Method for softening and rejuvenating metallic glass through ultralow-temperature full-elastic constraint compression

Abstract

The invention belongs to the field of mechanical property optimization of amorphous alloy materials, and discloses a method for softening and rejuvenating metallic glass through ultralow-temperature full-elastic constraint compression. Bulk metallic glass is taken as a research object, and full-elastic constraint compression deformation treatment is applied under an ultralow-temperature condition, so that the non-uniform shear fracture behavior of the metallic glass can be remarkably avoided, and the plasticity of the metallic glass is improved. No shear band is generated on the surface of the metal glass subjected to ultralow-temperature full-elastic constraint compression treatment, fine and dispersed multi-shear band distribution is shown in a subsequent mechanical behavior test, and the shear band stress concentration phenomenon which is not beneficial to plastic deformation is effectively inhibited. According to the present invention, the bulk metal glass is prepared, the liquid nitrogen medium is adopted to obtain the ultra-low temperature environment, the sheath is adopted to make the sample subjected to the triaxial constraint force, and the more free volume makes the atom migration and the rearrangement easily occur in the material so as to avoid the formation and the rapid expansion of the main shear band, and achieve the rejuvenation effect.

Description

Technical Field

[0001] The invention belongs to the technical field of metallic glass material structure and plasticity optimization, and relates to a method for softening and rejuvenating metallic glass through ultra-low temperature full elastic constraint compression. Background Art

[0002] Metallic glass has attracted increasing attention in the high-tech field due to its excellent comprehensive properties. Compared with traditional crystalline metals, metallic glass has significantly higher strength and hardness, and its tensile strength is usually more than 1.5GPa, which is more than three times that of ordinary steel. In addition, metallic glass also exhibits excellent elastic limit, which can usually reach 2%, while the elastic limit of most crystalline metals is only about 0.2%. The combination of high strength and high elasticity of this material gives it unique application advantages in many fields. For example, in the aerospace industry, metallic glass is used to manufacture structural components with high strength and lightweight characteristics, which significantly improves the overall performance and service life of spacecraft. In the biomedical field, metallic glass is widely used in the manufacture of high-end medical devices such as artificial joints and dental implants due to its good biocompatibility, corrosion resistance and antibacterial properties.

[0003] Although metallic glass has many properties that crystalline materials do not have due to its unique amorphous structure, this structure also brings some significant defects, especially the high brittleness of the material. Because amorphous materials lack the dislocation slip mechanism in the crystal structure, they cannot disperse stress through plastic deformation when subjected to external forces, resulting in rapid concentration of stress in local areas, thus causing sudden fracture. Specifically, the fracture toughness of metallic glass is usually only 10MPa·m 0.5 The fracture toughness of traditional steel is usually around 50MPa·m 0.5 This high brittleness severely limits the application of metallic glass in situations where it needs to withstand impact loads or large deformations, especially at room temperature, where metallic glass almost completely exhibits brittle fracture.

[0004] In recent years, in order to improve the brittleness of metallic glass, researchers have explored a variety of methods and made significant progress in improving its plastic properties. However, most modification methods focus on improving strength and toughness, while ignoring the "aging" problem of the internal atomic structure of the material under a highly brittle state. The "aging" of metallic glass is a structural degradation phenomenon, which is manifested as a gradual decrease in free volume and a decrease in atomic migration ability, resulting in poor plasticity of the material, an increase in the yield point, and even stress localization, forming a single main shear band. For this reason, the "rejuvenation" of metallic glass has been proposed as a concept of reversing aging. Its core is to increase the free volume inside the material through external treatment means, so that the metallic glass can re-transition from a low-energy, stable aging state to a high-energy, more active structural state, thereby reducing the yield point and significantly improving plasticity and ductility. Summary of the invention

[0005] In view of the above-mentioned situation, the present invention aims at the problem that the existing metallic glass is brittle and difficult to achieve wider engineering applications, and provides a method for softening and rejuvenating metallic glass through ultra-low temperature full elastic constraint compression, and prepares palladium-based bulk nano-metallic glass with good mechanical properties. The present invention applies a full elastic constraint compression process to the bulk metallic glass under ultra-low temperature conditions, and controls parameters such as additional loads, constraint forms, constraint sleeve materials, and process temperature. It is easier for atoms to migrate and rearrange inside the material, thereby preventing the formation of the main shear band and activating the free volume. The bulk metallic glass that is finally treated has fine diffuse shear bands when undergoing mechanical behavior tests, avoiding catastrophic local shear fractures and enhancing the plasticity of the sample.

