Papers by Varun Chaudhary
Nano, 2022
High-performance permanent magnets (PMs) have gained high and growing interest due to their exces... more High-performance permanent magnets (PMs) have gained high and growing interest due to their excessive demand in energy conversion systems and electric vehicles. PM-based electric machines exhibit great advantages over traditional motors due to their high efficiency of energy conversion. Nd–Fe–B magnet is the best available magnet in terms of energy-product at room temperature. Replacement of Nd by heavy rare earth (HRE) and of Fe by Co results in an enhanced anisotropy field and an improved thermal stability, but also increases the production costs. Developing a strong PM with minimum use of HRE elements is required due to their high cost, low availability and issues associated with international politics. Grain boundary diffusion (GBD) process allows the HRE to diffuse around the grain boundaries, unlike adding expensive HRE to the middle of a grain. Here, we review the recent progress in PMs, especially the novel development of grain boundary-diffused magnets and nanostructured magnets. GBD processes using RE, fluorides or hydrides of RE and eutectic alloys are discussed. Development of nanostructured PMs using physical and chemical methods such as melt spinning, high-energy ball milling, surfactant-assisted ball milling, mechanochemical method, etc. is elucidated. The current and future trends in the area of high performance permanent magnets are outlined.
iScience, 2025
Developing high-performance alloys is essential for applications in advanced electromagnetic ener... more Developing high-performance alloys is essential for applications in advanced electromagnetic energy conversion devices. In this study, we assess Fe-Co-Ni alloy compositions identified in our previous work through a machine learning (ML) framework, which used both multi-property ML models and multi-objective Bayesian optimization to design compositions with predicted high values of saturation magnetization, Curie temperature, and Vickers hardness. Experimental validation was conducted on two promising compositions synthesized using three different methods: arc melting, ball milling followed by spark plasma sintering (SPS), and chemical synthesis followed by SPS. The results show that the experimental property values of arc melted samples deviated less than 14% from predicted values. This work further explains how structural variations across synthesis methods impact property behavior, validating the robustness of ML-predicted compositions and highlighting a pathway for integrating processing conditions into alloy development.
Scripta Materialia, 2025
There is considerable interest in magnetic materials which also possess good mechanical propertie... more There is considerable interest in magnetic materials which also possess good mechanical properties. Hence, the effect of Ti/Al ratio on the microstructure, mechanical and magnetic properties of (FeCoNi)90Ti10-xAlx complex concentrated alloys (CCA) was investigated. An increase in the Ti/Al ratio in these CCA enhanced chemical ordering and substantially improved selected mechanical and magnetic properties. As the Ti/Al ratio changed from 10 to 0, the ductility increased from 7.5 to close to 50 %, the saturation magnetization (Ms) increased from 115.2 to 136.7 emu/g, and the coercivity (Hc) decreased from 17.9 to 4.2 Oe. The Fe30Co30Ni30Ti5Al5 alloy exhibit higher UTS×EL value than available soft magnetic materials and has relatively higher Ms and lower Hc compared with other CCA. These results provide a methodology to modulate the chemical order in the Fe-Co-Ni system by Al and Ti additions and synergistically tune the mechanical and magnetic properties for high performance rotating electrical machine applications.
