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Asghari-Rad, Peyman,Kim, Yongju,Nguyen, Nhung Thi-Cam,Kim, Hyoung Seop The Korean Powder Metallurgy Institute 2020 한국분말재료학회지 (KPMI) Vol.27 No.1
In this research, a new medium-entropy alloy with an equiatomic composition of FeCuNi was designed using a phase diagram (CALPHAD) technique. The FeCuNi MEA was produced from pure iron, copper, and nickel powders through mechanical alloying. The alloy powders were consolidated via a high-pressure torsion process to obtain a rigid bulk specimen. Subsequently, annealing treatment at different conditions was conducted on the four turn HPT-processed specimen. The microstructural analysis indicates that an ultrafine-grained microstructure is achieved after post-HPT annealing, and microstructural evolutions at various stages of processing were consistent with the thermodynamic calculations. The results indicate that the post-HPT-annealed microstructure consists of a dual-phase structure with two FCC phases: one rich in Cu and the other rich in Fe and Ni. The kernel average misorientation value decreases with the increase in the annealing time and temperature, indicating the recovery of HPT-induced dislocations.
Bae, Jae Wung,Park, Jeong Min,Moon, Jongun,Choi, Won Mi,Lee, Byeong-Joo,Kim, Hyoung Seop Elsevier 2019 JOURNAL OF ALLOYS AND COMPOUNDS Vol.781 No.-
<P><B>Abstract</B></P> <P>Non-equiatomic Co<SUB>17.5</SUB>Cr<SUB>12.5</SUB>Fe<SUB>55</SUB>Ni<SUB>10</SUB>Mo<SUB>5</SUB> (Mo5) and Co<SUB>18</SUB>Cr<SUB>12.5</SUB>Fe<SUB>55</SUB>Ni<SUB>7</SUB>Mo<SUB>7.5</SUB> (Mo7.5) medium-entropy alloys were synthesized by vacuum induction melting, cold rolling, and subsequent annealing treatment at various temperatures (900–1200 °C) and they were investigated to exploit the precipitation strengthening in addition to solid solution strengthening of alloys. The effect of annealing temperature and Mo content on the microstructure and mechanical properties are systematically analyzed. From the microstructural analysis, a Mo-rich μ phase is observed in the face-centered cubic (fcc) matrix. Increasing the Mo content and low annealing temperature enhance the formation of μ phase, which is consistent with the thermodynamic calculation results. The formation of μ phase effectively enhances the strength of the Mo7.5 alloy by precipitation strengthening, and suppression of grain growth and recrystallization by Zener pinning effect. These lead to superior combination of tensile strength as high as 1100 MPa and large ductility. Our results provide insights not only into μ-phase strengthening of fcc-structured alloys, but also into the future development of high-performance MEAs.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The effect of μ-precipitates in the non-equiatomic CoCrFeNiMo alloys is discussed. </LI> <LI> Further addition of Mo and decrease in annealing temperature enhances the formation of μ phase. </LI> <LI> Formation of μ phase retards the recrystallization and grain growth by Zener pinning effect. </LI> <LI> The present non-equiatomic CoCrFeNiMo alloys exhibits superior tensile properties by multiple strengthening mechanisms. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Precipitate behavior in nitrogen-containing CoCrNi medium-entropy alloys
Jodi, Dennis Edgard,Park, Joohyun,Park, Nokeun Elsevier 2019 Materials characterization Vol.157 No.-