[0006] The technical solution of the present invention is:

[0007] A method for softening and rejuvenating metallic glass by ultra-low temperature full elastic confinement compression.

[0008] This method subjects the original cast bulk metallic glass to a fully elastic constrained compression process, subjecting it to triaxial constraints during the elastic compression process. This process is carried out at ultra-low temperatures (liquid nitrogen medium), which allows for more powerful regulation of the microstructure of the bulk metallic glass.

[0009] The method comprises the following steps:

[0010] (1) Alloy composition preparation and smelting: Each elemental alloy raw material is accurately weighed according to the atomic ratio, and the mixture of the elemental alloy raw materials is melted in a high-purity argon atmosphere by arc melting to prepare a master alloy. The casting mold is a semi-ellipsoidal water-cooled copper mold;

[0011] (2) Synthesis of bulk metallic glass samples: First, the master alloy sample is placed in a melting device protected by an inert atmosphere, and purified by adding a flux medium (such as an oxide material) under high temperature conditions. The purification process needs to last for a certain period of time to remove impurities in the alloy and improve the purity. After the flux coating purification is completed, the sample is placed in a special melting and casting device, using a closed tube structure with different diameters at both ends, and the stability of the melting environment is maintained by vacuuming and filling with high-purity inert gas (such as argon). In an inert atmosphere, the alloy is melted by a high-temperature heat source, and the molten metal is introduced into a mold or container using a pressure difference. Finally, it is rapidly cooled (such as by quenching with a coolant) to obtain bulk metallic glass;

[0012] (3) The constraint sleeve is made of mature steel. After heat treatment, its hardness is much higher than that of the metallic glass, so that it can effectively constrain the force of the metallic glass under triaxial constraints;

[0013] (4) Calculate the inner and outer diameters of the constraint sleeve, which can effectively constrain the metallic glass to be subjected to triaxial constraints, and cut by electric sparks, so that the inner diameter of the sleeve is the same as that of the metallic glass;

[0014] (5) According to the principle of thermal expansion and contraction, the metallic glass is immersed in liquid nitrogen. At this time, the diameter of the metallic glass is smaller than the inner diameter of the sleeve. It is quickly taken out and assembled on the sleeve. After the temperature of the metallic glass returns to room temperature, the two can be tightly combined.

[0015] (6) Place the combined sample on the tensile machine pressure head and install the liquid nitrogen immersion device;

[0016] (7) Start the tensile machine, and the sample begins to be subjected to triaxial constraints. During this period, liquid nitrogen medium is continuously injected into the liquid nitrogen device so that the sample is always immersed in liquid nitrogen. When the sample is about to yield, stop the tensile machine and keep it statically loaded with the force before yielding for 3 hours;

[0017] (8) After the ultra-low temperature elastic compression process, the sample is removed from the package and then subjected to subsequent mechanical testing.

[0018] Compared with the prior art, the present invention has the following significant advantages:

[0019] The obtained metallic glass is subjected to full elastic constraint compression treatment. By selecting specific process means and controlling process parameters, it is easier for atoms to migrate and rearrange inside the material, without the formation of shear bands, and the free volume is activated to achieve a rejuvenation effect. The bulk metallic glass finally treated has fine diffuse shear bands during mechanical behavior testing. Atomic migration and rearrangement occur inside the material, thereby preventing the formation of the main shear band, activating the free volume, and preventing the local shear band from expanding to form cracks, thereby improving the plastic deformation capacity of the bulk metallic glass. This ultra-low temperature full elastic constraint compression process is different from the traditional large plastic deformation treatment process. First, by applying lateral constraints, the metallic glass can withstand large forces without introducing shear bands, so the nanoscale microstructure of the metallic glass can be artificially controlled to a greater extent; at the same time, a method for full elastic constraint compression process treatment in liquid nitrogen ultra-low temperature medium is proposed, which greatly inhibits the formation of shear bands and can more effectively enhance the control ability of the metallic glass nanostructure.

