Method for preparing high-performance CoCrNi alloy through selective laser melting by adding nano yttrium oxide and application of high-performance CoCrNi alloy

Abstract

The invention discloses a method for preparing a high-performance CoCrNi alloy by adding nano yttrium oxide through selective laser melting and application. The method comprises the following steps: (1) proportioning CoCrNi powder; (2) mixing the CoCrNi powder; (3) mixing the nanometer yttrium oxide with the CoCrNi powder; and (4) preparing the high-performance CoCrNi alloy. According to the method, the cobalt powder, the chromium powder and the nickel powder are evenly mixed in a three-dimensional mixing mode, and the CoCrNi alloying powder manufacturing cost is reduced; a small amount of nano yttrium oxide powder is uniformly mixed through an ultrasonic system, so that crystal grains of the alloy are refined, and the strength of the CoCrNi alloy is improved; and the generation of cracks is avoided by adjusting the parameters of the selective laser melting process, and the formability and the use performance of the alloy are improved. The prepared CoCrNi alloy is high in performance and suitable for the harsh working conditions of low-temperature friction wear or low-temperature cyclic loading.

Description

Technical Field

[0001] This invention belongs to the field of high-performance medium-entropy alloy preparation technology, specifically relating to a method and application of preparing high-performance CoCrNi alloy by selective laser melting with nano-yttrium oxide. Background Technology

[0002] Energy conservation, emission reduction, and the transformation of the energy structure are crucial, with the development of clean energy being a key factor. Hydrogen energy, as an important part of the clean energy system, is a vital vehicle for driving global energy transformation. Currently, hydrogen energy development faces many technical challenges, among which hydrogen storage and transportation technology is one. Current hydrogen storage technologies include gaseous hydrogen storage, liquid hydrogen storage, and solid-state hydrogen storage. Liquid hydrogen storage involves cooling hydrogen gas to -253°C and liquefying it, then storing it in an insulated container. This requires the storage container and its components to possess certain low-temperature resistance properties (e.g., the metal liquid hydrogen storage container must have sufficient strength and toughness at low temperatures, and the hydrogen storage valve must have good low-temperature friction and wear resistance and excellent fatigue resistance). High-entropy alloys, as a new type of structural material, possess unique microstructures and excellent comprehensive properties such as high strength, high toughness, friction and wear resistance, corrosion resistance, high temperature resistance, and low temperature resistance, making them highly promising for applications in numerous fields such as transportation, aviation, and aerospace. High-entropy alloys with face-centered cubic (FCC) structures generally possess an excellent combination of strength and toughness. Among the many FCC-structured high-entropy alloys, CoCrNi alloys exhibit a good balance of strength and toughness at both room temperature and low temperatures, showing promising application prospects in low-temperature conditions. Selective laser melting (SLM) is a metal additive manufacturing (3D printing) technology that uses a high-energy laser beam to melt metal powder layer by layer, directly forming complex three-dimensional parts. It is an important branch of powder bed melting (PBF) technology and is widely used in the manufacture of high-performance metal components in aerospace, medical, and automotive fields. Its core technical features include high precision, near-net-shape forming, and high design freedom, especially for the integrated forming of complex components such as liquid hydrogen storage tank parts (valves, etc.) and heat exchangers. Therefore, the application of CoCrNi alloys via selective laser melting technology in liquid hydrogen storage containers and components operating in alternating ambient and low-temperature environments has a huge market potential. Based on this, there is an urgent need for new high-performance CoCrNi alloys prepared by SLM to meet the growing market demand.

[0003] CN113042753A discloses a method for reducing cracks and improving the mechanical properties of SLM-formed nickel-based superalloys. The method involves preparing GH3536 nickel-based superalloy bulk samples by selective laser melting (SLM) of GH3536 nickel-based superalloy powder uniformly coated with yttrium oxide. The above patent has the following defects: 1) It uses a chemical method to mix yttrium oxide and metal powder. The yttrium oxide is prepared by mixing yttrium oxide powder (a precursor) with anhydrous ethanol, then adding it to the metal powder and ultrasonically mixing it in a liquid. Subsequent steps include drying, calcination, grinding, and sieving, making the process cumbersome; 2) The role of yttrium oxide in this patent is mainly to reduce the number of cracks during selective laser melting, and the strengthening mechanism is mainly through the second phase of yttrium oxide rather than through grain refinement; 3) The product prepared by this patent is used in high-temperature applications rather than low-temperature applications. Summary of the Invention

[0004] To address the challenge of achieving balanced performance of liquid hydrogen storage containers and their components at both room and low temperatures, this invention aims to provide a method for preparing high-performance CoCrNi alloys by selective laser melting with nano-yttrium oxide.

[0005] The present invention also aims to provide the application of the high-performance CoCrNi alloy prepared by the above method in the preparation of products subjected to low-temperature friction and wear and low-temperature cyclic loading stress.

