Substrate-free instantaneous liquid phase sintering method for fine-grain high-specific-gravity alloy bar billet

Abstract

The invention relates to a substrate-free instantaneous liquid phase sintering method for a fine-grain high-specific-gravity alloy bar blank, and belongs to the technical field of high-specific-gravity alloy, particle reinforced metal matrix composite materials, powder metallurgy and additive manufacturing. The substrate-free instantaneous liquid phase sintering method for the high-density fine-grain high-specific-gravity alloy bar billet is provided for solving the problems existing in preparation of high-specific-gravity alloy through an existing process, the high-density fine-grain high-specific-gravity alloy bar billet can be prepared on the basis of a coaxial powder feeding additive manufacturing platform, a substrate is not needed, the forming quality is high, raw material loss is low, and production cost is low. The method is suitable for preparing materials with the large length-diameter ratio, subsequent thermal deformation machining is not needed, and the method has the advantages of being short in preparation period, simple in process, low in cost and the like.

Description

Technical Field

[0001] The invention relates to a method for instantaneous liquid phase sintering of fine-grained high-density alloy rods without a substrate, and belongs to the technical fields of high-density alloys, particle-reinforced metal-based composite materials, powder metallurgy and additive manufacturing. Background Art

[0002] Heavy alloy is a kind of dual-phase composite material mainly composed of tungsten (the mass percentage of tungsten is usually greater than 80%) and a small amount of Ni, Cu, Fe and other elements. Its density is as high as 16.5-19.0g / cm 3 , commonly known as tungsten alloy, tungsten heavy alloy or high-density tungsten alloy, has high density, high hardness, high wear resistance, and high fracture toughness. It is widely used in gyro motor rotors, kinetic energy projectile cores and shielding instruments.

[0003] The main preparation methods for high-density alloys include liquid phase sintering, solid phase sintering, microwave sintering, and spark plasma sintering. Solid phase sintering is usually used to prepare low-tungsten content, fine-grained tungsten particle-reinforced metal matrix composites, but the alloys prepared by this method have low density and poor mechanical properties. In order to improve the density, extremely complex and tedious process is often introduced into the solid phase sintering method, or unconventional sintering methods such as high pressure and discharge are introduced. Microwave sintering and spark plasma sintering are used to prepare tungsten particle-reinforced metal matrix composites. They can quickly heat up and keep warm for a short time, and avoid excessive growth of tungsten grains, but they have the disadvantages of limited sample size and cannot prepare materials with a large aspect ratio; the technology is also immature.

[0004] Liquid-phase sintering is the most common method for preparing high-density tungsten particle-reinforced metal matrix composites (MMCs). It offers advantages such as high density, uniform microstructure, simple preparation, and low subsequent processing costs. However, this method has the following disadvantages: When the tungsten content is low, the MMCs will experience severe deformation and uneven microstructure; the hydrogen atmosphere used in liquid-phase sintering can cause hydrogen embrittlement, requiring a dehydrogenation process after sintering, significantly increasing production costs; and the resulting MMCs have relatively coarse grains, requiring subsequent thermal deformation processing, which inevitably increases costs significantly.

[0005] Additive manufacturing technology is an emerging technology for preparing high-density alloys in recent years. However, the samples currently produced by this technology have low density and unstable performance. The preparation of long rod-shaped billets also has problems such as substrate waste, poor forming quality and severe deformation, low raw material utilization and production efficiency. These problems will be seriously aggravated as the aspect ratio of the billet increases. Summary of the Invention

[0006] The technical problem solved by the present invention is: to overcome the shortcomings of the existing technology, and to propose a method for instantaneous liquid phase sintering of fine-grained high-density alloy rod blanks without a substrate. In view of the problems existing in the current process for preparing high-density alloys, a method for instantaneous liquid phase sintering of high-density fine-grained high-density alloy rod blanks without a substrate is provided. The method is based on a coaxial powder feeding additive manufacturing platform, and can prepare high-density fine tungsten particle high-density alloys without the need for a substrate, with high forming quality, low raw material loss, and almost no deformation of the billet. It is suitable for preparing materials with a large aspect ratio, and does not require subsequent thermal deformation processing. It has the advantages of short preparation cycle, simple process, and low cost.

