Unveiling the Strengthening and Ductility Mechanisms of a CoCr<sub>0</sub>.<sub>4</sub>NiSi<sub>0</sub>.<sub>3</sub> Medium-Entropy Alloy at Cryogenic Temperatures
Materials utilized in extreme environments, such as those necessitating protection and impact resistance at cryogenic temperatures, must exhibit high strength, ductility, and structural stability. However, most alloys fail to maintain adequate toughness at cryogenic temperatures, thereby compromisin...
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2025-02-01
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| author | Li Zhang Lingwei Zhang Xiang Chen |
| author_facet | Li Zhang Lingwei Zhang Xiang Chen |
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| description | Materials utilized in extreme environments, such as those necessitating protection and impact resistance at cryogenic temperatures, must exhibit high strength, ductility, and structural stability. However, most alloys fail to maintain adequate toughness at cryogenic temperatures, thereby compromising their safety during cryogenic temperature service. This study investigates the quasi-static mechanical properties of a CoCr<sub>0</sub>.<sub>4</sub>NiSi<sub>0</sub>.<sub>3</sub> medium-entropy alloy (MEA) at room temperature, −75 °C, and −150 °C. The deformation behavior and mechanisms responsible for strengthening and toughening at reduced cryogenic temperatures are analyzed, revealing that decreasing cryogenic temperature enhances the strength of the as-cast MEA. Specifically, both the yield strength (YS) and ultimate tensile strength (UTS) of the MEA increase significantly with decreasing temperature during cryogenic tensile testing. Under tensile testing at −150 °C, the YS reaches 617.5 MPa, the UTS is 1055.0 MPa, and the elongation to fracture remains approximately 21.0% at both −150 °C and −75 °C. After cryogenic temperature tensile deformation, the matrix exhibits a dispersed distribution of nanoscaled tetragonal and orthorhombic phases, a coherent hexagonal close-packed phase, L1<sub>2</sub> phase and layered long-period stacking ordered (LPSO) structures, which are rarely observed in the cryogenic deformation of metals and alloys. The metastable phase evolution path of this MEA at cryogenic temperatures is closely associated with the decomposition of perfect dislocations into a/6<112> Shockley partial dislocations and their subsequent evolution at reduced cryogenic temperatures. At −75 °C, the a/6<112> Shockley partial dislocation interacts with the L1<sub>2</sub> phase to form antiphase boundaries (APBs) approximately 3 nm thick. At −150 °C, two phase transition paths from stacking faults (SFs) to nanotwins and LPSO occur, leading to the formation of layered LPSO structures and deformation-induced nanotwins. The dispersion of these coherent nanophases and nanotwins induced by the reduced stacking fault energy under cryogenic temperatures is the key factor contributing to the excellent balance of strength and plasticity in the as-cast MEA, providing an important basis for research on the cryogenic mechanical properties of CoCrNi-based MEAs. |
| format | Article |
| id | doaj-art-e6d42e17fb8e4dfc9e27cad5bd9d201c |
| institution | DOAJ |
| issn | 2073-4352 |
| language | English |
| publishDate | 2025-02-01 |
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| spelling | doaj-art-e6d42e17fb8e4dfc9e27cad5bd9d201c2025-08-20T02:44:59ZengMDPI AGCrystals2073-43522025-02-0115217010.3390/cryst15020170Unveiling the Strengthening and Ductility Mechanisms of a CoCr<sub>0</sub>.<sub>4</sub>NiSi<sub>0</sub>.<sub>3</sub> Medium-Entropy Alloy at Cryogenic TemperaturesLi Zhang0Lingwei Zhang1Xiang Chen2School of Materials Science and Engineering, Shenyang Ligong University, Shenyang 110159, ChinaSchool of Materials Science and Engineering, Shenyang Ligong University, Shenyang 110159, ChinaSchool of Materials Science and Engineering, Shenyang Ligong University, Shenyang 110159, ChinaMaterials utilized in extreme environments, such as those necessitating protection and impact resistance at cryogenic temperatures, must exhibit high strength, ductility, and structural stability. However, most alloys fail to maintain adequate toughness at cryogenic temperatures, thereby compromising their safety during cryogenic temperature service. This study investigates the quasi-static mechanical properties of a CoCr<sub>0</sub>.