[0006] The first objective of this invention can be achieved through the following technical solution: A method for preparing high-performance CoCrNi alloys by selective laser melting with added nano-yttrium oxide includes the following steps: (1) Preparation of CoCrNi powder Weigh out the cobalt powder, chromium powder, and nickel powder according to the following weight percentages: Co 27.8%~41.7%, Cr 24.5%~36.8%, Ni 27.7%~41.5%; (2) Mixing of CoCrNi powder The three metal element powders are uniformly mixed using a three-dimensional mixer; (3) Mixing of nano-yttrium oxide with CoCrNi powder A certain mass ratio of nano-yttrium oxide powder is added to the uniformly mixed CoCrNi powder and mixed evenly. (4) Preparation of high-performance CoCrNi alloy: CoCrNi alloy powder with added nano-yttrium oxide powder was prepared by selective laser melting to obtain high-performance CoCrNi alloy.

[0007] The method of this invention obtains CoCrNi powder uniformly through three-dimensional mixing of cobalt, chromium, and nickel element powders. The mixing process greatly preserves the sphericity and flowability of the powder. Then, a small amount of nano-yttrium oxide is mixed in using an ultrasonic system. Finally, the CoCrNi alloy prepared by selective laser melting has good performance and is suitable for extreme working conditions such as low-temperature friction and wear and cyclic loading stress. This method of preparing CoCrNi alloy greatly improves the performance of the alloy and is suitable for the preparation of complex parts under low-temperature conditions, effectively improving forming efficiency and greatly reducing costs.

[0008] In the above method for preparing high-performance CoCrNi alloys by selective laser melting with added nano-yttrium oxide: Preferably, the cobalt powder, chromium powder and nickel powder mentioned in step (1) are prepared by gas atomization method, with good sphericity greater than 96%, Hall flow rate less than 45s / 50g, purity of each metal powder greater than 99.7%, oxygen content less than 0.08% and nitrogen content less than 0.05%.

[0009] More preferably, the Hall flow rate of each powder in step (1) is less than 30 s / 50 g.

[0010] More preferably, the Hall flow rate of each powder described in step (1) is less than 18 s / 50 g.

[0011] More preferably, the oxygen content of each powder in step (1) is less than 0.05%.

[0012] More preferably, the oxygen content of each powder described in step (1) is less than 0.03%.

[0013] More preferably, the nitrogen content of each powder in step (1) is less than 0.01%.

[0014] More preferably, the nitrogen content of each powder described in step (1) is less than 0.008%.

[0015] Preferably, the atomic ratio of Co, Cr and Ni in the cobalt powder, chromium powder and nickel powder mentioned in step (1) is 0.8-1.1:0.8-1.1:0.8-1.1.

[0016] More preferably, the atomic ratio of Co, Cr and Ni in the cobalt powder, chromium powder and nickel powder mentioned in step (1) conforms to 0.9-1.1:0.9-1.1:0.9-1.1.

[0017] Preferably, the particle size range of the three metal element powders mentioned in step (1) is 15-60 μm, and the D10-D90 range is 20-63 μm.

[0018] More preferably, the particle size range of the three metal element powders mentioned in step (1) is 15-53 μm, and the D10-D90 range is 22-58 μm.

[0019] Preferably, in step (2), the SHY three-dimensional mixer is used to mix the three metal element powders. The mixing method is a combination of rotation, swing and flipping motion in three-dimensional space. The mixing tank is protected by argon gas with a purity greater than 99.99% and the mixing tank is sealed. The cylinder speed is adjusted to 10-18 revolutions / minute and the mixing time is 30-150 minutes.

[0020] More preferably, in step (2), the SHY three-dimensional mixer is used to mix the three metal element powders. The mixing method is through a combination of rotation, swing and flipping motion in three-dimensional space. The mixing tank is protected by argon gas with a purity greater than 99.999% and the mixing tank is sealed. The cylinder speed is adjusted to 12-15 revolutions / minute and the mixing time is 30-120 minutes.

[0021] Three-dimensional mixing involves the mixing tank moving in three-dimensional space, performing a combination of rotation, translation, and tumbling in the X, Y, and Z dimensions. This generates three mixing effects within the tank: convection, diffusion, and shearing. This avoids the centrifugal force stratification problem of traditional two-dimensional mixers, ensuring a uniform distribution of powders with different densities or particle sizes. After three-dimensional mixing, CoCrNi powder exhibits high uniformity and retains its sphericity. Furthermore, the oxygen content is controlled under the protection of high-purity argon gas. The use of ceramic or plastic linings prevents impurities from being mixed in, while the mixing time is significantly shortened, thus improving efficiency.

[0022] Preferably, the yttrium oxide powder in step (3) has a particle size of 10-150 nm, and the amount of nano-yttrium oxide powder added accounts for 0.3%-2% of the mass ratio of CoCrNi powder. The nano-yttrium oxide powder and CoCrNi powder are mixed by an ultrasonic system with a power of 200-1000W and a time of 30-150 min.

[0023] More preferably, the yttrium oxide powder has a particle size of 10-100 nm.

[0024] More preferably, the yttrium oxide powder has a particle size of 10-80 nm.

