Complex Concentrated Alloys Research Articles

Composition-dependent slip planarity in mechanically-stable face centered cubic complex concentrated alloys and its mechanical effects

In metallic materials, enhancing strain hardening capacity positively affects ductility, fracture toughness, ultimate tensile strength, and other properties. Thus, activating mechanically-induced martensitic transformation or twinning mechanisms has been a captivating goal in the design of steels, titanium alloys, cobalt alloys, complex concentrated alloys (CCAs) and others, through modifications to composition or thermo-mechanical processing. Here instead, we focus on the most basic strain hardening effect, arising from dislocation kinematics, and interactions. For this purpose, we designed two model face centered cubic (FCC) CCAs, Ni2CoCrFe and Ni2CoCrFeTi0.2Al0.1. Both alloys develop single, mechanically-stable, FCC phase microstructures upon processing. Mechanical tests of these alloys reveal that the Al and Ti addition enhances the strain hardening capacity, leading to significant increases in strength and ductility. Microstructure analyses based on electron channeling contrast imaging (ECCI), electron-backscatter diffraction (EBSD), and transmission electron microscopy (TEM) confirm the absence of mechanically-induced twinning and martensitic transformation effects, revealing instead a transition from wavy slip to planar slip. In-situ synchrotron XRD tensile tests are used to discuss the origin of the dislocation glide mode transition and the effects on strain hardening. Based on these analyses, the increased degree of short-range ordering (SRO), rather than the changes in stacking fault energy (SFE), is proposed as the main cause for this transition, and the corresponding effects on strain hardenability.

Modeling and Characterization of Complex Concentrated Alloys with Reduced Content of Critical Raw Materials.

The continuous development of society has increased the demand for critical raw materials (CRMs) by using them in different industrial applications. Since 2010, the European Commission has compiled a list of CRMs and potential consumption scenarios with significant economic and environmental impacts. Various efforts were made to reduce or replace the CRM content used in the obtaining process of high-performance materials. Complex concentrated alloys (CCAs) are an innovative solution due to their multitude of attractive characteristics, which make them suitable to be used in a wide range of industrial applications. In order to demonstrate their efficiency in use, materials should have improved recyclability, good mechanical or biocompatible properties, and/or oxidation resistance, according to their destination. In order to predict the formation of solid solutions in CCAs and provide the optimal compositions, thermodynamic and kinetic simulations were performed. The selected compositions were formed in an induction furnace and then structurally characterized with different techniques. The empirical results indicate that the obtained CCAs are suitable to be used in advanced applications, providing original contributions, both in terms of scientific and technological fields, which can open new perspectives for the selection, design, and development of new materials with reduced CRM contents.

Process\u2013Structure\u2013Property Relationship in FeCoNiAlxMnx Complex Concentrated Alloys Processed by Additive Manufacturing

Fourteen alloys of the FeCoNiAlxMnx system were processed by laser metal deposition (LMD). The feedstock was a weighted and proportional blend of the containing elemental powders, targeting the nominal alloy compositions. Prior to processing, the composition and particle characteristics of the feedstock were assessed. The microstructural features and crystal structures of all LMD processed materials were characterized with scanning electron microscopy/energy dispersive spectroscopy and x-ray diffraction, in both as-received and heat-treated conditions. Selected samples were investigated via scanning transmission electron microscopy and electron backscattered diffraction for further structural understanding. Hardness tests, under various indentation loads and dwelling times, were performed to assess the mechanical properties of the processed samples. The results showed a rise in hardness as Al and Mn contents increase. The variation of hardness with composition follows a reverse sigma-type curve, reflecting the microstructural evolution and grain size variations in the alloys. Based on the hardness data, we suggest a trained and validated predictive model, which can be used in alloy design for future developments.

Element-resolved local lattice distortion in complex concentrated alloys: An observable signature of electronic effects

Complex concentrated alloys (CCAs) are of growing interest due to their outstanding mechanical properties that exceed the property limits of conventional alloys. Whereas the superior properties are often attributed to severe lattice distortion, to date it is not clear what controls the lattice distortion and how it affects the mechanical properties of CCAs. In this work, we study the element-resolved local lattice distortion (ELLD) in CCAs of 3d transition-metal elements (3d CCAs) by the extended X-ray absorption fine structure experiment and the density-functional theory calculations. We show that ELLD is primarily dependent upon charge transfer among elements and affects the properties through atomic-level pressure and orbital transition. The ELLD provides a qualitative measure of the effective atomic size for explaining element-specific properties and macroscopic properties.

