Double-phase deeply-alloyed alloy tungsten and preparation method thereof

Abstract

The invention discloses a double-phase deeply-alloyed alloy tungsten and a preparation method thereof, and belongs to the field of tungsten-based material preparation. According to the method, used metal element powder is mixed through mechanical stirring, and the double-phase deeply-alloyed alloy tungsten is obtained through cold isostatic pressing forming in combination with a four-step sintering method. In a prepared alloy tungsten system, body-centered cubic structure single-phase tungsten particles in a traditional tungsten alloy are successfully alloyed into body-centered cubic short-range ordered structure tungsten-based solid solution particles, and the particle sizes of the tungsten-based solid solution particles are in bimodal distribution; a face-centered cubic structure ternary solid solution binding phase in a traditional tungsten alloy is alloyed into a face-centered cubic structure multi-element solid solution binding phase, and meanwhile the semi-coherent interface relation between tungsten-based solid solution particles and the binding phase is kept; the prepared double-phase deeply-alloyed alloy tungsten has the tensile strength of 1100 MPa or above and the percentage elongation after fracture of 25% or above, the double problems of brittleness leading failure and strength-plasticity inversion of traditional tungsten alloy are effectively solved, and development and progress of tungsten-based materials are promoted.

Description

Technical Field

[0001] The invention belongs to the field of tungsten-based material preparation and relates to a two-phase deeply alloyed tungsten alloy and a preparation method thereof. Background Art

[0002] Tungsten alloy has high density (16~19g / cm 3 ), excellent mechanical properties, and other advantages have led to its widespread application in the weapons, nuclear, and electrical industries. It is a two-phase alloy consisting of tungsten particles and a binder phase. The tungsten particles impart high strength to the alloy, while the binder phase, composed of elements such as nickel, iron, copper, and cobalt, provides toughness. However, due to the inherent brittleness of pure tungsten and the relatively low strength of the binder phase, the mechanical properties of tungsten alloys have not seen significant breakthroughs in recent decades, and the challenge of achieving a synergistic improvement in strength and toughness urgently needs to be addressed.

[0003] The core challenge facing existing tungsten alloy strengthening and toughening technologies lies in breaking through the traditional design paradigm. Previous strengthening strategies, including solid solution strengthening, dispersion strengthening, medium- and high-entropy binder phase design, and deformation processing, have failed to fundamentally address the dual constraints of "tungsten particle brittleness-dominated failure" and "insufficient binder phase strength." The fundamental reason lies in the inherent brittleness of tungsten particles, insufficient effective slip systems, mechanical mismatch at the two-phase interface, grain boundary stress concentration, and imbalanced macroscopic strain distribution. These complex and interrelated factors make it difficult to achieve synergistic optimization of strength and toughness through single-point technological breakthroughs. Summary of the Invention

[0004] In view of the problems existing in the prior art such as the difficulty in breaking through the dual constraints of "brittle failure dominated by tungsten particles" and "insufficient strength of the bonding phase", the first object of the present invention is to provide a dual-phase deeply alloyed tungsten alloy, by alloying the body-centered cubic structure single-phase tungsten particles in traditional tungsten alloys into body-centered cubic short-range ordered structure tungsten-based solid solution particles, and alloying the face-centered cubic structure ternary solid solution bonding phase in traditional tungsten alloys into face-centered cubic structure multinary solid solution bonding phase, and forming a semi-coherent interface between the alloyed tungsten-based solid solution particles and the bonding phase matrix, synergistically achieving the bimodal distribution of tungsten-based solid solution particles, thereby simultaneously achieving the improvement of the strength and toughness of the alloy tungsten.

[0005] The second object of the present invention is to provide a method for preparing a dual-phase deeply alloyed tungsten alloy. The method selects specific metal element powder and combines the physical and chemical properties of the element powder to achieve dual-phase deep alloying of the tungsten alloy through short-term heat preservation of 850~1050℃, short-term heat preservation of 1300~1550℃, short-term heat preservation of 1000~1200℃ and long-term heat preservation of 600~800℃. The method has the advantages of simple process flow and significant effect.