Scientific Reports, Oct 22, 2018
While the AlCoFeNi high entropy alloy exhibits a single ordered B2 phase at high temperature, bot... more While the AlCoFeNi high entropy alloy exhibits a single ordered B2 phase at high temperature, both the substitution of ferromagnetic Co with antiferromagnetic Cr, and lower annealing temperatures lead to a tendency for this system to decompose into a two-phase mixture of ordered B2 and disordered BCC solid solution. The length scale of this decomposition is determined by the combination of composition and annealing temperature, as demonstrated in this investigation by comparing and contrasting AlCoFeNi with the AlCo 0.5 Cr 0.5 FeNi alloy. The resulting phase stability has been rationalized based on solution thermodynamic predictions. Additionally, it is shown that replacement of Co by Cr in the AlCoFeNi alloy resulted in a substantial reduction in saturation magnetization and increase in coercivity. The microhardness is also strongly influenced by the composition and the length scale of B2 + BCC decomposition in these high entropy alloys. High-entropy alloys (HEAs) have attracted a lot of attention in recent years, due to the unique combinations of structural, physical and chemical properties of these alloys 1-3 . HEAs usually form simple structures such as body-centered cubic (BCC) (e.g. TaNbHfZrTi 4 , NbTaVWZr 5 etc.) or face-centered cubic (FCC) (e.g., CoCrCuFeNi 6 , CoCrFeMnNi 7 etc.) solid solutions. The large number of the alloying elements in near-equiatomic proportions result in high configurational entropy in these solid solutions. However, these alloys can decompose to multiple phases upon changing the composition or annealing at different temperatures or a combination of both . Such a phase decomposition is often the result of the complex interplay of configurational entropy of mixing with the enthalpies of mixing of the constituent elements. Additionally, such multiphase microstructures are more likely to exhibit the desired properties for real engineering applications. Hence, tuning the composition and fractions of phases is critical for achieving the desired properties . Recently, it has been reported that AlCoCrFeNi based HEAs exhibit high hardness, good corrosion resistance, high yield strength and promising magnetic properties . A systematic investigation on a compositionally graded AlCoxCr 1-x FeNi sample, processed by laser engineered net shape (LENS) technology , revealed that all the compositions within this graded sample exhibited either a single B2 phase or a two-phase BCC + B2 microstructure. A separate study reported that annealing the AlCoCrFeNi HEA at 600 °C, exhibited a near single B2 phase microstructure, while the same alloy annealed in the temperature range of 800 to 1200 °C exhibited FCC precipitates in a B2 matrix . While the influence of Al content on the phases and microstructures, in the Al x CoCrFeNi class of HEAs has been extensively investigated , there is rather limited knowledge regarding the composition and temperature dependent microstructure and properties in the AlCo x Cr 1-x FeNi system 13 . Therefore, the role of Cr, an anti-ferromagnetic element, on the microstructural evolution and properties (magnetic and mechanical) of AlCo x Cr 1-x FeNi type HEAs, needs further investigation and forms the basis of the present study. This study focuses on two representative compositions, i.e., AlCoFeNi and AlCo 0.5 Cr 0.5 FeNi processed by conventional melt technology and subsequently annealed at specific temperatures/times to determine the phase stability as a function
Scientific Reports, Jun 9, 2022
A variety of high-performance materials are utilized in electrical, electronic, and mechanical sy... more A variety of high-performance materials are utilized in electrical, electronic, and mechanical systems. Such systems account for a significant fraction of the world's electricity consumption. The next generation of such systems urgently require new material compositions which possess a better combination of both structural and functional properties. Only accelerated methodologies can rapidly determine the required multiple property set. Hence, a range of iron-cobalt-nickel ternary alloy composition powders were chemically synthesized. Compositionally graded bulk materials libraries were prepared by spark plasma sintering of these powders. A multiple property set of the crystal structure, magnetic, mechanical, and electrical properties were determined for a range of compositions. This property set revealed that a good combination of magnetic and mechanical properties can be obtained from Fe 50 Co 40 Ni 10 , high electrical resistivity from Fe 54 Co 17 Ni 29 and high saturation magnetization as well as high hardness from Fe 57 Co 29 Ni 14 . Thus, this multiple property library, developed by accelerated methodologies, can be utilized to identify new ternary compositions satisfying diverse property sets relevant to next generation systems. Iron-cobalt-nickel based materials are widely used in many functional as well as structural components. For example, magnetic components are used in many applications, including rotating electrical machines, transformers, magnetic sensors and recording media . These alloys can also possess excellent mechanical properties 5 . Hence, it is attractive to consider such ternary alloys for next generation devices and machines, as such systems will operate in harsh service conditions and require