A high-strength and plastic heterogeneous nickel alloy and preparation method thereof

Abstract

The invention discloses a high-strength and plastic heterogeneous nickel alloy, the alloy is composed of Ni and alloy phase, the chemical composition is Ni-x (Ni-20Cr-yAl), wherein 30≤x≤50, 0≤y≤13, there are differences in size and composition between Ni and alloy phase in microstructure, and in preparation, by using Ni of different particle sizes as soft phase and Ni alloy phase of different compositions as hard phase, the alloy has the characteristics of heterogeneous composition and heterogeneous grain size. The heterogeneous nickel alloy prepared by the present invention adopts the method of low-temperature high-energy ball milling + liquid mixing, which effectively avoids the problems of excessive internal energy and uneven mixing during ball milling; the Ni-20Cr-yAl alloy with high strength and good stability is adopted as the reinforcing phase, and on the basis of improving the strength of the matrix, the alloy with strength improvement of>70.2% and maximum plasticity improvement of 59.5% is obtained, and the heterogeneous nickel alloy has obvious advantages of strong plasticity and has good application prospects in many fields such as engineering applications.

Description

Technical Field

[0001] The invention relates to the technical field of preparation of heterogeneous metal materials, and in particular to a method for preparing a heterogeneous nickel-based alloy material by spark plasma sintering. Background Art

[0002] Nickel alloy is a high melting point material with high strength and good stability in high temperature environment, so it is often used in aerospace, engine parts and other fields. However, with the changes in the application environment, the requirements for metal materials are becoming more and more stringent, causing some alloy materials to fail to meet the use requirements. Although nickel-chromium alloy has the advantages of high strength and good wear resistance, its poor strength-plasticity matching has always restricted its application. How to improve its strength-plasticity matching has become a research hotspot in recent years.

[0003] Strength and toughness are the two most core mechanical properties of metal materials. Like most materials, nickel alloys also follow the inverse relationship between strength and plasticity of traditional materials. Scientists "learn from nature" and draw inspiration from nature to propose the concept of heterogeneous materials. Compared with traditional materials, heterogeneous materials have uneven distribution characteristics in terms of microstructure or composition. They have excellent comprehensive mechanical properties and strength-plasticity matching, which makes it possible to solve the limitations of material use and improve the strength-plasticity matching of materials.

[0004] The patent document with publication number CN113444958A and publication date September 28, 2021 discloses a high-strength and high-toughness layered heterogeneous medium-entropy alloy and its preparation method. It mainly prepares a high-strength and toughness heterogeneous medium-entropy alloy with a tensile strength of 1440MPa by liquid nitrogen rolling and smelting. This method is not limited by specifications and dimensions, but has many process requirements and requires liquid nitrogen and high-temperature treatment. The patent document with publication number CN114427052A and publication date May 3, 2022 discloses a Ni3Al-based alloy and its additive manufacturing method, which mainly improves the mechanical properties of the alloy by laser cladding, but it is inevitable that the strength increases and the plasticity decreases, and the strength decreases and the plasticity increases. In this context, it is possible to consider improving this problem by preparing a heterogeneous structure.

[0005] Generally, heterogeneous structures are divided into gradient nanostructures, layered structures, bimodal structures, harmonic structures, etc. The main strengthening methods are: (1) regulating the grain size or structure of the material to prepare a microstructure with cross-scale grain distribution, (2) introducing special interfaces inside the metal to induce strain strengthening mechanisms, etc.; (3) regulating the elemental and phase composition of the material at the microscale to stimulate multi-scale strengthening and toughening mechanisms. In recent years, the design concept of heterogeneous metal materials has shown obvious strengthening and toughening advantages over the inverted performance relationship of traditional alloys. During the plastic deformation process of heterogeneous metals, the mechanical properties of the soft and hard zones inside the material are different, resulting in uneven deformation and an improvement in strength and plasticity.

[0006] As a rapid prototyping technology, spark plasma sintering technology has the advantages of fast heating, short sintering time, and high density of sintered samples. It does not need to be sintered at the liquidus temperature of the sample, which can effectively avoid the growth of grains, thereby ensuring the performance of the material. At the same time, alloys with different compositions and microstructures can be obtained by changing the ratio of powders to be sintered with different compositions and grain sizes. In addition, the gradient temperature sintering method can make the internal composition of the alloy more uniform at a lower heating rate, thereby reducing the internal porosity of the alloy and improving the mechanical properties. Therefore, the spark plasma sintering method can prepare heterogeneous nickel alloys with composition and grain size, thereby achieving a significant improvement in strength-plasticity matching.