[0025] More preferably, the amount of nano-yttrium oxide added accounts for 0.3%-1.5% of the mass ratio of CoCrNi powder.

[0026] More preferably, the amount of nano-yttrium oxide added accounts for 0.6%-1.2% of the mass ratio of CoCrNi powder.

[0027] More preferably, the ultrasonic vibration device has a power of 200-800W and a duration of 30-90min.

[0028] More preferably, the ultrasonic vibration device has a power of 500-800W and a duration of 60-90min.

[0029] In step (4), the parameters of the selected area laser melting method are: laser power 150-250W, scanning speed 800-1200mm / s, scanning path 80-120μm, and layer thickness 0.2-0.4μm.

[0030] Preferably, the parameters of the selective laser melting method in step (4) are: laser power 150-220W, scanning speed 800-1200mm / s, scanning path 80-120μm, and layer thickness 0.2-0.4μm.

[0031] More preferably, the laser power is 150-180W.

[0032] More preferably, the laser power is 160-180W.

[0033] More preferably, the scanning rate is 800-1000 mm / s.

[0034] More preferably, the scanning rate is 900-1000 mm / s.

[0035] More preferably, the scanning path is 80-100μm.

[0036] More preferably, the scanning path is 90-100 μm.

[0037] In step (4), the laser scanning strategy is a checkerboard pattern and the substrate preheating temperature is 250-300℃.

[0038] Preferably, in step (4), the laser scanning strategy is a checkerboard pattern and the substrate preheating temperature is 260-300℃.

[0039] More preferably, in step (4), the laser scanning strategy is a checkerboard pattern and the substrate preheating temperature is 280-300℃.

[0040] This invention involves adding a small amount of nano-yttrium oxide to CoCrNi powder and using ultrasonic vibration to prevent agglomeration of the nano-yttrium oxide, ensuring uniform mixing with the CoCrNi powder. During the selective laser melting (SLM) process to prepare CoCrNi alloys, the addition of nano-yttrium oxide not only reduces the temperature gradient of the molten pool but also acts as a heterogeneous nucleation site, increasing the nucleation rate and refining the grains. During the melt-solidification cycle of SLM, the nano-yttrium oxide particles are anchored within the grain boundaries, preventing localized grain growth during thermal cycling. The prepared CoCrNi alloy achieves a surface hardness of 311.9 HV. 0.2With a yield strength of over 703.1 MPa and a strain of over 40%, it is suitable for harsh working conditions of low-temperature friction and wear.

[0041] In the process of selective laser melting to prepare high-performance CoCrNi alloys, the strategy of using checkerboard scanning can reduce residual stress, reduce deformation and improve forming quality. Preheating the substrate can reduce the cooling rate, prevent crack formation and improve alloy density.

[0042] The present invention also provides a high-performance CoCrNi alloy, which is prepared by the above method.

[0043] The second objective of the present invention can be achieved by the following technical solution: the application of the above-mentioned high-performance CoCrNi alloy in the preparation of products subjected to low-temperature friction and wear or low-temperature cyclic stress.

[0044] The high-performance CoCrNi alloy prepared by the method of this invention is suitable for various low-temperature working conditions, especially low-temperature friction and wear and low-temperature cyclic loading stress working conditions, and can be used under low-temperature friction and wear and low-temperature cyclic loading stress.

[0045] The present invention has the following advantages: (1) The three-dimensional mixing of single-element powders used in this invention achieves efficient and uniform mixing in multiple dimensions, ensuring the sphericity, flowability, and oxygen content of the powders. Simultaneously, the mixing time is short and the efficiency is high. This invention directly mixes metal element powders with nano-yttrium oxide in a solid phase under high-power ultrasound, resulting in a simple and efficient process.

[0046] (2) The nano-yttrium oxide was uniformly mixed into the CoCrNi powder by ultrasonic vibration. This method is simple, effective, and quick, and it inhibits the agglomeration of the nano-yttrium oxide, resulting in good dispersion. The main function of the nano-yttrium oxide is to refine the grains and enhance the mechanical properties of CoCrNi. Crack control is achieved by preheating the substrate to a high temperature.

[0047] (3) Adding a small amount of nano-yttrium oxide during the selective laser melting of CoCrNi powder can refine the grains and improve the alloy properties. Due to its high melting point (>2400℃) and high-temperature stability, Y2O3 can maintain structural integrity in liquid or solid alloys, reduce the energy barrier required for nucleation, promote heterogeneous nucleation of grains, thereby increasing the nucleation rate and refining the grains. Nano-yttrium oxide particles are small in size and have a large specific surface area, which can effectively reduce the critical nucleation radius and allow more tiny grains to form. Nano-Y2O3 particles dispersed at grain boundaries or within grains can prevent abnormal grain growth by hindering grain boundary migration through the pinning effect.

[0048] (4) The high-performance CoCrNi alloy material prepared in this invention is suitable for various low-temperature extreme working conditions, especially low-temperature friction and wear and low-temperature cyclic loading working conditions. The prepared product achieved 39,494 low-cycle fatigue cycles under tensile-compressive strain control at -150℃. Attached Figure Description

[0049] Figure 1 The metallographic structures of the CoCrNi alloys in Example 3 and Comparative Example 1 are shown.