<P><B>Abstract</B></P> <P>The effect of nitrogen addition toward nitride precipitate formation and the corresponding behavior in a medium-entropy alloy system of N-CoCrNi was investigated. It was observed that the addition of N induced the formation of a Cr- and N-rich precipitate of Cr<SUB>2</SUB>N. Cr<SUB>2</SUB>N and the face-centered cubic (FCC) matrix in the N-CoCrNi system exhibited a Kikuchi orientation relation in the {111}<I>γ</I>//{0001}Cr<SUB>2</SUB>N plane and 〈110〉<I>γ</I>//〈 1 1 ¯ 00 〉Cr<SUB>2</SUB>N direction, where Cr<SUB>2</SUB>N was observed to be semi-coherent with the FCC matrix. The presence of Cr<SUB>2</SUB>N was also observed to contribute in the hindering of grain coarsening via Zener pinning pressure. The distribution of finer and higher fraction of Cr<SUB>2</SUB>N in the lower annealing temperatures of N-CoCrNi contributed more toward higher Zener pinning pressure compared to the coarser and lower fraction of Cr<SUB>2</SUB>N in the higher annealing temperatures, which subsequently affected grain growth during the annealing treatment.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The effect of nitrogen addition in CoCrNi medium-entropy alloy was investigated. </LI> <LI> Cr<SUB>2</SUB>N precipitate was formed along with the face-centered cubic matrix. </LI> <LI> A Kikuchi crystal orientation relation was observed between the Cr<SUB>2</SUB>N and the matrix. </LI> <LI> Cr<SUB>2</SUB>N precipitate contributed in Zener pinning pressure. </LI> <LI> These caused the formation of significantly finer grain size in N-CoCrNi than CoCrNi. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Effect of aluminum addition on solid solution strengthening in CoCrNi medium-entropy alloy
Agustianingrum, Maya Putri,Yoshida, Shuhei,Tsuji, Nobuhiro,Park, Nokeun Elsevier 2019 Journal of alloys and compounds Vol.781 No.-
<P><B>Abstract</B></P> <P>Solid solution strengthening effect was investigated in Al<SUB> <I>x</I> </SUB>CoCrNi medium-entropy alloy (MEA) with different Al content (<I>x</I> = 0–7 at.%). The result of X-ray diffraction indicates that the fully recrystallized phase was a single face-centered cubic (FCC) structure for all compositions. The average grain size regarding a twin boundary as a grain boundary was approximately 16 μm. Tensile testing shows that the yield strength increases with the addition of Al. Here, Labusch's approach to random solid solution alloys is applied to confirm the strengthening mechanism in Al<SUB> <I>x</I> </SUB>CoCrNi MEA by using lattice constants and elastic moduli. The experimental results were found to be in good agreement with quantitative predictions of the solid solution contribution in Al<SUB> <I>x</I> </SUB>CoCrNi MEA.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The effect of dilute addition of Aluminum in equiatomic CoCrNi is investigated. </LI> <LI> Single phase Al<SUB> <I>x</I> </SUB>CoCrNi have similar grain size but have different yield strength. </LI> <LI> Strengthening mechanism in Al<SUB> <I>x</I> </SUB>CoCrNi is quantified by extended Labusch's approach. </LI> <LI> Elastic constant and lattice constant highly involve in the strength prediction. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Ka‑Kin Wong,Hsueh‑Chuan Hsu,Shih‑Ching Wu,Wen‑Fu Ho 대한금속·재료학회 2022 METALS AND MATERIALS International Vol.28 No.10
In this study, novel nonequiatomic Ti-rich Ti-Zr-Nb-Mo medium-entropy alloys (Ti-MEAs) with a metastable body-centeredcubic structure were designed using Mo equivalent theory ([Mo]eq) for biomedical applications. The Ti65-Zr20-Nb14-Mo1(at%; Ti65-M1) and Ti65-Zr18-Nb16-Mo1 (at%; Ti65-M2) exhibited high yield strength of 1188 and 1118 MPa, respectively. Notably, the moduli of Ti65-M1 and Ti65-M2 were as low as 67.4 and 61 GPa, respectively, which were considerably lowerthan those of commercial biomedical alloys and several biomedical HEAs/MEAs. Transmission electron microscopy imagesindicated that Ti65-M2 reached a metastable state, resulting in a low elastic modulus. Furthermore, the yield-strength-to-elastic-modulus ratios (× 1000) of Ti65-M1 and Ti65-M2 were as high as 17.6 and 18.3, respectively, which were approximatelythree times greater than that of a commercial Ti-6Al-4V ELI implant. This study applied metastable theory for developingtwo metastable Ti-MEAs with low elastic moduli.