[0007] Traditional high-energy ball milling is usually carried out at room temperature, which may cause the energy generated inside the powder during the ball milling process to increase its temperature, thereby affecting the alloying of the powder and affecting the material properties. In addition, the common low-energy ball milling method cannot completely ensure that the powder is mixed evenly. Summary of the invention

[0008] In view of the problems of low strength and poor plasticity in the current application of nickel alloys in engineering applications and other fields, the present invention provides a method for preparing a high-strength and plastic heterogeneous nickel alloy. The low-temperature and high-energy ball milling process can effectively avoid the temperature influence during the ball milling process and enhance the alloying effect. The mixed powder can be made more uniform by using ethanol for liquid mixing and stirring, thereby improving the material performance. In spark plasma sintering, the powder is quickly condensed and formed in a short time by high temperature and high pressure, and the material is densified by adjusting the appropriate sintering parameters and the temperature control of gradient sintering, thereby achieving a good reinforcement effect.

[0009] In order to solve the above technical problems, the present invention proposes a high-strength and ductile heterogeneous nickel alloy, which is composed of Ni and an alloy phase, and has a chemical composition of Ni-x (Ni-20Cr-yAl), wherein 30≤x≤50, 0≤y≤13, and x and y are both mass ratios. In the microstructure, there are differences in size and composition between Ni and the alloy phase. In preparation, Ni of different particle sizes is used as a soft phase and Ni alloy phases of different compositions are used as a hard phase. The alloy has the characteristics of composition heterogeneity and grain size heterogeneity.

[0010] At the same time, the present invention also proposes a method for preparing the above-mentioned high-strength and ductile heterogeneous nickel alloy, comprising the following steps:

[0011] Step 1, taking a pre-alloyed powder with a chemical composition of Ni-20Cr-yAl, wherein 0≤y≤13, y is a mass ratio, and placing the pre-alloyed powder into a ball mill filled with argon gas and a process control agent with a mass fraction of 3-10%, and performing low-temperature high-energy ball milling. During the ball milling process, the temperature of the ball mill body is kept constant at 0-10° C., and after the ball milling is completed, drying is performed to obtain an ultrafine Ni-20Cr-yAl alloy powder;

[0012] Step 2: Place Ni powder and the ultrafine Ni-20Cr-yAl alloy powder obtained in step 1 in an anhydrous ethanol solution in a mass ratio of 7:3 to 5:5, mix and stir in a liquid state at room temperature, stir evenly, filter and dry, and obtain a mixed powder with a chemical composition of Ni-x (Ni-20Cr-yAl), wherein 30≤x≤50, 0≤y≤13, and x and y are both mass ratios;

[0013] Step 3: The mixed powder obtained in step 2 is loaded into a mold, pre-pressed on a tablet press, and then subjected to spark plasma sintering, and a high-strength and plastic heterogeneous nickel alloy is obtained by adopting a gradient temperature rise sintering method.

[0014] Furthermore, the preparation method of the present invention, wherein:

[0015] In step 1, the particle size of the pre-alloyed powder is 200-800 meshes, and the process parameters of low-temperature high-energy ball milling are: rotation speed is 250-500rpm, ball-to-material ratio is 10:1-20:1, ball milling time is 18-24h, ball milling temperature is 0-10°C, and industrial refrigerator or other low-temperature refrigeration equipment is used for temperature control during low-temperature high-energy ball milling. The process control agent is anhydrous ethanol or stearic acid.

[0016] In step 2, the particle size of the Ni powder is 200nm-30μm, and the purity is ≥99.9%. The mass volume ratio of the sum of the Ni powder and the Ni-20Cr-yAl alloy powder to the anhydrous ethanol solution is 1g / 10-20mL. The parameters of liquid mixing and stirring are: the speed is 40-100rpm, and the time is 2-10h.

[0017] In step 3, the process conditions of spark plasma sintering are: sintering temperature of 800-1100° C., heating rate of 50-100° C. / min, sintering pressure of 50-120 MPa, vacuum degree <6 Pa, and holding time of 5-20 min.