[0007] The technical solution of the present invention is:

[0008] A substrate-free instantaneous liquid phase sintering method for a high-density, fine-grained, high-density alloy billet, wherein the high-density alloy consists of a tungsten phase and a matrix phase (also called a binder phase), wherein the mass percentage of the tungsten phase is generally greater than 80%, and includes tungsten-nickel-iron alloys and other similar alloys and composite materials. The method is characterized in that: in an atmosphere-protected chamber, a laser or an electric arc is used as a heat source, the mass percentage of tungsten in a mixed powder flow of tungsten and matrix alloy is greater than 85%, a thin rod of tungsten, tungsten alloy, or high-density alloy having a tungsten mass percentage not less than that of the mixed powder is selected as a billet core, the billet core is rotated continuously or intermittently during the forming process, and the mixed powder flow is continuously deposited on the billet core in a spiral manner, and liquid phase sintering conditions are maintained in the molten pool, that is, the matrix alloy powder in the molten pool is melted while the tungsten particles are kept unmelted or only slightly melted, and are deposited layer by layer to a target size, thereby obtaining a high-density, fine-grained, high-density alloy billet with a tungsten particle size that retains the original powder particle size;

[0009] The steps of substrate-free instantaneous liquid phase sintering of the high-density, fine-grained, high-density alloy billet are as follows:

[0010] Step 1: Place the matrix alloy powder and tungsten powder into two powder tanks of the powder feeder respectively, or mix them evenly and place them into the same powder tank. The mass percentage of tungsten in the mixed powder output by the powder feeder is higher than 85%.

[0011] Step 2: Place the high-density alloy core into the atmosphere protection chamber, clamp it into the chuck, calibrate the coaxiality and tighten it;

[0012] Step 3: Fill the atmosphere protection chamber with protective gas such as nitrogen, argon or helium to make the oxygen content in the atmosphere protection chamber lower than 50ppm;

[0013] Step 4: Introduce the laser beam or electric arc, and synchronously start the powder feeder to deliver the mixed powder flow of tungsten and matrix alloy. The forming process is completed by the continuous lifting of the high-energy beam heat source processing head and the rotation of the chuck. The laser beam or electric arc melts and deposits the synchronously delivered mixed powder flow in a spiral manner on the core, forming instantaneous liquid phase sintering conditions in the process molten pool.

[0014] Step 5: After the prepared fine-grained high-density alloy billet is cooled to below 100°C, the atmosphere protection chamber is opened and it is taken out;

[0015] Step 6: Heat treat the prepared billet with the following process parameters: temperature 700°C to 1200°C, treatment time 2 hours to 8 hours, and cooling method of water cooling or air cooling.

[0016] The equipment used in this method includes:

[0017] a laser or arc heat source;

[0018] a powder delivery system for delivering tungsten and matrix alloy powders;

[0019] A dynamically sealed atmosphere controlled processing protection chamber or a closed atmosphere controlled processing chamber;

[0020] a rotary shaft machining table with a chuck;

[0021] The average particle size of raw tungsten powder is 1 to 25 microns, and is usually produced by processes such as granulation and plasma spheroidization. The average particle size of matrix alloy or pure metal spherical powder is -60 to +300 mesh, and is usually produced by processes such as gas atomization or rotating electrode.

[0022] High-density alloys are composed of a tungsten phase and a matrix phase (also called a bonding phase). They can be tungsten-nickel-iron alloys with different tungsten contents, or other similar alloys and composite materials with different tungsten contents, such as tungsten-high entropy alloy composites, tungsten-amorphous alloy composites, etc. That is, the matrix phase can be the bonding phase of the existing tungsten alloy system, or it can be other high-entropy alloys, high-temperature alloys and other alloys or pure metals.

[0023] The forming process is coordinated by the continuous lifting of the heat source (i.e., laser or arc) and the rotation of the chuck, so that the synchronously conveyed mixed powder flow is melted and deposited on the blank core in a spiral manner. The pitch of the spiral line should be determined according to the size of the molten pool / melt channel generated by the heat source and the sample size, that is, the molten pool width / 4 ≤ pitch ≤ sample length;

[0024] A high-density alloy thin rod with a tungsten mass percentage not less than that of the mixed powder is selected as the billet core. The billet core rotates continuously or intermittently during the forming process. The billet core can be pure tungsten, tungsten-nickel-iron alloy with different tungsten contents, or a thin rod with the same composition as the mixed powder. The length and diameter are determined according to the billet size. The length should be greater than the billet length and can be: diameter 3 to 25 mm, length 50 to 2000 mm.

[0025] During the preparation process, the oxygen content in the atmosphere protection chamber was lower than 50 ppm.