[0020] Compared with the prior art, the present invention has the following significant advantages:

[0021] 1. By simply applying external constraints, performing full elastic constraint compression treatment and adjusting its process parameters, the generation of the main shear band in the mechanical test can be significantly prevented, the occurrence of non-uniform deformation that is unfavorable to the plasticity of metallic glass can be suppressed, and the plastic deformation capacity of metallic glass can be greatly improved. Compared with the early second phase introduction and composition regulation methods, it avoids the more complicated process and composition regulation process, and the negative impact on the metallic glass matrix.

[0022] 2. While applying constraints, an ultra-low temperature environment is obtained through liquid nitrogen medium. The liquid nitrogen used in the present invention is an ultra-low temperature liquid gas commonly used in laboratories, which is cheap, easy to store and transport, has stable chemical properties, is non-toxic and pollution-free, and has low cost.

[0023] 3. The metallic glass treated by the present invention does not produce shear bands. The free volume of the sample is not increased by introducing shear bands, but the sample is rejuvenated by changing the atomic microstructure inside the sample.

[0024] 4. The technology for preparing bulk metallic glass used in the present invention is simple to operate, has low production cost, simple equipment operation, simple maintenance, high preparation efficiency, and has good prospects for large-scale industrial application. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 For Example 1 of the present invention, Comparative Example 1, 2Pd 82 Si 18 Process diagram of ultra-low temperature full elastic confinement compression treatment of bulk metallic glass;

[0026] Figure 2 For Example 1 of the present invention, Comparative Example 1Pd 82 Si 18 Engineering stress-strain curves of bulk metallic glass in ultra-low temperature fully elastic confined compression process;

[0027] Figure 3 For Example 1 of the present invention, Comparative Example 1, 2Pd 82 Si 18 Stress-strain curves of bulk metallic glass during compression after ultra-low temperature, room temperature and ultra-low temperature 50% yield force full elastic constraint compression treatment;

[0028] Figure 4 For Example 1 of the present invention, Pd 82 Si 18 DSC curves of bulk metallic glass without any treatment and after compression after ultra-low temperature confinement treatment;

[0029] Figure 5 Pd after full elastic constraint compression of Example 1 82 Si 18 Scanning electron micrograph of a bulk metallic glass without shear banding. DETAILED DESCRIPTION

[0030] The present invention is described in detail below

[0031] Existing rejuvenation methods for metallic glass include ultra-low temperature full-constraint treatment, mechanical loading and heat treatment technology, etc. Among them, the ultra-low temperature full-constraint treatment of the present invention is an efficient and innovative rejuvenation method. This method combines the ultra-low temperature conditions provided by the liquid nitrogen environment with the full-constraint process to significantly prevent the formation of the main shear band, inhibit the local stress concentration phenomenon that is not conducive to plastic deformation, and achieve the softening and rejuvenation effect by regulating the atomic free volume inside the material. This method can form diffuse small shear bands while lowering the yield point, thereby improving the plastic deformation ability of the material and enhancing ductility.

[0032] The present invention provides a method for softening and rejuvenating metallic glass by ultra-low temperature full elastic constraint compression, the method comprising:

[0033] (1) Alloy composition preparation and smelting: Each elemental alloy raw material is accurately weighed according to the atomic ratio, and the mixture of the elemental alloy raw materials is melted in a high-purity argon atmosphere by arc melting to prepare a master alloy. The casting mold is a semi-ellipsoidal water-cooled copper mold;

[0034] (2) Synthesis of bulk metallic glass samples: First, the master alloy sample is placed in a melting device protected by an inert atmosphere, and purified by adding a flux medium under high temperature conditions to remove impurities in the alloy and improve the purity; after the flux coating purification is completed, the sample is placed in a special melting and casting device, and the stability of the melting environment is maintained by vacuuming and filling with high-purity inert gas; in the inert atmosphere, the alloy is melted by a high-temperature heat source, and the molten metal is introduced into a mold or container using a pressure difference; finally, it is rapidly cooled to obtain bulk metallic glass;

[0035] (3) The constraint sleeve is made of mature steel. After heat treatment, its hardness is much higher than that of the metallic glass, so that it can effectively constrain the force of the metallic glass under triaxial constraints;

[0036] (4) Calculate the inner and outer diameters of the constraint sleeve, which can effectively constrain the metallic glass to be subjected to triaxial constraint forces, and cut it by electric spark, so that the inner diameter of the sleeve is the same as that of the metallic glass;

[0037] (5) Based on the principle of thermal expansion and contraction, the metallic glass is immersed in liquid nitrogen. At this time, the diameter of the metallic glass is smaller than the inner diameter of the sleeve. It is quickly taken out and assembled on the sleeve. After the temperature of the metallic glass returns to room temperature, the two are tightly combined.

