EP3693483A1 - Alliage à entropie élevée de plasticité induite par la transformation, et son procédé de fabrication - Google Patents

Alliage à entropie élevée de plasticité induite par la transformation, et son procédé de fabrication Download PDF

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Publication number
EP3693483A1
EP3693483A1 EP18814482.8A EP18814482A EP3693483A1 EP 3693483 A1 EP3693483 A1 EP 3693483A1 EP 18814482 A EP18814482 A EP 18814482A EP 3693483 A1 EP3693483 A1 EP 3693483A1
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EP
European Patent Office
Prior art keywords
transformation
entropy alloy
phase
induced plasticity
fcc
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Pending
Application number
EP18814482.8A
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German (de)
English (en)
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EP3693483A4 (fr
Inventor
Byeong-joo Lee
Sung-Hak Lee
Seok-Su SOHN
Hyoung-Seop KIM
Dong-Geun Kim
Yong-hee JO
Won-mi CHOI
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Academy Industry Foundation of POSTECH
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Academy Industry Foundation of POSTECH
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Priority claimed from KR1020170139052A external-priority patent/KR20190009229A/ko
Application filed by Academy Industry Foundation of POSTECH filed Critical Academy Industry Foundation of POSTECH
Publication of EP3693483A1 publication Critical patent/EP3693483A1/fr
Publication of EP3693483A4 publication Critical patent/EP3693483A4/fr
Pending legal-status Critical Current

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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C30/00—Alloys containing less than 50% by weight of each constituent
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
    • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/001—Austenite