[0050] Figure 2 The stress-strain curves of the CoCrNi alloy in tensile tests in Example 3 and Comparative Example 1 are shown.

[0051] Figure 3 Nanoscale hardness curves of the CoCrNi alloys in Example 3 and Comparative Examples 2-3 are shown.

[0052] Figure 4 The stress-strain curves of the CoCrNi alloy tensile test in Example 3 and Comparative Examples 2-3 are shown.

[0053] Figure 5 The metallographic structures of the CoCrNi alloys in Example 3 and Comparative Example 4 are shown.

[0054] Figure 6 The stress-strain curves of the CoCrNi alloy tensile test in Example 3 and Comparative Example 5 are shown.

[0055] Figure 7 The image shows a three-dimensional morphology of the wear tracks after low-temperature friction and wear of the CoCrNi alloy prepared in Example 3 and commercially available 316L stainless steel under continuous liquid nitrogen.

[0056] Figure 8 The figure shows the volume loss of the CoCrNi alloy prepared in Example 3 and commercially available 316L stainless steel after low-temperature friction and wear under continuous liquid nitrogen.

[0057] Figure 9 The fatigue life versus stress amplitude curves of the CoCrNi alloy prepared in Example 3 and commercially available 316L stainless steel under continuous liquid nitrogen are shown. Detailed Implementation

[0058] The specific embodiments of the present invention will be further described below. It should be noted that these descriptions are for the purpose of aiding understanding the present invention, but do not constitute a limitation thereof. Furthermore, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0059] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0060] Unless otherwise specified, the experimental methods used in the following implementation methods are all conventional experimental methods.

[0061] Unless otherwise specified, the terms used in the following implementation methods and embodiments generally have the meanings commonly understood by those skilled in the art.

[0062] Part 1: Preparation of a High-Performance CoCrNi Alloy with Added Yttrium Nanoparticles via Selective Laser Melting Example 1 The method for preparing high-performance CoCrNi alloys by selective laser melting with added nano-yttrium oxide provided in this embodiment includes the following steps: (1) Preparation of CoCrNi powder Commercially available atomized cobalt, chromium, and nickel powders were weighed and prepared according to the following mass fractions: Co 34.74%, Cr 30.66%, and Ni 34.6%. All three powders exhibited good sphericity (greater than 96%), Hall flow rates (less than 16.8 s / 50 g), purity greater than 99.7%, oxygen content less than 0.03%, nitrogen content less than 0.008%, and particle size ranging from 15 to 53 μm, with a D10-D90 range of 23-58 μm.

[0063] (2) Mixing of CoCrNi powder The mixture is prepared using a three-dimensional mixing method. The mixing tank is protected by argon gas with a purity greater than 99.999% and is sealed. The cylinder rotation speed is adjusted to 12 revolutions per minute, and the mixing time is 60 minutes.

[0064] (3) Mixing of nano-yttrium oxide with CoCrNi powder The nano-yttrium oxide powder has a purity of 99.99% and a particle size of 50 nm. The amount of nano-yttrium oxide added accounts for 0.6% of the mass ratio of CoCrNi powder. The nano-yttrium oxide and CoCrNi powder are mixed by an ultrasonic system with a power of 500W and a duration of 60 minutes.

[0065] (4) Preparation of high-performance CoCrNi alloys The dried powder was then used to prepare a high-performance CoCrNi alloy by selective laser melting (SLM). The printing parameters were: laser power 160W, scanning speed 900mm / s, scanning path 90μm, layer thickness 0.3μm, and substrate heating temperature 250℃.

[0066] Example 2 The method for preparing high-performance CoCrNi alloys by selective laser melting with added nano-yttrium oxide provided in this embodiment includes the following steps: (1) Preparation of CoCrNi powder Commercially available atomized cobalt, chromium, and nickel powders were weighed and prepared according to the following mass fractions: Co 34.74%, Cr 30.66%, and Ni 34.6%. All three powders exhibited good sphericity (greater than 96%), Hall flow rates (less than 16.8 s / 50 g), purity greater than 99.7%, oxygen content less than 0.03%, nitrogen content less than 0.008%, and particle size ranging from 15 to 53 μm, with a D10-D90 range of 23-58 μm.

[0067] (2) Mixing of CoCrNi powder The mixture is prepared using a three-dimensional mixing method. The mixing tank is protected by argon gas with a purity greater than 99.999% and is sealed. The cylinder rotation speed is adjusted to 15 revolutions per minute, and the mixing time is 60 minutes.

[0068] (3) Mixing of nano-yttrium oxide with CoCrNi powder The nano-yttrium oxide powder has a purity of 99.99% and a particle size of 50 nm. The amount of nano-yttrium oxide added accounts for 0.9% of the mass ratio of CoCrNi powder. The nano-yttrium oxide and CoCrNi powder are mixed by an ultrasonic system with a power of 500W and a duration of 60 minutes.