[0018] The temperature control of the gradient temperature rise sintering is: the temperature rise process is divided into two stages, the first stage is from room temperature to 100°C lower than the sintering temperature, and the second stage is from the highest temperature of the first stage to the sintering temperature; the heating rate of the first stage is 100°C / min, and the heating rate of the second stage is 50°C / min.

[0019] Compared with the prior art, the enhancement effects of the present invention are:

[0020] (1) The present invention uses the characteristics of spark plasma sintering to quickly condense and form powder in a short time, ignoring the difference in melting points between different components. On the one hand, high temperature and high pressure are used to improve the density of the alloy and reduce its internal defects. The energy impact caused by powder collision and deformation during the ball milling process can be effectively avoided by low temperature and high energy ball milling, thereby improving the alloying effect. On the other hand, the gradient temperature sintering method can effectively control the uniformity of the distribution of the reinforcing phase in the matrix, thereby obtaining a heterogeneous nickel alloy with uniform distribution of soft and hard phases, and achieving a balance of strength and toughness of the alloy.

[0021] (2) The present invention effectively avoids the damage and uneven mixing that may be caused by other mixing methods during the mixing process by mixing the Ni-20Cr-yAl reinforcement phase with the matrix material of different particle sizes in a liquid state, thereby achieving the purpose of preparing a uniform mixed powder.

[0022] (3) The present invention uses Ni-20Cr-yAl alloy with high strength and good stability as the reinforcement phase, which effectively improves the strength of the matrix without reducing its plasticity, and obtains an alloy with a strength increase of >70.2% and a maximum plasticity increase of 59.5%. Figure 3 From the strength-plasticity relationship diagrams of alloys reported in some prior arts, it can be found that the heterogeneous alloy prepared by the present invention is better than some reported Ni-W, Ni-Al, Ni-Ti alloys, etc., and achieves a balance between strength and toughness. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Schematic diagram of heterogeneous structure distribution of nickel alloy of the present invention;

[0024] Figure 2 It is a tensile performance diagram of Example 10 of the present invention and Comparative Examples 1, 2, 3, and 4;

[0025] Figure 3 A comparison chart of the nickel alloy performance of Examples 3, 4, 9, and 10 of the present invention and the yield strength and elongation of the Ni alloy in the prior art and their fitting curves;

[0026] Figure 4 The particle size statistics of the mixed powder obtained in step 2 of Example 10 of the present invention;

[0027] Figure 5 This is a tensile fracture morphology diagram of the nickel alloy of Example 10 of the present invention. DETAILED DESCRIPTION

[0028] The present invention is described in detail below with reference to the accompanying drawings and specific implementations, which mainly include mechanical property testing and microscopic morphology characterization, including tensile testing and scanning electron microscopy (SEM).

[0029] The present invention proposes a design concept for preparing a high-strength and ductile heterogeneous nickel alloy, such as Figure 1 As shown, the alloy is composed of Ni and Ni alloy phases, and the chemical composition is Ni-x (Ni-20Cr-yAl), wherein 30≤x≤50, 0≤y≤13, and x and y are both mass ratios. In the microstructure, there are differences in size and composition between Ni and Ni alloy phases. In the preparation, Ni with different particle sizes is used as the soft phase, and Ni alloy phases with different compositions are used as the hard phase. The alloy has the characteristics of composition isomerism and grain size isomerism. The composition isomerism is mainly achieved by selecting different Ni alloys as the reinforcement phase and pure Ni powder as the matrix material; the size isomerism is achieved by the size difference between the reinforcement phase and the matrix material. The powder is first alloyed by low-temperature high-energy ball milling, and then homogenized by liquid mixing and stirring, so as to achieve size isomerism with the reinforcement phase; finally, the target alloy material is obtained by selecting appropriate sintering pressure, heating rate, and holding time by gradient temperature rise sintering. The main steps for preparing the alloy are as follows:

[0030] Step 1, take a pre-alloyed powder with a chemical composition of Ni-20Cr-yAl, wherein 0≤y≤13, y is a mass ratio, and the particle size of the pre-alloyed powder is 200-800 meshes, and put the pre-alloyed powder into a ball mill filled with argon and a process control agent with a mass fraction of 3-10% for low-temperature high-energy ball milling, wherein the process control agent is anhydrous ethanol or stearic acid. The process parameters of low-temperature high-energy ball milling are: a rotation speed of 250-500rpm, a ball-to-material ratio of 10:1-20:1, and a ball milling time of 18-24h. During the ball milling process, the temperature of the ball mill body is kept constant at 0-10°C. An industrial refrigerator or other low-temperature refrigeration equipment is used for temperature control during the low-temperature high-energy ball milling process. After the ball milling is completed, the powder is dried to obtain an ultrafine Ni-20Cr-yAl alloy powder;

[0031] Step 2, take Ni powder with a particle size of 200nm to 30μm and a purity of ≥99.9%, place the Ni powder and the ultrafine Ni-20Cr-yAl alloy powder obtained in step 1 in an anhydrous ethanol solution at a mass ratio of 7:3 to 5:5, the mass volume ratio of the sum of the mass of the two mixed powders to the mass volume of the anhydrous ethanol solution is 1g / 10 to 20mL, and liquid mixing and stirring are performed at room temperature. The parameters of liquid mixing and stirring are: speed of 40 to 100rpm, time of 2 to 10h. After fully stirring, filter and dry to obtain a mixed powder with a chemical composition of Ni-x (Ni-20Cr-yAl), wherein 30≤x≤50, 0≤y≤13, and x and y are both mass ratios;

[0032] Step 3, after removing the control agent from the mixed powder obtained in step 2 in an oven, put it into high-strength graphite, separate the middle and the inner wall with carbon paper, put it on a tablet press after pre-pressing, and then perform spark plasma sintering, the sintering temperature is 800-1100°C, the heating rate is 50-100°C / min, the sintering pressure is 50-120MPa, the vacuum degree is less than 6Pa, and the holding time is 5-20min. The temperature control of the gradient temperature sintering is: the temperature rising process is divided into two stages, the first stage is from room temperature to 100°C lower than the sintering temperature, and the second stage is from the highest temperature of the first stage to the sintering temperature; the heating rate of the first stage is 100°C / min, and the heating rate of the second stage is 50°C / min.

[0033] In order to help researchers in this field better understand the technical ideas of this experiment, the present invention is further described below in conjunction with the accompanying drawings and specific embodiments. However, the following embodiments are by no means limiting the present invention in any way, and the embodiments are all conventional methods unless otherwise specified.

[0034] Example 1

[0035] The Ni-50 (Ni-20Cr) alloy is prepared by sintering, and the steps are as follows:

[0036] Step 1, put Ni-20Cr pre-alloyed powder with a particle size of 400 mesh and a purity of ≥99.9% into a ball mill, with a ball-to-material ratio of 10:1, and add 5% by mass ethanol as a control agent (PCA) to prevent cold welding during ball milling. Under the protection of argon atmosphere, low-temperature high-energy ball milling is performed at a rotation speed of 250rpm for 24 hours, wherein the ball mill and the grinding balls are made of cemented carbide. At the same time, an industrial refrigerator is used as a temperature controller during the ball milling process of the present invention, and other equipment with similar functions can be used as a temperature control instrument. The temperature is controlled at 0-10°C. After the ball milling is completed, the powder is placed in an oven for drying to obtain ultrafine Ni-20Cr alloy powder for standby use.

[0037] Step 2: Put 5 g of pure Ni powder with a particle size of 500 mesh, 5 g of the dried Ni-20Cr alloy powder and 50 mL of anhydrous ethanol into a beaker, stir in liquid state at 60 rpm for 6 h, filter after sufficient stirring, and dry after completion to obtain ultrafine Ni-50 (Ni-20Cr) powder.

[0038] Step 3, the powder obtained in step 2 is loaded into a high-strength graphite mold, pre-pressed on a tablet press with a force of 15 MPa for 5 minutes, and then placed in a chamber for gradient sintering. The sintering pressure is 80 MPa, and the temperature is increased to 700°C at a rate of 100°C / min, and then increased to 800°C at 50°C / min. The holding time is 10 minutes. After the sintering is completed, the temperature is cooled to room temperature at a cooling rate of 50°C / min. Vacuum or inert gas protection is used during the sintering process. After the end, the desired alloy is obtained, which is recorded as Ni-50(Ni-20Cr)-1.

