Phase Evolution and Microstructure Analysis of CoCrFeNiMo High-Entropy Alloy for Electro-Spark-Deposited Coatings for Geothermal Environment

In this work, a CoCrFeNiMo high-entropy alloy (HEA) material was prepared by the vacuum arc melting (VAM) method and used for electro-spark deposition (ESD). The purpose of this study was to investigate the phase evolution and microstructure of the CoCrFeNiMo HEA as as-cast and electro-spark-deposited (ESD) coating to assess its suitability for corrosvie environments encountered in geothermal energy production. The composition, morphology, and structure of the bulk material and the coating were analyzed using scanning electron microscopy (SEM) coupled with energy-dispersive spectroscopy (EDS), and X-ray diffraction (XRD). The hardness of the bulk material was measured to access the mechanical properties when preselecting the composition to be pursued for the ESD coating technique. For the same purpose, electrochemical corrosion tests were performed in a 3.5 wt.% NaCl solution on the bulk material. The results showed the VAM CoCrFeNiMo HEA material had high hardness (593 HV) and low corrosion rates (0.0072 mm/year), which is promising for the high wear and corrosion resistance needed in the harsh geothermal environment. The results from the phase evolution, chemical composition, and microstructural analysis showed an adherent and dense coating with the ESD technique, but with some variance in the distribution of elements in the coating. The crystal structure of the as-cast electrode CoCrFeNiMo material was identified as face centered cubic with XRD, but additional BCC and potentially σ phase was formed for the CoCrFeNiMo coating.

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Cutting Edge of High-Entropy Alloy Superconductors from the Perspective of Materials Research

Metals ◽

10.3390/met10081078 ◽

2020 ◽

Vol 10 (8) ◽

pp. 1078

Author(s):

Jiro Kitagawa ◽

Shusuke Hamamoto ◽

Naoki Ishizu

Keyword(s):

Material Design ◽

High Entropy Alloy ◽

Face Centered Cubic ◽

Simple Material ◽

Σ Phase ◽

High Entropy ◽

Cscl Type ◽

Materials Research ◽

Face Centered ◽

New Phenomena

High-entropy alloys (HEAs) are a new class of materials which are being energetically studied around the world. HEAs are characterized by a multicomponent alloy in which five or more elements randomly occupy a crystallographic site. The conventional HEA concept has developed into simple crystal structures such as face-centered-cubic (fcc), body-centered-cubic (bcc) and hexagonal-closed packing (hcp) structures. The highly atomic-disordered state produces many superior mechanical or thermal properties. Superconductivity has been one of the topics of focus in the field of HEAs since the discovery of the bcc HEA superconductor in 2014. A characteristic of superconductivity is robustness against atomic disorder or extremely high pressure. The materials research on HEA superconductors has just begun, and there are open possibilities for unexpectedly finding new phenomena. The present review updates the research status of HEA superconductors. We survey bcc and hcp HEA superconductors and discuss the simple material design. The concept of HEA is extended to materials possessing multiple crystallographic sites; thus, we also introduce multisite HEA superconductors with the CsCl-type, α-Mn-type, A15, NaCl-type, σ-phase and layered structures and discuss the materials research on multisite HEA superconductors. Finally, we present the new perspectives of eutectic HEA superconductors and gum metal HEA superconductors.

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High Strength and Deformation Mechanisms of Al0.3CoCrFeNi High-Entropy Alloy Thin Films Fabricated by Magnetron Sputtering

Entropy ◽

10.3390/e21020146 ◽

2019 ◽

Vol 21 (2) ◽

pp. 146 ◽

Cited By ~ 7

Author(s):

Wei-Bing Liao ◽

Hongti Zhang ◽

Zhi-Yuan Liu ◽

Pei-Feng Li ◽

Jian-Jun Huang ◽

...

Keyword(s):

Thin Film ◽

Thin Films ◽

Magnetron Sputtering ◽

High Hardness ◽

Deformation Mechanisms ◽

High Entropy Alloy ◽

Alloy Thin Film ◽

Face Centered Cubic ◽

High Entropy ◽

Strength And Deformation

Recently, high-entropy alloy thin films (HEATFs) with nanocrystalline structures and high hardness were developed by magnetron sputtering technique and have exciting potential to make small structure devices and precision instruments with sizes ranging from nanometers to micrometers. However, the strength and deformation mechanisms are still unclear. In this work, nanocrystalline Al0.3CoCrFeNi HEATFs with a thickness of ~4 μm were prepared. The microstructures of the thin films were comprehensively characterized, and the mechanical properties were systematically studied. It was found that the thin film was smooth, with a roughness of less than 5 nm. The chemical composition of the high entropy alloy thin film was homogeneous with a main single face-centered cubic (FCC) structure. Furthermore, it was observed that the hardness and the yield strength of the high-entropy alloy thin film was about three times that of the bulk samples, and the plastic deformation was inhomogeneous. Our results could provide an in-depth understanding of the mechanics and deformation mechanism for future design of nanocrystalline HEATFs with desired properties.

