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Design and development of novel high entropy alloys (HEAs) having balance magnetic properties with other functional properties are vital for industrial applications of these alloys. In this study, a novel Co35Cr5Fe10Ni30Ti5Al15 HEA was synthesized through mechanical alloying and studied for phase evolution and its effects on magnetic properties with annealing at different temperatures. As-synthesized HEA has a major fcc phase with minor concentrations of bcc and R phases. The as-synthesized HEA is also annealed at different temperatures of 500, 700 and 900°C and found that the phase identity of formed phases maintained after annealing. However, for HEA annealed at 1000°C, slight amount of new σ-phase has formed along with initial phases. Values of Ms and Hc were found to be 75 emu g−1 and 18 Oe for as-synthesized Co35Cr5Fe10Ni30Ti5Al15 HEA. We found that after annealing at different temperatures, magnetic properties of Co35Cr5Fe10Ni30Ti5Al15 HEA show significant improvement. Co35Cr5Fe10Ni30Ti5Al15 HEA annealed at 900°C exhibited good soft magnetic characteristics with high Ms (99 emu g−1), low values of Hc (3.8 Oe) and Mr (0.45 emu g−1), as compared to other samples developed in the present study. Thus, designed and developed 900°C annealed Co35Cr5Fe10Ni30Ti5Al15 HEA can be further used for magnetic switching applications due to the high value of Ms and low value of Mr. [ABSTRACT FROM AUTHOR]

Soft magnetic high entropy alloys (HEAs) have great potential to be used as industrial material because of their good magnetic properties and balanced mechanical, electrical, and corrosion resistance properties. To further optimize high saturation magnetization (Ms) along with other functional properties, it is critical to understand the effect of Mn, Cu, and Al on the magnetic properties and phase evolution of FeCoNi-based magnetic HEAs. In the present study, a combinatorial approach is adopted to optimize the magnetic properties of Co35 Fe10Ni30Ti20M5 (M = Mn, Cu, and Al) HEA through the variation of a single alloying element and its effects on the phase evolution, microstructure, and magnetic properties. Co35Fe10Ni30Ti20Mn5, Co35Fe10Ni30Ti20Cu5, and Co35 Fe10Ni30Ti20Al5 high entropy alloys were synthesized through mechanical alloying, and the as-synthesized HEAs were comprised of fcc and bcc solid solution phases. The as-synthesized Co35Fe10Ni30Ti20Mn5, Co35Fe10Ni30Ti20Cu5, and Co35Fe10Ni30Ti20Al5 HEAs have the value of saturation magnetization (Ms)- 81, 85 & 79 emu/g and coercivity (Hc)- 18, 28 & 27 Oe respectively. The phase stability of the developed alloys was also investigated through vacuum annealing at 700°C for 2 h duration. After vacuum annealing, both the Ms and Hc increased to 90 emu/g & 37 Oe, 105 emu/g & 43 Oe, and 104 emu/g & 46 Oe, respectively, for Mn, Cu, and Al – containing Co35Fe10Ni30Ti20M5 (M = Mn, Cu, and Al) HEAs. The present study provides a detailed insight into how the variation of a single alloying element and the annealing temperature significantly affect the magnetic properties of CoFeNiTi-based HEA. [ABSTRACT FROM AUTHOR]

• A novel Co 35 Cr 5 Fe 20 Ni 20 Ti 20 HEA was synthesized through MA. • Co 35 Cr 5 Fe 20 Ni 20 Ti 20 HEA exhibits mixture FCC and BCC Phase. • Synthesized Co 35 Cr 5 Fe 20 Ni 20 Ti 20 HEA has low H c. • 200 °C annealed Co 35 Cr 5 Fe 20 Ni 20 Ti 20 HEA has high Ms. • Found Ms for annealed Co 35 Cr 5 Fe 20 Ni 20 Ti 20 HEA is highest for CoCrFeNiTi based HEA. A novel Co 35 Cr 5 Fe 20 Ni 20 Ti 20 high entropy alloy (HEA) is synthesized through mechanical alloying (MA). The synthesized HEA is comprised of mixture of FCC and BCC phases and exhibits soft magnetic properties with M s = 46 emu/g and H c = 15 Oe. After annealing at 200 °C, the value of Ms is increased approximately two times and coercivity remains the same to as synthesized HEA. The found value of Ms (81 emu/g) is the highest value of Ms for the CoCrFeNiTi-based HEA, reported so far. [ABSTRACT FROM AUTHOR]