Microstructure and optical properties of AgCuAl medium entropy films with nanoparticles induced by pulsed-laser dewetting

AgCuAl equimolar complex concentrated alloy (CCA) thin films are deposited on glass substrates using a high-vacuum sputtering system. The films are annealed at 400 °C for 5 min to stabilize the structure and are then dewetted using a NIR pulsed-laser system at various pulse powers, repetition rates and scan speeds to form nanoparticles. It is shown that the dewetting process prompts a diffusion of the Al atoms toward the glass substrate. The resulting low concentration of Al within the AgCuAl film results in the formation of CCA nanoparticles consisting mainly of Ag and Cu with neither elemental segregation nor phase separation. The nanoparticles exhibit local surface plasmon resonance (LSPR) peaks at wavelengths in the range of 510–550 nm. The nanoparticle size and peak wavelength vary linearly with the accumulated energy density, which is controllable through the dewetting parameters. Overall, the present results suggest that AgCuAl CCA thin films have significant potential for such applications as tuning the absorption wavelength peak.

Insights into Defect-Mediated Nucleation of Equilibrium B2 Phase in Face-Centered Cubic High-Entropy Alloys

Though a fine-scale second-phase distribution is a potent strengthening mechanism for alloys, achieving a high precipitate density is often difficult owing to sluggish precipitation kinetics and limited nucleation sites. More specifically, in case of transition-element-based complex concentrated alloys (CCAs) or high-entropy alloys (HEAs), precipitation of the equilibrium strengthening phase, such as the ordered B2 phase, can be limited due to its high nucleation barrier for homogeneous precipitation within the face-centered cubic (FCC) matrix. This can lead to competing homogeneous nucleation of a metastable ordered L12 phase, which has a substantially lower nucleation barrier since it is isostructural with the FCC matrix. Using three different CCAs/HEAs as examples, thermomechanical processing has been employed to introduce a large number density of homogeneously distributed heterogeneous nucleation sites within the FCC matrix, to manipulate the phase fraction, morphology, and distribution of B2 precipitates. This approach of tailoring the microstructure is widely applicable to other multicomponent alloys.

Tuning the degree of chemical ordering in the solid solution of a complex concentrated alloy and its impact on mechanical properties

Using the binary enthalpies of mixing in a Co-Cr-Fe-Ni base alloy system, a high entropy alloy (HEA) or complex concentrated alloy (CCA), the equiatomic CoFeNi has been identified, which should form a random solid solution. Subsequent experimental validation established that this alloy is indeed a near-ideal, random face centered cubic (FCC) solid solution. The same thermodynamic basis has been employed to systematically engineer the degree of chemical ordering within the random CoFeNi alloy, from localized domains of short-range ordering (SRO), also referred to as clustered ordering, to well-defined long-range ordered (LRO) domains, by adding controlled amounts of Al and Ti, since these elements have a strong ordering tendency (negative enthalpy of mixing) with Co, Fe, and Ni. A series of seven alloys were designed in this study, based on enthalpies of mixing among 3d transition metals. This change in the degree of chemical ordering has a strong influence on the tensile yield strength of the alloy, for the same nominal grain size, ranging from ~181 MPa in case of CoFeNi to ~793 MPa in case of the Al0.3Ti0.2Co0.7FeNi1.7 CCA. These experimentally measured yield strengths of the candidate CCAs are in close agreement with predicted values afforded by simple strengthening models.

Designing [formula omitted]-strengthened Al-Cr-Fe-Ni-Ti complex concentrated alloys for high temperature applications

For alloys with nanoprecipitate/matrix microstructures, the lattice coherency between the two phases plays an important role in determining the mechanical performances at high temperature. In this work, we systematically investigate the AlxCr13.3Fe71.5-xNi11.2Ti4 (x=8, 10, 12, 14, 16 at%) complex concentrated alloys with an aim to enhance the lattice coherency between the BCC matrix and L21 precipitate. The precipitate microstructures, lattice misfit and the resultant coherency strain evolution are comprehensively studied. With increasing Al from 8 at% to 16 at%, the interfacial structure gradually transforms from semicoherent to fully coherent interface by the decrease in precipitate size and lattice misfit, which leads to the stronger elastic interaction between the matrix and precipitate. Meanwhile, the crystal structure of precipitate is slightly distorted from cubic to tetragonal. The yield strength of alloys at room temperature continuously increases with the addition of Al by the solid-solution strengthening and precipitation hardening effect. Here, the mechanism of precipitation hardening changes from Orowan process to coherency strengthening. Interestingly, the strengthening effect by Al addition is further amplified in the tensile test at 700 °C. The higher degree of lattice coherency and the distorted structure of the precipitate resulting from the Al addition lead to the effective strain transfer and the stronger precipitate, respectively. Therefore, the Al16Cr13.3Fe55.5Ni11.2Ti4 alloy exhibits an excellent combination of yield strength (400.8 MPa) and ultimate tensile strength (572.9 MPa). These values are much higher than those of the previously reported nanoprecipiate-strengthened alloys, suggesting that the alloy is highly promising as high temperature structural applications.

