A co-ni-cr sub-eutectic medium-entropy alloy and a preparation method thereof

Abstract

The application discloses a CoNiCr hypoeutectic medium-entropy alloy and a preparation method thereof. The alloy is composed of Co, Ni and Cr in an atomic percentage ratio of 26:26:48. The alloy is prepared by a laser melting method, has a microstructure characterized by FCC dendrites and interdendritic FCC+BCC lamellar eutectic phases, has excellent strength-plasticity matching, good casting performance, and has a wide application prospect in the fields of aerospace, automobile manufacturing and robots. The preparation method used in the application is advanced in technology, convenient to operate and high in preparation efficiency.

Description

Technical Field

[0001] This invention relates to the field of medium-entropy alloy technology, specifically to a CoNiCr-based hypoeutectic medium-entropy alloy and its preparation method. Background Technology

[0002] Medium-entropy alloys are alloys whose configuration entropy is between 1 and 2. R Up to 1.5 R ( R CoNiCr alloys are a class of multi-component alloys with a molar constant between that of gases. The most representative equiatomic CoNiCr alloy has attracted much attention due to its excellent strength-ductility balance at low temperatures. However, its low strength at room temperature limits the expansion of its application range.

[0003] Eutectic medium-entropy alloys are a class of medium-entropy alloys with multiphase eutectic structures, combining the casting properties of eutectic alloys with the performance advantages of medium-entropy alloys. However, in terms of mechanical properties, eutectic medium-entropy alloys do not always possess optimal strength-plasticity matching, due to differences in the properties and volume fractions of their constituent phases. Therefore, developing CoNiCr-based hypoeutectic medium-entropy alloys that meet the requirements for both excellent strength-plasticity matching and good casting properties is a feasible solution. Summary of the Invention

[0004] To address the issue of low strength of CoNiCr alloys at room temperature, the first aspect of this invention develops a CoNiCr-based hypoeutectic medium-entropy alloy, and the second aspect of this invention develops a method for preparing the aforementioned CoNiCr-based hypoeutectic medium-entropy alloy.

[0005] According to a first aspect of the present invention, a CoNiCr hypoeutectic medium-entropy alloy is provided, which is composed of three elements: Co, Ni and Cr, with the atomic percentage of each element being Co:Ni:Cr = 26:26:48. The phase composition of the alloy is two phases: FCC and BCC, with the volume fraction of the FCC phase being greater than that of the BCC phase. The microstructure of the alloy includes FCC dendrites and interdendritic FCC + BCC two-phase lamellar eutectic.

[0006] According to the CoNiCr hypoeutectic medium-entropy alloy, the volume fraction of the FCC phase is 94.7%, and the volume fraction of the BCC phase is 5.3%.

[0007] According to the CoNiCr hypoeutectic medium-entropy alloy, the alloy has a compressive yield strength of not less than 341 MPa, a compressive strength of not less than 2250 MPa, and a compressive fracture strain of not less than 49.0% at room temperature.

[0008] According to a second aspect of the present invention, a method for preparing a CoNiCr-based hypoeutectic medium-entropy alloy is provided, comprising the following steps: Step 1, Ingredient preparation: Using each element as raw material, weigh each element according to the atomic percentage of each element in the CoNiCr hypoeutectic entropy alloy to complete the raw material preparation; Step 2, Loading: Load the prepared raw materials into the smelting container inside the cavity of the laser melting equipment. The raw materials are laid from bottom to top in the order of Ni, Co, and Cr into the groove of the melting container. At the same time, titanium blocks are laid into the groove of another smelting container inside the cavity. Step 3: Circulate argon gas to purge air from the cavity: After sealing the cavity, turn on the water cooler of the laser melting equipment, open the inlet valve and the exhaust valve, and continuously introduce argon gas at the first flow rate to replace the air in the cavity. Step 4, Laser Melting: Set the argon gas flow rate to the second flow rate, turn on the laser, and first melt the titanium block to absorb the residual oxygen in the cavity; then, use the laser to melt the loaded raw material at the first power for the first time, so that the raw material is completely melted, and then turn off the laser; after the alloy cools to room temperature in the cavity, flip the alloy ingot, and continue to melt the alloy ingot a second time with the laser at the second power, so that the raw material is completely melted, and then turn off the laser. Step 5: After melting, the alloy ingot is cooled to room temperature and then removed to obtain a CoNiCr hypoeutectic medium-entropy alloy.

