Shock wave compaction and sintering of mechanically alloyed CoCrFeMnNi high-entropy alloy powders

Yim, Dami,Kim, Wooyeol,Praveen, S.,Jang, Min Ji,Bae, Jae Wung,Moon, Jongun,Kim, Eunbin,Hong, Soon-Jik,Kim, Hyoung Seop Elsevier 2017 Materials science & engineering. properties, micro Vol.708 No.-

<P><B>Abstract</B></P> <P>In this study, mechanically alloyed CoCrFeMnNi high-entropy alloy (HEA) powders were compacted using static and shock wave compaction methods followed by pressureless sintering. The microstructural evolution and the mechanical properties were analyzed using optical microscopy, scanning electron microscopy, finite element method simulations, and tensile tests. The alloy consists of an FCC phase with a minor amount of ZrO<SUB>2</SUB> in the as-milled and sintered condition. The presence of ZrO<SUB>2</SUB> is due to the contamination during milling, and it led to the formation of composite microstructure after sintering. The static compaction of the alloyed powders resulted in an increase in compaction density (~ 85 to 88%) with the increasing pressure (1–3GPa), and the shock wave compaction of the alloyed powders resulted in the high relative density (~ 95%) with relatively fine and isolated pores. After sintering, almost full densification (~ 99.5%) with smaller grain size and better mechanical properties was achieved in the shock wave compacted specimens as compared to the sintering of static compacted specimens. The sintered shock wave compacted specimen exhibited high yield strength of ~ 630MPa and uniform strain distributions.</P>

Fabrication and mechanical properties of TiC reinforced CoCrFeMnNi high-entropy alloy composite by water atomization and spark plasma sintering

Yim, Dami,Sathiyamoorthi, Praveen,Hong, Soon-Jik,Kim, Hyoung Seop Elsevier 2019 Journal of alloys and compounds Vol.781 No.-

<P><B>Abstract</B></P> <P>In this study, the TiC-reinforced CoCrFeMnNi high-entropy alloy (HEA) composite was fabricated using water atomization (WA), mechanical milling (MM), and spark plasma sintering (SPS). The microstructural evolution and mechanical properties of TiC-reinforced HEA composite are investigated using electron backscatter diffraction, transmission electron microscopy, and room temperature compression tests. The addition of 5 wt% of TiC nano-particles to CoCrFeMnNi HEA resulted in fine grain size, high yield strength, and high strain hardening. The average grain size achieved for alloys with and without TiC after sintering is 5.1 μm and 10.6 μm, respectively. The addition of TiC increases the compressive yield strength from ∼507 MPa to ∼698 MPa and compressive fracture strength from ∼1527 MPa to ∼2216 MPa, without sacrificing the ductility. The strengthening behavior of TiC-reinforced CoCrFeMnNi HEA composite is quantitatively discussed based on grain boundary strengthening, dislocation strengthening, and dispersion strengthening. The role of TiC nano-particles in the strain hardening improvement is investigated with respect to the dislocation-particle interaction and consequently increased dislocation density.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Fabrication of TiC reinforced CoCrMnFeNi high entropy alloy composite by powder metallurgy route. </LI> <LI> TiC particles prevents grain boundary movement and results in fine grain size of FCC matrix after sintering. </LI> <LI> CoCrMnFeNi-TiC composite shows enhanced mechanical properties as compared to CoCrMnFeNi alloy. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Compaction behavior of water-atomized CoCrFeMnNi high-entropy alloy powders

Yim, Dami,Jang, Min Ji,Bae, Jae Wung,Moon, Jongun,Lee, Chul-Hee,Hong, Soon-Jik,Hong, Sun Ig,Kim, Hyoung Seop Elsevier 2018 Materials chemistry and physics Vol.210 No.-

<P><B>Abstract</B></P> <P>In this work, compaction behavior of CoCrFeMnNi high-entropy alloy powders with various particle sizes and size distributions, produced by water atomization, was investigated experimentally and theoretically. Theoretical modeling was employed using a pressure-dependent yield function in associated with a phenomenological constitutive model. Results for the quantitative densification behaviors from the experimental and theoretical analyses are in good agreement. We found that the size and size-distribution of the powder particles are important factors in the tap density as with conventional powder compaction. The compact density of large powder particles with coarse dendrite arm spacing is high due to low deformation resistance and low strain hardening (i.e., low evolution of dislocation density).</P> <P><B>Highlights</B></P> <P> <UL> <LI> The compaction behavior of CoCrFeMnNi high-entropy alloy powders of various sizes is studied. </LI> <LI> The size and size-distribution of the powder particles are important factors in the tap density. </LI> <LI> The strength of the matrix is the factor governing the final compact density. </LI> <LI> The simulation densification behaviors are in good agreement with experimental ones. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

