CN113652586A - Special nano modified tungsten alloy for selective laser melting and preparation method thereof - Google Patents
Special nano modified tungsten alloy for selective laser melting and preparation method thereof Download PDFInfo
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C27/00—Alloys based on rhenium or a refractory metal not mentioned in groups C22C14/00 or C22C16/00
- C22C27/04—Alloys based on tungsten or molybdenum
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F10/00—Additive manufacturing of workpieces or articles from metallic powder
- B22F10/20—Direct sintering or melting
- B22F10/28—Powder bed fusion, e.g. selective laser melting [SLM] or electron beam melting [EBM]
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F9/00—Making metallic powder or suspensions thereof
- B22F9/02—Making metallic powder or suspensions thereof using physical processes
- B22F9/04—Making metallic powder or suspensions thereof using physical processes starting from solid material, e.g. by crushing, grinding or milling
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B33—ADDITIVE MANUFACTURING TECHNOLOGY
- B33Y—ADDITIVE MANUFACTURING, i.e. MANUFACTURING OF THREE-DIMENSIONAL [3-D] OBJECTS BY ADDITIVE DEPOSITION, ADDITIVE AGGLOMERATION OR ADDITIVE LAYERING, e.g. BY 3-D PRINTING, STEREOLITHOGRAPHY OR SELECTIVE LASER SINTERING
- B33Y70/00—Materials specially adapted for additive manufacturing
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
- B22F9/00—Making metallic powder or suspensions thereof
- B22F9/02—Making metallic powder or suspensions thereof using physical processes
- B22F9/04—Making metallic powder or suspensions thereof using physical processes starting from solid material, e.g. by crushing, grinding or milling
- B22F2009/043—Making metallic powder or suspensions thereof using physical processes starting from solid material, e.g. by crushing, grinding or milling by ball milling
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- Y02P10/25—Process efficiency
Abstract
The invention discloses a special nano modified tungsten alloy for selective laser melting and a preparation method thereof, wherein in alloy powder, the content of nickel is 0.5-2.5 percent, the content of iron is 0.5-2.5 percent and the balance is tungsten according to weight percentage; wherein the mass ratio of nickel to iron is 1: 1, nickel and iron are nano-scale particles, and the average particle size of the particles is 50-100 nm; adding a certain amount of nano nickel and nano iron powder into pure tungsten powder, uniformly dispersing nano particles in the pure tungsten by a high-energy ball milling method, forming the powder under the condition of proper parameters based on a selective laser melting technology, and obtaining a tungsten alloy product which has no crack, high density and isometric crystal structure. The invention utilizes the nanometer modification technology to improve the melt viscosity and the crystal boundary strength, solves the problems of holes and cracks in selective laser melting forming of the tungsten material, and improves the comprehensive mechanical property of the tungsten material.
Description
Technical Field
The invention belongs to metal materials based on additive manufacturing, and particularly relates to a special nano modified high-performance tungsten alloy for selective laser melting and a preparation method thereof.
Background
Tungsten (W) is widely used in aerospace, weaponry, chemical and nuclear industries because of its unique physical and chemical properties, such as high melting point, high density, high strength hardness, high thermal conductivity, high radiation shielding ability, etc. In addition, tungsten has excellent radiation shielding capability and structural stability, making it the most promising plasma wall material. However, the ductile-brittle transition temperature of tungsten is as high as 200-400 ℃, the plasticity at room temperature is extremely low, and the tungsten is difficult to machine and form. In addition, the high melting point of tungsten places higher demands on the high temperature properties of the forming dies, especially in the manufacture of complex structures. Tungsten materials are typically manufactured by conventional manufacturing methods, such as Powder Metallurgy (PM), Hot Isostatic Pressing (HIP), and plasma sintering (SPS), which have a common challenge of difficult formation of complex structures, and thus new manufacturing methods are required to exploit the potential of tungsten materials.