[0039] Example 2

[0040] Ni-50 (Ni-20Cr) alloy was prepared by sintering. The preparation method was basically the same as that in Example 1, except that in step 2, pure Ni powder with a particle size of 500 mesh was replaced with pure Ni powder with a particle size of 200 nm. The final alloy was recorded as Ni-50 (Ni-20Cr) -2.

[0041] Example 3

[0042] Preparation of Ni-40 (Ni-20Cr) alloy by sintering: The preparation method is basically the same as that in Example 1, except that in step 2, the masses of pure Ni powder and Ni-20Cr alloy powder are changed to 6 g and 4 g, respectively; the final alloy is recorded as Ni-40 (Ni-20Cr) -1.

[0043] Example 4

[0044] Preparation of Ni-40 (Ni-20Cr) alloy by sintering: The preparation method is basically the same as that in Example 2, except that in step 2, the masses of pure Ni powder and Ni-20Cr alloy powder are changed to 6 g and 4 g, respectively; the final alloy is recorded as Ni-40 (Ni-20Cr) -2.

[0045] Example 5

[0046] Preparation of Ni-30 (Ni-20Cr) alloy by sintering: The preparation method is basically the same as that in Example 1, except that in step 2, the masses of pure Ni powder and Ni-20Cr alloy powder are changed to 7g and 3g respectively; the final alloy is recorded as Ni-30 (Ni-20Cr) -1.

[0047] Example 6

[0048] Preparation of Ni-30 (Ni-20Cr) alloy by sintering: The preparation method is basically the same as that in Example 2, except that in step 2, the masses of pure Ni powder and Ni-20Cr alloy powder are changed to 7g and 3g respectively; the final alloy is recorded as Ni-30 (Ni-20Cr) -2.

[0049] Example 7

[0050] Ni-50 (Ni-20Cr-13Al) alloy was prepared by sintering. The preparation method was basically the same as that in Example 1, except that the Ni-20Cr pre-alloyed powder with a particle size of 400 mesh and a purity of ≥99.9% was replaced with Ni-20Cr-13Al pre-alloyed powder with a particle size of 400 mesh and a purity of ≥99.9%; the final alloy was recorded as Ni-50 (Ni-20Cr-13Al) -1.

[0051] Example 8

[0052] Ni-50 (Ni-20Cr-13Al) alloy was prepared by sintering. The preparation method was basically the same as that in Example 7, except that in step 2, the pure Ni powder with a particle size of 500 mesh was replaced with pure Ni powder with a particle size of 200 nm. The final alloy was recorded as Ni-50 (Ni-20Cr-13Al) -2.

[0053] Example 9

[0054] Preparation of Ni-40 (Ni-20Cr-13Al) alloy by sintering: The preparation method is basically the same as that in Example 7, except that in step 2, the masses of pure Ni powder and Ni-20Cr-13Al alloy powder are changed to 6 g and 4 g, respectively; the final alloy is recorded as Ni-40 (Ni-20Cr-13Al) -1.

[0055] Example 10

[0056] Preparation of Ni-40 (Ni-20Cr-13Al) alloy by sintering: The preparation method is basically the same as that in Example 8, with the only difference being that in step 2, the masses of pure Ni powder and Ni-20Cr-13Al alloy powder are changed to 6 g and 4 g, respectively; the final alloy is recorded as Ni-40 (Ni-20Cr-13Al) -2.

[0057] Embodiment 11

[0058] Preparation of Ni-30 (Ni-20Cr-13Al) alloy by sintering: The preparation method is basically the same as that in Example 7, except that in step 2, the masses of pure Ni powder and Ni-20Cr-13Al alloy powder are changed to 7g and 3g, respectively; the final alloy is recorded as Ni-30 (Ni-20Cr-13Al) -1.

[0059] Example 12

[0060] Preparation of Ni-30 (Ni-20Cr-13Al) alloy by sintering: The preparation method is basically the same as that in Example 8, except that in step 2, the masses of pure Ni powder and Ni-20Cr-13Al alloy powder are changed to 7g and 3g, respectively; the final alloy is recorded as Ni-30 (Ni-20Cr-13Al) -2.