[0069] (4) Preparation of high-performance CoCrNi alloys The dried powder was then used to prepare a high-performance CoCrNi alloy by selective laser melting (SLM). The printing parameters were: laser power 180W, scanning speed 900mm / s, scanning path 90μm, layer thickness 0.3μm, and substrate heating temperature 250℃.

[0070] Example 3 The method for preparing high-performance CoCrNi alloys by selective laser melting with added nano-yttrium oxide provided in this embodiment includes the following steps: (1) Preparation of CoCrNi powder Commercially available atomized cobalt, chromium, and nickel powders were weighed and prepared according to the following mass fractions: Co 34.74%, Cr 30.66%, and Ni 34.6%. All three powders exhibited good sphericity (greater than 96%), Hall flow rates (less than 16.8 s / 50 g), purity greater than 99.7%, oxygen content less than 0.03%, nitrogen content less than 0.008%, and particle size ranging from 15 to 53 μm, with a D10-D90 range of 23-58 μm.

[0071] (2) Mixing of CoCrNi powder The mixture is prepared using a three-dimensional mixing method. The mixing tank is protected by argon gas with a purity greater than 99.999% and is sealed. The cylinder rotation speed is adjusted to 15 revolutions per minute, and the mixing time is 60 minutes.

[0072] (3) Mixing of nano-yttrium oxide with CoCrNi powder The nano-yttrium oxide powder has a purity of 99.99% and a particle size of 50 nm. The amount of nano-yttrium oxide added accounts for 0.9% of the mass ratio of CoCrNi powder. The nano-yttrium oxide and CoCrNi powder are mixed by an ultrasonic system with a power of 800W and a duration of 60 minutes.

[0073] (4) Preparation of high-performance CoCrNi alloys The dried powder was then used to prepare a high-performance CoCrNi alloy by selective laser melting (SLM). The printing parameters were: laser power 180W, scanning speed 900mm / s, scanning path 90μm, layer thickness 0.3μm, and substrate heating temperature 300℃.

[0074] Example 4 The method for preparing high-performance CoCrNi alloys by selective laser melting with added nano-yttrium oxide provided in this embodiment includes the following steps: (1) Preparation of CoCrNi powder Commercially available atomized cobalt, chromium, and nickel powders were weighed and prepared according to the following mass fractions: Co 34.74%, Cr 30.66%, and Ni 34.6%. All three powders exhibited good sphericity (greater than 96%), Hall flow rates (less than 16.8 s / 50 g), purity greater than 99.7%, oxygen content less than 0.03%, nitrogen content less than 0.008%, and particle size ranging from 15 to 53 μm, with a D10-D90 range of 23-58 μm.

[0075] (2) Mixing of CoCrNi powder The mixture is prepared using a three-dimensional mixing method. The mixing tank is protected by argon gas with a purity greater than 99.999% and is sealed. The cylinder rotation speed is adjusted to 15 revolutions per minute, and the mixing time is 60 minutes.

[0076] (3) Mixing of nano-yttrium oxide with CoCrNi powder The nano-yttrium oxide powder has a purity of 99.99% and a particle size of 50 nm. The amount of nano-yttrium oxide added accounts for 1.2% of the mass ratio of CoCrNi powder. The nano-yttrium oxide and CoCrNi powder are mixed by an ultrasonic system with a power of 800W and a duration of 60 minutes.

[0077] (4) Preparation of high-performance CoCrNi alloys The dried powder was then used to print high-performance CoCrNi alloys using selective laser melting (SLM). The printing parameters were: laser power of 180W, scanning speed of 900mm / s, scanning path of 90μm, layer thickness of 0.3μm, and substrate heating temperature of 300℃.

[0078] Comparative Example 1 The difference compared to Example 3 is that no nano-yttrium oxide is added.

[0079] Comparative Example 2 Compared with Example 3, the difference is that in step (3), the nano-yttrium oxide and CoCrNi powder are mixed by a vibrating screen.

[0080] Comparative Example 3 Compared with Example 3, the difference is that in step (3), the nano-yttrium oxide and CoCrNi powder are mixed by a three-dimensional mixer.

[0081] Comparative Example 4 Compared with Example 3, the difference is that the substrate is not preheated in step (4).

[0082] Comparative Example 5 Compared with Example 3, the difference is that in step (1), the CoCrNi powder is directly alloyed powder and non-single element powder.

[0083] Part Two: Microstructure and Property Testing of High-Performance CoCrNi Alloys Prepared by Selective Laser Melting with Added Yttrium Oxide Nanoparticles 1) The physical and mechanical properties of the CoCrNi alloys in Examples 1-4 were tested.

[0084] The density of the CoCrNi alloys in Examples 1-4 was measured according to the standard test method for density determination of additively manufactured metallic parts in ASTM B962-23; the hardness of the CoCrNi alloys in Examples 1-4 was tested according to the method in Vickers hardness test of metallic materials in GB / T4340.1-2009. Seven data points were collected, and the average value was taken after removing the extreme values. The density and hardness of the CoCrNi alloys in Examples 1-4 are shown in Table 1.