Definitions

  • the present invention relates to a transformation-induced plasticity high-entropy alloy and preparation method thereof which can provide improved mechanical properties compared to those obtained by conventional methods, due to the phase transformation occurring when deformed at a cryogenic temperature.
  • High-entropy alloys which are multi-element alloys obtained by alloying similar proportions of five or more constituent elements without the main elements constituting the alloys (for example, general alloys such as steel, aluminum alloys, titanium alloys, etc.), are metallic materials that have a single-phase structure (e.g., face-centered cubic (FCC), body-centered cubic (BCC)) in which an intermetallic compound or intermediate phase is not formed due to high entropy of mixing within the alloys.
  • FCC face-centered cubic
  • BCC body-centered cubic
  • Co-Cr-Fe-Mn-Ni based HEAs have excellent cryogenic properties, high fracture toughness, and corrosion resistance, and are thus in the limelight as a material applicable to extreme environments.
  • composition ratio of HEAs a typical HEA should consist of at least five major alloy elements, and the composition ratio of each alloy constituent element is defined as 5-35 at%, and if an element other than the main alloy constituent elements is added, the addition amount should be less than 5 at%.
  • An object of the present invention is to provide a transformation-induced plasticity high-entropy alloy, which mainly consists of FCC phase and are capable of achieving more improved mechanical properties at a cryogenic temperature (-196°C), compared to previously reported HEAs having an FCC single-phase.
  • an aspect of the present invention provides a transformation-induced plasticity high-entropy alloy, which contains 10-35 at% of Co, 3-15 at% of Cr, 3-15 at% of V, 35-48 at% of Fe, and 0-25 at% of Ni (exclusive of 25), and mainly consists of an FCC phase at room temperature, wherein transformation-induced plasticity, in which at least part of the FCC phase changes to a BCC phase, occurs at a cryogenic temperature (-196°C).
  • Another aspect of the present invention provides a method for preparing a transformation-induced plasticity high-entropy alloy, the method including: a homogenization step, which includes heating and cooling for homogenizing the microstructure of a high-entropy alloy (HEA), which contains 10-35 at% of Co, 3-15 at% of Cr, 3-15 at% of V, 35-48 at% of Fe, and 0-25 at% of Ni (exclusive of 25); a step of rolling the homogenized HEA to a sheet having a predetermined thickness; and an annealing step, in which the rolled HEA is heated up to an FCC single-phase region, and then cooled at a cooling rate by which the FCC phase is able to be maintained.
  • a homogenization step which includes heating and cooling for homogenizing the microstructure of a high-entropy alloy (HEA), which contains 10-35 at% of Co, 3-15 at% of Cr, 3-15 at% of V, 35-48 at% of Fe, and 0-25 at% of Ni (exclusive
  • a high-entropy alloy (HEA) according to the present invention can provide a single-phase FCC structure by having a quaternary or quinary HEA composition that essentially contains Co, Cr, Fe, and V, and optionally containing Ni.
  • a HEA according to the present invention causes transformation-induced plasticity at a cryogenic temperature (-196°C), and thus has a more excellent tensile strength, ductility, and fracture properties at a cryogenic temperature (-196°C), than conventional single-phase HEAs.
  • FIG. 1 shows phase equilibrium information on an alloy according to mole fractions of the alloy, as a cobalt (Co) content changes in a composition, where iron (Fe) is fixed at 45 at%, chromium (Cr) is fixed at 10 at%, and vanadium (V) is fixed at 10 at%, whereas cobalt (Co) is contained in an amount of X at% and nickel (Ni) is contained in an amount of 35-X at%.
  • Co cobalt
  • FIG. 2 shows the stability of an FCC phase with respect to a BCC phase through thermodynamic calculations, as a cobalt (Co) content changes at 298k in a composition where the iron (Fe) is fixed at 45 at%, the chromium (Cr) is fixed at 10 at%, and the vanadium (V) is fixed at 10 at%, whereas cobalt (Co) is contained in an amount of X at% and nickel (Ni) is contained in an amount of 35-X at%.
  • FIG. 3 shows phase equilibrium information on an alloy according to mole fractions of the alloy as an iron (Fe) content changes in a composition, where the chromium (Cr) is fixed at 10 at%, the vanadium (V) is fixed at 10 at%, and the cobalt (Co) is fixed at 30 at%, whereas the iron (Fe) is contained in an amount of X at% and nickel (Ni) is contained in an amount of 50-X at%.
  • iron (Fe) and nickel (Ni) are substituted in 10Cr-10V-30Co (values are in unit of at%), it is confirmed that an FCC single-phase region is expanded as the iron (Fe) content is decreased, and it can be seen that the iron (Fe) content be preferably in an amount of 48 at% or less so as to maintain the FCC single-phase.
  • FIG. 4 shows the stability of an FCC phase with respect to a BCC phase through thermodynamic calculations, as an iron (Fe) content changes at 298k in a composition where the chromium (Cr) is fixed at 10 at%, the vanadium (V) is fixed at 10 at%, and the cobalt (Co) is fixed at 30 at%, whereas the iron (Fe) is contained in an amount of X at% and nickel (Ni) is contained in an amount of 50-X at%.
  • the iron (Fe) content be in an amount of 35 at% or more, in consideration of a driving force required for transformation from an FCC phase to a BCC phase.
  • a HEA which mainly consists of an FCC phase and in which the Gibbs free energy of the body-center cubic structure (BCC) is smaller than that of the face-centered cubic structure (FCC)
  • BCC body-center cubic structure
  • FCC face-centered cubic structure
  • the HEA according to the present invention is developed in accordance with the alloy designing principle described above, and is characterized in that the HEA essentially contains Co, Cr, Fe, and V, and optionally contains Ni, and mainly consists of an FCC phase, wherein transformation-induced plasticity from an FCC phase to a BCC phase occurs when plastic deformation is applied at a cryogenic temperature (-196°C).
  • the HEA according to the present invention may preferably contain 10-35 at% of Co, 3-15 at% of Cr, 3-15 at% of V, 35-48 at% of Fe, and 0-25 at% of Ni (exclusive of 25), and the remaining unavoidable impurities.
  • the Co content is preferably in a range of 10-35 at%, and more preferably 15-30 at%.
  • the Cr content is preferably in a range of 3-15 at%, and more preferably 5-10 at%.
  • the Ni content is equal to or greater than 25 at%, transformation-induced plasticity may not occur, and thus the Ni content is preferably less than 25 at%.
  • the Ni content is 0 at%, a complete FCC single-phase may not be obtained by the heat treatment at 900°C. Therefore, in order to achieve an FCC single-phase structure by the heat treatment at 900°C, the Ni content is more preferably in a range of 2.5-20 at% (exclusive of 20).
  • the Fe content is less than 35 at% or greater than 48 at%, transformation-induced plasticity may not occur or a phase in which the FCC phase is dominant may not be obtained. Therefore, the Fe content is preferably in a range of 35-48 at%, and more preferably 40-45 at%.
  • the V content is preferably in a range of 3-15 at%, and more preferably 5-10 at%.
  • the unavoidable impurities are components other than the above-described alloy elements, which are raw materials or components unavoidably incorporated during the preparation process, and the impurities are included in an amount of 1 at% or less, preferably 0.1 at% or less, and more preferably 0.01 at% or less.
  • the transformation-induced plasticity HEA according to the present invention is characterized by mainly consisting of an FCC phase, and the fraction of the FCC phase is preferably 95% or greater, and may consist of an FCC single-phase.