Machine learning of phases and mechanical properties in complex concentrated alloys

The mechanical properties of complex concentrated alloys (CCAs) depend on their formed phases and corresponding microstructures. The data-driven prediction of the phase formation and associated mechanical properties is essential to discovering novel CCAs. The present work collects 557 samples of various chemical compositions, comprising 61 amorphous, 167 single-phase crystalline, and 329 multi-phases crystalline CCAs. Three classification models are developed with high accuracies to category and understand the formed phases of CCAs. Also, two regression models are constructed to predict the hardness and ultimate tensile strength of CCAs, and the correlation coefficient of the random forest regression model is greater than 0.9 for both of two targeted properties. Furthermore, the Shapley additive explanation (SHAP) values are calculated, and accordingly four most important features are identified. A significant finding in the SHAP values is that there exists a critical value in each of the top four features, which provides an easy and fast assessment in the design of improved mechanical properties of CCAs. The present work demonstrates the great potential of machine learning in the design of advanced CCAs.

High entropy alloys – Tunability of deformation mechanisms through integration of compositional and microstructural domains

The paradigm shift of alloying approach that led to high entropy alloys (HEAs) is now well established. Although the initial years were dominated by equiatomic approach, recent years have seen expansion in non-equiatomic compositional space that can be termed as complex concentrated alloys (CCAs). These HEAs/CCAs provide opportunities for tunable performance by manipulating deformation mechanisms. Understanding has advanced to the point that certain aspects of core effects (entropy of mixing, lattice distortion, sluggish diffusion, and cocktail effect) can be critically examined. In addition, new aspects of metastability engineering and emergence of a wide range of processing strategies has put this field on an exponential growth path. In this review, we categorize the compositional and microstructural approaches that exhibit potential for a combination of shear induced phase transformation and twinning, thereby expanding beyond the slip based mechanisms. The emerging HEAs give greater flexibility for tailoring transformation-induced plasticity (TRIP) and twinning-induced plasticity (TWIP), which have guided design of next-generation steels over the last 20 years to a new level. For TRIP HEAs, the ductility can be extended to as high as 50% while maintaining a strength exceeding 1 GPa. On the other hand, hierarchical microstructural engineering in Al x CoCrFeNi alloys can lead to over 2 GPa strength and >10% ductility. Observations of evolving c/a ratio in HCP phase of certain HEAs hint at possibility of new micromechanisms. While crack tip twin-bridging has been shown as a key mechanism to extend the toughness, concurrent phase transformation at the crack tip has been shown to push the fatigue endurance limit. Tunability of deformation mechanisms in HEAs is unprecedented as compared to the conventional metallic materials, particularly in compositions that exhibit shear induced transformation. The opportunities can be further enhanced by integrating the compositional and microstructure domains, and these aspects are highlighted in this review. The microstructural tailoring can take advantage of high enthalpy states in metastable HEAs with low stacking fault energy values of < 40 mJ m −2 . The range of microstructural engineering in HEAs include, heterogeneous grain structure, duplex and triplex microstructures with intermetallic phases, twinning engineered microstructure, coherent boundary engineered microstructure, and dual-phase and triple-phase microstructure with solid solution phases.

Anomalous dislocation core structure in shock compressed bcc high-entropy alloys

Recent studies of complex concentrated alloys suggest unusual dislocation core structure and motion, thanks to a collective concentration/structural inhomogeneity. Less is known whether these effects also work in extreme conditions where the solid solution effect is overwhelmed by the large driving force. Here, we investigate the dislocation structure behind a shock-wave front in bcc high-entropy alloys (HEAs) using large-scale molecular dynamics (MD) simulations. In contrast to bcc elemental metals, we find anomalous “extended“ edge dislocation structure (6 ~ 8 Burgers vector) with high stability in shock compressed TiZrNb and NiCoFeTi HEAs. The unique dislocation structures can facilitate faster dislocation motion, thus deterring the early nucleation of deformation twins. Combined with continuum elasticity theory, we show that the “extended“ dislocation structure can be attributed to the presence of local structures with low elastic stability that are imparted by the nanoscale chemical heterogeneities in HEAs. We also show how the dislocation structures are affected by the interatomic potentials.