In recent years, additive manufacturing technology based on layer-by-layer accumulation, also called 3D printing technology, opens up a new manufacturing approach for the processing and forming of materials. As one of the most promising methods in metal additive manufacturing technology, Selective Laser Melting (SLM) technology has a unique advantage in manufacturing complex structural parts. The SLM utilizes a high-energy laser beam to melt powder layer by layer point by point, line by line according to the slicing path planning of three-dimensional model software, and finally the part is manufactured. The SLM has the advantages of high degree of freedom, capability of processing parts with any complex shapes, high manufacturing precision and the like. The technology provides a new method for manufacturing the traditional metal material and also provides a new technical support for the development of a new material. Based on the technology, the application verification of common structural metal materials such as high-performance aluminum alloy, titanium alloy, nickel-based superalloy and the like is realized at present. The SLM technology utilizes controllable high-energy laser to melt refractory metals W, Mo, Ta, etc. to achieve near-net-shape of the refractory metals. However, the inherent properties of tungsten, such as high melting point, high ductile-to-brittle transition temperature, present even greater challenges for SLM. Because the melting point of tungsten is high, the melt viscosity is high at high temperature, the high-temperature melt is not easy to wet and spread during SLM forming, and a formed part is easy to have a hole defect. In addition, the ductile-brittle transition temperature of tungsten is high, and the interval cannot be avoided during SLM forming, so that cracks of formed parts are difficult to eliminate. These defects affect the overall performance of the component and cannot be fundamentally solved by the adjustment of process parameters, and therefore, new tungsten materials need to be developed to meet the SLM forming requirements.
Disclosure of Invention
The purpose of the invention is as follows: the first purpose of the invention is to provide a tungsten alloy special for selective laser melting, which has low porosity, less cracks and high performance; the second purpose of the invention is to provide a preparation method of the tungsten alloy.
The technical scheme is as follows: according to the special nano modified tungsten alloy for selective laser melting, the alloy powder comprises, by weight, 0.5% -2.5% of nickel, 0.5% -2.5% of iron and the balance of tungsten; wherein the mass ratio of nickel to iron is 1: 1, the nickel and the iron are nano-scale particles, and the average particle size of the particles is 50-100 nm.
Further, the particle size distribution of the tungsten is 5-25 μm.
According to the scheme, the tungsten adopts micron-sized particles, the nickel and the iron adopt nanoscale particles, the nanoscale nickel-iron powder is modified on the surface of the pure tungsten, and the nanoscale nickel and iron particles have high reaction activity and can be moved to a grain boundary under the action of high-energy laser in the forming process, so that the grain boundary defects are eliminated, the grain boundary strength is improved, cracks are inhibited from being generated, the ferronickel with larger size, such as micron-sized, can only be used as bonding to connect the tungsten particles in the forming process, so that the forming defects, such as cracks, holes, thick tissues and poor performance of a formed member are caused; in addition, the nanometer ferronickel is attached to the surface of tungsten, the melting point of the nanometer ferronickel is low, the temperature of a tungsten melt is reduced, and the fluidity of the melt is increased, so that the viscosity of tungsten is reduced, and the generation of holes is reduced.
The invention also provides a preparation method of the special nano modified tungsten alloy for selective laser melting, which comprises the following steps:
(1) weighing nickel powder and iron powder according to a proportion, adding absolute ethyl alcohol, performing ultrasonic oscillation, and then placing the mixed solution after ultrasonic oscillation in a vacuum drying oven for drying to obtain uniformly dispersed nickel-iron mixed powder;
(2) putting the dispersed nickel-iron mixed powder and the weighed tungsten powder into a ball milling tank after pretreatment, introducing argon for protection, and carrying out ball milling treatment;
(3) putting the mixed powder subjected to ball milling treatment into a forming cavity of selective laser melting equipment, and introducing argon gas into the forming cavity as protective gas;
(4) establishing a printing model, introducing the model into slice software for digital-analog processing, and introducing the processed digital-analog into selective laser melting equipment;
(5) setting technological parameters in the processing process, determining a scanning strategy, starting a laser, selecting a set powder area according to a slicing path to perform laser melting, and finishing the printing of the part;
(6) and carrying out surface decontamination on the printed part to obtain the nano modified tungsten alloy.
Further, in the step (5), the process parameters include laser power, scanning speed, scanning interval and thickness of the powder layer; wherein the diameter of the laser spot is 60-90 μm; the laser power is 350-450W; the laser scanning speed is 350 mm/s-550 mm/s; the laser scanning interval is 50-70 μm; the thickness of the powder layer is 30-50 μm.
Furthermore, the scanning strategy is a subarea island strategy, the laser scanning path is a subarea island scanning mode, and the size of the island is 5mm by 5 mm.