  • the transformation-induced plasticity HEA according to the present invention is characterized in that phase transformation, in which at least part of the FCC phase before deformation changes to a BCC phase during a deformation process, occurs at a cryogenic temperature (-196°C).
  • phase transformation in which at least part of the FCC phase before deformation changes to a BCC phase during a deformation process, occurs at a cryogenic temperature (-196°C).
  • all of the FCC phases may be changed to BCC phases.
  • the transformation-induced plasticity HEA according to the present invention may preferably have a tensile strength of 650 MPa or greater and has an elongation of 50% or greater, at room temperature (25°C).
  • the transformation-induced plasticity HEA according to the present invention may preferably have a tensile strength of 1,100 MPa or greater and has an elongation of 65% or greater, at a cryogenic temperature (-196°C) .
  • a difference between an impact energy at room temperature (25°C) and an impact energy at a cryogenic temperature (-196°C) may be 10% or less.
  • transformation-induced plasticity HEA may preferably be prepared through the following steps of (a) to (c):
  • the temperature for homogenization treatment when the temperature for homogenization treatment is lower than 1,000°C, the homogenization effect is insufficient; however, when the temperature for homogenization treatment is higher than 1,200°C, the heat treatment costs become excessive. Therefore, the temperature for homogenization treatment is preferably in a range of 1,000 to 1,200°C.
  • the time for homogenization treatment is less than 6 hours, the homogenization effect is insufficient; however, when the time for homogenization treatment exceeds 24 hours, the heat treatment cost becomes excessive. Therefore, the time for heat treatment is preferably in a range of 6 to 24 hours.
  • the temperature for annealing treatment when the temperature for annealing treatment is lower than 800°C, it is not possible to achieve complete recrystallization; however, when the temperature for annealing treatment is higher than 1,000°C, grain coarsening becomes more severe. Therefore, the temperature for annealing treatment is preferably in a range of 800°C to 1, 000°C. When the time for annealing treatment is less than 3 minutes, it is not possible to achieve complete recrystallization; however, when the time for annealing treatment is greater than 1 hour, the heat treatment cost becomes excessive. Therefore, the time for annealing treatment is preferably in a range of 3 minutes to 1 hour.
  • the cooling at steps (a) and (c) may be performed through water quenching, but is not particularly limited as long as a microstructure, which is required after each cooling treatment, can be achieved.
  • the raw material metals prepared at the above ratio were charged into a crucible, dissolved using vacuum induction melting equipment, and an alloy ingot in a rectangular parallelepiped shape (thickness: 8 mm, width: 35 mm, and length: 100 mm) was cast.
  • the cast ingot (thickness: 8 mm) was subjected to homogenization heat treatment at a temperature of 1,100°C for 6 hours, followed by water quenching, as shown in FIG. 5 .
  • the thickness of the ground ingot was 7 mm, and cold rolling was performed such that the thickness thereof changes from 7 mm to 1.5 mm.
  • each of the cold-rolled alloy sheets was subjected to annealing treatment by heating at 900°C for 10 minutes to maintain the FCC phase, followed by quenching to maintain the FCC phase at room temperature.
  • FIG. 6 shows the results of XRD measurement of the alloys at room temperature according to Examples 1 to 3 and Comparative Example prepared according to the process described above.
  • the XRD measurement was performed after performing the grinding in the order of sandpaper Nos. 600, 800, 1200, and 2000, followed by electrolytic etching in 8% perchloric acid.
  • Example 2 As observed in FIG. 6 , it was confirmed that all the alloys according to Example 2, Example 3, and Comparative Example consist of FCC single-phases by XRD analysis.
  • the alloy according to Example 1 mainly contained FCC phase and small amount of BCC phase. This is consistent with what is predicted from the equilibrium phase diagram of FIG. 1 , and if the annealing temperature is higher than 900°C, the alloys can be prepared to have an FCC single-phase, as is the case with the alloys according to Examples 2 and 3.
  • FIG. 7 shows the fractions of a BCC phase in the microstructure after the tensile tests of the HEAs, which were prepared according to Examples 1 to 3 and Comparative Example at room temperature and at a cryogenic temperature (-196°C), according to Ni content.
  • Example 1 As shown in FIG. 7 , in the case of Example 1, about 24% of phase transformation was achieved even when a tensile test performed at room temperature, whereas the amount of phase transformation was 0.8% in Example 2, very low to be 0.3% in Example 3, and 0% in Comparative Example.
  • FIGS. 8 and 9 and Table 2 show the tensile test results of the alloys of Examples 1 to 3 and Comparative Example of the present invention at room temperature (25°C) and a cryogenic temperature (-196°C).
  • the HEAs according to Examples 1 to 3 of the present invention at room temperature, showed a yield strength of 339 MPa to 427 MPa, a tensile strength of 679 MPa to 745 MPa, and an elongation of 51.1% to 70.1%, and the HEA according to Comparative Example showed a yield strength of 339 MPa, a tensile strength of 684 MPa, and an elongation of 47%, thus showing no significant difference compared to those of Examples 1 to 3.
  • the HEAs according to Examples 1 to 3 of the present invention at a cryogenic temperature, showed a yield strength of 569 MPa to 653 MPa, a tensile strength of 1,142 MPa to 1,623 MPa, and an elongation of 65.0% to 82.3%, and the HEA according to Comparative Example showed a yield strength of 468 MPa, a tensile strength of 996 MPa, and an elongation of 69.4%, thus showing lower mechanical properties compared to those of Examples 1 to 3.
  • the Comparative Example shows a significant difference compared to Example 3 that exhibits mechanical properties similar to those of Comparative Example at room temperature. These differences are assumed to be due to the transformation-induced plasticity.
  • the HEA according to Example 1 at a cryogenic temperature, showed a high tensile strength of 1,623 MPa, and good elongation of 65.0%, which proves that the HEA according to Example 1 has high strength and good elongation.
  • FIG. 10 shows the comparison results of the tensile strength and elongation at a cryogenic temperature of the HEAs (herein indicated as 'start' mark) according to Examples 1 to 3 of the present invention and other HEAs reported previously.
  • the tensile strength and elongation of the HEAs according to Examples 1 to 3 of the present invention were extremely high thus exhibiting excellent characteristics compared to any conventional alloys or HEAs.
  • FIG. 11 shows the results of the Charpy impact test performed under the conditions from room temperature to a cryogenic temperature.
  • the Charpy impact test sub-sized samples with a thickness of 5 mm were used.
  • the HEA according to Example 2 of the present invention showed constant values, that is, almost no difference between an impact energy value at room temperature and an impact energy value at a cryogenic temperature, and thus exhibited peculiar characteristics which could be hardly seen in existing materials, in which, generally, as the temperature decreases, the impact energy value decreases, and the BCC phase present at a cryogenic temperature causes the impact energy to be rapidly decreased.