Microstructural evolution and mechanisms in additively manufactured AlCrCuFeNix complex concentrated alloys via selective laser melting

This article discusses the influence of the Ni content on the microstructures of AlCrCuFeNix complex concentrated alloys prepared by selective laser melting. The microstructural evolution mechanisms were also uncovered. It is found that the as-built Ni1.0 alloy possesses equiaxed-columnar bimodal grain structures and basket-weave microstructure consisting of striped body-centered cubic (bcc) nano-precipitates and ordered bcc (B2) phase. Adding Ni triggers the lattice transition from B2 to face-centered cubic (fcc), leading to the change of the primary solidification phase from B2 to fcc beyond the critical content of Ni. Meanwhile, the striped bcc nano-precipitates inside the B2 lamellae gradually transform into spherical morphologies due to the consumption of Fe and Cr solutes in eutectic reaction. Furthermore, the microstructures change from hypo-eutectic (Ni2.0, Ni2.5) to near-eutectic (Ni3.0) to hyper-eutectic (Ni3.5), accompanied by a columnar-to-equiaxed transformation due to the large constitutional supercooling induced by the eutectic reaction.

Complex Concentrated Alloys for Substitution of Critical Raw Materials in Applications for Extreme Conditions.

The paper is proposing a mini-review on the capability of the new complex concentrated alloys (CCAs) to substitute or reduce the use of critical raw materials in applications for extreme conditions. Aspects regarding the regulations and expectations formulated by the European Union in the most recent reports on the critical raw materials were presented concisely. A general evaluation was performed on the CCAs concept and the research directions. The advantages of using critical metals for particular applications were presented to acknowledge the difficulty in the substitution of such elements with other materials. In order to establish the level of involvement of CCAs in the reduction of critical metal in extreme environment applications, a presentation was made of the previous achievements in the field and the potential for the reduction of critical metal content through the use of multi-component compositions.

A comparative study of solid-solution strengthening in Cr-Co-Ni complex concentrated alloys: The effect of magnetism

The effect of magnetism on the solid solution strengthening (SSS) of CrxCoyNi1–x–y alloys formulated by Varvenne’s and Toda-Caraballo’s (TC’s) models has been investigated comparatively by first-principles. It is found that for a reliable estimation of the model parameters for the paramagnetic (PM) and ferromagnetic (FM) alloys one should adopt the atomic radii and elastic moduli of the constituent metals corresponding to the same magnetic state. Furthermore, we show that Varvenne’s model underestimates the SSS when compared to the experimental data, while TC’s model correctly predicts the SSS of PM CrxCoyNi1–x–y alloys when adopting the PM parameters as inputs. Therefore, the magnetic states should be correctly accounted when estimating the atomic radii and elastic moduli of the constituent elements as input parameters for both models to capture the SSS in complex concentrated alloys properly.

Grain boundary phase transformation in a CrCoNi complex concentrated alloy

The phase-transformation-like behavior of grain boundaries, where their chemistry, structure and properties change discontinuously, is emerging as a fundamental interest in the context of grain boundary engineering. The cases studied so far pertain primarily to elemental metals and dilute alloy systems. The next step of complexity would be a system still of a single phase structure but involving multiple and concentrated elements. The recently emerging high/medium entropy alloys (H/MEAs), alternatively known as complex concentration alloys (CCAs), fit the bill in this regard. Here we use CoCrNi as a model CCA to highlight that intricate interatomic interactions influence the grain boundary element distribution and consequently phase transitions. By combining classical molecular dynamics simulations and first-principles density functional theory calculations, we reveal that grain boundary phase transition temperature is sensitive to the grain boundary atomic configuration. The CCA grain boundary with random atomic distribution is more apt to transform due to a larger thermodynamic driving force and faster diffusion kinetics, compared to a hypothetical reference that bears the same bulk properties but no distinguishable constituent components. In contrast, when the three elements redistribute with local Ni-clustering and Co–Cr ordering in the grain boundary structure, diffusion is rendered more sluggish, delaying grain boundary phase transformation. Our work is a step forward in understanding critical phenomena in grain boundaries and CCAs, and enriches the knowledge base for materials design via grain boundary engineering.