[0009] According to the preparation method of the CoNiCr hypoeutectic medium entropy alloy, in step 1, the Co, Ni and Cr elemental raw materials used are in block or granular form, and the mass percentage purity is not less than 99.999%.

[0010] According to the preparation method of the CoNiCr hypoeutectic medium entropy alloy, in step 2, the smelting container is set as a water-cooled copper crucible. The bottom of the groove of the water-cooled copper crucible is arc-shaped. The raw material placed inside the water-cooled copper crucible should meet the following requirements: the volume of the raw material under compacted state should not exceed three-quarters of the volume of the groove of the water-cooled copper crucible.

[0011] According to the preparation method of the CoNiCr hypoeutectic medium entropy alloy, in step 3, the purity of the argon gas is not less than 99.999%.

[0012] According to the preparation method of the CoNiCr hypoeutectic medium-entropy alloy, in step 3, the temperature of the water chiller is set to no higher than 20°C. When argon gas is continuously introduced at a first flow rate to replace the air in the cavity, the first flow rate is set to 0.5-1 L / min (in actual operation, the first flow rate is set to a fixed value, such as 0.5 L / min, 0.6 L / min, 0.7 L / min, 0.8 L / min, 0.9 L / min, 1 L / min, etc.). When the amount of argon gas introduced reaches the volume of the cavity, argon gas is continued to be introduced for 5-10 minutes.

[0013] According to the preparation method of the CoNiCr hypoeutectic medium entropy alloy, in step 4, the mass percentage purity of the titanium block is not less than 99.999%.

[0014] According to the preparation method of the CoNiCr hypoeutectic medium-entropy alloy, in step 4, the second flow rate is set to 0.1-0.5 L / min (in actual operation, the second flow rate is set to a fixed value, such as 0.1 L / min, 0.2 L / min, 0.3 L / min, 0.4 L / min, 0.5 L / min, etc.), the first power of the laser is set to 1800-2000 W (in actual operation, the first power is set to a fixed value, such as 1800 W, 1900 W, 2000 W, etc.), and the second power is set to 2000-2200 W (in actual operation, the second power is set to a fixed value, such as 2000 W, 2100 W, 2200 W, etc.); and during the two melting processes of the raw materials, after the raw materials are completely melted, the raw materials are kept rotating and stirred for 15-30 seconds under the action of thermal capillary convection and back pressure, and then the laser is turned off.

[0015] Compared with the prior art, the present invention has the following beneficial effects: This invention provides a CoNiCr-based hypoeutectic medium-entropy alloy and its preparation method. This CoNiCr-based hypoeutectic medium-entropy alloy consists of two phases, FCC and BCC, exhibiting microstructure characteristics of FCC dendrites and interdendritic FCC + BCC two-phase lamellar eutectic. Composed of only Co, Ni, and Cr elements, it is easy to formulate and melt, possesses excellent strength-plasticity matching, and good casting performance, showing broad application prospects in aerospace, automotive manufacturing, and robotics. The preparation method used in this invention for preparing the CoNiCr-based hypoeutectic medium-entropy alloy is technologically advanced, convenient to operate, and highly efficient.

[0016] The present invention will now be described in further detail with reference to the accompanying drawings. Attached Figure Description

[0017] Figure 1 This is the electron backscattering diffraction phase distribution diagram of the hypoeutectic medium-entropy alloy prepared in Example 1 of the present invention.

[0018] Figure 2 This is a low-magnification morphology image of the hypoeutectic medium-entropy alloy prepared in Example 1 of the present invention, obtained by scanning electron microscopy backscattering electron imaging mode.

[0019] Figure 3 This is a high-magnification morphology image of the hypoeutectic medium-entropy alloy prepared in Example 1 of the present invention, obtained by scanning electron microscopy backscattering electron imaging mode.

[0020] Figure 4The stress-strain curve of the hypoeutectic medium-entropy alloy prepared in Example 1 of this invention is shown under room temperature conditions. Detailed Implementation

[0021] To further illustrate the technical means and effects of the present invention in achieving its intended purpose, the specific implementation methods, structural features and effects of the present invention will be described below in conjunction with the accompanying drawings and embodiments.