[0085] Table 1. Physical and mechanical properties of the CoCrNi alloys prepared in Examples 1-4

[0086] Nano-yttrium oxide promotes heterogeneous nucleation of grains and refines the grains during the solidification process of CoCrNi alloy. Simultaneously, when nano-yttrium oxide is dispersed at grain boundaries or within grains, it hinders dislocation movement through pinning, thus improving the alloy's strength. The addition of nano-yttrium oxide also purifies the molten pool, improves its wettability, and reduces defects during the printing process. In Examples 2 and 3, the amount of nano-yttrium oxide added is higher than in Example 1, resulting in a lower heterogeneous nucleation core, a more pronounced pinning effect, and stronger molten pool spreadability, leading to a more significant reduction in defects such as porosity. Therefore, the density and hardness of Examples 2 and 3 are slightly higher than those of Example 1. The preheating temperature of the substrate in Example 3 is slightly higher than that in Example 2, resulting in slightly higher density and hardness of the alloy in Example 3. Further increasing the nano-yttrium oxide content to 1.2% (Example 4), while keeping other conditions the same as in Example 3, does not significantly increase the density and hardness.

[0087] 2) Metallographic structure observation and grain size measurement were performed on the CoCrNi alloy in Example 1 and the CoCrNi alloy in Comparative Example 1. The microstructure of the CoCrNi alloy in Example 3 and the CoCrNi alloy in Comparative Example 1 was observed according to GB / T 13298-2015, "Methods for Examination of Metal Microstructure". The grain size of the CoCrNi alloy in Example 3 and the CoCrNi alloy in Comparative Example 1 was measured according to GB / T 15749-2008, "Quantitative Metallographic Determination Method". Metallographic microstructure diagrams are shown below. Figure 1 As shown in Table 2, the grain size results are as follows.

[0088] Depend on Figure 1 It can be seen that, compared with Example 3, the CoCrNi alloy in Comparative Example 1 has more pores and defects in its metallographic structure. This is because nano-yttrium oxide was added in Example 3. Nano-yttrium oxide reduces the surface tension of the melt, enhances the spreadability of the molten pool, and reduces defects such as pores.

[0089] Table 2. Grain size statistics of CoCrNi alloys in Example 3 and Comparative Example 1

[0090] As can be seen from Table 2, compared with Comparative Example 1, the grain size of the CoCrNi alloy after adding nano-yttrium oxide in Example 3 was improved, and the grains were finer.

[0091] 3) Physical and mechanical properties of the CoCrNi alloy in Example 3 and the CoCrNi alloy in Comparative Example 1 were tested. The density of the CoCrNi alloys in Example 3 and Comparative Example 1 was measured according to the standard test method for density determination of additively manufactured metallic parts (ASTM B962-23). ​​The hardness of the CoCrNi alloys in Example 3 and Comparative Example 1 was tested according to the method in Vickers hardness test of metallic materials (GB / T 4340.1-2009). Seven data points were collected, and the average value was taken after removing the extreme values. The tensile properties of the CoCrNi alloys in Example 3 and Comparative Example 1 were tested according to tensile testing of metallic materials (GB / T 228.1-2021). The density, hardness, yield strength, and elongation of the CoCrNi alloys in Example 3 and Comparative Example 1 are shown in Table 3, and the stress-strain curves are shown in... Figure 2 As shown.

[0092] Table 3. Physical and mechanical properties of the CoCrNi alloys prepared in Example 3 and Comparative Example 1.

[0093] From Table 3 and Figure 2 It can be seen that the density, hardness, yield strength, and elongation of the CoCrNi alloy in Example 3 after adding nano-yttrium oxide are all higher than those of the CoCrNi alloy in Comparative Example 1 without adding nano-yttrium oxide. This is because nano-yttrium oxide plays a role in refining the grains during the selective laser melting process of the CoCrNi alloy, while reducing defects in the microstructure, resulting in a significant improvement in the physical and mechanical properties of the alloy.

[0094] 4) The physical and mechanical properties of the CoCrNi alloy in Example 3 and the CoCrNi alloy in Comparative Examples 2-3 were tested.

[0095] Density measurements were performed on the CoCrNi alloys in Example 3 and Comparative Examples 2-3 according to the standard test method for density determination of additively manufactured metallic parts (ASTM B962-23). ​​Hardness tests were performed on the CoCrNi alloys in Example 3 and Comparative Examples 2-3 according to the Vickers hardness test method in GB / T4340.1-2009, with seven data points collected, and the average value was taken after removing the extreme values. Nanohardness tests were performed on the CoCrNi alloys in Example 3 and Comparative Examples 2-3 according to ISO 14577-1:2015, Instrumented indentation tests on metallic materials—Part 1: Test methods. Tensile properties tests were performed on the CoCrNi alloys in Example 3 and Comparative Examples 2-3 according to GB / T 228.1-2021, Tensile tests on metallic materials—Part 1: Test methods at room temperature. Density, hardness, average nanohardness, yield strength, and elongation are shown in Table 4. The nanohardness results are as follows: Figure 3 As shown, the stress-strain curves of the tensile test are as follows: Figure 4 As shown.