Theory of solid solution strengthening of BCC Chemically Complex Alloys

An analytic model describing substitutional solid solution strengthening in body-centered cubic (BCC) complex, concentrated alloys (CCAs) based on a/2<111> screw dislocation mobility is developed and presented. At lower temperatures it is assumed that dipole dragging is the rate limiting strengthening mechanism, and as the temperature increases this changes to a jog dragging mechanism. While both mechanisms are contained in Suzuki's classical model for substitutional solid solution strengthening developed for BCC alloys significant modifications are required to apply such a model to the refractory CCA's. First, two approaches for incorporating the net effects of the complex solute chemistry are developed and contrasted using a ternary NbTaTi alloy and four quaternary alloys, MoNbTaTi, WNbTaTi, CrMoNbTi and CrMoTaTi . Our model is extended to higher temperatures and applied to analyze experimental yield data as a function of temperature (0.15–0.7TL, where TL is the absolute liquidus temperature) and strain rate (10−5 to 10−2/s) in a range of BCC chemically complex alloys including stoichiometric NbTiZr and HfNbTaTiZr. We find that the model, based on just these two mechanisms, gives excellent agreement with experimental yield data in both these BCC CCAs, NbTiZr and HfNbTaTiZr. The experimental yield data of these two BCC CCA's as well as NbTaTi and four quaternaries are also analyzed using Maresca's edge dislocation model developed for these types of alloys. The screw model presented is useful in predicting BCC CCAs with adequate high temperature strength, which will accelerate development of high temperature, high strength BCC alloys for aerospace applications.

Dilatational strain biplots against enthalpy of mixing for predicting high-entropy alloys and complex concentrated alloys phase stability

Multiple principal component alloy systems are a new class of alloys that can provide interesting combinations of functional and mechanical properties. Due to the multiple principal components, their interactions are complex, and their structural stabilities are often not easily predicted. Prediction parameter biplots offer a good way to distinguish between structural stabilities of different compositions. The enthalpy of mixing is one parameter that is often used in such biplots. Although it does not accurately follow quantum principles, it is nevertheless this deviation that gives it its predictive power when combined with other parameters in a biplot. This deviation can be in part attributed to the mechanical strain energy (from large atomic size difference) that may be present in alloy systems. Such a biplot can leverage on their expected deviations to provide a prediction scheme. Here, we investigate the predictive efficacy of enthalpy-of-mixing/strain-energy biplots using cluster analysis. The results are validated against enthalpy-of-mixing/valence electron concentration biplots. The investigated biplot not only maintains the ability to distinguish between the intermetallic and solid solutions phases but offers enhanced ability to distinguish between individual intermetallic phases (Sigma, Laves, Mu, and B2).

Preface

The development of new materials drives the progress of human society, which experienced the stone age, the iron age, the steam engine age, and the information age. Metal and alloys were considered as state of art materials for structural applications for centuries. For example, during the XX century progress in metallurgy has enabled the humanity to build cars, planes, and space rockets, i.e. to create modern transportation industry. However, currently metallic alloys face severe competition from other materials like plastics, ceramics, composites, etc. To widen the application range of metals and alloys, we need to obtain alloy materials with superior combinations of different properties for daily life, national defense, and outer space exploration.In recent years, “high-entropy alloys (HEAs)” or “complex concentrated alloys (CCAs)”, consisting of equal or near equal atomic multi-elements, have attracted a large number of scholars from different fields. HEAs/CCAs belong to central, weakly explored, areas of multicomponent phase diagrams, and thus can have unique structures and properties. For example, it was found that they can have superior mechanical properties in a wide temperature range (from cryogenic to extremely high temperatures). Recently, it has been shown that they also demonstrate promising functional properties. Moreover, extension of HEAs/CCAs concept to other, non-metallic materials has brought us new classes of materials like high entropy ceramics, high entropy intermetallics, etc. These new materials can also have unique structural and functional properties.Therefore, International Conference and Annual School of Young Scientists: “Synthesis, structure and properties of high entropy materials” is organized and held at Belgorod State University. The main aim of the school is to gather the young scientists interested in HEAs and related materials and give them the platform to listen to established international experts in the field and share their own research. The first School was successfully held on October 9-11, 2019 with 17 invited speakers and more than 60 attendees. Despite the Coronavirus pandemic, the next meeting was held on October 14-16, 2020. The Conference and School has attracted 11 invited speakers and more than 80 young scientists. The topics of interest included:High- and medium-entropy alloys, complex concentrated alloys, methods of their preparation, structure, mechanical and functional properties, phase stability and structural phase transformations, deformation mechanisms, diffusion and ordering processes.High-entropy and complex concentrated coatings, methods of their preparation, structure, and properties.High-entropy ceramics, methods of their preparation, structure, and properties.Research and development of new complex concentrated materials for technology and medicine, including nanostructured materials, microstructural design of multicomponent materials, prospects for practical application.Advanced methods of obtaining and processing metallic and non-metallic materials for structural and functional applications, including additive technologies, new casting, powder metallurgy, welding, surface treatment technologies.Other promising directions in the development of new metallic and non-metallic materials.Computational modeling of complex concentrated alloys, coatings, and ceramics in different environments.The selected works presented at the International Conference and Annual School of Young Scientists 2020: “Synthesis, structure and properties of high entropy materials” are published in this special issue. The School was supported by Russian Science Foundation Grant № 19-79-30066.Organizing committee:Gennady SalishchevAnderey RempelNikolay RepnikovYuri ChumlyakovNikolay KashaevVladimir SaninYulia IvanisenkoIrina KireevaDmitry LuzginEvgeniy TrofimovElena AstafurovaDmitry MoskovskikhSergey ZherebtsovNikita StepanovAlexey LipnitskyMarina Tikhonova