고엔트로피 합금의 제조 방법과 연구 동향: 리뷰

임다미 ( Dami Yim ),김형섭 ( Hyoung Seop Kim ) 대한금속ㆍ재료학회 2017 대한금속·재료학회지 Vol.55 No.10

High-entropy alloys (HEAs), which are defined as a single phase crystalline solid solution with the composition of each constituent element in the range of 5-35 at%, have been the subject of intensive study in the last decade. Most of the HEA research is focused on alloy design, microstructural characterization, and mechanical testing, not manufacturing, processing, and industrialization, although the properties, microstructures, and performance are strongly dependent on processing. In this review article, we aim to describe the manufacturing processes applied to HEAs. The manufacturing process of HEAs can be classified into three main routes. First, liquid processing that includes arc melting, Bridgman solidification, atomization, and laser cladding is the most commonly used methods because the processing facilities are already widespread in many laboratory and the liquid processing can be easily scaled-up for commercialization. Second, mechanical alloying. i.e. powder metallurgy, is a process starting from a solid particle state and employing sintering procedures for bulk manufacturing. In particular, the mechanical alloying has been used for achieving super saturated solid solution which cannot be obtaiend using the conventional liquid prcesses. Third, the HEAs can be manufactured by mixing elements of the vapor state, which includes sputter deposition, atomic layer deposition, and vapor phase deposition. Explanation and comparison between various manufacturing methods of the HEAs are systematically described and demonstrated in this review. †(Received July 24, 2017; Accepted August 16, 2017)

Physics-Based Constitutive Model of Porous Materials for Die/Isostatic Compaction of Metallic Powders

Yujin Seong,Dami Yim,Min Ji Jang,Jeong Min Park,Seong Jin Park,Hyoung Seop Kim 대한금속·재료학회 2020 METALS AND MATERIALS International Vol.26 No.2

A physics-based constitutive model of porous materials is proposed to enhance the accuracy of numerical analysis in die/isostatic compaction. The correlation between the yield function and equivalent work equation was derived, and the numericalintegration method was modifed with the correlation. It is found that the apparent work of porous materials is lower than theproduct of relative density and equivalent work of solid materials at the beginning of compaction, implying the kinematicmotion of powders and the resultant particle rearrangement. For verifcation of the proposed model, fnite element analyseswere performed for the die/isostatic compaction of three metal powders: Ti, SUS316L, and Al6061 powders. Compared withtwo conventional constitutive models, the proposed model improves the accuracy of the densifcation behaviors in all thestage during die/isostatic compaction. Furthermore, this study is a groundwork to link the densifcation behavior of porousmaterials at bulk scale to the particulate behavior of powders at microscale.

분말야금법으로 제조한 새로운 Co₁₀Fe₁₀Mn₃₅Ni₃₅Zn₁₀ 고엔트로피 합금

임다미,박형근,이병주,김형섭,Yim, Dami,Park, Hyung Keun,Tapia, Antonio Joao Seco Ferreira,Lee, Byeong-Joo,Kim, Hyoung Seop 한국분말야금학회 2018 한국분말재료학회지 (KPMI) Vol.25 No.3

In this paper, a new $Co_{10}Fe_{10}Mn_{35}Ni_{35}Zn_{10}$ high entropy alloy (HEA) is identified as a strong candidate for the single face-centered cubic (FCC) structure screened using the upgraded TCFE2000 thermodynamic CALPHAD database. The $Co_{10}Fe_{10}Mn_{35}Ni_{35}Zn_{10}$ HEA is fabricated using the mechanical (MA) procedure and pressure-less sintering method. The $Co_{10}Fe_{10}Mn_{35}Ni_{35}Zn_{10}$ HEA, which consists of elements with a large difference in melting point and atomic size, is successfully fabricated using powder metallurgy techniques. The MA behavior, microstructure, and mechanical properties of the $Co_{10}Fe_{10}Mn_{35}Ni_{35}Zn_{10}$ HEA are systematically studied to understand the MA behavior and develop advanced techniques for fabricating HEA products. After MA, a single FCC phase is found. After sintering at $900^{\circ}C$, the microstructure has an FCC single phase with an average grain size of $18{\mu}m$. Finally, the $Co_{10}Fe_{10}Mn_{35}Ni_{35}Zn_{10}$ HEA has a compressive yield strength of 302 MPa.

An approach for screening single phase high-entropy alloys using an in-house thermodynamic database

Tapia, Antonio Joã,o Seco Ferreira,Yim, Dami,Kim, Hyoung Seop,Lee, Byeong-Joo Elsevier 2018 INTERMETALLICS Vol.101 No.-

<P><B>Abstract</B></P> <P>A new screening methodology is proposed to aid in the development of high-entropy alloys (HEAs). This approach takes into account three commonly used criteria and methods to guide the design of HEAs: empirical parameters, binary phase diagram inspection and the Calculation of Phase Diagrams (CALPHAD) method. In addition, two novel concepts are introduced: a criterion to evaluate the likeliness of single phase solid solution in an alloy system's non-equiatomic compositional space, and a binary priority list, which allows us to make the employed in-house thermodynamic database a more reliable tool for solid solution screening in a time-effective manner.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A novel and easy to replicate screening methodology was proposed in order to guide the design of high-entropy alloys (HEAs). </LI> <LI> A criterion to evaluate the likeliness of single phase solid solution in the non-equiatomic compositional space was proposed. </LI> <LI> A criterion to identify the most relevant weaknesses for solid solution screening in a thermodynamic database was proposed. </LI> <LI> Over one hundred thousand compositions of HEAs candidate systems were analyzed; promising new HEA systems were identified. </LI> <LI> Two novel HEAs (Co<SUB>10</SUB>Fe<SUB>10</SUB>Mn<SUB>35</SUB>Ni<SUB>35</SUB>Zn<SUB>10</SUB> and Co<SUB>10</SUB>Fe<SUB>10</SUB>Mn<SUB>30</SUB>Ni<SUB>30</SUB>Zn<SUB>20</SUB>) were fabricated. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Trade-off between tensile property and formability by partial recrystallization of CrMnFeCoNi high-entropy alloy