[0026] According to the shape and size of the prepared rod blank, it is necessary to reasonably match the power of the laser or arc heat source with the beam spot size, powder delivery rate, scanning speed, single-layer deposition height and other process parameters to ensure that only the matrix powder is melted during the forming preparation process, while the tungsten powder does not melt or only melts slightly. At the same time, the matrix molten pool quickly solidifies and remains dense after the heat source is removed, and liquid phase sintering is completed in a very short time, and finally a high-density fine tungsten particle high-density alloy rod blank is prepared; the power of the laser or arc heat source is 0.1~20kW, the beam spot size of the laser or arc heat source is 1~30mm, the beam spot moving rate is 1~30mm / min, and the powder feeding rate of the powder feeder can be 1~200g / min.

[0027] Beneficial effects

[0028] 1. High-density alloys are composed of a tungsten phase and a matrix phase (also called a bonding phase). They can be tungsten-nickel-iron alloys with different tungsten contents, or other similar alloys and composite materials with different tungsten contents, such as tungsten-high entropy alloy composites, tungsten-amorphous alloy composites, etc. That is, the matrix phase can be the bonding phase of the existing tungsten alloy system, or other high-entropy alloys, high-temperature alloys, or pure metals.

[0029] 2. The forming process is coordinated by the continuous lifting of the heat source (i.e., laser or arc) and the rotation of the chuck, so that the synchronously conveyed mixed powder flow is melted and deposited on the blank core in a spiral manner. The pitch of the spiral line should be determined according to the size of the molten pool / melt channel generated by the heat source and the sample size, that is, the molten pool width / 4 ≤ pitch ≤ sample length;

[0030] 3. Select a high-density alloy thin rod with a tungsten mass percentage not less than that of the mixed powder as the billet core. The billet core rotates continuously or intermittently during the forming process. The billet core can be pure tungsten, tungsten-nickel-iron alloy with different tungsten contents, or a thin rod with the same composition as the mixed powder. The length and diameter are determined according to the billet size. The length should be greater than the billet length, which can be: diameter 3 to 25 mm, length 50 to 2000 mm.

[0031] 4. According to the shape and size of the prepared rod blank, it is necessary to reasonably match the process parameters such as the power and beam spot size of the laser or arc heat source, the powder delivery rate, the scanning speed, and the single-layer deposition height, so as to ensure that only the matrix powder is melted during the forming preparation process, while the tungsten powder does not melt or only melts slightly. At the same time, the matrix molten pool quickly solidifies and remains dense after the heat source is removed, and liquid phase sintering is completed in a very short time, and finally a high-density fine tungsten particle high-density alloy rod blank is prepared; the power of the laser or arc heat source is 0.1~20kW, the beam spot size of the laser or arc heat source is 1~30mm, the beam spot moving rate is 1~30mm / min, and the powder feeding rate of the powder feeder can be 1~200g / min.

[0032] 5. The present invention provides a substrate-free instantaneous liquid-phase sintering method for high-density, high-density alloy billets. This method can rapidly produce high-density, high-density alloy billets. After forming, the billet core directly serves as part of the billet, eliminating the need for removal (as with traditional additive methods, where the base material must be removed). This method offers high forming quality, low raw material loss, and no billet deformation. This method is suitable for producing materials with large aspect ratios (which are subject to severe warping and cracking with traditional additive methods). Subsequent thermal deformation processing is unnecessary, resulting in a short production cycle, a simple process, and low cost. High-density alloy billets produced using the substrate-free instantaneous liquid-phase sintering method described herein exhibit advantages such as fine, uniformly distributed tungsten grains, dense samples, a wide range of applicable material systems, and excellent billet mechanical properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 Schematic diagram of the substrate-free instantaneous liquid phase sintering method for high-density, fine-grained, and high-density alloy billets;

[0034] Figure 2 This is a photo of the high-density alloy rod prepared in Example 1;

[0035] Figure 3 This is a scanning electron microscope (SEM) image of the high-density alloy rod prepared in Example 1. DETAILED DESCRIPTION

[0036] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0037] A method for instantaneous liquid phase sintering of fine-grained high-density alloy billets without a substrate, such as Figure 1 As shown, the equipment used in this method includes an atmosphere protection chamber, a chuck 1, a blank core 6, a powder nozzle 3, and a high-energy beam heat source 4;

[0038] The chuck 1, the blank core 6, the powder nozzle 3, and the high-energy beam heat source 4 are all located in the atmosphere protection chamber;

[0039] The chuck 1 is used to fix the core 6 and can drive the core 6 to rotate;

[0040] The outer surface of the core 6 is consistent with the inner surface of the high-density alloy rod to be processed;

[0041] The powder nozzle 3 is located above the blank core 6 and is used to deliver the mixed powder onto the blank core 6.