The present report describes phase formation, magnetic and corrosion behavior of the AlCrFeMnNiTi high entropy alloy (HEA) synthesized through mechanical alloying. Simple solid solution of FCC and BCC phases are evolved after 25 h of MA. DSC analysis confirms that the synthesized phases of AlCrFeMnNiTi HEA are stable up to 550 °C and a re-crystallization is occurred at temperature greater than 550 °C. In order to investigate the effect of annealing on phase formation and magnetic characteristics, the synthesized HEA was annealed at 700 °C for 1 h and found that the volume fraction of BCC phase decreased. The synthesized HEA shows better ferromagnetic behavior with Ms = 17.55 emu/g and Hc = 153.8 Oe as compared to some of the recently reported HEAs and previously reported CrFeMnNiTi HEA by us. Moreover, corrosion behavior of the annealed AlCrFeMnNiTi high entropy alloy in 0.5 M and 1 M NaCl solution is also investigated. It is found that the annealed HEA shows good corrosion resistance in 0.5 M NaCl solution due to the presence of Al. [ABSTRACT FROM AUTHOR]

Highlights • Effect of annealing condition on magnetic properties of TiFeNiCrMn HEA is investigated. • FCC, BCC and a minor sigma phase has been evolved for in synthesized TiFeNiCrCo HEA. • Synthesized HEA was annealed under vacuum and open air at 500 and 700 oC. • Oxide (Mn 2 O 3) and a spinel type (Fe,Ti) 3 O 4 phases are evolved after open air annealing. • Spinel phase formation in HEAs open new area for magnetic properties of HEAs. Graphical abstract (a) Volume fraction of formed phases in different samples (b) Ms. and Hc of samples (1,2,3,4,5 represents the SA-1, SA-2, SA-3, SA-4 and SA-5 respectively. Abstract An equiatomic CrFeMnNiTi high entropy alloy (HEA) was synthesized through mechanical alloying (MA) technique. The synthesized HEA consists of FCC, BCC and a minor σ-phase. In order to investigate the phase evolution and magnetic characteristics, the synthesized HEA was annealed under different conditions (vacuum and open air) at two different temperatures (500 and 700 °C). After vacuum annealing at 500 and 700 °C the volume fraction of FCC and BCC phases are changed. However, after open air annealing, the volume fraction of synthesized phases (FCC and BCC) is altered effectively along with the formation of an oxide (Mn 2 O 3) and a spinel type (Fe,Ti) 3 O 4 phase. The synthesized sample exhibits ferromagnetic characteristic and the value of saturation magnetization (Ms) and coercivity (Hc) are found to be 13.39 emu/g (A-m2/kg) and 162.2Oe (12.9 × 103 A/m) respectively. After annealing in vacuum and open air at 700 °C the value of Ms. is found to be 2.95 and 11.63 emu/g (A-m2/kg) respectively. Open air annealed sample at 500 °C shows better magnetic characteristics with Ms = 32.85 emu/g (A-m2/kg) and Hc = 159.34Oe (12.67 × 103 A/m) as compared to the synthesized and annealed samples. The enhanced value of Ms for open air annealed HEA at 500 °C corresponds to increase in the volume fraction of BCC phase and the formation of Mn 2 O 3 and (Fe,Ti) 3 O 4 spinel phase. The effect of annealing conditions on the phase formation and their correlation with magnetic characteristic are discussed and described in detail. [ABSTRACT FROM AUTHOR]

The report describes the effect of elemental addition (Mn and Co) on the phase evolution and magnetic properties of equiatomic TiFeNiCr based high entropy alloys (HEAs). HEAs were synthesized through mechanical alloying (MA) of constituent elements for different milling duration. XRD analysis confirms that simple solid solution of face cantered cubic structure is formed for all the three selected HEAs. Double FCC and a sigma phase are evolved for TiFeNiCr and TiFeNiCrMn HEAs. However, for TiFeNiCrCo HEA single FCC phase is formed. Synthesized HEAs show soft magnetic characteristics and the value of saturation magnetization increases as the content of magnetic element increases. Moreover, the investigation also describes the effect of annealing on phase evolution and magnetic properties of synthesized HEAs. The value of saturation magnetization altered for annealed TiFeNiCrM (M = Mn, Co) HEAs. [ABSTRACT FROM AUTHOR]