an adequate combination of mechanical, magnetic, and electrical properties. For example, next-generation high frequency, high torque, rotating electrical machines, such as motors, need materials with an attractive combination of functional and structural properties. Such electrical machines account for a significant fraction of the world's electricity consumption. Hence, there is an urgent need to identify new material compositions with the appropriate property combination. Some reported values of commercially available materials for such applications are: Permendur (Fe 49 Co 49 V 2 ) based alloys have M s ~ 228 emu/g, H c ~ 0.4-1.25 Oe, T c = 930 °C, electrical resistivity ~ 40 µΩ cm and Vickers hardness between 180 and 220 HV. Fe-Ni based alloys like Permalloy or Mumetall (Fe 15 Ni 80 Mo 5 or Fe 14 Ni 77 Mo 4 Cu 5 ) have M s ~ 69 emu/g, H c ~ 0.004-0.03 Oe, low T c of 420 °C, electrical resistivity ~ 70 µΩ cm and Vickers hardness of 160 HV. Equimolar Fe-Ni (Fe 52 Ni 48 ) have M s ~ 157 emu/g, H c ~ 0.05 Oe, low T c of 450 °C, electrical resistivity ~ 48 µΩ cm and Vickers hardness of 120 HV 6 . Literature data for the properties of Fe-Co-Ni ternary alloys are scattered and often confined to single property databases rather than property sets. The magnetic properties are available for equi-atomic alloys 7,8 and a limited set of alloys of other compositions 1,9,10 , however, there are only a few reports on the crystal structure, mechanical and electrical properties as a function of ternary alloy composition . Thus, there is no property library with integrated data on the magnetic, electrical and mechanical properties over a range of ternary Fe-Co-Ni alloy compositions. Traditional methods to develop such a property set will require unrealistically large time and resources. Hence, we deployed accelerated methodologies to create such a multiple property set. A range of Fe-Co-Ni alloy compositions can be prepared for such accelerated studies by mechanical alloying 1,7-10 but milling times of several hours are required to get suitable powder samples. Earlier 15 , the properties of a permalloy-cobalt system (Ni-21Fe)-xCo (x = 0, 20, 40 and 60) were studied by this methodology. Spark plasma sintering (SPS) was performed using ball-milled powders, and only Ni-rich and Co-rich regions of the
JOM, Jan 27, 2017
MASTER OF SCIENCE UNIVERSITY OF NORTH TEXAS August 2017 Mikler, Calvin Vijay. Laser Additive Manu... more MASTER OF SCIENCE UNIVERSITY OF NORTH TEXAS August 2017 Mikler, Calvin Vijay. Laser Additive Manufacturing of Magnetic Materials. Master of Science (Materials Science and Engineering), August 2017, 64 pp., 2 tables, 21 figures, chapter references. A matrix of variably processed Fe-30at%Ni was deposited with variations in laser travel speeds as well and laser powers. A complete shift in phase stability occurred as a function of varying laser travel speed. At slow travel speeds, the microstructure was dominated by a columnar fcc phase. Intermediate travel speeds yielded a mixed microstructure comprised of both the columnar fcc and a martensite-like bcc phase. At the fastest travel speed, the microstructure was dominated by the bcc phase. This shift in phase stability subsequently affected the magnetic properties, specifically saturation magnetization. Ni-Fe-Mo and Ni-Fe-V permalloys were deposited from an elemental blend of powders as well. Both systems exhibited featureless microstructures dominated by an fcc phase. Magnetic measurements yielded saturation magnetizations on par with conventionally processed permalloys, however coercivities were significantly larger; this difference is attributed to microstructural defects that occur during the additive manufacturing process. Finally, a compositionally graded AlCoxCr1-xFeNi (0.0<x<1.0) complex concentrated alloy was deposited with six distinct compositional steps. As a function of composition, the microstructure varied from single phase B2 (ordered) to a mixture of B2 + bcc (disordered). Increasing chromium content results in a spinodal decomposition within the matrix, forming a B2+bcc microstructure. Saturation magnetizations are highest at x=1.0 (AlCoFeNi), and lowest at x=0.0 (AlCrFeNi). The coercivity reached a maximum at x=0.4.
Materials Advances
One-step magnetocuring and AC-magnetorheology of AMF susceptible materials.
Scientific Reports, 2021
Superior passive cooling technologies are urgently required to tackle device overheating, consequ... more Superior passive cooling technologies are urgently required to tackle device overheating, consequent performance degradation, and service life reduction. Magnetic cooling, governed by the thermomagnetic convection of a ferrofluid, is a promising emerging passive heat transfer technology to meet these challenges. Hence, we studied the performance metrics, non-dimensional parameters, and thermomagnetic cooling performance of various ferrite and metal-based ferrofluids. The magnetic pressure, friction factor, power transfer, and exergy loss were determined to predict the performance of such cooling devices. We also investigated the significance of the magnetic properties of the nanoparticles used in the ferrofluid on cooling performance. γ-Fe2O3, Fe3O4, and CoFe2O4 nanoparticles exhibited superior cooling performance among ferrite-based ferrofluids. FeCo nanoparticles had the best cooling performance for the case of metallic ferrofluids. The saturation magnetization of the magnetic nan...