[0038] (6) Place the combined sample on the tensile machine pressure head and install the liquid nitrogen immersion device;

[0039] (7) Start the tensile machine, and the sample begins to be subjected to triaxial constraints. During this period, liquid nitrogen medium is continuously injected into the liquid nitrogen device so that the sample is always immersed in liquid nitrogen. When the sample is about to yield, stop the tensile machine and keep the force before yielding statically loaded for 3 hours;

[0040] (8) After the ultra-low temperature elastic compression process, the sample is removed from the package and then subjected to subsequent mechanical testing.

[0041] The characteristics of the bulk metallic glass finally prepared are: a completely amorphous structure, no shear bands generated, enhanced plasticity of the sample, and increased free volume.

[0042] Example 1

[0043] Pd 82 Si 18The master alloy ingot is used through J-quenching technology to prepare metallic glass rods with a diameter of 1mm and a length of 50-60mm. The rods are cut into cylinders with a height of 2.5mm and a diameter of 1mm through wire cutting. The restraining sleeve is made of Cr12 steel. After quenching at 1000℃, tempering at 500℃, and annealing at 500℃, the hardness of the steel reaches about 650HV, which is much higher than the hardness of metallic glass. This restraining sleeve can effectively restrain the surrounding of metallic glass and constrain it by forces on three axes. The restraining sleeve is cut by electric spark cutting, and the dimensions are 3mm in diameter, 1mm in inner diameter, and 2.5mm in height. Pd 82 Si 18 The linear thermal expansion coefficient of metallic glass is 10×10 -6 K -1 , according to the calculated Pd of 1 mm 82 Si 18 The diameter shrinkage of metallic glass at 77K is 2.23×10 -3 mm, immerse the sample in liquid nitrogen, then quickly take it out and assemble it on the sleeve so that the two are tightly combined. Figure 1 Then, the sample placed in the restraining sleeve is placed in a tensile machine for compression and restraint treatment. First, the sample is compressed until it just yields as shown in the figure below. Figure 2 Then stop the compression and keep the compression force at the yield point, then static load for 3 hours, at which time the sample is constrained by triaxial force. During the whole process, pour liquid nitrogen inside, so that the sample is always in liquid nitrogen environment and compresses in triaxial directions for 3 hours, then take the sample out of the sleeve and perform mechanical testing at room temperature. The sample name is 77K3h, and the compression curve is as follows Figure 3 shown.

[0044] Comparative Example 1

[0045] The sample in Example 1 is selected, except that a cylinder with a height of 2.5 mm and a diameter of 1 mm is tightly placed in a Cr12 steel restraint sleeve. Then the sample placed in the restraint sleeve is placed in a tensile machine for a compression restraint treatment process. First, the sample is compressed until it just yields as shown in the attached Figure 2 , then stop the compression, keep the compression force before the yield point, and then statically load for 3 hours. At this time, the sample is constrained by triaxial force. After 3 hours of compression at room temperature, the sample is taken out of the constraint sleeve and then re-compressed at room temperature. The sample name is 300K 3h Figure 3 It can be seen that the yield strength of the material is greatly reduced.

[0046] Comparative Example 2

[0047] The sample in Example 1 is selected, except that a cylinder with a height of 2.5 mm and a diameter of 1 mm is tightly placed in a Cr12 steel constraint sleeve. Then the sample placed in the constraint sleeve is placed in a tensile machine for a compression constraint treatment process. This time, 50% yield force compression is selected for static loading for 3 hours, and liquid nitrogen immersion is also used throughout the process. Then the sample is taken out of the sleeve and mechanical testing is carried out at room temperature. Test sample number 77K 3h 50%σ s , Figure 3 It can be seen that the yield strength of the sample is higher than the yield strength of static load for 3h at 77K, indicating that the yield force has a more important influence on this treatment process.

[0048] like Figure 4 It shows that the relaxation enthalpy of the sample increased from 975.8 J / mol in the cast state to 1737.5 J / mol after ultra-low temperature full-constraint compression. This shows that the combination of high pressure and low temperature will cause local structural rearrangement of the material, which may cause the atomic distribution in the glassy state to become more disordered, causing the system to store more internal energy, thereby increasing the relaxation enthalpy and rejuvenating the sample.