Further, in the step (1), the power of ultrasonic oscillation is 400-800W, the ultrasonic time is 6-10 h, the drying temperature is 70-90 ℃, and the drying time is 10-12 h.
Further, in the step (1), the ultrasonic vibration treatment of the nickel powder and the iron powder is performed in an atmosphere protected by argon gas.
Further, in the step (2), the rotation speed of ball milling treatment is 200-250 rpm, the ball milling time is 6-8 h, and the ball-to-material ratio is 1: and 2, stopping the ball milling for 5 minutes every 15 minutes.
Further, in the step (2), the pretreatment of the ball mill pot specifically includes: adding tungsten powder and grinding balls into a ball milling tank, introducing argon for protection, performing ball milling at the rotating speed of 250-300 rpm for 4-6 hours, stopping the ball milling for 5 minutes every 15 minutes, screening out the tungsten powder after the ball milling is finished, and leaving the grinding balls
Further, in the step (3), the oxygen content in the forming cavity is controlled to be lower than 100 ppm.
The preparation principle of the invention is as follows: the invention prepares tungsten alloy by selective laser melting technology, wherein, the nanometer ferronickel is uniformly dispersed on the surface of tungsten particles by high-energy ball milling nanometer modification technology, meanwhile, the high-energy ball milling can promote the micro-alloying between the nanometer ferronickel and the tungsten particles, the powder preparation technology solves the problem of easy agglomeration of nanometer phase, and simultaneously, the tungsten matrix particles keep good sphericity. After the selective laser melting molding, the nano ferronickel is rapidly diffused in the molten pool under the action of laser and migrates to a crystal boundary, so that the crystal boundary strength is improved, and meanwhile, the huge specific surface area of the nano ferronickel provides an effective nucleation position, so that the effect of refining crystal grains is achieved, and the material strength is improved.
Has the advantages that: compared with the prior art, the invention has the following remarkable advantages: (1) according to the invention, a certain amount of nano nickel and nano iron powder is added into pure tungsten powder, nano particles are uniformly dispersed in pure tungsten through a high-energy ball milling method, the powder is formed under the condition of proper parameters based on a selective laser melting technology, a tungsten alloy product which is free of cracks, high in density and provided with an isometric crystal structure is obtained, the melt viscosity is improved and the crystal boundary strength is improved by utilizing a nano modification technology, the problems of holes and cracks in selective laser melting forming of tungsten materials are solved, and the comprehensive mechanical property of the tungsten materials is improved. (2) The performance of the tungsten alloy obtained by the invention is far higher than that of a pure tungsten product obtained by additive manufacturing, the obtained printed part has no cracks, the density is 98-99.6%, the metallographic structure is isometric crystal, the compressive strength is 2260-2680 MPa, the method process is reasonable and simple, and a new method is provided for preparing the high-performance tungsten alloy.
Drawings
FIG. 1 is a polished tungsten alloy structure obtained in example 1 of the present invention;
FIG. 2 is a structure of a tungsten alloy obtained in example 1 of the present invention after polishing and etching;
FIG. 3 is a compressive stress-strain curve of a tungsten alloy obtained in example 1 of the present invention;
FIG. 4 shows a polished tungsten alloy structure obtained in example 2 of the present invention;
FIG. 5 shows the structure of the tungsten alloy obtained in example 2 of the present invention after polishing and etching;
FIG. 6 is a compressive stress-strain curve of a tungsten alloy obtained in example 2 of the present invention;
FIG. 7 shows a polished tungsten alloy structure obtained in example 3 of the present invention;
FIG. 8 shows the structure of the tungsten alloy obtained in example 3 of the present invention after polishing and etching;
FIG. 9 is a compressive stress-strain curve of a tungsten alloy obtained in example 3 of the present invention;
FIG. 10 shows a polished tungsten alloy structure obtained in example 4 of the present invention;
FIG. 11 shows the structure of the tungsten alloy obtained in example 4 of the present invention after polishing and etching;
FIG. 12 is a graph of the compressive stress strain of the tungsten alloy obtained in example 4 of the present invention;
FIG. 13 shows a polished structure of pure tungsten obtained in example 5 of the present invention;
FIG. 14 shows the structure of pure tungsten obtained in example 5 of the present invention after polishing and etching;
fig. 15 is a compressive stress strain curve of pure tungsten obtained in example 5 of the present invention.