Advanced Materials Interfaces, 2021
Magnetocuring of adhesives refers to the curing of an epoxy + Curie temperature controlled magnet... more Magnetocuring of adhesives refers to the curing of an epoxy + Curie temperature controlled magnetic nanoparticles (CNP) composite using a suitable alternating magnetic field. The controlled heating of the CNP results in remote, wireless curing without resin overheating. However, typical CNP possess only a fraction of the heat output of ferric oxide nanoparticles, quantified as the specific absorption rate (SAR). Previous investigations of epoxy + CNP adhesives revealed a SAR of 5 W.g−1, which is 10–100× less than that of ferric oxides. Here, it is demonstrated that SAR can be improved to up to 60 W.g−1 by tuning CNP composition and by the addition of carbon allotropes (CA) within the resin. Heat generation and dissipation can be also regulated by electromagnetic shielding, resin conductivity, and viscosity. Nanocoils and nanotubes of CA result in improved heating profiles of epoxy thermosets. Magnetocured composites achieve activation within 180 s due to the improved SAR and additio...
The hierarchical microstructures of high-entropy alloys (HEAs) can result in highly complex magne... more The hierarchical microstructures of high-entropy alloys (HEAs) can result in highly complex magnetic textures and properties. Here, we use high spatial resolution correlative magnetic, structural and chemical imaging to investigate magnetic textures in phase separated AlCoxCr1 – xFeNi (x = 0.5 and 1) HEAs. The AlCoFeNi HEA, which contains nm-sized A2 precipitates in a B2 matrix, supports large magnetic domains with small-angle magnetization variations. In contrast, the AlCo(Cr)FeNi HEA, which undergoes hierarchical phase separation, contains an unexpected distribution of magnetic vortices within individual A2 precipitates in a weakly ferromagnetic B2 host, in addition to weakly ferromagnetic or nonmagnetic B2 precipitates in large magnetic domains of the A2 phase, as well as Fe-Co-rich inter-phase A2 regions that have strong magnetization. The coercivity is attributed to a complicated magnetization reversal process, which includes the successive reversal of the magnetic vortices. Th...
Progress in Materials Science, 2019
Iron and manganese based magnetocaloric materials for near room temperature thermal management
Materialia, 2023
Fe-3.8wt%Si transformer steels were processed using two different additive manufacturing (AM) tec... more Fe-3.8wt%Si transformer steels were processed using two different additive manufacturing (AM) techniques, laser powder bed fusion (LPBF) and directed energy deposition (DED). While the LPBF processed samples exhibited a strong <001> orientation of the BCC grains along the build axis, the DED processed samples exhibited a randomized texture along the build axis. DED processed samples showed substantially coarser columnar grains as compared to their LPBF counterparts. The columnar grains exhibited a substantial number of low-angle sub-grain boundaries. All samples exhibited very good soft magnetic properties, with saturation magnetization (M s) values ranging from 205-232 emu/gm, and coercivity (H c) values ranging from 1.2-4.2 Oe. The Coercivity (H c) values were significantly lower when the magnetic field was applied parallel to the build axis, as compared to being perpendicular, which can be rationalized based on the columnar nature of the grains, resulting in a higher number density of grain boundaries in case of the field applied perpendicular to the build axis.
Scripta Materialia, 2023
Varying the Al content, strongly influences the microstructure, magnetic and microhardness of add... more Varying the Al content, strongly influences the microstructure, magnetic and microhardness of additively manufactured Alx(CoFeNi) (x = 0, 10, 30) complex concentrated alloys (CCA). Compared to the single FCC phase of CoFeNi, the hierarchical FCC/L12+BCC/B2 heterostructure of heat treated Al10(CoFeNi) CCA displayed substantially improved saturation magnetization, Curie temperature and microhardness. However, there was no significant change in the properties of heat treated CoFeNi and Al30(CoFeNi) CCA. These findings can be rationalized via thermodynamic modelling of the phase stability. We have demonstrated the feasibility of exploiting additive manufacturing for rapidly screening and developing novel high-performance alloys for next generation rotating electrical machines.