[0061] Comparative Example 1

[0062] Preparation of pure Ni by sintering: In this example, the particle size of Ni powder is 500 mesh, the sintering pressure is 80 MPa, the temperature rise method adopts the gradient sintering method, the insulation time is 10 min, and the sintering temperature is 800°C. The pure Ni prepared in this comparative example 1 is recorded as Ni-1.

[0063] Comparative Example 2

[0064] Preparation of pure Ni by sintering: In this example, the particle size of Ni powder is 200 nm, the sintering pressure is 80 MPa, and the sintering process conditions are the same as those of Comparative Example 1. The pure Ni prepared in Comparative Example 2 is recorded as Ni-2.

[0065] Comparative Example 3

[0066] Preparation of Ni-20Cr by sintering: The sintering process conditions are the same as those in Comparative Example 1.

[0067] Comparative Example 4

[0068] Preparation of Ni-20Cr-13Al by sintering: the sintering pressure is 80MPa, the temperature rise method adopts the gradient sintering method, the holding time is 10min, and the sintering temperature is 1100℃.

[0069] Performance Testing:

[0070] The powder morphology and room temperature tensile tests were performed on the above Examples 1 to 6 and Comparative Example 1. The specific methods are as follows:

[0071] 1) Room temperature tensile test

[0072] The sintered samples were polished with sandpaper and cut into standard tensile specimens. After being polished, they were subjected to room temperature axial tensile tests on an INSTRON-6800 series double-column tabletop testing machine. The tensile rate was kept constant at 10 -3 s -1 , in order to compare and analyze the effects of composition heterogeneity and size heterogeneity on mechanical properties such as strength and plasticity.

[0073] 2) Morphology test

[0074] Zeiss GeminiSEM 300 was used to photograph the morphology of mixed powders and tensile fracture morphology. The powder distribution was observed to determine whether it was evenly distributed and its size heterogeneity characteristics, and the fracture mode was determined by the fracture morphology.

[0075] Examples 1 to 6 and comparative example 1 were subjected to room temperature stretching experiments in sequence. After testing, the experimental results are shown in Table 1.

[0076] Table 1 Tensile properties of different components

[0077]

[0078]

[0079] Table 1

[0080]

[0081] In the design of initial composition, there is a significant difference in particle size between Ni and its alloy powders, such as Figure 4As shown, it has the characteristics of size isomerism. From Table 1, it can be seen from the comparison of Examples 1 to 12 with Comparative Examples 1 to 4 that the strength and plasticity of the embodiments have been improved to varying degrees. By comparing the alloys in Examples 1, 3, 5 and Examples 2, 4, and 6, it can be found that with the reduction of the proportion of alloy phase in the alloy, the yield strength of the material gradually decreases and the elongation gradually increases. By comparing Examples 1 and 2; Examples 3, 4 and Examples 5 and 6, it can be found that with the reduction of the soft phase grain size, the yield strength of the material gradually increases. However, in Examples 3, 4 and 5 and 6, it was found that the elongation of the material decreased, which may be due to the decrease in plasticity caused by fine grain strengthening. In Examples 7, 9, and 11, the yield strength of the alloy with coarse-grained Ni as the soft phase also decreases with the reduction of the proportion of the alloy phase, and the elongation gradually increases. However, in the alloy with nanocrystalline Ni as the soft phase in Examples 8, 10, and 12, this situation does not exist, and the elongation of the alloys of all components has been significantly improved. Among them, Ni-40 (Ni-20Cr-13Al)-2 in Example 10 has the best comprehensive strength and plasticity. Figure 2 As shown in the figure, its yield strength is increased by 56.2% compared with pure Ni, its tensile strength is increased by 50.8%, and its elongation is also increased by 26.4%. Figure 3 From the strength-plasticity relationship of Ni alloys reported in some prior art, it can be seen that the strength-plasticity matching relationship of Ni alloys with heterogeneous structures is better than that of traditional alloys, showing its superiority. There are many defects such as pores and pits on the fracture of coarse-grained Ni, and the dimples are relatively large; while nanocrystalline Ni is relatively dense, no obvious defects are found, and the cross section is covered with small and dense dimples. Figure 5 The reinforced Ni-20Cr-yAl phase is a small and smooth section, which belongs to brittle fracture, which is consistent with the tensile results. Figure 5 The tensile fracture morphology shows that the reinforcement phase is evenly distributed in the matrix, while the matrix is ​​dissolved and distributed around the reinforcement phase. The reinforcement phase is grayish white and the matrix is ​​white. The reinforcement phase forms a smooth brittle fracture, while many tiny dimples appear in the matrix. Under this multi-mode fracture mechanism, while the reinforcement phase fractures, the matrix provides it with plasticity, thereby achieving an increase in sample strength without a decrease in plasticity, thus achieving an improvement in overall performance. The reason for this is that the increase in strength is provided by the reinforcement phase, which is the result of the combined action of low porosity, grain boundaries, and the reinforcement-rich phase therein.