Bae, Jae Wung,Moon, Jongun,Jang, Min Ji,Yim, Dami,Kim, Daeyong,Lee, Sunghak,Kim, Hyoung Seop Elsevier 2017 Materials science & engineering. properties, micro Vol.703 No.-

<P><B>Abstract</B></P> <P>In this work, a high-entropy alloy of equiatomic CrMnFeCoNi was processed by vacuum induction melting followed by rolling. After cold rolling, annealing for one hour was conducted during which the annealing temperature was varied from 650 to 1000°C. This was done to investigate the effect of microstructure on tensile properties and stretch formability (defined as the capability of materials to undergo plastic deformation under biaxial stretching). The strengthening effect of partial recrystallization, with a remaining small fraction of sigma phase particles, led to improved yield and tensile strengths while minimizing the loss of ductility. Fully recrystallized microstructure resulted in a slight increase in ductility, and a considerable decrease in strength, during a tensile test. On the other hand, the results for stretch formability suggest that partial recrystallization had exactly the opposite results. In this regard, the present results raise a new issue to consider when utilizing partial recrystallization for improvement of mechanical properties.</P>

Mechanical behavior and solid solution strengthening model for face-centered cubic single crystalline and polycrystalline high-entropy alloys

Moon, Jongun,Jang, Min Ji,Bae, Jae Wung,Yim, Dami,Park, Jeong Min,Lee, Jehyun,Kim, Hyoung Seop Elsevier 2018 INTERMETALLICS Vol.98 No.-

<P><B>Abstract</B></P> <P>In the present work, a solid solution strengthening effect in high-entropy alloys (HEAs) was studied by investigating mechanical characteristics of single crystalline CoCrFeMnNi HEA and a corresponding model was developed. (100) and (110) oriented single crystals of the CoCrFeMnNi alloy were grown and their single crystallinity was identified using X-ray diffraction (XRD), energy dispersive spectroscopy (EDS), and electron backscatter diffraction (EBSD) analyses. The mechanical testing of the single crystalline CoCrFeMnNi alloy was performed and the critical resolved shear stress (CRSS) was obtained. A solid solution strengthening modeling based on the lattice friction stress and an intrinsic residual strain of HEAs was performed. The solid solution strengthening effect of HEAs was verified using the model proposed.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Mechanical behavior of CoCrFeMnNi single crystals shows a typical face-centered cubic single crystal response. </LI> <LI> The root mean square residual strain of a CoCrFeMnNi alloy system was calculated using a geometrical model. </LI> <LI> A novel model for solid solution strengthening in high-entropy alloys was developed. </LI> <LI> The proposed model predicts the intrinsic yield strength of face-centered cubic high-entropy alloys with remarkable accuracy. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Effects of homogenization temperature on cracking during cold-rolling of Al_0.5CoCrFeMnNi high-entropy alloy

Moon, Jongun,Bae, Jae Wung,Jang, Min Ji,Baek, Seung Mi,Yim, Dami,Lee, Byeong-Joo,Kim, Hyoung Seop Elsevier Sequoia S.A 2018 Materials chemistry and physics Vol.210 No.-

<P><B>Abstract</B></P> <P>In this work, the effects of homogenization annealing temperature of Al<SUB>0.5</SUB>CoCrFeMnNi HEA on cracking during cold-rolling were investigated. AlNi B2 phases were formed by low-temperature homogenization and affected the cracking phenomenon during cold-rolling. X-ray diffraction, microstructure, and composition analyses and thermodynamic calculations were conducted to identify the crystal structure of the alloy after the homogenization annealing treatment. The phase fraction and hardness of the homogenized alloy confirmed that the formation of the AlNi B2 phase induces cracking during cold-rolling of the Al<SUB>0.5</SUB>CoCrFeMnNi alloy. High-temperature annealing for homogenization of the alloy is recommended to prevent cracking during cold-rolling.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The Al<SUB>0.5</SUB>CoCrFeMnNi HEA annealed at 1200 °C was successfully cold-rolled. </LI> <LI> The alloys annealed at low temperatures were cracked during cold-rolling. </LI> <LI> AlNi-rich B2 phases were formed at lower annealing temperatures than 1200 °C. </LI> <LI> The formation of AlNi-rich B2 phases hardened the alloy. </LI> <LI> The method to prevent cracking during the cold-rolling of the alloy was proposed. </LI> </UL> </P>