[0022] Example 1 This invention provides a CoNiCr-based hypoeutectic medium-entropy alloy, composed of Co, Ni, and Cr elements, with an atomic percentage of Co:Ni:Cr = 26:26:48. The alloy consists of two phases: FCC and BCC, with the FCC phase having a higher volume fraction (94.7%) than the BCC phase (5.3%). The microstructure exhibits FCC dendrites and interdendritic FCC + BCC two-phase lamellar eutectic characteristics. This alloy demonstrates high strength and high ductility at room temperature, and combined with the good fluidity of hypoeutectic metals in the liquid state, it holds promise as a novel structural material for aerospace, automotive manufacturing, and robotics fields.

[0023] In this embodiment, the chemical formula of this CoNiCr-based hypoeutectic medium-entropy alloy can be written as CoNiCr according to the molar ratio of each component. 1.846 Its preparation method specifically includes the following steps: Step 1, Ingredients: Using each element as raw material, the raw materials are weighed according to the atomic percentage of each component in the CoNiCr hypoeutectic entropy alloy Co:Ni:Cr = 26:26:48 to complete the raw material preparation.

[0024] The raw materials Co, Ni, and Cr can be in granular, block, or flake form. Preferably, the raw materials Cr, Co, and Ni are in granular form (the particle size is set to prevent them from being blown away by argon gas). This shape of raw material ensures that it is not blown away by circulating argon gas (powdered raw materials are easily blown away by argon gas, causing component loss, and may also enter adjacent smelting containers and contaminate other alloys to be smelted). Under the premise of ensuring that the raw materials are not blown away by circulating argon gas (powdered raw materials are easily blown away by argon gas, causing component loss, and may also enter adjacent smelting containers and contaminate other alloys to be smelted), the space utilization rate of the smelting container is higher.

[0025] Step 2, Loading: The prepared raw materials are loaded into the smelting container (e.g., a water-cooled copper crucible) inside the cavity of the laser melting equipment. The raw materials are laid from bottom to top in the order of Ni, Co, and Cr inside the groove of the smelting container. At the same time, titanium blocks are laid in the groove of another smelting container inside the cavity.

[0026] Considering the surface-to-interior characteristic of laser heating and the fact that the melting point of Cr is more than 400℃ higher than that of Co and Ni, placing the Cr raw material at the top of the water-cooled copper crucible's groove facilitates its melting. In this invention, a water-cooled copper crucible is used as the smelting container, and the bottom of its groove should be arc-shaped. The amount of material placed inside the water-cooled copper crucible should meet the following requirements: the volume under compaction should not exceed three-quarters of the groove volume of the water-cooled copper crucible, ensuring sufficient space utilization while avoiding molten material splashing loss.

[0027] Step 3: Circulate argon gas to purge the air from the cavity: After sealing the cavity, turn on the water chiller of the laser melting equipment (the temperature of the water chiller is set to 20℃), open the inlet valve and the exhaust valve, and continuously introduce argon gas into the cavity at the first flow rate to replace the air in the cavity. In this process, the cavity is first sealed, and then the chiller is turned on to prevent water vapor in the air from condensing on the outer wall of the water-cooled components inside the cavity, which could vaporize at high temperatures during melting and enter the melt, causing alloy oxidation. In addition, the initial flow rate is set to 1L / min. Once the argon gas flow rate reaches the volume of the cavity (calculated based on the cavity being empty without any molten material), argon gas is continued for 10 minutes before proceeding to the next step.

[0028] Step 4, Laser Melting: After turning on the laser, the titanium block is first melted to absorb the residual oxygen in the cavity; then the loaded raw materials are melted, the laser power is adjusted to make the raw materials completely melted, and then the laser is turned off. After the alloy cools to room temperature in the cavity, the alloy ingot is flipped over and remelted in the same way.

[0029] In this embodiment, the melting process is repeated only once. This is a result of considering the high energy density of laser melting and the fact that repeated remelting would exacerbate alloy composition loss. In this embodiment, the raw material mass used is 6g, and the laser power during melting is 2000W. During each melting process, after the raw material is completely melted, it is continuously stirred for 20 seconds under the action of thermal capillary convection and back pressure, and then the laser is turned off. During the laser melting process, argon gas is continuously introduced at a second flow rate (0.5L / min).