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Effect of Zr Addition on the Microstructure and Mechanical Properties of CoCrFeNiMn High-Entropy Alloy Synthesized by Spark Plasma Sintering

Entropy ◽

10.3390/e20110810 ◽

2018 ◽

Vol 20 (11) ◽

pp. 810 ◽

Cited By ~ 10

Author(s):

Hongling Zhang ◽

Lei Zhang ◽

Xinyu Liu ◽

Qiang Chen ◽

Yi Xu

Keyword(s):

Spark Plasma Sintering ◽

Raw Materials ◽

Alloy System ◽

High Entropy Alloy ◽

Face Centered Cubic ◽

Σ Phase ◽

High Entropy ◽

Plasma Sintering ◽

Spark Plasma ◽

Fcc Phase

As a classic high-entropy alloy system, CoCrFeNiMn is widely investigated. In the present work, we used ZrH2 powders and atomized CoCrFeNiMn powders as raw materials to prepare CoCrFeNiMnZrx (x = 0, 0.2, 0.5, 0.8, 1.0) alloys by mechanical alloying (MA), followed by spark plasma sintering (SPS). During the MA process, a small amount of Zr (x ≤ 0.5) can be completely dissolved into CoCrFeNiMn matrix, when the Zr content is above 0.5, the ZrH2 is excessive. After SPS, CoCrFeNiMn alloy is still as single face-centered cubic (FCC) solid solution, and CoCrFeNiMnZrx (x ≥ 0.2) alloys have two distinct microstructural domains, one is a single FCC phase without Zr, the other is a Zr-rich microstructure composed of FCC phase, B2 phase, Zr2Ni7, and σ phase. The multi-phase microstructures can be attributed to the large lattice strain and negative enthalpy of mixing, caused by the addition of Zr. It is worth noting that two types of nanoprecipitates (body-centered cubic (BCC) phase and Zr2Ni7) are precipitated in the Zr-rich region. These can significantly increase the yield strength of the alloys.

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Effects of interstitial carbon atoms on texture structure and mechanical properties of FeMnCoCr alloys

PLoS ONE ◽

10.1371/journal.pone.0242322 ◽

2020 ◽

Vol 15 (12) ◽

pp. e0242322

Author(s):

Chenhao Qian ◽

Yuanhe Qiu ◽

Ziyang He ◽

Weiwei Mu ◽

Yongmeng Tang ◽

...

Keyword(s):

Elastic Modulus ◽

Carbon Content ◽

Empirical Relation ◽

Vacuum Arc ◽

High Entropy Alloy ◽

Face Centered Cubic ◽

Interstitial Carbon ◽

High Entropy ◽

Diffraction Patterns ◽

Face Centered

In this paper, a (Fe50Mn30Co10Cr10)100-xCx high-entropy alloy (HEA) was successfully prepared by using the vacuum arc melting method. The peak shape analysis of the X-ray diffraction patterns, the EBSD observations, and the EDS spectra of the alloys with different compositions show that the characteristics of the dendrites and the hard phase, Cr23C6, into the initial single-phase face-centered cubic (FCC) matrix becomes gradually visible as the carbon content increases from 0 to 4%. The crystal phase variations lead to a non-linear orientation of the microstructure, to a refinement of the grains, and to a higher elastic modulus. This study presents the solid saturation limit of the interstitial carbon atoms in such alloys and establishes an empirical relation between an alloy’s elastic modulus and its carbon content.

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High-Entropy FeCoNiB0.5Si0.5 Alloy Synthesized by Mechanical Alloying and Spark Plasma Sintering

Crystals ◽

10.3390/cryst10100929 ◽

2020 ◽

Vol 10 (10) ◽

pp. 929

Author(s):

Kaouther Zaara ◽

Mahmoud Chemingui ◽

Sophie Le Gallet ◽

Yves Gaillard ◽

Lluisa Escoda ◽

...