[0006] In order to achieve the above technical objectives, the present invention provides a two-phase deeply alloyed tungsten alloy, comprising alloyed tungsten-based solid solution particles and a multinary solid solution binder phase, and the particle size of the alloyed tungsten-based solid solution particles presents a bimodal distribution; the preparation process of the tungsten alloy is as follows: at least one of copper powder and cobalt powder and metal element powder including tungsten powder, refractory metal element powder, nickel powder and iron powder are mixed to obtain a mixed element powder; after the mixed element powder is pressed and formed, it is sintered A at 850-1050°C with a holding time of ≤1h, and then sintered B at 1300-1550°C with a holding time of ≤1.5h, and then first cooled to 1000-1200°C for sintering C with a holding time of ≤2h, and then cooled to 600-800°C for sintering D with a holding time of ≥3h to obtain the obtained powder; wherein the refractory metal element powder is selected from any one or two of vanadium powder, niobium powder, molybdenum powder, tantalum powder and rhenium powder.

[0007] In the technical solution of the present invention, the significant improvement in the performance of the tungsten alloy is due to the synergistic strengthening effect in many aspects. Specifically, the present invention significantly improves the strength of the binder phase itself by transforming the traditional ternary binder phase into a multi-component solid solution binder phase with a face-centered cubic structure, and utilizes the high entropy effect and solid solution strengthening to significantly improve the strength of the binder phase itself. More importantly, the refractory elements are simultaneously dissolved in the tungsten particles and the binder phase. The spherical tungsten-based solid solution particles formed by the introduction of the refractory elements have a unique body-centered cubic short-range ordered structure that can increase the dislocation source density, while activating the slip deformation of edge dislocations in the tungsten-based solid solution particles, promoting the cross-slip of screw dislocations, and improving the mobility of screw dislocations, thereby significantly improving the toughness of the tungsten alloy. In addition, the unique bimodal particle size distribution of the tungsten-based solid solution particles also contributes to both strength and toughness: the large number of dispersed small-sized particles can effectively refine the structure, hinder dislocation slip, achieve significant grain refinement, and evenly disperse stress, reduce stress concentration points, and force the crack propagation path to be more tortuous; and the spherical particles themselves also minimize the risk of stress concentration at sharp corners.

[0008] The key to forming the unique microphases of the tungsten alloy of the present invention lies in the specific metal element powders used and the four-step sintering temperature sequence. Specifically, the present invention first uniformly mixes high-melting-point tungsten powder and refractory element powder with low-melting-point nickel powder, iron powder, and at least one of copper and cobalt powders to produce a mixed metal element powder. During the sintering process, the refractory element displaces into the tungsten to form a body-centered cubic tungsten-based solid solution. It also displaces into the binder phase to form a face-centered cubic solid solution, reducing the solubility of tungsten in the binder phase and refining the tungsten-based solid solution particles. At temperatures between 850 and 1050°C, numerous sintering necks form in the alloy, providing initial connections between the tungsten particles, promoting the formation of a tungsten skeleton, and inhibiting tungsten particle coarsening. Furthermore, tungsten, the refractory element, and at least one of copper and cobalt dissolve into the Ni-Fe solid solution phase through substitutional solid solution, forming a multicomponent solid solution phase. The short-term heat retention during this stage ensures the stable formation of the tungsten skeleton and binder phase solid solution, while also preventing eutectic reactions between the nickel and the refractory element to form brittle intermetallic compounds. When the temperature reaches 1300-1550°C, short-term holding promotes microstructure homogenization and densification. The binder phase melts into a liquid phase, selectively dissolving small tungsten particles, while large particles grow moderately through ripening. When the temperature is lowered to 1000-1200°C, tungsten particles precipitate, but diffusion is inhibited within the binder phase. Short-term holding allows the extremely fine newly precipitated particles and incompletely dissolved medium-sized particles to form a fine particle cluster, resulting in a bimodal distribution. Finally, when the temperature is lowered to 600-800°C, long-term holding allows for deep alloying of the tungsten particles with refractory elements through low-temperature diffusion, forming tungsten-based solid solution particles. If this stage is omitted, or if the temperature is too long or the holding time is too short, the tungsten particles will maintain the "strong but not tough" state of the pure tungsten structure, resulting in a failure to achieve a synergistic improvement in alloy toughness. Interfacial mismatch stresses accumulate, becoming fatigue crack sources and leading to strength degradation. Saturated precipitation of refractory elements in the binder phase destroys the semi-coherent interface between the tungsten-based solid solution particles and the binder phase.