Abstract: In the present study, we have investigated the combined effect of different transition metals such as Ti, Fe and Ni on the de/rehydrogenation characteristics of nano MgH2. Mechanical milling of MgH2 with 5 wt% each of Ti, Fe and Ni for 24 h at 12 atm of H2 pressure lead to the formation of nano MgH2-Ti5Fe5Ni5. The decomposition temperature of nano MgH2-Ti5Fe5Ni5 is lowered by 90 °C as compared to nano MgH2 alone. It is also found that the nano MgH2-Ti5Fe5Ni5 absorbs 5.3 wt% within 15 min at 270 °C and 12 atm hydrogen pressures. However, nano MgH2 reabsorbs only 4.2 wt% under identical condition. An interesting result of the present study is that mechanical milling of MgH2 separately with Fe and Ni besides refinement in particle size also leads to the formation of alloys Mg2NiH4 and Mg2FeH6 respectively. On the other hand, when MgH2 is mechanically milled together with Ti, Fe and Ni, the dominant result is the formation of nano particles of MgH2. Moreover the activation energy for dehydrogenation of nano MgH2 co-catalyzed with Ti, Fe and Ni is 45.67 kJ/mol which is 35.71 kJ/mol lower as compared to activation energy of nano MgH2 (81.34 kJ/mol). These results are one of the most significant in regard to improvement in de/rehydrogenation characteristics of known MgH2 catalyzed through transition metal elements. [Copyright &y& Elsevier]

• A novel low-density HEA were synthesized through MA. • Synthesized Al 20 Fe 20 Mg 20 Ni 20 Ti 20 HEA is comprised of the mixture of bcc and fcc phase. • Al 20 Fe 20 Mg 20 Ni 20 Ti 20 HEA showed good semi-hard magnetic characteristics. • The effect of annealing on phase evolution and magnetic behavior was also investigated. A relatively low density nanocrystalline high entropy alloy (HEA) with a nominal composition of Al 20 Fe 20 Mg 20 Ni 20 Ti 20 is synthesized through the mechanical alloying process. The synthesized HEA is comprised of the mixture of bcc and fcc solid solution with crystallite size of the order of 6 to 7 nm. To understand the phase stability, the synthesized HEA is annealed at 200 °C and 500 °C for 2 hr. The 200 °C annealed HEA does not show any significant change in the XRD pattern. However, annealing at 500 °C affects the relative volume fraction of the formed phases. The synthesized Al 20 Fe 20 Mg 20 Ni 20 Ti 20 HEA showed better magnetic characteristics with Ms (54.28 emu/g) and Hc (43.4 Oe) as compared to the many of recently reported HEAs. Moreover, for 200 °C annealed HEA, the found value of Ms (54.92 emu/g) and Hc (42.4 Oe) is similar to the as-synthesized HEA. An interesting change in magnetic behaviour has been observed after annealing at 500 °C, which may be related to the change in the fcc to bcc phase volume and change in the lattice parameter of these phases. [ABSTRACT FROM AUTHOR]