[0049] like Figure 5 This shows that no shear bands were produced after the sample was compressed under full elastic constraint. The entire treatment process did not increase the free volume of the sample by introducing a large number of shear bands, but rejuvenated the sample by changing the internal microstructure of the sample.

[0050] In summary, for bulk metallic glass, by rationally selecting the constraint process and adopting appropriate process parameters, its microstructure can be effectively regulated and the plastic deformation properties of bulk metallic glass can be improved. Here, applying an ultra-low temperature environment through liquid nitrogen can further promote changes in the microstructure.

[0051] The above embodiments of the present invention are merely examples for illustrating the present invention, and are not intended to limit the embodiments of the present invention. For those skilled in the art, other different forms of changes and modifications can be made based on the above description. It is impossible to list all the embodiments here. Any obvious changes or modifications derived from the technical solution of the present invention are still within the scope of protection of the present invention. Matters not covered in the present invention are known technologies.

Claims

1. A method for softening and rejuvenating metallic glass by ultra-low temperature full elastic constraint compression, characterized in that: The original cast bulk metallic glass is subjected to a fully elastic constrained compression process, so that it is affected by triaxial constraints during the elastic compression process, ensuring that the compression force remains before the yield point. At the same time, it is carried out under ultra-low temperature conditions, so that the bulk metallic glass can recover to a higher energy state.

2. The method for softening and rejuvenating metallic glass by ultra-low temperature full elastic constraint compression according to claim 1, characterized in that: (1) Alloy composition preparation and smelting; (2) Synthesis of bulk metallic glass samples; (3) Select a restraining sleeve made of mature steel and heat treat the restraining sleeve; (4) Cutting is performed using a constrained sleeve, the inner diameter of which is the same as that of the metallic glass, which can effectively constrain the stress of the metallic glass in three axes; (5) Soaking the metallic glass in liquid nitrogen, at which point the diameter of the metallic glass is smaller than the inner diameter of the sleeve, quickly taking it out and assembling it on the sleeve, and the two are tightly combined after the temperature of the metallic glass returns to room temperature; (6) preparing the combined sample for stretching and soaking it in liquid nitrogen; (7) Start stretching, and the sample begins to be subjected to triaxial constraints. During this period, liquid nitrogen medium is continuously injected so that the sample is always immersed in liquid nitrogen; when the sample is about to yield, stop stretching and keep it in the state before yielding for 3 hours; (8) After treatment, take out the sample.

3. The method for softening and rejuvenating metallic glass by ultra-low temperature full elastic constraint compression according to claim 2, characterized in that: In step (1), the alloy is selected as Pd 82 Si 18 The master alloy ingot is smelted.

4. The method for softening and rejuvenating metallic glass by ultra-low temperature full elastic constraint compression according to claim 2, characterized in that: In step (2), a bulk metallic glass sample is synthesized: first, the master alloy sample is placed in a melting device protected by an inert atmosphere, and a purification treatment is performed under high temperature conditions by adding a flux medium to remove impurities in the alloy and improve the purity; after the flux coating purification is completed, the sample is placed in a special melting and casting device, and the stability of the melting environment is maintained by vacuuming and filling with high-purity inert gas; in the inert atmosphere, the alloy is melted by a high-temperature heat source, and the molten metal is introduced into a mold or container by using a pressure difference; finally, it is rapidly cooled to obtain a bulk metallic glass.

5. The method for softening and rejuvenating metallic glass by ultra-low temperature full elastic constraint compression according to claim 4, characterized in that: The prepared bulk metallic glass samples were cut into cylinders of specified sizes by wire cutting.

6. The method for softening and rejuvenating metallic glass by ultra-low temperature full elastic constraint compression according to claim 2, characterized in that: In step (3), the constraint sleeve is made of mature system steel. After the heat treatment process, the hardness of the steel is much higher than that of the metallic glass, which can effectively constrain the metallic glass to be subject to triaxial constraints.

7. The method for softening and rejuvenating metallic glass by ultra-low temperature full elastic constraint compression according to claim 2, characterized in that: In step (4), the restraining sleeve is cut by electric spark cutting, and the inner diameter is consistent with the metallic glass.

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