[0009] As a preferred solution, the tungsten-based solid solution particles are a body-centered cubic short-range ordered structure, wherein the short-range ordered structure is specifically a B2 ordered structure, the tungsten element occupies the corner positions of the cubic unit cell, and the refractory element occupies the body center position of the cubic unit cell.

[0010] In the present invention, the construction of a body-centered cubic short-range ordered B2 structure inside the tungsten-based solid solution particles is another key factor in achieving a synergistic improvement in the strength and toughness of the tungsten alloy. The short-range ordered B2 structure formed by the construction of refractory elements inside the body-centered cubic structure tungsten particles has an ordered energy barrier of strong chemical bonds, which improves the strength of the tungsten alloy. At the same time, the short-range ordered B2 structure can activate the secondary slip system, promote cross-slip and multi-slip deformation, and thus improve toughness. If only the tungsten particles are solid-dissolved with refractory elements, a disordered structure of random substitution solid solution is formed instead of this short-range ordered B2 structure. Its strengthening mainly depends on the elastic interaction between solute atoms and dislocations, the strengthening efficiency is low, and the toughness will deteriorate sharply with the increase of solute concentration.

[0011] As a preferred solution, the multi-component solid solution binder phase has a face-centered cubic structure, wherein the elemental components are specifically tungsten, refractory metal, nickel, iron and copper.

[0012] As a preferred solution, the multi-component solid solution binder phase has a face-centered cubic structure, wherein the elemental components are specifically tungsten, refractory metal, nickel, iron and cobalt.

[0013] Experimental findings indicate that, due to the high eutectic sensitivity of refractory elements to nickel and iron during sintering, the aforementioned compositional control of tungsten and refractory elements requires that the tungsten alloy simultaneously achieve the alloying of tungsten particles to form tungsten-based solid solution particles with a short-range ordered structure, and the alloying of the binder phase to form a quaternary binder phase solid solution, while ensuring that no intermetallic compounds form within the binder phase. Therefore, the nickel and iron content must maintain a specific ratio. However, the nickel-to-iron ratio within the quaternary binder phase solid solution after alloying cannot meet the 7:3 ratio found in classic tungsten-based alloys, which inevitably reduces interfacial compatibility with the tungsten-based solid solution particles and significantly reduces the alloy's toughness. The present invention, however, perfectly addresses this issue by adding copper or cobalt. Copper and cobalt, like nickel and iron, belong to the fourth period and share some similar properties. Copper and cobalt can form an infinite solid solution with nickel, so the addition of copper and cobalt powders can partially replace nickel in the binder phase without reacting with the refractory elements. Therefore, by adding and regulating the content of copper powder and cobalt powder, it is possible to optimize interface matching and improve alloy strength and toughness while ensuring dual-phase alloying and the short-range ordered structure of tungsten-based solid solution particles.

[0014] As a preferred solution, the tungsten-based solid solution particles are nearly spherical, the large particle size is 10-20 μm, and the small particle size is 0.5-5 μm.

[0015] As a preferred solution, the mixed element powder is composed of tungsten powder, refractory metal element powder, nickel powder, iron powder and copper powder in a mass ratio of (80~97): (0.5~7.5): (1~12): (0.5~5): (1~3).

[0016] As a preferred solution, the mixed element powder is composed of tungsten powder, refractory metal element powder, nickel powder, iron powder and cobalt powder in a mass ratio of (80~97): (0.5~7.5): (1~12): (0.5~5): (0.1~1).

[0017] The properties of high-density tungsten alloys, especially strength and toughness, are strongly dependent on the tungsten content. As the tungsten content increases, the tensile strength of the alloy tends to increase, while the toughness decreases significantly. This is mainly because tungsten particles serve as the main load-bearing phase and constitute the alloy skeleton. Increasing the tungsten content means that more high-strength phases bear the load, and the tensile strength increases. However, the higher the tungsten content, the more brittle interfaces will be formed between the continuous tungsten skeleton and more tungsten particles in direct contact, and the volume fraction of the bonding phase will be directly reduced, thereby reducing the toughness of the alloy. This rule also applies to dual-phase deeply alloyed tungsten alloys, so a high content of tungsten powder is also used in the metal element powder of the present invention.

