Faculty Publications
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Item Emerging processing routes(De Gruyter, 2023) Prakash, O.; Kumar, R.; Tapas, V.; Kumar, A.; Naveen, B.High-entropy alloys (HEAs) are produced using a number of processing techniques. HEAs have been produced in a variety of materials, including films, dense solid castings, and powder metallurgy components. The three types of processing routes-melting and casting, powder metallurgy, and deposition techniques-can be broadly divided into three classes. In order to create HEAs in the form of rods, bars, and ribbons, melting and casting procedures have been used, along with equilibrium and nonequilibrium cooling rates. The vacuum arc melting, vacuum induction melting, and melt spinning processes are the most widely used melt processing methods. The primary solid-state processing method to create sintered goods has been mechanical alloying (MA), followed by sintering. The surface modification methods utilized to create both thin films and thick layers of HEAs on various substrates include plasma nitriding, cladding, and sputtering. This chapter provides a brief overview of the various synthesis and processing methods used to create HEAs. The processing pathways for equiatomic and nonequiatomic HEAs are comparable. © 2023 Walter de Gruyter GmbH, Berlin/Boston. All rights reserved.Item Additive manufacturing of an aluminum matrix composite reinforced with nanocrystalline high-entropy alloy particles(Elsevier Ltd, 2017) Karthik, G.M.; Panikar, S.; Janaki Ram, G.D.J.; Kottada, R.S.In the present work, a metal-metal composite consisting of aluminum-magnesium alloy AA5083 matrix and nanocrystalline CoCrFeNi high-entropy alloy reinforcement particles in 12 vol% was successfully friction deposited in multiple layers. The layer interfaces or the reinforcement/matrix interfaces showed no brittle intermetallic formation – thanks to the inert nature as well as the high strength and hardness of the high-entropy alloy reinforcement particles. The composite showed significantly higher tensile and compressive strengths as compared to standard wrought-processed alloy AA5083-H112 and offered a much better combination of strength and ductility when compared to conventional aluminum matrix composites reinforced with ceramic particles. The current study establishes friction deposition as a viable technique for additive manufacturing of novel high-performance composite materials. © 2016 Elsevier B.V.Item Tribological Behaviour of Graphite-Reinforced FeNiCrCuMo High-Entropy Alloy Self-Lubricating Composites for Aircraft Braking Energy Applications(Springer New York LLC barbara.b.bertram@gsk.com, 2019) Prabhu, T.R.; Arivarasu, M.; Chodancar, Y.; Arivazhagan, N.; Cadambi, G.; Mishra, R.K.In the present study, the graphite-reinforced FeNiCrCuMo high-entropy alloy-based self-lubricating composites are fabricated through the powder metallurgy. The sintering temperatures (900 and 1000 °C) are varied to study the densification and properties of the composites. The composites are characterized for microstructure, density, and hardness. The brake performance of the composites is evaluated for the braking condition of a military aircraft. The microstructure consists of two phases: one phase (lamella structure) rich with the Fe, Cr, C, and Cu and another white phase rich with the Ni, Cu, C, and Fe along with the uniformly distributed graphite. The EDS analysis confirms the presence of Fe, Cr, Ni, Cu, and Mo in the matrix. The composite sintered at 1000 °C shows improved densification, high hardness, high wear resistance, and excellent braking performance. With the increase of braking energy (speed), the wear rate increases due to the increased intensity of abrasive wear, oxidation wear, and plastic deformation-assisted wear, whereas the friction coefficient has not changed much. Low porosity content and mild abrasive wear are responsible for the high wear resistance in the composite sintered at 1000 °C. Compared to the C/C, C/SiC C/C/SiC composites and Fe- or Cu-based composites, the high-entropy alloy-based composites show great potential for improved braking properties in the high-energy braking applications. © 2019, Springer Science+Business Media, LLC, part of Springer Nature.Item Microstructural and mechanical properties of AlCoCrCuFeNiSix (x = 0 and 0.9) high entropy alloys(Elsevier Ltd, 2021) Chandrakar, R.; Kumar, A.; Chandraker, S.; Rao, K.R.; Chopkar, M.In this work, the effect of addition of Si on the phase evolution and mechanical properties of AlCoCrCuFeNiSix alloy system has been studied. The High Entropy Alloys (x = 0 and 0.9) have been synthesised by powder metallurgy route which includes mechanical alloying (MA) and spark plasma sintering. X-ray diffraction technique was performed to understand the alloying behaviour and to investigate the phase formation of the high entropy alloys. The samples after spark plasma sintering comprised mainly of body centered cubic structured phase with a small extent of face centered cubic structured phase. With the addition of silicon, the XRD peak intensity of body centered cubic appears strong compared to the face centered cubic structured phase. Moreover, no intermetallic is observed in AlCoCrCuFeNi high entropy alloy system. However, further accumulation of Silicon results in the evolution of sigma (?) phase. © 2020 Elsevier LtdItem Phase Evolution of Novel MoNbSiTiW Refractory High-Entropy Alloy Prepared by Mechanical Alloying(Springer, 2022) Prakash, O.; Chandrakar, R.; Chandraker, S.; Rao, K.R.; Kumar, R.; Kumar, A.; Dubey, V.Refractory high-entropy alloys (RHEAs) are new types of material that have been developed for high-temperature applications. RHEAs should have enhanced high-temperature strength while maintaining a sufficient level of room-temperature toughness. The phase evolution of novel MoNbSiTiW RHEAs was investigated after mechanical alloying (MA) for 35 h. X-ray diffraction (XRD) was used to analyze the phase evolution, and analysis of particle morphologies was done using a scanning electron microscope (SEM) equipped with energy dispersive spectroscopy (EDS). XRD results indicate that NbMoSiTiW RHEAs with up to 10 h of mechanical alloying have a stable solid solution phase with body centered cubic (BCC) structure. Further milling of NbMoSiTiW RHEAs promotes the evolution of intermetallic compounds until 35 h of mechanical alloying. The Williamson-Hall process was incorporated for crystalline size and lattice strain measurement and the results show that, after 35 h of mechanical alloying, the crystalline size decreased from 298 nm to 25 nm, and an enhancement in lattice strain was observed from 0.1% to 0.65%. © 2022, The Minerals, Metals & Materials Society.Item Phase evolution and high-temperature wear behavior of non-equiatomic metastable CoCrNiTiMox HEA coatings fabricated by high-velocity oxy-fuel technique(Elsevier Ltd, 2023) Addepalli, S.N.; Joladarashi, S.; Ramesh, M.R.The current research aims to enhance the tribological performance of maraging steels at high temperatures by surface modification techniques. CoCrNiTiMox (x; molar fraction, x = 0.5, 1.5) high-entropy alloy (HEA) coatings with dense lamellar microstructures were deposited onto maraging steels using high-velocity oxy-fuel spray (HVOF). In order to achieve a uniform distribution of constituent elements for thermal spray deposition, mechanical alloying was employed to synthesize the HEA feedstock. The phases and microstructure of the synthesized HEA powder, as-sprayed coatings, and worn surfaces were examined using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The as-sprayed HEA coatings exhibited metastability, with a BCC phase solid solution, NiTiO3 spinel, and an intermetallic MoNi phase for CoCrNiTiMo0.5 and Co2Mo3 phase for CoCrNiTiMo1.5. The average microhardness of CoCrNiTiMo0.5 and CoCrNiTiMo1.5 HEA coatings were 841 ± 62 HV0.3 and 952 ± 23 HV0.3, respectively. The specific wear rate and friction coefficients of CoCrNiTiMox HEA coatings exhibited a decreasing trend with an increase in temperature, owing to the formation of tribofilms on the worn surface. X-ray diffraction studies revealed the formation of NiMoO4 spinel for CoCrNiTiMo0.5 and MoO2, Co3O4 phases for CoCrNiTiMo1.5 HEA at a wear temperature of 600 °C. The investigation of worn surfaces showed a transformation in wear mechanisms from abrasive wear at room temperature to oxidative wear with mild fatigue at elevated temperatures. © 2023 Elsevier LtdItem Elevated temperature tribological performance of non-equiatomic CoCrNiTiWx high entropy alloy coatings developed by mechanical alloying and high-velocity oxy-fuel spray(Elsevier B.V., 2024) Addepalli, S.N.; Joladarashi, S.; Ramesh, M.R.High entropy alloys (HEA) have applications in multiple fields owing to their exceptional mechanical and physical properties. In the current study, mechanical alloyed CoCrNiTiWx (x; a molar fraction, x = 0.5 and 1.5) HEA feedstock powders were deposited on maraging steel substrate using high-velocity oxy-fuel spray (HVOF). The phase evolution and the microstructure of the milled powders and as-sprayed coatings were analysed by X-ray diffraction (XRD) and scanning electron microscope (SEM). The tribological behaviour of CoCrNiTiW0.5 and CoCrNiTiW1.5 HEA coatings at elevated temperatures was studied extensively using a Pin-on-Disc tribometer. The CoCrNiTiW0.5 and CoCrNiTiW1.5 HEA coatings retained