[0030] Step 5: After melting is completed, wait for the alloy ingot to cool to room temperature and then take it out to obtain a CoNiCr hypoeutectic medium-entropy alloy.

[0031] The preparation method used in this invention is advanced, convenient to operate, and highly efficient in preparing CoNiCr hypoeutectic medium-entropy alloys. With the upgrade of the laser and supporting facilities, it is possible to prepare alloy ingots with larger volumes to meet the needs of multiple applications.

[0032] In the above scheme, the purity of the elemental raw materials Co, Ni and Cr, as well as the titanium block and argon gas used should not be less than 99.999%.

[0033] Figure 1 It is Co 26 Ni 26 Cr 48 Electron backscattering diffraction phase distribution diagram of hypoeutectic medium entropy alloy shows that the alloy is composed of two phases, FCC and BCC, with volume fractions of 94.7% and 5.3%, respectively.

[0034] Figure 2 and Figure 3 They are Co 26 Ni 26 Cr 48 Low- and high-magnification scanning electron microscopy (SEM) backscattered electron imaging modes of hypoeutectic medium-entropy alloys. Figure 2 and Figure 3 It can be seen from the Co 26 Ni 26 Cr 48 The hypoeutectic medium-entropy alloy has the microstructure characteristics of FCC dendrites and interdendritic FCC + BCC two-phase lamellar eutectic, with the FCC phase having a significantly higher volume fraction than the BCC phase.

[0035] Figure 4 It is Co 26 Ni 26 Cr 48 The strain rate of the hypoeutectic medium-entropy alloy φ3×6mm cylindrical sample at room temperature was 10. - 3 s -1 The compressive stress-strain curves of the alloy show that the compressive yield strength is 341 MPa, the compressive strength is 2250 MPa, and the compressive fracture strain is 49.0%, indicating excellent compressive strength-plasticity matching.

[0036] Comparative Example 1 The same preparation method and process parameters as in Example 1 were used to prepare 6g of Co. 25 Ni 25 Cr 50 A eutectic medium-entropy alloy was prepared, with the atomic percentages of each component being Co:Ni:Cr = 25:25:50. This example yielded an alloy sample exhibiting a fully eutectic lamellar microstructure. This alloy sample was also subjected to room temperature strain at a rate of 10... -3 s -1 The compression stress-strain test results were as follows: compressive yield strength 448 MPa, compressive strength 2203 MPa, and compressive fracture strain 39.7%. Therefore, Co...25 Ni 25 Cr 50 The compressive strength and compressive fracture strain of the eutectic medium-entropy alloy are significantly lower than those of Co. 26 Ni 26 Cr 48 Hypoeutectic medium-entropy alloy, Co 26 Ni 26 Cr 48 Hypoeutectic medium-entropy alloys exhibit a superior compressive strength-plasticity match.

[0037] Comparative Example 2 A preparation method using non-consumable vacuum arc melting was employed to prepare 6g of Co. 26 Ni 26 Cr 48 A hypoeutectic medium-entropy alloy with a component atomic percentage of Co:Ni:Cr = 26:26:48 was prepared. The melting current during the arc melting process was 200A, and the electromagnetic stirring time was 20s after the alloy raw materials were completely melted each time. This example prepared an alloy sample with FCC dendrites and interdendritic FCC+BCC two-phase lamellar eutectic microstructure characteristics. This alloy sample was also subjected to room temperature strain rate of 10. -3 s -1 The compression stress-strain test results showed that the compressive yield strength was 296 MPa, the compressive strength was 2153 MPa, and the compressive fracture strain was 46.4%. Therefore, the laser melting of Co used in this invention... 26 Ni 26 Cr 48 The hypoeutectic medium-entropy alloying method is not only technologically advanced, easy to operate, and highly efficient, but also produces alloys with superior room-temperature compressive mechanical properties.

[0038] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention.