Detailed Description
The technical solution of the present invention will be described in further detail with reference to examples.
Example 1
A special nano-modified high-performance tungsten alloy powder for selective laser melting and a preparation method thereof comprise the following steps:
(1) preparing raw materials: in a vacuum glove box filled with argon protective atmosphere, weighing 4.9kg of pure tungsten powder, 0.05kg of nano nickel powder and 0.05kg of nano iron powder as raw materials according to the content of nickel and iron of 1 percent respectively, wherein the weight ratio of Ni: fe is 1: 1, wherein the average particle size of tungsten powder is 16 mu m, the average particle size of nickel powder is 80nm, and the average particle size of iron powder is 80 nm; adding the nano nickel iron into a beaker filled with absolute ethyl alcohol, putting the beaker into an ultrasonic oscillator, and carrying out ultrasonic oscillation for 6 hours at the ultrasonic power of 400W to uniformly disperse the nano nickel and the nano iron in the absolute ethyl alcohol medium. Placing the mixed solution after ultrasonic dispersion into a vacuum drying oven, setting the drying temperature at 80 ℃, and drying for 10 hours to obtain uniformly dispersed mixed powder of nano nickel and nano iron;
(2) pretreating the grinding balls and the interior of a ball milling tank, adding a proper amount of pure tungsten powder, adding the grinding balls, introducing argon protective atmosphere, carrying out ball milling for 6 hours in a ball mill at the rotating speed of 300rpm, stopping for 5 minutes every 15 minutes during ball milling, screening out powder after the ball milling is finished, and leaving the grinding balls; then, the dispersed nano nickel-iron powder and tungsten powder are weighed and put into a ball milling tank with a ball-material ratio of 1: 2, introducing argon protective atmosphere, carrying out ball milling for 6h in a ball mill at the rotating speed of 250rpm, stopping for 5 minutes every 15 minutes during ball milling, screening out powder after ball milling is finished, and then putting the powder into a vacuum drying box;
(3) introducing argon gas into a forming cavity of the printing equipment as protective gas, filling the prepared powder into a powder cavity of the printing equipment after the cavity is filled with the protective gas, and controlling the oxygen content in the cavity to be lower than 100 ppm;
(4) establishing a printed model by using three-dimensional modeling software Solidworks, wherein the model is a block of 10mm by 8mm, introducing the model into Magics slicing software for digital-analog processing, and introducing the processed digital-analog into selective laser melting equipment;
(5) setting technological parameters in the processing process, wherein a laser spot is 60 micrometers, the laser power is 350W, the scanning speed is 550mm/s, the scanning interval is 50 micrometers, the thickness of a powder layer is 30 micrometers, and the scanning strategy is a partitioned island strategy, and the size of an island is 5mm x 5 mm;
(6) starting a laser, and selecting a set powder area according to a slicing path to perform laser melting to complete the printing of the part;
(7) cutting the printed part from the substrate, putting the part into acetone, and ultrasonically cleaning to remove surface stains to obtain a nano modified tungsten alloy;
(8) and (3) preparing and observing a metallographic phase of the obtained tungsten alloy part according to a metallographic phase standard preparation method, and simultaneously testing the compression performance.
Referring to a metallographic microscopic picture in figure 1, the tungsten alloy prepared by the method has compact structure and no crack, and the compactness is 99.2%; as shown in FIG. 2, the metallographic structure after the etching was uniform, and it was found that the tungsten alloy prepared by this method had a uniform equiaxed structure. Referring to the stress-strain curve of FIG. 3, it can be seen that the compressive strength of the alloy reaches 2680MPa and the elongation reaches 47%.