<sub>4</sub>NiSi<sub>0</sub>.<sub>3</sub> medium-entropy alloy (MEA) at room temperature, −75 °C, and −150 °C. The deformation behavior and mechanisms responsible for strengthening and toughening at reduced cryogenic temperatures are analyzed, revealing that decreasing cryogenic temperature enhances the strength of the as-cast MEA. Specifically, both the yield strength (YS) and ultimate tensile strength (UTS) of the MEA increase significantly with decreasing temperature during cryogenic tensile testing. Under tensile testing at −150 °C, the YS reaches 617.5 MPa, the UTS is 1055.0 MPa, and the elongation to fracture remains approximately 21.0% at both −150 °C and −75 °C. After cryogenic temperature tensile deformation, the matrix exhibits a dispersed distribution of nanoscaled tetragonal and orthorhombic phases, a coherent hexagonal close-packed phase, L1<sub>2</sub> phase and layered long-period stacking ordered (LPSO) structures, which are rarely observed in the cryogenic deformation of metals and alloys. The metastable phase evolution path of this MEA at cryogenic temperatures is closely associated with the decomposition of perfect dislocations into a/6<112> Shockley partial dislocations and their subsequent evolution at reduced cryogenic temperatures. At −75 °C, the a/6<112> Shockley partial dislocation interacts with the L1<sub>2</sub> phase to form antiphase boundaries (APBs) approximately 3 nm thick. At −150 °C, two phase transition paths from stacking faults (SFs) to nanotwins and LPSO occur, leading to the formation of layered LPSO structures and deformation-induced nanotwins. The dispersion of these coherent nanophases and nanotwins induced by the reduced stacking fault energy under cryogenic temperatures is the key factor contributing to the excellent balance of strength and plasticity in the as-cast MEA, providing an important basis for research on the cryogenic mechanical properties of CoCrNi-based MEAs.https://www.mdpi.com/2073-4352/15/2/170cryogenic tensile propertiesstrengthL1<sub>2</sub> phaseLPSOstacking faultsCoCrNi based alloys |
| spellingShingle | Li Zhang Lingwei Zhang Xiang Chen Unveiling the Strengthening and Ductility Mechanisms of a CoCr<sub>0</sub>.<sub>4</sub>NiSi<sub>0</sub>.<sub>3</sub> Medium-Entropy Alloy at Cryogenic Temperatures Crystals cryogenic tensile properties strength L1<sub>2</sub> phase LPSO stacking faults CoCrNi based alloys |
| title | Unveiling the Strengthening and Ductility Mechanisms of a CoCr<sub>0</sub>.<sub>4</sub>NiSi<sub>0</sub>.<sub>3</sub> Medium-Entropy Alloy at Cryogenic Temperatures |
| title_full | Unveiling the Strengthening and Ductility Mechanisms of a CoCr<sub>0</sub>.<sub>4</sub>NiSi<sub>0</sub>.<sub>3</sub> Medium-Entropy Alloy at Cryogenic Temperatures |
| title_fullStr | Unveiling the Strengthening and Ductility Mechanisms of a CoCr<sub>0</sub>.<sub>4</sub>NiSi<sub>0</sub>.<sub>3</sub> Medium-Entropy Alloy at Cryogenic Temperatures |
| title_full_unstemmed | Unveiling the Strengthening and Ductility Mechanisms of a CoCr<sub>0</sub>.<sub>4</sub>NiSi<sub>0</sub>.<sub>3</sub> Medium-Entropy Alloy at Cryogenic Temperatures |
| title_short | Unveiling the Strengthening and Ductility Mechanisms of a CoCr<sub>0</sub>.<sub>4</sub>NiSi<sub>0</sub>.<sub>3</sub> Medium-Entropy Alloy at Cryogenic Temperatures |
| title_sort | unveiling the strengthening and ductility mechanisms of a cocr sub 0 sub sub 4 sub nisi sub 0 sub sub 3 sub medium entropy alloy at cryogenic temperatures |
| topic | cryogenic tensile properties strength L1<sub>2</sub> phase LPSO stacking faults CoCrNi based alloys |
| url | https://www.mdpi.com/2073-4352/15/2/170 |
| work_keys_str_mv | AT lizhang unveilingthestrengtheningandductilitymechanismsofacocrsub0subsub4subnisisub0subsub3submediumentropyalloyatcryogenictemperatures AT lingweizhang unveilingthestrengtheningandductilitymechanismsofacocrsub0subsub4subnisisub0subsub3submediumentropyalloyatcryogenictemperatures AT xiangchen unveilingthestrengtheningandductilitymechanismsofacocrsub0subsub4subnisisub0subsub3submediumentropyalloyatcryogenictemperatures |