Keyword(s):

Mechanical Alloying ◽

Spark Plasma Sintering ◽

Milled Powder ◽

Phase Evolution ◽

High Entropy Alloy ◽

Face Centered Cubic ◽

High Entropy ◽

Plasma Sintering ◽

Spark Plasma ◽

Fcc Phase

A FeCoNi(B0.5Si0.5) high-entropy alloy with the face-centered cubic (FCC) crystal structure was synthesized by mechanical alloying and spark plasma sintering (SPS). Phase evolution, microstructure, morphology and annealing behaviors were investigated. It was found that a single FCC solid solution appears after 50 h of milling. The grain size was 10 nm after 150 h of milling. Microstructure parameters were calculated by the Rietveld fitting of the X-ray Diffraction patterns. Magnetic characterizations of milled and annealed powders at 650 °C for 1 h were investigated. The heat treatment improves the magnetic properties of the milled powders by enhancing the saturation magnetization value from 94.31 to 127.30 emu/g and decreasing the coercivity from 49.07 to 29.57 Oe. The cohabitation of the FCC phase with the equilibrium crystalline phases observed after annealing is responsible of this magnetic softening. The as-milled powder was also consolidated by spark plasma sintering at 750 and 1000 °C. The obtained specimen consolidated at 750 °C improved the coercivity to 25.06 Oe and exhibited a compressive strength of 1062 Mpa and Vickers hardness of 518 ± 14 HV, with a load of 2 kN. The nanoindentation technique with the Berkovich indentor gave hardness and indentation elastic modulus of 6.3 ± 0.3 Gpa (~640 HV) and 111 ± 4 Gpa for samples consolidated by SPS at 750 °C.

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Phase Evolution, Microstructure and Mechanical Property of AlCoCrFeNiTi High-Entropy Alloy Coatings Prepared by Mechanical Alloying and Laser Cladding

Metals ◽

10.3390/met9101036 ◽

2019 ◽

Vol 9 (10) ◽

pp. 1036

Author(s):

Weijie Yu ◽

Yun Wang ◽

Ruitao Li ◽

Junhong Mao

Keyword(s):

Mechanical Alloying ◽

Laser Cladding ◽

Steel Substrate ◽

Phase Evolution ◽

High Entropy Alloy ◽

Second Phase ◽

Face Centered Cubic ◽

High Entropy ◽

Fcc Phase ◽

Bcc Phase

AlCoCrFeNiTi high-entropy alloy coatings (HEACs) were prepared by mechanical alloying (MA) and laser cladding (LC) process on H13 hot-working die steel substrate. Phase evolution, microstructure, and mechanical properties of the alloyed powder and HEACs were investigated in detail. The final milling AlCoCrFeNiTi coating powders exhibited simple body centered cubic (BCC) phase and mean granular size of less than 4 μm. With the increase of heat input of the laser, partial BCC phase transformed into minor face centered cubic (FCC) phase during LC. AlCoCrFeNiTi HEACs showed excellent metallurgical bonding with the substrate, and few defects. Moreover, the microhardness of AlCoCrFeNiTi HEACs reached 1069 HV due to the existence of the hard oxidation and the second phase grains, which are about five times that of the substrate. The laser surface cladding HEACs exhibited deteriorated tensile property compared with that of the substrate and the fracture generally occurred in the region of HEACs. The fracture mechanism of AlCoCrFeNiTi HEACs was dominated by the comprehensive influence of brittle fracture and ductile fracture.

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Research on Electromagnetic Properties of High Entropy Alloys

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.837.277 ◽

2013 ◽

Vol 837 ◽

pp. 277-282 ◽

Cited By ~ 1

Author(s):

Iulia Florea ◽

Raluca Maria Florea ◽

Oana Bălţătescu ◽

Vasile Soare ◽

Costel Roman ◽

...

Keyword(s):

Thermal Stability ◽

High Hardness ◽

Electromagnetic Properties ◽

High Entropy Alloy ◽

High Entropy Alloys ◽

Face Centered Cubic ◽

Metallic Elements ◽

High Entropy ◽

Good Thermal Stability ◽

Structural Applications

In 1995, Yeh suggested the formation of an alloy made up of at least five metallic elements which have large mixing entropy solutions with many elements forming solide alloys. This alloy appeared because traditional alloys are characteised by high fragility and are difficult to process. High entropy alloys are alloys which have approximately equal concentrations, formed by a group of 5 to 11 elements majority in composition, mole fraction of each major metallic element in the alloy is between 5% and 30%. During the research it has been proved that this alloy has a high hardness and it is also corrosion proof and also resistance and good thermal stability It should be mentioned that High Entropy Alloys are characterized as alloys consisting of roughly equal concentrations of at least five metallic elements and are claimed to favor close-packed, disordered structures due to high configurational entropy. Such crystal structures, e.g. face-centered cubic (FCC), are advantageous in that they should offer multiple active slip systems usually observed in ductile metals and alloys. This opens the door to a large number of rich chemistries which would otherwise contain unacceptable volume fractions of intermetallic compounds to be useful in structural applications That way in this paper will carry out research to one specific high entropy alloy, we analyze the physical, chemical, electrical, magnetic, corrosion resistance of these materials, heat treatments corresponding and plastic deformation. This paper is divided into several chapters which will present application domains, and also a number of conclusions. Key words : high entropy alloys, properties of alloys, application domains, corrosion proof, thermal stability