[0018] Furthermore, the refractory elements selected in the present invention can undergo a eutectic reaction with nickel, forming a variety of nickel-based intermetallic compounds within the binder phase. Most of these nickel-based intermetallic compounds have excessively large grain sizes or their crystal structures cannot achieve a semi-coherent relationship with the face-centered cubic structure of the binder phase, significantly reducing the toughness of the alloy. Simultaneously, the refractory elements can undergo a eutectic reaction with iron, forming a large number of iron-based intermetallic compounds within the binder phase. These iron-based intermetallic compounds exhibit extremely poor interface compatibility with the face-centered cubic crystal structure of the binder phase, making it impossible to screen for suitable iron-based intermetallic compounds to strengthen the binder phase. Therefore, it is necessary to control the ratio of refractory element powder to nickel powder and iron powder to avoid the presence of these nickel- and iron-based intermetallic compounds in the alloy.

[0019] As a preferred embodiment, the tungsten alloy has a density of ≥98%, more preferably ≥98.5%; a tensile strength of ≥1100 MPa, more preferably ≥1150 MPa; and an elongation of ≥25%, more preferably ≥30%. In the most preferred embodiment, the tensile strength and elongation can reach 1250 MPa and 30% respectively. The dual-phase deep-alloyed tungsten alloy prepared using the present invention has high strength, fine grains, and strong deformability. Compared with the tensile strength (800-900 MPa) and elongation (20-25%) of traditional tungsten-based alloys, its strength and toughness are significantly improved.

[0020] The present invention also provides a method for preparing a dual-phase deeply alloyed tungsten alloy, which comprises mixing at least one of copper powder and cobalt powder with metal element powders including tungsten powder, refractory metal element powder, nickel powder and iron powder to obtain a mixed element powder; after the mixed element powder is pressed into shape, it is sintered A at 850-1050°C with a holding time of ≤1 hour, and then sintered B at 1300-1550°C with a holding time of ≤1.5 hours, and then first cooled to 1000-1200°C for sintering C with a holding time of ≤2 hours, and then cooled to 600-800°C for sintering D with a holding time of ≥3 hours to obtain the obtained tungsten alloy; wherein the refractory metal element powder is selected from any one or two of vanadium powder, niobium powder, molybdenum powder, tantalum powder and rhenium powder.

[0021] As a preferred solution, the mixing is carried out using a three-dimensional mixer, and the mixing time is 8 to 12 hours; sufficient mixing by the three-dimensional mixer is more conducive to obtaining uniformly mixed metal element powders.

[0022] As a preferred solution, the compression molding method is cold isostatic pressing, and the cold isostatic pressing pressure is 250-300 MPa. Experimental findings show that due to the large variety of powders used in the present invention, the packaging is difficult, and the loose density is low, it is difficult to obtain a reliable green compact by molding using a conventional unidirectional press. However, cold isostatic pressing, with the pressure controlled within the above range, can produce a reliable green compact.

[0023] As a preferred solution, the conditions for sintering A are: a heating rate of 10~20℃ / min, a temperature of 900~1000℃, and a holding time of 0.5~1h; the conditions for sintering B are: a heating rate of 5~15℃ / min, a temperature of 1350~1500℃, and a holding time of 0.5~1.5h.

[0024] It is further preferred that the heating rate of the sintering A is 10-15° C. / min, and the heating rate of the sintering B is 5-10° C. / min.

[0025] As a preferred solution, the conditions for sintering C are: temperature of 1050~1150℃, holding time of 1~2h, and cooling rate of 10~20℃ / min; the conditions for sintering D are: temperature of 650~750℃, holding time of 3~5h, and cooling rate of 10~20℃ / min. Experiments have found that the specific sintering procedure of the present invention is crucial for obtaining a dual-phase deeply alloyed tungsten alloy material. Even if the holding temperature and time are the same, if the procedure is different from that of the present invention, the ideal structure cannot be obtained, thereby achieving dual-phase alloying and having both high strength and toughness. In particular, in the holding stages of sintering C and sintering D, if tungsten pre-alloyed powder is used instead of metal element powder, the special dual-phase deeply alloyed structure of the present invention cannot be formed at the temperature of the present invention through the same holding time.