[0082] In summary, the above embodiments are only preferred examples of the present invention and should not be construed as limiting the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a high-strength and ductile heterogeneous nickel alloy, Features: The alloy is composed of Ni and an alloy phase, and has a chemical composition of Ni-x (Ni-20Cr-yAl), wherein 30≤x≤50, 0≤y≤13, and x and y are both mass ratios; in terms of microstructure, Ni and the alloy phase have differences in size and composition; in terms of preparation, Ni with different particle sizes is used as a soft phase, and Ni alloy phases with different compositions are used as a hard phase; the alloy has the characteristics of composition heterogeneity and grain size heterogeneity; and is prepared according to the following steps: Step 1, taking a pre-alloyed powder with a chemical composition of Ni-20Cr-yAl, wherein 0≤y≤13, y is a mass ratio, and placing the pre-alloyed powder into a ball mill filled with argon gas and a process control agent with a mass fraction of 3-10%, and performing low-temperature high-energy ball milling. During the ball milling process, the temperature of the ball mill body is kept constant at 0-10° C., and after the ball milling is completed, drying is performed to obtain an ultrafine Ni-20Cr-yAl alloy powder; Step 2: Place Ni powder and the ultrafine Ni-20Cr-yAl alloy powder obtained in step 1 in an anhydrous ethanol solution in a mass ratio of 7:3 to 5:5, mix and stir in a liquid state at room temperature, stir evenly, filter and dry, and obtain a mixed powder with a chemical composition of Ni-x (Ni-20Cr-yAl), wherein 30≤x≤50, 0≤y≤13, and x and y are both mass ratios; Step 3: The mixed powder obtained in step 2 is loaded into a mold, pre-pressed on a tablet press, and then subjected to spark plasma sintering, and a high-strength and plastic heterogeneous nickel alloy is obtained by adopting a gradient temperature rise sintering method.

2. The preparation method according to claim 1, It is characterized in that In step 1, the particle size of the pre-alloyed powder is 200-800 mesh, and the process parameters of low-temperature high-energy ball milling are: rotation speed is 250-500rpm, ball-to-material ratio is 10:1-20:1, ball milling time is 18-24h, ball milling temperature is 0-10°C, and industrial refrigerator or other low-temperature refrigeration equipment is used for temperature control during the low-temperature high-energy ball milling process.

3. The preparation method according to claim 1, It is characterized in that In step 1, the process control agent is anhydrous ethanol or stearic acid.

4. The preparation method according to claim 1, It is characterized in that In step 2, the particle size of the Ni powder is 200 nm to 30 μm, and the purity is ≥ 99.9%.

5. The preparation method according to claim 1, It is characterized in that In step 2, the mass volume ratio of the sum of the Ni powder and the Ni-20Cr-yAl alloy powder to the anhydrous ethanol solution is 1 g / 10 to 20 mL. .

6. The preparation method according to claim 1, It is characterized in that In step 2, the parameters of liquid mixing and stirring are: rotation speed is 40 to 100 rpm, and time is 2 to 10 hours.

7. The preparation method according to claim 1, It is characterized in that In step 3, the process conditions of spark plasma sintering are: sintering temperature of 800-1100° C., heating rate of 50-100° C. / min, sintering pressure of 50-120 MPa, vacuum degree <6 Pa, and holding time of 5-20 min.

8. The preparation method according to claim 1 or 7, It is characterized in that In step 3, the temperature control of the gradient temperature rise sintering is: the temperature rise process is divided into two stages, the first stage is from room temperature to 100° C. lower than the sintering temperature, and the second stage is from the highest temperature of the first stage to the sintering temperature; The heating rate in the first stage was 100°C / min, and the heating rate in the second stage was 50°C / min.

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