the BCC solid solution phases formed during the milling stage. However, additional oxide and intermetallic phases were formed owing to the in-flight oxidation and high temperatures experienced during the HVOF deposition. The deposited coatings exhibited a lamellar structure and good mechanical bonding with the substrate. The porosities of CoCrNiTiW0.5 and CoCrNiTiW1.5 HEA coatings were found to be 1.69 ± 0.32 % and 1.51 ± 0.37 % respectively.Consequently, the CoCrNiTiW0.5 and CoCrNiTiW1.5 HEA coatings displayed average microhardness values of 863 ± 52 HV0.3 and 1025 ± 39 HV0.3, respectively. Further, the wear rates of coatings exhibited a significant reduction at elevated temperatures, owing to the formation of TiO2, NiCr2O4 oxide tribofilms for CoCrNiTiW0.5, and CoCr2O4, NiWO4, WO3 oxides for CoCrNiTiW1.5. The specific wear rate of CoCrNiTiW0.5 HEA coating dropped by 73.6 % from 22.7 ± 2.6 × 10−6 mm3/N-m to 5.99 ± 1.9 × 10−6 mm3/N-m, while CoCrNiTiW1.5 dropped by 78.8 % from 11.86 ± 3.5 × 10−6 mm3/N-m to 2.51 ± 1.5 × 10−6 mm3/N-m, with a rise in the temperature from RT to 600 °C. Likewise, The frictional coefficients of CoCrNiTiW0.5 HEA dropped from 0.504 ± 0.015 to 0.397 ± 0.005, while CoCrNiTiW1.5 HEA dropped from 0.578 ± 0.025 to 0.471 ± 0.004, with a rise in temperature from RT to 600 °C. At room temperature, the wear mechanisms of the as-sprayed CoCrNiTiWx coatings were dominated by adhesive wear. However, at elevated temperatures, a shift towards oxidative wear was observed. © 2023 Elsevier B.V.Item Laser cladding technology for high entropy alloys: effect and applications(Institute of Physics, 2024) Prakash, O.; Chandrakar, R.; Martin, L.; Verma, J.; Kumar, A.; Jaiswal, A.A multi-component category of an alloy containing very specific properties revolutionized the area of material science and the present engineering era. Laser cladding, a technique for surface coating, enhances surface quality and modifies properties using advanced coating technologies. In current trends, Laser cladding is mainly used in equipment and machine parts for enhancing surface properties, repairing damaged parts and surface coating caused by its advantages such as small heat-affected zone, low substrate damage, low dilution rate and exceptional metallurgical material bonding among coating and used substrate. Laser cladding improves substrates’ mechanical and various functional-specific properties, ensuring a high-quality balance between mechanical and surface attributes. The research society was able to investigate laser-cladding HEAs coatings because of the superior attributes of HEAs compared to ordinary alloys. This paper reviews current developments in laser-cladding HEAs coatings and the application of laser-cladding technology to HEAs materials. The laser cladding high-entropy alloy coatings have potential applications in corrosion, wear, and oxidation resistance, as well as their respective substrates. Cladded coatings composed of HEAs materials are measured to have shown potential applications in recent technology, opening exciting possibilities for the future. The study also discusses current trends and future prospects. © 2024 The Author(s). Published by IOP Publishing Ltd.Item Investigation of phase transformation and mechanical properties of silicon addition on AlCrFeMnNi high entropy alloys(Institute of Physics, 2024) Chandrakar, R.; Chandraker, S.; Kumar, A.; Jaiswal, A.This paper examines the impact of silicon in the AlCrFeMnNi high-entropy alloy system, focusing on both its microstructural and mechanical properties. Alloys with varying silicon content (x = 0, 0.3, 0.6, 0.9 atomic ratio) were synthesized using vacuum arc melting. The phase formation of these high-entropy alloys was analyzed using x-ray diffraction to comprehend the alloying process behaviour. The findings revealed that the solidification of the AlCrFeMnNi alloy occurred in dendritically, with dendrite cores containing Cr, Fe, and Ni, while interdendritic regions were enriched in Al and Ni after adding Silicon. Increasing the silicon content from 0 to 0.9 led to significant improvements in microhardness and wear resistance. This improvement is attributed to the reinforcement of grain boundaries provided by silicon. The formation of an Al and Ni rich B2 phase is crucial in resisting dislocation motion and preventing further deformation. Additionally, the addition of silicon led to improved corrosion resistance, as demonstrated by potentiodynamic polarization measurements. However, a trade-off was observed between compressive strength and ductility: compressive strength increased with higher silicon concentrations, but at the expense of ductility. © 2024 The Author(s). Published by IOP Publishing Ltd.