Enhancing Strength-Ductility Synergy of a Co-Free Complex-Concentrated Alloy Via Tailored Multi-Heterogeneous Microstructure

The development of high-performance alloys with excellent strength-ductility synergy is a long-lasting research theme for materials science community, which also holds for the newly emerged complex-concentrated alloys (CCAs). Here, a multi-heterogeneous microstructure: featuring a multiscale grain distribution involving recrystallized ultrafine and fine grains mixed with unrecrystallized coarse grains, and high-content L1 2 nanoprecipitates, was intentionally introduced into a Co-free CCA through appropriate thermomechanical processing strategy. As such, the hetero-deformation induced (HDI) hardening and precipitation strengthening were co-effectively used, resulting in a high yield strength of 1.2 GPa, and an ultimate tensile strength of 1.4 GPa with exceptional uniform elongation of ~17.6%. The strength-ductility synergy of the multi-hetero microstructure was much enhanced over its precipitate-strengthened counterparts without heterogenous grains. We demonstrated that the high yield strength is mainly due to both the precipitate strengthening from nanoprecipitates and HDI strengthening from heterogeneous grains distribution. Benefiting from the structurally incompatible deformation accompanying with copious geometrically necessary dislocations near the hetero-interfaces, such multi-hetero microstructure revealed a distinctive up-turn strain hardening behavior due to the HDI hardening upon straining, and thus delayed the onset of plastic instability. Particularly, the unique lamellar-like distribution between recrystallized fine and ultrafine grains with high density of interfaces could effectively induce massive HDI hardening during deformation. The processing strategy described here is relatively simple and desirable for large scale process in modern industry at an economic cost.

Discontinuous precipitation leading to nano-rod intermetallic precipitates in an Al0.2Ti0.3Co1.5CrFeNi1.5 high entropy alloy results in an excellent strength-ductility combination

The phenomenon of discontinuous precipitation (DP) leading to the formation of nano-rod FCC (γ) + L12 (γ’) colonies, has been typically considered deleterious for mechanical properties. However, the present study shows clear evidence that substantially large fractions of FCC + nano-rod L12 microstructure within a thermo-mechanically processed high entropy alloys (HEA) or complex concentrated alloys (CCA) of composition Al0.2Ti0.3Co1.5CrFeNi1.5, formed via recrystallization coupled with discontinuous precipitation, can lead to an excellent combination of room temperature strength and ductility. The extent of thermomechanical processing can be engineered to modify the phase transformation pathway from homogenous L12 precipitation to discontinuous L12 precipitation in the same HEA. This predominantly FCC + nano-rod L12 microstructure exhibits a yield stress ~1.4 GPa, ultimate tensile strength ~1.6 GPa, and tensile ductility of ~14%, making it one of the best combinations of room temperature tensile properties for FCC-based HEAs, that have been reported to date, as well as better than current generation wrought nickel base superalloys. A high yield strength of the order of ~1 GPa is also retained to a temperature of 500 °C in this alloy. However, at higher temperatures (>550 °C), the DP microstructures exhibit a rapid decline in strength and become less competitive as compared to microstructures consisting of homogeneously precipitated L12 within the FCC matrix.