[0042] The high energy beam heat source 4 is a laser or an electric arc, which is used to melt the mixed powder delivered by the powder nozzle 3;

[0043] A method for instantaneous liquid phase sintering of fine-grained high-density alloy billets without a substrate, comprising the following steps:

[0044] The first step is to install the core 6 on the chuck 1;

[0045] The second step is to fill the atmosphere protection chamber with protective gas such as nitrogen, argon or helium to make the oxygen content in the atmosphere protection chamber lower than 50ppm;

[0046] In the third step, the high-energy beam heat source 4 is turned on and the chuck 1 is simultaneously started, so that the chuck 1 drives the core 6 to rotate, and the mixed powder is output to the top of the core 6 through the powder nozzle 3. The mixed powder output by the powder nozzle 3 is melted and deposited layer by layer on the core 6 in a track-by-track or spiral manner;

[0047] In the fourth step, after the deposition is completed, a rod blank 2 with a blank core is obtained. After cooling to below 100°C, it is removed from the chuck for heat treatment. The process parameters are: temperature 700°C ~ 1200°C, treatment time 2 to 8 hours, and the cooling medium can be water, brine, oil or air.

[0048] Example

[0049] The specific steps for preparing a fine-grained tungsten-AlCrFeNiV high-entropy alloy composite (a high-density alloy) billet with a size of φ15mm×260mm based on the substrate-free transient liquid phase sintering method are as follows:

[0050] (1) Tungsten powder with an average particle size of about 7 μm and high entropy alloy matrix powder with a particle size of 75 to 150 μm were mixed in a mass ratio of 93:7. After mixing the powders in a mixer for 120 min, the mixed powders were placed in a single powder feeding tank of a powder feeder.

[0051] (2) A core made of tungsten-nickel-iron (tungsten accounts for 93 wt%) and having a size of φ8 mm × 300 mm was placed in an atmosphere protection chamber and fastened in a chuck. High-purity argon gas was filled into the atmosphere protection chamber to reduce the oxygen content to less than 50 ppm.

[0052] (3) Turn on the laser heat source and use the coaxial powder feeding method to deliver the mixed powder to the surface of the tungsten-nickel-iron core. The laser will melt and deposit the synchronously delivered mixed powder flow on the core in a spiral manner layer by layer ( Figure 1 ), and obtain the rod blank, the actual photo of the rod blank is as follows Figure 2 As shown; the process parameters are as follows: laser spot diameter 3mm, chuck speed is set so that the laser moves at a linear speed of 10mm / s relative to the rod blank, spot path interval 1.6mm, laser power 1200W, powder feeding rate about 0.8kg / h, and single layer deposition thickness is 0.2mm.

[0053] Figure 3The light-colored particles are tungsten particles (also called tungsten grains), with an average particle size of about 7 microns. The dark matrix between the particles is AlCrFeNiV high-entropy alloy, and the tungsten particles are evenly distributed on the high-entropy alloy matrix. Measurements show that the density of the prepared composite material is greater than 17.0 g / cm 3 The quasi-static tensile test showed that the tensile strength of the prepared composite material was 1189 MPa.

[0054] In summary, the above are only preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for instantaneous liquid phase sintering of fine-grained high-density alloy billets without a substrate, characterized by: The high specific gravity alloy consists of a tungsten phase and a matrix phase, wherein the mass percentage of the tungsten phase is greater than 80%; In an atmosphere protection chamber, laser or arc is used as a heat source. The mass percentage of tungsten in the mixed powder flow of tungsten and matrix is more than 85%. A tungsten, tungsten alloy or high-density alloy thin rod with a tungsten mass percentage not less than that of the mixed powder is selected as the billet core. During the forming process, the billet core rotates continuously or intermittently, and the mixed powder flow is continuously deposited on the billet core in a spiral manner. The liquid phase sintering conditions are maintained in the molten pool, that is, the matrix alloy powder in the molten pool is melted while the tungsten particles are kept unmelted or melted in a small amount. The tungsten particles are deposited layer by layer to the target size, and a high-density, fine-grained, high-density alloy rod billet with the tungsten particle size maintaining the original powder particle size is obtained.