[0026] It is further preferred that the cooling rate of the sintering C is 15-20° C. / min, and the cooling rate of the sintering D is 15-20° C. / min.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] (1) The present invention alloys the body-centered cubic single-phase tungsten particles in the traditional tungsten alloy into body-centered cubic short-range ordered tungsten-based solid solution particles with a bimodal distribution, alloys the face-centered cubic ternary solid solution bonding phase in the traditional tungsten alloy into a face-centered cubic multinary solid solution bonding phase, and realizes a semi-coherent interface between the alloyed tungsten-based solid solution particles and the bonding phase matrix, thereby simultaneously achieving an improvement in the strength and toughness of the alloy tungsten. In the most preferred embodiment, the alloy sintering process designed by the present invention and the metal element powder selected can prepare a tungsten alloy with a tensile strength and elongation of 1250 MPa and a dual-phase deep alloying of 30%. This alloy has extremely high density, extremely fine grains, and good deformation ability.

[0029] (2) The present invention makes full use of the melting point characteristics and solid solubility characteristics between high-melting-point tungsten powder, refractory element powder and low-melting-point nickel powder, iron powder and copper powder or cobalt powder, and promotes the stable formation of tungsten skeleton and multi-component bonding phase solid solution by adopting short-time heat preservation of 850~1050℃; short-time heat preservation of 1300~1550℃ promotes the formation of multi-component melt and the dissolution of small-sized tungsten particles and the ripening and moderate growth of large-sized tungsten particles, so as to make the alloy structure homogenized and the alloy densified; short-time heat preservation of 1000~1200℃ solidifies and precipitates small-sized tungsten particles to form a bimodal distribution structure; long-time heat preservation of 600~800℃ promotes the diffusion of refractory elements in the bonding phase into the interior of the tungsten particles, and transforms the tungsten particles into tungsten-based solid solution particles with a body-centered cubic short-range ordered structure through substitutional solid solution, and realizes a semi-coherent interface between the tungsten-based solid solution and the bonding phase, thereby realizing the deep alloying of the two-phase tungsten alloy, which has the advantages of simple process flow and significant effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 The microstructure of the dual-phase deeply alloyed tungsten alloy obtained in Examples 1 to 4 is shown in FIG. Figure 1 (a) is a scanning electron microscope photograph of the microstructure of the dual-phase deeply alloyed tungsten alloy obtained in Example 1; Figure 1 (b) is a scanning electron microscope photograph of the microstructure of the dual-phase deeply alloyed tungsten alloy obtained in Example 2; Figure 1 (c) is a scanning electron microscope photograph of the microstructure of the dual-phase deeply alloyed tungsten alloy obtained in Example 3; Figure 1 (d) is a scanning electron microscope photograph of the microstructure of the dual-phase deeply alloyed tungsten alloy obtained in Example 4.

[0031] Figure 2 (a) is a transmission electron micrograph of the microstructure at the interface between the tungsten-based solid solution particles and the multi-component binder phase of the dual-phase deeply alloyed tungsten alloy obtained in Example 1; Figure 2 (b) is a high-resolution atomic image of the interface between the tungsten-based solid solution particles and the multi-component bonding phase of the dual-phase deeply alloyed tungsten alloy obtained in Example 1 using a transmission electron microscope.

[0032] Figure 3 (a) is a transmission electron microscope high-resolution atomic image of the short-range ordered structure of tungsten-based solid solution particles of the dual-phase deeply alloyed tungsten alloy obtained in Example 1; Figure 3 (b) shows the tungsten element distribution result of the short-range ordered structure tungsten-based solid solution particles of the dual-phase deeply alloyed tungsten alloy prepared by the method of Example 1; Figure 3 (c) is the refractory element distribution result of the short-range ordered structure tungsten-based solid solution particles of the dual-phase deeply alloyed tungsten alloy prepared by the method of Example 1.

[0033] Figure 4 Statistical diagram of relative density of dual-phase deeply alloyed tungsten alloy prepared by the methods of Examples 1 to 4.