High Entropy Alloys (HEAs) are advanced materials having multi-functional properties. These materials have the potential to overcome the shortcomings of conventional soft magnetic alloys. In this study, an integrative approach is adopted to enhance the magnetic and electrical properties of CoCrFeNiTi-based HEA by the addition of Al in different content for Ti and annealing for different temperatures and durations. Firstly, Co 35 Cr 5 Fe 10 Ni 30 Ti 20-x Al x (x= 10, 15, 20) HEAs were synthesized through mechanical alloying and investigated for phase formation and magnetic properties. Major fcc with minor bcc and intermetallic R phase has formed for Co 35 Cr 5 Fe 10 Ni 30 Ti 10 Al 10 and Co 35 Cr 5 Fe 10 Ni 30 Ti 5 Al 15 HEAs. However, the mixture of fcc and bcc phase with a minor fraction of σ phase has been found for Co 35 Cr 5 Fe 10 Ni 30 Al 20 HEA. The value of M s is slightly decreased for Co 35 Cr 5 Fe 10 Ni 30 Ti 5 Al 15 HEA as compared to Co 35 Cr 5 Fe 10 Ni 30 Ti 10 Al 10 HEA, but for Co 35 Cr 5 Fe 10 Ni 30 Al 20 HEA, the value of M s has drastically decreased when Ti completely removed for Al. Among these three synthesized HEAs, the highest value of Ms is found for Co 35 Cr 5 Fe 10 Ni 30 Ti 10 Al 10 HEA (Ms=78 emu/g). Further, we investigated the effect of annealing at different temperatures for 2 h on phase evolution, microstructure, and their correlation with magnetic properties of Co 35 Cr 5 Fe 10 Ni 30 Ti 10 Al 10 HEA. Among annealed HEA, 700°C annealed Co 35 Cr 5 Fe 10 Ni 30 Ti 10 Al 10 HEA has high Ms (104 emu/g), and the value of Hc was found to be 29 Oe. The long-duration annealing is also performed at 700°C for 10 h to improve the magnetic properties of the as-synthesized Co 35 Cr 5 Fe 10 Ni 30 Ti 10 Al 10 HEA and found good soft magnetic behaviour (Ms=103.5 emu/g and Hc=13 Oe). Moreover, the electrical resistivity of the long-duration annealed Co 35 Cr 5 Fe 10 Ni 30 Ti 10 Al 10 HEA is also recorded in the temperature range 2–350 K, and the value of electrical resistivity at 2 K and 300 K is found to be 180.2 ×102 µΩ.cm and 200.80 ×102 µΩ.cm, respectively. The found value of electrical resistivity is the highest value of resistivity reported so far in the case of soft magnetic HEA. [Display omitted] • Integrative approach adopted to improve soft Magnetic properties of HEA. • Novel Co 35 Cr 5 Fe 10 Ni 30 Ti 10 Al 10 HEA was optimized for better magnetic properties. • The developed HEA has highest value of resistivity reported so far. • Optimized Co 35 Cr 5 Fe 10 Ni 30 Ti 10 Al 10 HEA can use as a soft magnet with minimum core loss. [ABSTRACT FROM AUTHOR]

Previously, we designed and developed a promising excellent soft magnetic Co 35 Cr 5 Fe 10 Ni 30 Ti 20 High Entropy Alloy (HEA) through mechanical alloying (MA) followed by annealing at 790 ̊C. Densification of the powder sample synthesized through MA is critical for industrial a pplications, particularly as amagnetic material. Therefore, in the present study,optimizedCo 35 Cr 5 Fe 10 Ni 30 Ti 20 HEA is synthesized again through the radio frequency (RF) induction melting.The X-ray diffraction (XRD) analysis of the RF induction melted HEA revealed the formation of mixture of fcc and ordered B2 phase. The phase stability of synthesized HEA has also been investigated through annealing at 790 °C for 2 h. Thesynthesized HEA maintained its phase identity after annealing. The synthesized and annealed Co 35 Cr 5 Fe 10 Ni 30 Ti 20 HEAs showed ferromagnetic behavior with high saturation magnetization (M s) and low coercivity (H c). For as-synthesized Co 35 Cr 5 Fe 10 Ni 30 Ti 20 HEA, the value of M s and H c is found to be 80.22 emu/g and 4.63 Oe, respectively. However, after annealing, the value of H c is increased to 7.89 Oe, while M s remained same to as synthesized HEA.Vickers hardness test was also performed on the synthesized and annealed HEAs. The results displayed that hardness increased after annealing upto 512.50 Hv. The present studynot only investigates phase formation and magnetic properties of RF induction melted HEA but it also emphasizes the effect of the processing route on the structural, magnetic, and mechanical properties of the most promising magnetic Co 35 Cr 5 Fe 10 Ni 30 Ti 20 HEA. The found value of hardness for the RF- melted Co 35 Cr 5 Fe 10 Ni 30 Ti 20 HEA is excellent as compared to the conventional soft magnetic materials such as polycrystalline Fe (100–150 Hv), Fe 50 Ni 50 (120 Hv) etc. The present investigation is also important for the industrial development of the magnetic Co 35 Cr 5 Fe 10 Ni 30 Ti 20 HEA. • A promising Co 35 Cr 5 Fe 10 Ni 30 Ti 20 HEA is synthesized through RF-melting. • The synthesized HEA has mixture of fcc and B2 phase. • The synthesized phases are stable after annealing at 790 C. • The found value of Ms and Hc for synthesized and annealed HEA are 80.22 emu/g &4.63 Oe and 79.70 emu/g, &7.89 Oe respectively. • The hardness value of annealed HEA (512.50 HV) is highest as compared to most of conventional soft magnets. [ABSTRACT FROM AUTHOR]