Example 2
A special nano-modified high-performance tungsten alloy powder for selective laser melting and a preparation method thereof comprise the following steps:
(1) preparing raw materials: in a vacuum glove box filled with argon protective atmosphere, weighing 4.8kg of pure tungsten powder, 0.1kg of nano nickel powder and 0.1kg of nano iron powder as raw materials according to the content of nickel and iron of 2 percent respectively, wherein the weight ratio of Ni: fe is 1: 1, wherein the average particle size of tungsten powder is 18 mu m, the average particle size of nickel powder is 90nm, and the average particle size of iron powder is 90 nm; adding the nano nickel iron into a beaker filled with absolute ethyl alcohol, putting the beaker into an ultrasonic oscillator, and carrying out ultrasonic oscillation for 10 hours at the ultrasonic power of 800W to uniformly disperse the nano nickel and the nano iron in the absolute ethyl alcohol medium. Placing the mixed solution after ultrasonic dispersion into a vacuum drying oven, setting the drying temperature at 90 ℃, and drying for 12 hours to obtain uniformly dispersed mixed powder of nano nickel and nano iron;
(2) pretreating the grinding balls and the interior of a ball milling tank, adding a proper amount of pure tungsten powder, adding the grinding balls, introducing argon protective atmosphere, carrying out ball milling for 6 hours in a ball mill at the rotating speed of 300rpm, stopping for 5 minutes every 15 minutes during ball milling, screening out powder after the ball milling is finished, and leaving the grinding balls; weighing the dispersed nano nickel-iron powder and tungsten powder, and putting the nano nickel-iron powder and tungsten powder into a ball milling tank with a ball-material ratio of 1: 2, introducing argon protective atmosphere, performing ball milling for 8 hours in a ball mill at the rotating speed of 250rpm, stopping the ball milling for 5 minutes every 15 minutes, screening out powder after the ball milling is finished, and then putting the powder into a vacuum drying box;
(3) introducing argon gas into a molding cavity of the printing equipment as protective gas, filling the prepared powder into a powder cavity of the printing equipment after the cavity is filled with the protective gas, and controlling the oxygen content in the cavity to be lower than 100 ppm;
(4) establishing a printed model by using three-dimensional modeling software Solidworks, wherein the model is a block of 10mm by 8mm, introducing the model into Magics slicing software for digital-analog processing, and introducing the processed digital-analog into selective laser melting equipment;
(5) setting technological parameters in the processing process, namely a laser spot of 90 micrometers, a laser power of 450W, a scanning speed of 350mm/s, a scanning interval of 70 micrometers, a powder layer thickness of 50 micrometers, a scanning strategy and partition island strategy, wherein the size of an island is 5mm x 5 mm;
(6) starting a laser, and selecting a set powder area according to a slicing path to perform laser melting to complete the printing of the part;
(7) cutting the printed part from the substrate, putting the part into acetone, and ultrasonically cleaning to remove surface stains to obtain a nano modified tungsten alloy;
(8) and (3) preparing and observing a metallographic phase of the obtained tungsten alloy part according to a metallographic phase standard preparation method, and simultaneously testing the compression performance.
Referring to fig. 4, the metallographic microscopic picture shows that the tungsten alloy prepared by the method has compact structure and no cracks, and the compactness is 98.4%; as shown in FIG. 5, the metallographic structure after etching was uniform and equiaxed, as can be seen from the figure. Referring to the stress-strain curve of FIG. 6, it can be seen that the compressive strength of the alloy reaches 2260MPa and the elongation reaches 43%.
Example 3
A special nano-modified high-performance tungsten alloy powder for selective laser melting and a preparation method thereof comprise the following steps:
(1) preparing raw materials: in a vacuum glove box filled with argon protective atmosphere, according to the nickel content and the iron content of 0.5 percent respectively, weighing 4.95kg of pure tungsten powder, 0.025kg of nano nickel powder and 0.025kg of nano iron powder as raw materials, wherein the weight ratio of Ni: fe is 1: 1, wherein the average particle size of tungsten powder is 20 mu m, the average particle size of nickel powder is 60nm, and the average particle size of iron powder is 60 nm; adding the nano nickel iron into a beaker filled with absolute ethyl alcohol, putting the beaker into an ultrasonic oscillator, and carrying out ultrasonic oscillation for 8 hours at the ultrasonic power of 600W to uniformly disperse the nano nickel and the nano iron in the absolute ethyl alcohol medium. Placing the mixed solution after ultrasonic dispersion into a vacuum drying oven, setting the drying temperature at 80 ℃, and drying for 11 hours to obtain uniformly dispersed mixed powder of nano nickel and nano iron;