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EP18814482.8A 2017-10-25 2018-03-30 Alliage à entropie élevée de plasticité induite par la transformation, et son procédé de fabrication Pending EP3693483A4 (fr)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
KR1020170139052A KR20190009229A (ko) 2017-07-18 2017-10-25 변태유기소성 고엔트로피 합금 및 이의 제조방법
KR1020180006851A KR102054735B1 (ko) 2017-07-18 2018-01-19 변태유기소성 고엔트로피 합금 및 이의 제조방법
PCT/KR2018/003772 WO2019083103A1 (fr) 2017-10-25 2018-03-30 Alliage à entropie élevée de plasticité induite par la transformation, et son procédé de fabrication

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EP3693483A1 true EP3693483A1 (fr) 2020-08-12
EP3693483A4 EP3693483A4 (fr) 2021-08-18

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CN112962014B (zh) * 2021-02-03 2022-05-13 湖南大学 一种基于退火硬化提高多组元合金强塑性的方法
CN113430343B (zh) * 2021-07-05 2022-09-20 陕西科技大学 一种纳米析出强化CoCrNi基高熵合金的处理方法
CN114657437B (zh) * 2022-04-06 2022-08-12 大连理工大学 一种具有优异热改性的Co-Cr-Fe-Ni-V-B共晶高熵合金及其制备方法

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JPS5298613A (en) * 1976-02-14 1977-08-18 Inoue K Spenodal dissolvic magnet alloy
US20020159914A1 (en) * 2000-11-07 2002-10-31 Jien-Wei Yeh High-entropy multielement alloys
TWI315345B (en) * 2006-07-28 2009-10-01 Nat Univ Tsing Hua High-temperature resistant alloys
JP6388381B2 (ja) * 2014-07-23 2018-09-12 日立金属株式会社 合金構造体
US10364487B2 (en) * 2016-02-15 2019-07-30 Seoul National University R&Db Foundation High entropy alloy having TWIP/TRIP property and manufacturing method for the same
KR101813008B1 (ko) * 2016-03-11 2017-12-28 충남대학교산학협력단 석출경화형 고 엔트로피 합금 및 그 제조방법
KR101888299B1 (ko) * 2016-03-21 2018-08-16 포항공과대학교 산학협력단 극저온용 고 엔트로피 합금

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