2. The method for instantaneous liquid phase sintering of fine-grained high-density alloy billets without a substrate according to claim 1, characterized in that The specific steps of this method are: Step 1: Place the matrix alloy powder and tungsten powder into two powder tanks of the powder feeder respectively, or mix them evenly and place them into the same powder tank. The mass percentage of tungsten in the mixed powder output by the powder feeder is higher than 85%. Step 2: Place the high-density alloy core into the atmosphere protection chamber, clamp it into the chuck, calibrate the coaxiality and tighten it; Step 3: Fill the atmosphere protection chamber with protective gas nitrogen, argon or helium to make the oxygen content in the atmosphere protection chamber lower than 50ppm; Step 4: Introduce the laser beam or electric arc, and synchronously start the powder feeder to deliver the mixed powder flow of tungsten and matrix alloy. The forming process is completed by the continuous lifting of the high-energy beam heat source processing head and the rotation of the chuck. The laser beam or electric arc melts and deposits the synchronously delivered mixed powder flow in a spiral manner on the core, forming instantaneous liquid phase sintering conditions in the process molten pool. Step 5: After the prepared fine-grained high-density alloy billet is cooled to below 100°C, the atmosphere protection chamber is opened and it is taken out; Step 6: Heat treat the prepared billet with the following process parameters: temperature 700°C to 1200°C, treatment time 2 hours to 8 hours, and cooling method of water cooling or air cooling.

3. The method for instantaneous liquid phase sintering of fine-grained high-density alloy billets without a substrate according to claim 1 or 2, characterized in that: The equipment used in this method includes: a laser or arc heat source; a powder delivery system for delivering tungsten and matrix alloy powders; A dynamically sealed atmosphere controlled processing protection chamber or a closed atmosphere controlled processing chamber; A rotary axis machining table with a chuck.

4. The method for instantaneous liquid phase sintering of fine-grained high-density alloy billets without a substrate according to claim 1, characterized in that: The average particle size of the raw tungsten powder is 1 to 25 microns and is produced by granulation or plasma spheroidization process; The average particle size of the matrix alloy or pure metal spherical powder is -60 to +300 mesh, and it is produced by processes such as gas atomization or rotating electrode.

5. The method for instantaneous liquid phase sintering of fine-grained high-density alloy billets without a substrate according to claim 1, characterized in that: High specific gravity alloys are composed of tungsten phase and matrix phase, and are tungsten-nickel-iron alloys with different tungsten contents, other similar alloys with different tungsten contents, and composite materials.

6. The method for instantaneous liquid phase sintering of fine-grained high-density alloy billets without a substrate according to claim 1, characterized in that: The high-density alloy is a tungsten-high entropy alloy composite material, a tungsten-amorphous alloy composite material, a binder phase of a tungsten alloy system, a high entropy alloy, a high-temperature alloy or a pure metal.

7. The method for instantaneous liquid phase sintering of fine-grained high-density alloy billets without a substrate according to claim 1, characterized in that: The forming process is coordinated by the continuous lifting of the heat source, i.e., the laser or electric arc, and the rotation of the chuck, so that the synchronously transported mixed powder flow is melted and deposited on the blank core in a spiral manner. The pitch of the spiral line should be determined according to the size of the molten pool / melt channel generated by the heat source and the sample size, that is: molten pool width / 4≤pitch≤sample length.

8. The method for instantaneous liquid phase sintering of fine-grained high-density alloy billets without a substrate according to claim 1, characterized in that: A high-density alloy thin rod with a tungsten mass percentage not less than that of the mixed powder is selected as the billet core. The billet core rotates continuously or intermittently during the forming process. The billet core is a thin rod made of pure tungsten, tungsten-nickel-iron alloy with different tungsten contents, or the same composition as the mixed powder. The length and diameter are determined according to the billet size. The length should be greater than the billet length, with a diameter of 3 to 25 mm and a length of 50 to 2000 mm.

9. The method for instantaneous liquid phase sintering of fine-grained high-density alloy billets without a substrate according to claim 1, characterized in that: During the preparation process, the oxygen content in the atmosphere protection chamber was lower than 50 ppm.

10. The method for instantaneous liquid phase sintering of fine-grained high-density alloy billets without a substrate according to claim 1, characterized in that: The power and beam spot size of the laser or arc heat source, powder delivery rate, scanning speed, and single-layer deposition height process parameters need to be matched according to the shape and size of the prepared rod blank, so as to ensure that only the matrix powder is melted during the forming preparation process, while the tungsten powder does not melt or only melts slightly. At the same time, the matrix molten pool quickly solidifies and remains dense after the heat source is removed, and liquid phase sintering is completed in a very short time, and finally a high-density fine tungsten particle high-density alloy rod blank is prepared; the power of the laser or arc heat source is 0.1~20kW, the beam spot size of the laser or arc heat source is 1~30mm, the beam spot moving rate is 1~30mm / min, and the powder feeding rate of the powder feeder is 1~200g / min.

Images