The present study investigates the effect of different annealing temperatures on phase formation, microstructure, and their correlation with magnetic properties of a promising soft magnetic Co 35 Cr 5 Fe 10 Ni 30 Ti 20 High Entropy Alloy (HEA) design developed by our research group previously. We reproduced the Co 35 Cr 5 Fe 10 Ni 30 Ti 20 HEA through the mechanical alloying and found the mixture of fcc and R-phase having M s = 74.8 emu/g and H c = 12.92 Oe. The different annealing temperature was decided based on the DTA analysis of the synthesized sample. The samples were annealed at 200, 500, 700, 790, 870, and 965 ͦ C for 2 h to study the change in the phase evolution and magnetic behavior. Phase transformation was observed for 500 ͦ C annealed HEA, and the value of M s (82.38 emu/g) and H c (41.49 Oe) increased after annealing at 500 ͦC. Interestingly, the samples annealed at high temperatures (>700 °C) have a high value of M s and a significantly low value of H c (<2 Oe). Among annealed Co 35 Cr 5 Fe 10 Ni 30 Ti 20 HEA, 790 ͦ C annealed HEA has the highest value of M s (90.79 emu/g) and the lowest H c (1.66 Oe)of HEAs reported so far. The concluding reason behind the high value of M s for annealed HEAs area decrease in lattice parameter, i.e., improved magnetic interaction and a change in volume phase fraction of synthesized phases. However, the soft magnetic behavior of high-temperature annealed HEA is attributed to the synergetic effect of the decrease in magneto-crystalline anisotropy, particle size, and surface anisotropy. The value of M s and H c for the 790 ̊C annealed HEA is comparable to some commercial soft magnets, such as Supermalloy, Ni-Zn ferrite, and Mn-Zn ferrite. Thus, the designed and developed Co 35 Cr 5 Fe 10 Ni 30 Ti 20 HEA showed excellent soft magnetic characteristics even after annealing at high temperatures and may be further considered for industrial applications. [Display omitted] • Co 35 Cr 5 Fe 10 Ni 30 Ti 20 high entropy alloy synthesized through mechanical alloying. • Effect of different annealing temperatures on Co 35 Cr 5 Fe 10 Ni 30 Ti 20 HEA was studied. • XRD and TEM analysis confirmed the formation of FCC (major) and intermetallic R-phase. • The Reported value of Hc for 790°C annealed HEA is second losed value for HEA. • 790 °C annealed HEA exhibited comparable magnetic behavior compared to commercial materials. [ABSTRACT FROM AUTHOR]

• The influence of Fe/Ni content on structural and magnetic behavior is studied for Co 35 Cr 5 Fe 20−x Ni 20+x Ti 20 HEAs. • The mixture of the fcc, and a minor R-phase are evolved for all the synthesized HEAs. • The coercivity decreased more than five times to the initial value after the heat treatment. • Annealed Co 35 Cr 5 Fe 10 Ni 30 Ti 20 HEA exhibits excellent soft magnetic properties Ms = 78.01 emu/g and extremely low Hc = 1.7 Oe • The found coercivity is the lowest value of coercivity reported so far for the case of magnetic HEAs. The design and development of excellent soft magnetic materials are fascinating research areas in materials science. A series of Co 35 Cr 5 Fe 20−x Ni 20+x Ti 20 (x = 5, 10, 15) High Entropy Alloys (HEAs) were synthesized through mechanical alloying (MA) technique and heat-treated at two different temperatures at 200 °C and 700 °C for 2 h. The XRD analysis confirmed that the HEAs comprised of face-centered cubic (fcc) phase and a minor fraction of an intermetallic R-phase at as-synthesized and annealed state. SEM-EDS observation confirmed the homogeneous compositional distribution and showed that after annealing at 700 °C, tiny spherical particles precipitated over the large grains. The synthesized HEAs showed soft magnetic behavior with low coercivity (12–16 Oe). However, the coercivity decreased more than five times to the initial value after the annealing at 700 °C. Co 35 Cr 5 Fe 10 Ni 30 Ti 20 HEA annealed at 700 °C shows excellent soft magnetic properties with a high value of Ms (78.01 emu/g) and an extremely low value of Hc (1.7 Oe). The found value of the coercivity is the lowest value of the coercivity reported so far for the case of magnetic CoCrFeNiTi based HEAs. In addition, the present work provides a novel design strategy for the development of magnetic HEAs with excellent magnetic softness. [ABSTRACT FROM AUTHOR]