarsened the grains. At x = 1.8, BCC exceeded the B2 phase volume. Furthermore, in the dendrite region, reversion of the microstructure occurred: when 0 <x < 1.8 - BCC spherical particles were embedded uniformly in the B2 matrix, while at x = 1.8 cuboidal B2 particles were found to be homogenously spread in the BCC matrix. Complex behavior of the microhardness value was noted as a function of Cr content. These results were explained by solid solution strengthening mechanism.

A STUDY OF THE STRUCTURE AND MECHANICAL PROPERTIES OF NB-MO-CO-X (X = HF, ZR, TI) REFRACTORY HIGH-ENTROPY ALLOYS

Refractory high-entropy alloys (HEAs) are a new class of metallic materials based on group 4-6 elements of the periodic table with possible additions of Al, Si, Re, C, or B. Some single-phase refractory HEAs can maintain high strength up to 1600°C, while multiphase compositions have more attractive specific properties at temperatures up to 1200°C. Here we examine the structure and mechanical properties of refractory HEAs Nb30Mo30Co20Hf20, Nb30Mo30Co20Zr20, and Nb30Mo30Co20Ti20 (at %). The alloys consisted of an intermetallic B2 matrix and particles of a disordered bcc phase, as well as a minor volume fraction of additional bcc (Nb30Mo30Co20Hf20 and Nb30Mo30Co20Zr20) or fcc (Nb30Mo30Co20Ti20) phases. When tested for uniaxial compression, Nb30Mo30Co20Ti20 alloy showed higher yield strength in the temperature range of 22-1000°C than Nb30Mo30Co20Hf20 and Nb30Mo30Co20Zr20 alloys. Nb30Mo30Co20Zr20 alloy did not fail at temperatures of 22-800°C to a given 50% strain, while Nb30Mo30Co20Ti20 alloy turned out to be brittle. All alloys demonstrated high strain hardening in the temperature range of 22-800°C, and they can compete in terms of specific strength with commercial nickel and cobalt superalloys.

Excellent strength-ductility combination in Co36Cr15Fe18Ni18Al8Ti4Mo1 multi-principal element alloys by dual-morphology B2 precipitates strengthening

Precipitation strengthening provides one of the most widely-used mechanisms for strengthening multi-principal-element alloys (MPEAs). Here, we report dual-morphology B2 precipitates in Co36Cr15Fe18Ni18Al8Ti4Mo1 MPEA obtained by thermo-mechanical processing. Electron microscopy characterization reveals that the dual-morphology B2 precipitates are either recrystallized B2 particles formed at the grain boundaries or triple junctions with recrystallization process, or rod-like within the non-recrystallized FCC matrix. The dual-morphology B2 precipitates enhance the yield strength and ultimate tensile strength up to 1120 MPa and 1480 MPa, respectively. This work suggests the mechanical properties of the alloy can be optimized by B2 precipitation strengthening to meet the needs of engineering applications.