[0034] Figure 5 Statistical graphs of tensile strength and elongation after fracture of the dual-phase deeply alloyed tungsten alloys prepared by the methods of Examples 1 to 4 are shown. DETAILED DESCRIPTION

[0035] The present invention is further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments. Obviously, the embodiments described below are only a part of the embodiments, and all other embodiments obtained by professionals in this field without making creative efforts are still within the scope of protection of the present invention.

[0036] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or prepared by existing methods.

[0037] Example 1

[0038] A method for preparing a dual-phase deeply alloyed tungsten alloy comprises the following steps:

[0039] Step 1: Prepare tungsten alloy mixed powder by mechanical mixing

[0040] Take 850g of tungsten powder, with an average particle size of 3~5μm and a purity greater than 99.8%; 50g of vanadium powder, with an average particle size of 3~5μm and a purity greater than 99.5%; 64g of nickel powder, with an average particle size of 3~5μm and a purity greater than 99.9%; 6g of iron powder, with an average particle size of 3~5μm and a purity greater than 99.5%; 30g of copper powder, with an average particle size of 3~5μm and a purity greater than 99.8%; put the above powders together into a three-dimensional mixer and mix for 10 hours to obtain alloy tungsten mixed powder.

[0041] Step 2: Prepare tungsten alloy blanks by cold isostatic pressing

[0042] The mixed powder is placed in a rubber sleeve and placed in a cold isostatic pressing furnace for cold pressing at a pressure of 250 MPa to obtain a pressed embryo.

[0043] Step 3: Prepare tungsten alloy using liquid phase sintering

[0044] The sintering process uses a hot pressing sintering furnace; the specific sintering process is: heating to 900°C at a heating rate of 10°C / min and keeping it warm for 0.5h in sintering stage A; then heating to 1350°C at a heating rate of 5°C / min and keeping it warm for 0.5h in sintering stage B; then cooling to 1100°C at a cooling rate of 15°C / min and keeping it warm for 1.5h in sintering stage C; then cooling to 650°C at a cooling rate of 15°C / min and keeping it warm for 3h in sintering stage D; finally cooling to room temperature at a cooling rate of 20°C / min to obtain a dual-phase deeply alloyed tungsten alloy.

[0045] The dual-phase deeply alloyed tungsten alloy prepared in Example 1 has a relative density of 98.89%, a tensile strength of 1260 MPa, and an elongation after fracture of 30.08%.

[0046] Example 2

[0047] A method for preparing a dual-phase deeply alloyed tungsten alloy comprises the following steps:

[0048] Step 1: Prepare tungsten alloy mixed powder by mechanical mixing

[0049] Take 850g of tungsten powder, with an average particle size of 3~5μm and a purity greater than 99.8%; 50g of vanadium powder, with an average particle size of 3~5μm and a purity greater than 99.5%; 80g of nickel powder, with an average particle size of 3~5μm and a purity greater than 99.9%; 15g of iron powder, with an average particle size of 3~5μm and a purity greater than 99.5%; 5g of cobalt powder, with an average particle size of 3~5μm and a purity greater than 99.9%; put the above powders together into a three-dimensional mixer and mix for 10 hours to obtain alloy tungsten mixed powder.

[0050] Step 2: Prepare tungsten alloy blanks by cold isostatic pressing

[0051] The mixed powder is placed in a rubber sleeve and placed in a cold isostatic pressing furnace for cold pressing at a pressure of 250 MPa to obtain a pressed embryo.

[0052] Step 3: Prepare tungsten alloy using liquid phase sintering

[0053] The sintering process uses a hot pressing sintering furnace; the specific sintering process is: heating to 1000°C at a heating rate of 10°C / min and keeping warm for 0.5h in sintering stage A; then heating to 1500°C at a heating rate of 5°C / min and keeping warm for 1.5h in sintering stage B; then cooling to 1050°C at a cooling rate of 15°C / min and keeping warm for 2h in sintering stage C; then cooling to 700°C at a cooling rate of 15°C / min and keeping warm for 4h in sintering stage D; finally cooling to room temperature at a cooling rate of 20°C / min to obtain a dual-phase deeply alloyed tungsten alloy.