Materials Today Communications , 2023
Bulk Ti-48Al alloy samples were prepared by the high energy ball milling (HBM) of elemental powde... more Bulk Ti-48Al alloy samples were prepared by the high energy ball milling (HBM) of elemental powders, followed by spark plasma sintering (SPS) of the HBM processed powders. The microstructure, phase evolution and mechanical properties of the bulk alloy were studied. The resulting TiAl + Ti 3 Al two phase alloy possessed an equiaxed fine grain structure, unlike the usual lamellar structure produced by arc melting. The process parameters of HBM and SPS, e.g., milling speed, milling time and sintering temperature were used to tune the phase fraction, microstructure, and grain size. A very high nanohardness of up to ~12 GPa was obtained, ~2.4 times higher than the corresponding value of the as-cast counterpart. The combined influence of powder size reduction during HBM, high Ti 3 Al phase fraction and microstructural development during SPS resulted in higher hardness, wear resistance and yield pressure. Thus, a HBM+SPS processing approach is a promising processing route for the manufacture of high hardness bulk TiAl alloys.
Nano, 2022
High-performance permanent magnets (PMs) have gained high and growing interest due to their exces... more High-performance permanent magnets (PMs) have gained high and growing interest due to their excessive demand in energy conversion systems and electric vehicles. PM-based electric machines exhibit great advantages over traditional motors due to their high efficiency of energy conversion. Nd–Fe–B magnet is the best available magnet in terms of energy-product at room temperature. Replacement of Nd by heavy rare earth (HRE) and of Fe by Co results in an enhanced anisotropy field and an improved thermal stability, but also increases the production costs. Developing a strong PM with minimum use of HRE elements is required due to their high cost, low availability and issues associated with international politics. Grain boundary diffusion (GBD) process allows the HRE to diffuse around the grain boundaries, unlike adding expensive HRE to the middle of a grain. Here, we review the recent progress in PMs, especially the novel development of grain boundary-diffused magnets and nanostructured ma...
Scientific Reports, 2016
Low cost, earth abundant, rare earth free magnetocaloric nanoparticles have attracted an enormous... more Low cost, earth abundant, rare earth free magnetocaloric nanoparticles have attracted an enormous amount of attention for green, energy efficient, active near room temperature thermal management. Hence, we investigated the magnetocaloric properties of transition metal based (Fe 70 Ni 30) 100−x Cr x (x = 1, 3, 5, 6 and 7) nanoparticles. The influence of Cr additions on the Curie temperature (T C) was studied. Only 5% of Cr can reduce the T C from ~438 K to 258 K. These alloys exhibit broad entropy v/s temperature curves, which is useful to enhance relative cooling power (RCP). For a field change of 5 T, the RCP for (Fe 70 Ni 30) 99 Cr 1 nanoparticles was found to be 548 J-kg −1. Tunable T C in broad range, good RCP, low cost, high corrosion resistance and earth abundance make these nanoparticles suitable for low-grade waste heat recovery as well as near room temperature active cooling applications. Energy efficient magnetocaloric materials for magnetic cooling have attracted intense research interest due to unsustainable energy consumption and limitations of current cooling technology 1-9. A well-known milestone in magnetic cooling is the development of a compressor free wine cooler based on magnetic cooling, developed by Haier, BASF and Astronautics corporation 10,11. Magnetic cooling has already been shown to use 35% less power than conventional cooling 11. Magnetic cooling is an energy efficient, low noise and low vibration technology which does not use ozone layer depleting hydrofluorocarbons and is, therefore, environmentally friendly 12. The magnetocaloric effect (MCE) is the change in temperature of a material due to the adiabatic application or removal of an external magnetic field 13. This temperature change is related to the magnetic entropy change (∆ S M). Generally, MCE is large in the vicinity of the Curie temperature (T C), where the magnetic spins undergo an order-disorder phase transition. Gd 5 (Si x Ge 1−x) 4 and other R 5 T 4 (R = Rare earth, T = Transition metal) materials can exhibit promising magnetocaloric performance and are known as "Giant magnetocaloric materials" 14,15. However, issues surrounding rare-earths are very complex due to strategic reasons and economics. China is the main supplier of rare earths since several decades, accounting for ~97% and ~90% of world production in 2009 and 2013, respectively 16. This control may result in supply instabilities. In addition, rare earth based materials are corrosion prone and not earth abundant. These undesirable factors motivate us to develop non rare earth based magnetocaloric materials 17-23. First order transition materials (FOTM) which exhibit simultaneous magnetic and structural transition result in high isothermal entropy change 24-26. However, the narrow working