Claims

1. A CoNiCr-based hypoeutectic medium-entropy alloy, characterized in that, Composed of three elements, Co, Ni, and Cr, with an atomic percentage of Co:Ni:Cr = 26:26:48, the alloy has a phase composition of two phases, FCC and BCC, with the volume fraction of the FCC phase being greater than that of the BCC phase. The microstructure of the alloy includes FCC dendrites and interdendritic FCC + BCC two-phase lamellar eutectic.

2. The CoNiCr-based hypoeutectic medium-entropy alloy as described in claim 1, characterized in that, The volume fraction of the FCC phase was 94.7%, and the volume fraction of the BCC phase was 5.3%.

3. The CoNiCr-based hypoeutectic medium-entropy alloy as described in claim 1 or 2, characterized in that, The alloy has a compressive yield strength of not less than 341 MPa, a compressive strength of not less than 2250 MPa, and a compressive fracture strain of not less than 49.0% at room temperature.

4. The method for preparing the CoNiCr-based hypoeutectic medium-entropy alloy according to any one of claims 1 to 3, characterized in that, Includes the following steps: Step 1, Ingredient preparation: Using each element as raw material, weigh each element according to the atomic percentage of each element in the CoNiCr hypoeutectic entropy alloy to complete the raw material preparation; Step 2, Loading: Load the prepared raw materials into the smelting container inside the cavity of the laser melting equipment. The raw materials are laid from bottom to top in the order of Ni, Co, and Cr into the groove of the melting container, and titanium blocks are laid into the groove of another smelting container inside the cavity. Step 3: Circulate argon gas to purge air from the cavity: After sealing the cavity, turn on the water cooler of the laser melting equipment, open the inlet valve and the exhaust valve, and continuously introduce argon gas at the first flow rate to replace the air in the cavity. Step 4, Laser Melting: Set the argon gas flow rate to the second flow rate, turn on the laser, and first melt the titanium block to absorb the residual oxygen in the cavity; then, use the laser to melt the loaded raw material at the first power for the first time, so that the raw material is completely melted, and then turn off the laser; after the alloy cools to room temperature in the cavity, flip the alloy ingot, and continue to melt the alloy ingot a second time with the laser at the second power, so that the raw material is completely melted, and then turn off the laser. Step 5: After melting, the alloy ingot is cooled to room temperature and then removed to obtain a CoNiCr hypoeutectic medium-entropy alloy.

5. The method for preparing the CoNiCr-based hypoeutectic medium-entropy alloy as described in claim 4, characterized in that, In step 1, the elemental raw materials Co, Ni and Cr used are in block or granular form, and the mass percentage purity is not less than 99.999%.

6. The method for preparing the CoNiCr-based hypoeutectic medium-entropy alloy as described in claim 4, characterized in that, In step 2, the smelting container is set as a water-cooled copper crucible. The bottom of the groove of the water-cooled copper crucible is arc-shaped. The raw material is placed inside the water-cooled copper crucible to meet the following condition: the volume of the raw material in the compacted state does not exceed three-quarters of the volume of the groove of the water-cooled copper crucible.

7. The method for preparing the CoNiCr-based hypoeutectic medium-entropy alloy as described in claim 4, characterized in that, In step 3, the purity of the argon gas is not less than 99.999%.

8. The method for preparing the CoNiCr-based hypoeutectic medium-entropy alloy as described in claim 4, characterized in that, In step 3, the temperature of the water chiller is set to no higher than 20°C. When argon gas is continuously introduced at a first flow rate to replace the air in the cavity, the first flow rate is set to 0.5-1 L / min. After the amount of argon gas introduced reaches the volume of the cavity, argon gas is continued to be introduced for 5-10 minutes.

9. The method for preparing the CoNiCr-based hypoeutectic medium-entropy alloy as described in claim 4, characterized in that, In step 4, the mass percentage purity of the titanium block is not less than 99.999%.

10. The method for preparing the CoNiCr-based hypoeutectic medium-entropy alloy as described in claim 4, characterized in that, In step 4, the second flow rate is set to 0.1-0.5 L / min, the first power of the laser is set to 1800-2000 W, and the second power is set to 2000-2200 W. During the two melting processes of the raw material, after the raw material is completely melted, it is kept rotating and stirred for 15-30 seconds under the action of thermal capillary convection and back pressure, and then the laser is turned off.

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