(2) pretreating the grinding balls and the interior of a ball milling tank, adding a proper amount of pure tungsten powder, adding the grinding balls, introducing argon protective atmosphere, carrying out ball milling for 5 hours in a ball mill at the rotating speed of 280rpm, stopping for 5 minutes every 15 minutes during ball milling, screening out powder after the ball milling is finished, and leaving the grinding balls; weighing the dispersed nano nickel-iron powder and tungsten powder, and putting the nano nickel-iron powder and tungsten powder into a ball milling tank with a ball-material ratio of 1: 2, introducing argon protective atmosphere, performing ball milling for 7 hours in a ball mill at the rotating speed of 240rpm, stopping for 5 minutes every 15 minutes during ball milling, screening out powder after the ball milling is finished, and then putting the powder into a vacuum drying box;
(3) introducing argon gas into a molding cavity of the printing equipment as protective gas, filling the prepared powder into a powder cavity of the printing equipment after the cavity is filled with the protective gas, and controlling the oxygen content in the cavity to be lower than 100 ppm;
(4) establishing a printed model by using three-dimensional modeling software Solidworks, wherein the model is a block of 10mm by 8mm, introducing the model into Magics slicing software for digital-analog processing, and introducing the processed digital-analog into selective laser melting equipment;
(5) setting technological parameters in the processing process, wherein a laser spot is 80 microns, the laser power is 400W, the scanning speed is 500mm/s, the scanning interval is 60 microns, the thickness of a powder layer is 40 microns, and the scanning strategy is a partitioned island strategy, and the size of an island is 5mm x 5 mm;
(6) starting a laser, and selecting a set powder area according to a slicing path to perform laser melting to complete the printing of the part;
(7) and cutting the printed part from the substrate, putting the part into acetone, and ultrasonically cleaning to remove surface stains to obtain the nano modified tungsten alloy.
Referring to fig. 7, the metallographic microscopic picture shows that the tungsten alloy prepared by the method has compact structure and no cracks, and the compactness is 98.6%; as shown in FIG. 8, the metallographic structure after etching was uniform and equiaxed, as can be seen from the figure. Referring to the stress-strain curve of FIG. 9, it can be seen that the compressive strength of the alloy reaches 2360MPa and the elongation reaches 42%.
Example 4
The preparation process is the same as that in example 1, except that the nickel powder and the iron powder are micron-sized, wherein the average particle size of the nickel powder is 10 μm, and the average particle size of the iron powder is 10 μm.
And (3) preparing and observing a metallographic phase of the prepared alloy according to a metallographic phase standard preparation method, and simultaneously testing the compression performance.
Referring to fig. 10, the metallographic micrograph shows that the tungsten alloy structure prepared by the method has holes, and the density is 97.5%; the metallographic structure after etching is shown in fig. 11, and it is understood from the figure that the tungsten alloy structure prepared by this method is composed of unmelted tungsten particles and a nickel-iron solid solution, and the structure is coarse. Referring to the stress-strain curve of fig. 12, it can be seen that the compressive strength of the alloy reaches 1810MPa, and the elongation reaches 17%.
From the data of examples 1 and 4, it can be seen that the sizes of nickel powder and iron powder directly affect the structure and compression properties of the alloy, mainly because micron ferronickel melts to form binder phase under the action of laser, tungsten is not completely melted, and the obtained structure is coarse, and the properties of tungsten cannot be fully explored.
Example 5
The preparation process is the same as example 1, except that pure tungsten powder is selected for preparation.
The metallographic microscopic picture of the pure tungsten obtained by the preparation method is shown in figure 13, the directly printed pure tungsten member has more cracks and holes, the density is only 96%, the metallographic structure after corrosion is shown in figure 14, and the metallographic structure of the directly prepared pure tungsten is a thick columnar crystal structure.
Referring to the stress-strain curve of fig. 15, it can be seen that the compressive strength of the directly prepared pure tungsten is only 900MPa, and the elongation is only 8%.
As can be seen from the data of examples 1 and 5, the directly prepared pure tungsten has many defects, particularly, cracks are obvious, mainly because the pure tungsten has a columnar crystal structure, the grain boundary strength is low, cracks are easy to generate, and the obtained compressive strength is low.
Example 6
Two groups of parallel tests are designed, and the preparation process is the same as that in example 1, except that only nano nickel powder is added into one group of the system, and nano iron powder is not added, namely 4.9kg of pure tungsten powder and 0.1kg of nano nickel powder are weighed according to the nickel content of 1 percent respectively; the other group of systems only adds nano iron powder and does not add nano nickel powder, namely 4.9kg of pure tungsten powder and 0.1kg of nano iron powder are weighed according to the iron content of 1 percent respectively.