[0096] Table 4. Physical and mechanical properties of CoCrNi prepared in Example 3 and Comparative Examples 2-3

[0097] From Table 4, Figure 3 and Figure 4 It can be seen that the CoCrNi alloy in Example 3 has higher density, hardness, average nanohardness, yield strength, and elongation than the CoCrNi alloys in Comparative Examples 2 and 3. This is because the dispersion of nano-yttrium oxide in Example 3 is achieved through 500W high-power ultrasonic vibration, which effectively prevents the agglomeration of nano-yttrium oxide and makes its dispersion in the CoCrNi mixed powder more uniform. Its mixing effect is better than that of vibrating screen mixing and three-dimensional mixing. Figure 3 The distribution of nanoscale hardness can also corroborate each other: the nanoscale hardness of the CoCrNi alloy in Example 3 is more uniform, while the nanoscale hardness values ​​of Comparative Examples 2 and 3 are more dispersed.

[0098] 5) Observation of the metallographic structure of the CoCrNi alloys prepared in Example 3 and Comparative Example 4 The microstructure of the CoCrNi alloy in Example 3 and the CoCrNi alloy in Comparative Example 4 was observed according to GB / T 13298-2015, the method for examining the microstructure of metals. The metallographic images are shown below. Figure 5 As shown.

[0099] Depend on Figure 5 It is evident that microcracks appeared in the microstructure of the CoCrNi alloy in Comparative Example 4. This is because, during selective laser melting, after the laser locally melts the metal powder at high temperatures, the substrate was not preheated, and the molten pool cooled rapidly due to the significant temperature difference between it and the surrounding cold substrate. CoCrNi alloy has a high coefficient of thermal expansion, and rapid cooling leads to stress concentration due to shrinkage. When the stress exceeds the tensile strength of the material, microcracks form. Therefore, a suitable substrate preheating temperature can improve the forming quality of CoCrNi alloys obtained through selective laser melting.

[0100] 6) The physical and mechanical properties of the CoCrNi alloys prepared in Example 3 and Comparative Example 5 were tested. The density of the CoCrNi alloys in Example 3 and Comparative Example 5 was measured according to the standard test method for density determination of additively manufactured metallic parts (ASTM B962-23). ​​The hardness of the CoCrNi alloys in Example 3 and Comparative Example 5 was tested according to the method in Vickers hardness test of metallic materials (GB / T 4340.1-2009). Seven data points were collected, and the average value was taken after removing the extreme values. The tensile properties of the CoCrNi alloys in Example 3 and Comparative Example 5 were tested according to tensile testing method (GB / T 228.1-2021). The density, hardness, yield strength, and elongation of the CoCrNi alloys in Example 3 and Comparative Example 5 are shown in Table 5. The stress-strain curves of the tensile test results are shown in the figure. Figure 6 As shown.

[0101] Table 6. Density and hardness of CoCrNi prepared in Example 3 and Comparative Example 5

[0102] From Table 6 and Figure 6 It can be seen that the density and hardness of the CoCrNi alloys prepared in Example 3 and Comparative Example 5 are not much different. This indicates that the performance of the CoCrNi alloy prepared by selective laser melting using single-element cobalt powder, chromium powder and nickel powder through three-dimensional mixing is comparable to that of the alloy prepared by CoCrNi alloyed powder. This greatly saves costs and also confirms that the three-dimensional mixing method can effectively and uniformly mix the powder without damaging the powder morphology or affecting the powder performance.

[0103] 7) The CoCrNi alloy from Example 3 was subjected to low-temperature friction and wear tests with commercially available 316L stainless steel. According to the ASTM G133 linear reciprocating friction and wear test method, the CoCrNi alloy in Example 3 was subjected to low-temperature reciprocating friction and wear against a commercially available 316L stainless steel sample. The test involved continuous liquid nitrogen flow, a load of 30 N, a reciprocating friction frequency of 10 Hz, a test time of 30 min, and the use of GCr15 steel balls as the grinding balls. After the test, 3D images of the wear tracks and cross-sectional images of the deepest point of the wear tracks were captured using a laser confocal microscope. Figure 7 , Figure 8 As shown in Table 7, the low-temperature wear amount is as follows.

[0104] Table 7. Volumetric wear rate of the CoCrNi alloy prepared in Example 3 after low-temperature friction and wear with commercially available 316L stainless steel under continuous liquid nitrogen.

[0105] Depend on Figure 7 , Figure 8As shown in Table 7, under the extreme low-temperature environment of continuous liquid nitrogen, the CoCrNi alloy in Example 3 exhibits shallower wear tracks and a lower volumetric wear rate than 316L. The product prepared in Example 3 achieved 39,494 low-cycle fatigue cycles under tensile-compressive strain control at -150°C, indicating that the CoCrNi alloy in Example 3 is more wear-resistant than 316L under low-temperature friction and wear. This is because the face-centered cubic (FCC) structure of the CoCrNi alloy has multiple slip systems, making it prone to plastic deformation during deformation, leading to dislocation multiplication and dislocation interaction. Simultaneously, due to its low stacking fault energy, twinning is easily generated during deformation, resulting in a high hardening rate for the CoCrNi alloy during deformation. This condition is more pronounced at low temperatures, thus demonstrating excellent low-temperature wear resistance.