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Understanding the Role of the Constituting Elements of the AlCoCrFeNi High Entropy Alloy through the Investigation of Quaternary Alloys

Metals ◽

10.3390/met10101275 ◽

2020 ◽

Vol 10 (10) ◽

pp. 1275 ◽

Cited By ~ 1

Author(s):

Guy Hillel ◽

Lior Natovitz ◽

Shai Salhov ◽

Shlomo Haroush ◽

Malki Pinkas ◽

...

Keyword(s):

Mechanical Properties ◽

High Hardness ◽

Recent Decade ◽

Eutectic Solidification ◽

High Entropy Alloy ◽

Face Centered Cubic ◽

Quaternary Alloys ◽

High Entropy ◽

Fine Microstructure

Quinary AlCoCrFeNi high entropy alloy (HEA) is one of the most studied alloys in the recent decade due to its outstanding properties. However, it is still far from becoming an applicable industrial alloy. To our understanding, in order to promote this, the role of elements, constituting the quinary alloy, needs to be defined. Knowing the role of each element, modification of the quinary alloy toward minimization of its disadvantages will be possible. In the current research, we shed some light on this subject, presenting a thorough investigation of the microstructure (carried out using scanning and transmission electron microscopy) and mechanical properties, performed by microhardness and fractography post small punch test (SPT), of five equiatomic quaternary alloys, constituting the quinary system, namely: CoCrFeNi, AlCoFeNi, AlCoCrNi, AlCoCrFe, and AlCrFeNi. CoCrFeNi (i.e., w/o Al) was found to be Face Centered Cubic (FCC) solid solution, exhibiting relatively low micro-hardness and ductile fracture post SPT measurement. AlCoFeNi (i.e., w/o Cr) was essentially single phase B2. Other alloys had a mixed BCC + B2 dual phase content with variable microstructures and sizes of particles. The fine microstructure of the alloy without Ni implies eutectic solidification or spinodal decomposition. This fine microstructure imposed remarkable high hardness though the alloy was too brittle and unmachinable. Among the BCC/B2 mixture alloys, Fe and Co-less ones resembled the most quinary AlCoCrFeNi in terms of microstructure and mechanical properties.

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Effect of Aging Temperature on Microstructure and Hardness of CoCrFeNiTi0.5 High Entropy Alloy

Materials Science Forum ◽

10.4028/www.scientific.net/msf.789.48 ◽

2014 ◽

Vol 789 ◽

pp. 48-53 ◽

Cited By ~ 1

Author(s):

Yong Dong ◽

Qiu Shi Chen ◽

Yi Ping Lu ◽

Peng Chao Zhang ◽

Ting Ju Li

Keyword(s):

Aging Temperature ◽

Volume Fraction ◽

High Entropy Alloy ◽

Induction Melting ◽

Face Centered Cubic ◽

Micro Hardness ◽

Rich Phase ◽

Σ Phase ◽

High Entropy ◽

Temperature Range

A bulk casting ingot (Ø70 × 150mm) of CoCrFeNiTi0.5 high entropy alloy was prepared by vacuum medium frequency induction melting. The samples from the ingot were aged for 12h in the temperature range of 900-1100°C and then quenched in water to investigate the effect of aging temperature on the microstructure and hardness of CoCrFeNiTi0.5 alloy. The crystalline structure of as-cast CoCrFeNiTi0.5 alloy consisted of the principal face-centered cubic (FCC) dendrite phase plus (Ni, Ti)-rich R phase, (Fe, Cr)-rich σ phase, (Co, Ti)-rich Laves phase within the inter-dendrite area. The dendrite contained approximately equivalent amount of Co, Cr, Fe, Ni and a smaller amount of Ti element. After aging treatment in the temperature range of 900-1000°C, the (Co, Ti)-rich phase disappeared while the amount of (Ni, Ti)-rich phase and (Fe, Cr)-rich phase increased. But the volume fraction of FCC dendrite phase increased and the intermetallic phases decreased after aging at 1100°C. The micro-hardness and the macro-hardness of the as-cast CoCrFeNiTi0.5 alloy were HV616.8 and HRC52, respectively. After heat treatment at 1000°C, the micro-hardness and macro-hardness decreased from HV616.8 to HV386.8 and from HRC52 to HRC42.7, respectively.

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