And respectively preparing and observing metallography for the prepared alloy according to a metallography standard preparation method, and simultaneously testing the compression performance.
When only the nano iron powder is added, the density of the alloy reaches 98.4%, the obtained metallographic structure is an isometric crystal structure, the compressive strength of the alloy is 1920MPa, and the elongation is 32%.
When only the nano nickel powder is added, the density of the alloy reaches 98.6 percent, the obtained metallographic structure is an isometric crystal structure, the compressive strength of the alloy is 1930MPa, and the elongation is 30 percent.
From the data of the embodiment 1 and the embodiment 6, the density of the alloy can be improved and the isometric crystal structure can be obtained by adding the nickel or iron system alone, but the compressive strength of the alloy is not good, which shows that the compressive strength and the elongation of the alloy can be comprehensively improved only by adding the nano-nickel iron composite.
Example 7
5 groups of parallel tests are designed, and the specific preparation process is the same as that in the example 1, except that in the printing parameters in the step (5), the laser spots are set differently and are respectively 50 micrometers, 70 micrometers, 80 micrometers, 90 micrometers and 100 micrometers.
The prepared alloys were tested for compression properties and the results are shown in table 1 below.
TABLE 1
| Laser spot mum | Compressive | Elongation percentage | |
| 50 | 2140MPa | 38％ | |
| 70 | 2342MPa | 42％ | |
| 80 | 2416MPa | 45％ | |
| 90 | 2368MPa | 44％ | |
| 100 | 2075MPa | 37％ |
As can be seen from Table 1, when the laser spot is too small or too large, the compressive strength and elongation of the prepared alloy are affected, because when the laser spot is too small, the energy input per unit area is large, ferronickel in the alloy is easy to burn, and meanwhile, the alloy structure is coarse, so that the performance is poor; when the laser spot is too large, the energy input per unit area is small, the ferronickel is not easy to diffuse, the grain boundary strength is low, and the alloy performance is poor.
Example 8
4 sets of parallel tests are designed, and the specific preparation process is the same as that in the embodiment 1, except that in the printing parameters in the step (5), the laser power parameters are set to be 300W, 400W, 450W and 500W respectively.
The prepared alloys were tested for compression properties and the results are shown in table 2 below.
TABLE 2
| Laser power W | Compressive strength | Elongation percentage |
| 300 | 1968MPa | 34％ |
| 400 | 2482MPa | 45％ |
| 450 | 2585MPa | 46％ |
| 500 | 2012MPa | 35％ |
As can be seen from Table 2, when the laser power is too low or too high, the compressive strength and elongation of the prepared alloy are affected, because when the laser power is too low, the energy input is insufficient, tungsten cannot be completely melted to form a compact alloy, and the alloy performance is poor; when the laser power is too large, the energy input is too large, so that the ferronickel element is burnt and the structure is coarsened, and the alloy performance is poor.
Example 9
5 groups of parallel tests are designed, and the specific preparation process is the same as that in the example 1, except that in the printing parameters in the step (5), the scanning speed parameters are set differently and are respectively 300mm/s, 400mm/s, 450mm/s, 500mm/s and 600 mm/s.
The prepared alloys were tested for compression properties and the results are shown in table 3 below.
TABLE 3
| Scanning speed mm/s | Compressive strength | Elongation percentage |
| 300 | 1926MPa | 33％ |
| 400 | 2365MPa | 44％ |
| 450 | 2512MPa | 46％ |
| 500 | 2486MPa | 45％ |
| 600 | 1986MPa | 34％ |
As can be seen from Table 3, when the scanning speed is too low or too high, the compressive strength and elongation of the prepared alloy are affected, because when the scanning speed is too low, the unit linear energy density is too high, so that the burning loss of the alloy element ferronickel in the molten pool is caused, and the performance of the prepared alloy is reduced; when the scanning speed is too high, the energy density of a unit line is too low, tungsten cannot be completely melted, the compactness of the alloy is reduced, and the performance is poor.