[0106] 8) Low-temperature fatigue tests were conducted on the CoCrNi alloy from Example 3 and commercially available 316L stainless steel. According to GB / T 15248-2008, the CoCrNi alloy in Example 3 and commercially available 316L stainless steel were subjected to low-cycle fatigue tests using a tension-compression strain control mode with a strain ratio R = -1. The loading waveform was sinusoidal, the loading strain was controlled at 0.3%, and the frequency was 1 Hz. The number of fatigue cycles was recorded after the test. Figure 9 As shown.

[0107] Depend on Figure 9 It is evident that during cyclic loading at a constant strain of 0.3%, the CoCrNi alloy in Example 3 exhibits a higher fatigue life compared to 316L, and the CoCrNi alloy in Example 3 also withstands greater stress. This is because the CoCrNi alloy has a lower stacking fault energy, making dislocation cross-slip difficult during cyclic loading deformation. Dislocations tend to decompose into partial dislocations, forming stacking faults between them. When multiple stacking faults are arranged in an orderly manner on adjacent slip planes, it leads to lattice rearrangement, forming twins. This mechanism gives the CoCrNi alloy both high strength and ductility, resulting in a higher fatigue life during cyclic loading compared to 316L stainless steel.

[0108] The embodiments of the present invention have been described in detail above, but the present invention is not limited to the described embodiments. For those skilled in the art, various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and these variations still fall within the protection scope of the present invention.

Claims

1. A method for preparing CoCrNi alloy by selective laser melting with added nano-yttrium oxide, characterized in that, Includes the following steps: (1) Weigh out cobalt powder, chromium powder and nickel powder according to weight percentage, and mix the three metal element powders evenly using a three-dimensional mixer; (2) Add nano-yttrium oxide powder to the uniformly mixed CoCrNi powder and mix it uniformly using an ultrasonic system; (3) The powder mixed evenly in step (2) is printed into shape by selective laser melting technology to prepare a high-performance CoCrNi alloy.

2. The method for preparing CoCrNi alloy by selective laser melting with added nano-yttrium oxide according to claim 1, characterized in that, In step (1), the cobalt powder, chromium powder and nickel powder are prepared by gas atomization method, with good sphericity greater than 95%, Hall flow rate less than 50s / 50g, purity of each metal powder greater than 99.5%, oxygen content less than 0.1% and nitrogen content less than 0.01%.

3. The method for preparing CoCrNi alloy by selective laser melting with added nano-yttrium oxide according to claim 1, characterized in that, The atomic ratio of Co, Cr and Ni in the cobalt powder, chromium powder and nickel powder mentioned in step (1) is 0.8-1.1:0.8-1.1:0.8-1.

1. The particle size range of the three metal element powders is 15~68μm, and the D10-D90 range is 20-72μm.

4. The method for preparing CoCrNi alloy by selective laser melting with added nano-yttrium oxide according to claim 1, characterized in that, In step (1), the cobalt powder, chromium powder and nickel powder are mixed using a SHY three-dimensional mixer. The mixing method involves a combination of rotation, oscillation and tumbling in three-dimensional space. The mixing tank is protected by argon gas with a purity greater than 99.9% and is sealed. The cylinder speed is adjusted to 8-20 revolutions per minute, and the mixing time is 30-180 minutes.

5. The method for preparing CoCrNi alloy by selective laser melting with added nano-yttrium oxide according to claim 1, characterized in that, In step (2), the purity of the nano-yttrium oxide powder is greater than 99.9%, the particle size is 10-200nm, the amount of nano-yttrium oxide powder added accounts for 0.3%~2% of the mass ratio of CoCrNi powder, and the nano-yttrium oxide powder and CoCrNi powder are mixed by an ultrasonic system with a power of 200-1200W and a time of 30-150min.

6. The method for preparing CoCrNi alloy by selective laser melting with added nano-yttrium oxide according to claim 1, characterized in that, In step (3), the parameters of the selected area laser melting method are: laser power 150-250W, scanning speed 800-1200mm / s, scanning path 80-120μm, and layer thickness 0.2-0.4μm.

7. The method for preparing CoCrNi alloy by selective laser melting with added nano-yttrium oxide according to claim 1, characterized in that, In step (3), the laser scanning strategy is a checkerboard pattern and the substrate preheating temperature is 250-300℃.

8. A CoCrNi alloy material, characterized in that, It is prepared by any one of the methods of claims 1-7.

9. The application of the high-performance CoCrNi alloy material according to claim 8 in the preparation of products subjected to low-temperature friction and wear or low-temperature cyclic stress.

10. The application according to claim 9, characterized in that, The prepared product achieved 39,494 low-cycle fatigue cycles under tensile-compressive strain control at -150℃.

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