temperature span and large magnetic and thermal hysteresis in FOTM limit real-world applications 5,13,27,28. The magneto-structural transition is often associated with field and temperature hysteresis, which reduce maximum operating frequency. In addition, the repetitive structural transition in FOTM can cause result in mechanical instability, which cause failure of the system 2,29,30. On the other hand, second order transition materials (SOTM) exhibit a magnetic transition. These materials generally have lower isothermal entropy change compared to those of FOTM. However, SOTM are superior in terms of negligible magnetic and temperature hysteresis and also exhibit large working temperature span, and therefore, high relative cooling power (RCP) 5,13,28,31,32. Hence, there is a considerable interest in rare earth free, cost effective and readily available Fe based materials exhibiting a second order magnetic phase transition 5,13,28,31,33-35. Typically, bulk magnetocaloric materials have been developed for cooling systems. The magnetocaloric effect in nanostructured materials has received considerable interest recently since they possess additional advantages 5,13,28,31,32,36-38. These nanomaterials can be useful for active magnetic cooling devices, microfluidic reactors
Magnetocaloric properties and critical behavior of high relative cooling power FeNiB nanoparticles
Journal of Applied Physics, 2014
ABSTRACT Low cost magnetocaloric nanomaterials have attracted considerable attention for energy e... more ABSTRACT Low cost magnetocaloric nanomaterials have attracted considerable attention for energy efficient applications. We report a very high relative cooling power (RCP) in a study of the magnetocaloric effect in quenched FeNiB nanoparticles. RCP increases from 89.8 to 640 J kg1 for a field change of 1 and 5 T, respectively, these values are the largest for rare earth free iron based magnetocaloric nanomaterials. To investigate the magnetocaloric behavior around the Curie temperature (T), the critical behavior of these quenched nanoparticles was studied. Detailed analysis of the magnetic phase transition using the modified Arrott plot, Kouvel-Fisher method, and critical isotherm plots yields critical exponents of b ¼0.364, c ¼1.319, d ¼4.623, and a ¼�0.055, which are close to the theoretical exponents obtained from the 3D-Heisenberg model. Our results indicate that theseFeNiB nanoparticles are potential candidates for magnetocaloric fluid based heat pumps and low grade waste heat recovery.
Magnetic high entropy alloys (HEAs) are a new category of high-performance magnetic materials, wi... more Magnetic high entropy alloys (HEAs) are a new category of high-performance magnetic materials, with multi-component concentrated compositions and complex multi-phase structures. Although there have been numerous reports of their interesting magnetic properties, there is very limited understanding about the interplay between their hierarchical multi-phase structures and their local magnetic structures. By employing high spatial resolution correlative magnetic, structural and chemical studies, we reveal the influence of a hierarchically decomposed B2 + A2 structure in an AlCo0.5Cr0.5FeNi HEA on the formation of magnetic vortex states within individual A2 (disordered BCC) precipitates, which are distributed in an ordered B2 matrix that is weakly ferromagnetic. Non-magnetic or weakly ferromagnetic B2 precipitates in large magnetic domains of the A2 phase, and strongly magnetic Fe-Co-rich interphase A2 regions, are also observed. These results provide important insight into the origin of...
Bulk-nano spark plasma sintered Fe-Si-B-Cu-Nb based magnetic alloys
Intermetallics, 2020
Abstract Iron-based soft magnetic alloys (FeSiB, FeSiBNb, FeSiBCu, and FeSiBNbCu (Finemet)) have ... more Abstract Iron-based soft magnetic alloys (FeSiB, FeSiBNb, FeSiBCu, and FeSiBNbCu (Finemet)) have been fabricated via mechanical alloying followed by spark plasma sintering (SPS) process. FeSiB alloy powder was obtained by high energy ball milling of an elemental blend Fe, Si, and B powders. The effect of milling time on crystallite size and phase transformation was studied. Additionally, FeSiBCu, FeSiBNb, and FeSiBCuNb alloy powders were milled to study the effect of Cu and Nb on phase transformation, mechanical, and magnetic behavior. The mechanically alloyed powders were sintered via SPS process to achieve full densification. The microhardness and magnetic permeability of sintered FeSiB alloys were found to be increased monotonically with milling time primarily due to the smaller crystallite size and more uniform microstructure. Interestingly, the alloying of Cu or (and) Nb to FeSiB resulted in higher saturation magnetization and lower coercivity mainly due to large volume fraction of α-Fe3Si nanocrystals. Overall, these alloys exhibit reasonably good soft magnetic behavior along with excellent microhardness. Mechanical alloying followed by spark plasma sintering opens up a new avenue of processing amorphous-nanocrystalline alloys into bulk shape with good mechanical and magnetic properties.
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Papers by Varun Chaudhary