It can be known from the parallel test data of examples 7, 8 and 9 that the process parameters in the processing process directly affect the performance of the obtained tungsten alloy, wherein the influence of the laser spot, the laser power and the scanning speed is most obvious, the process parameter settings of the laser spot, the laser power and the scanning speed are mutually affected, and the compressive strength performance of the tungsten alloy is kept between 2260MPa and 2680MPa within the set interval range, which is far superior to the performance of the tungsten and the tungsten alloy prepared by the conventional method.
Claims (10)
1. A special nano modified tungsten alloy for selective laser melting is characterized in that: in the alloy powder, the content of nickel is 0.5-2.5 wt%, the content of iron is 0.5-2.5 wt%, and the balance is tungsten; wherein the mass ratio of nickel to iron is 1: 1, the nickel and the iron are nano-scale particles, and the average particle size of the particles is 50-100 nm.
2. The special nano modified tungsten alloy for selective laser melting according to claim 1, which is characterized in that: the particle size distribution of the tungsten is 5-25 mu m.
3. The preparation method of the special nano modified tungsten alloy for selective laser melting in claim 1 or 2, which is characterized by comprising the following steps:
(1) weighing nickel powder and iron powder according to a proportion, adding absolute ethyl alcohol, performing ultrasonic oscillation, and then placing the mixed solution after ultrasonic oscillation in a vacuum drying oven for drying to obtain uniformly dispersed nickel-iron mixed powder;
(2) putting the dispersed nickel-iron mixed powder and the weighed tungsten powder into a ball milling tank after pretreatment, introducing argon for protection, and carrying out ball milling treatment;
(3) putting the mixed powder subjected to ball milling treatment into a forming cavity of selective laser melting equipment, and introducing argon gas into the forming cavity as protective gas;
(4) establishing a printing model, introducing the model into slice software for digital-analog processing, and introducing the processed digital-analog into selective laser melting equipment;
(5) setting technological parameters in the processing process, determining a scanning strategy, starting a laser, selecting a set powder area according to a slicing path to perform laser melting, and finishing the printing of the part;
(6) and carrying out surface decontamination on the printed part to obtain the nano modified tungsten alloy.
4. The preparation method of the special nano modified tungsten alloy for selective laser melting according to claim 3, characterized by comprising the following steps: in the step (5), the process parameters include laser power, scanning speed, scanning interval and powder layer thickness; wherein the diameter of the laser spot is 60-90 μm; the laser power is 350-450W; the laser scanning speed is 350 mm/s-550 mm/s; the laser scanning interval is 50-70 mu m; the thickness of the powder layer is 30 μm to 50 μm.
5. The preparation method of the special nano modified tungsten alloy for selective laser melting according to claim 3, characterized by comprising the following steps: the scanning strategy is a subarea island strategy, the laser scanning path is a subarea island scanning mode, and the size of the island is 5mm by 5 mm.
6. The preparation method of the special nano modified tungsten alloy for selective laser melting according to claim 3, characterized by comprising the following steps: in the step (1), the power of ultrasonic oscillation is 400-800W, the ultrasonic time is 6-10 h, the drying temperature is 70-90 ℃, and the drying time is 10-12 h.
7. The preparation method of the special nano modified tungsten alloy for selective laser melting according to claim 3, characterized by comprising the following steps: in the step (1), the ultrasonic vibration treatment of the nickel powder and the iron powder is carried out in the atmosphere of argon protection.
8. The preparation method of the special nano modified tungsten alloy for selective laser melting according to claim 3, characterized by comprising the following steps: in the step (2), the rotation speed of ball milling treatment is 200-250 rpm, the ball milling time is 6-8 h, and the ball-to-material ratio is 1: and 2, stopping the ball milling for 5 minutes every 15 minutes.
9. The preparation method of the special nano modified tungsten alloy for selective laser melting according to claim 3, characterized by comprising the following steps: in the step (2), the pretreatment of the ball milling tank specifically comprises the following steps: adding tungsten powder and grinding balls into a ball milling tank, introducing argon for protection, carrying out ball milling for 4-6 h at the rotating speed of 250-300 rpm, stopping for 5 min every 15 min during ball milling, and screening out the tungsten powder after ball milling is finished, and leaving the grinding balls.
10. The preparation method of the special nano modified tungsten alloy for selective laser melting according to claim 3, characterized by comprising the following steps: in the step (3), the oxygen content in the forming cavity is controlled to be lower than 100 ppm.
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