[0054] The dual-phase deeply alloyed tungsten alloy prepared in Example 2 has a relative density of 99.25%, a tensile strength of 1130 MPa, and an elongation after fracture of 31.58%.

[0055] Example 3

[0056] A method for preparing a dual-phase deeply alloyed tungsten alloy comprises the following steps:

[0057] Step 1: Prepare tungsten alloy mixed powder by mechanical mixing

[0058] Take 900g of tungsten powder, with an average particle size of 3~5μm and a purity greater than 99.8%; 30g of niobium powder, with an average particle size of 3~5μm and a purity greater than 99.5%; 44g of nickel powder, with an average particle size of 3~5μm and a purity greater than 99.9%; 6g of iron powder, with an average particle size of 3~5μm and a purity greater than 99.5%; 20g of copper powder, with an average particle size of 3~5μm and a purity greater than 99.8%; put the above powders together into a three-dimensional mixer and mix for 10 hours to obtain alloy tungsten mixed powder.

[0059] Step 2: Prepare tungsten alloy blanks by cold isostatic pressing

[0060] The mixed powder is placed in a rubber sleeve and placed in a cold isostatic pressing furnace for cold pressing at a pressure of 250 MPa to obtain a pressed embryo.

[0061] Step 3: Prepare tungsten alloy using liquid phase sintering

[0062] The sintering process uses a hot pressing sintering furnace; the specific sintering process is: heating to 950°C at a heating rate of 10°C / min and keeping warm for 1 hour in sintering stage A; then heating to 1350°C at a heating rate of 5°C / min and keeping warm for 0.5 hour in sintering stage B; then cooling to 1100°C at a cooling rate of 15°C / min and keeping warm for 1.5 hours in sintering stage C; then cooling to 700°C at a cooling rate of 15°C / min and keeping warm for 4 hours in sintering stage D; finally cooling to room temperature at a cooling rate of 20°C / min to obtain a dual-phase deeply alloyed tungsten alloy.

[0063] The dual-phase deeply alloyed tungsten alloy prepared in Example 3 has a relative density of 99.13%, a tensile strength of 1240 MPa, and an elongation after fracture of 25.89%.

[0064] Example 4

[0065] A method for preparing a dual-phase deeply alloyed tungsten alloy comprises the following steps:

[0066] Step 1: Prepare tungsten alloy mixed powder by mechanical mixing

[0067] Take 900g of tungsten powder, with an average particle size of 3~5μm and a purity greater than 99.8%; 30g of niobium powder, with an average particle size of 3~5μm and a purity greater than 99.5%; 55g of nickel powder, with an average particle size of 3~5μm and a purity greater than 99.9%; 12g of iron powder, with an average particle size of 3~5μm and a purity greater than 99.5%; 3g of cobalt powder, with an average particle size of 3~5μm and a purity greater than 99.9%; put the above powders together into a three-dimensional mixer and mix for 10 hours to obtain alloy tungsten mixed powder.

[0068] Step 2: Prepare tungsten alloy blanks by cold isostatic pressing

[0069] The mixed powder is placed in a rubber sleeve and placed in a cold isostatic pressing furnace for cold pressing at a pressure of 250 MPa to obtain a pressed embryo.

[0070] Step 3: Prepare tungsten alloy using liquid phase sintering

[0071] The sintering process uses a hot pressing sintering furnace; the specific sintering process is: heating to 1000°C at a heating rate of 10°C / min and keeping warm for 1 hour in sintering stage A; then heating to 1500°C at a heating rate of 5°C / min and keeping warm for 1.5 hours in sintering stage B; then cooling to 1050°C at a cooling rate of 15°C / min and keeping warm for 2 hours in sintering stage C; then cooling to 750°C at a cooling rate of 15°C / min and keeping warm for 5 hours in sintering stage D; finally cooling to room temperature at a cooling rate of 20°C / min to obtain a dual-phase deeply alloyed tungsten alloy.

[0072] The dual-phase deeply alloyed tungsten alloy prepared in Example 4 has a relative density of 99.36%, a tensile strength of 1197 MPa, and an elongation after fracture of 29.65%.

[0073] Figure 1 (a) to (d) are the organizational morphology diagrams of the dual-phase deeply alloyed tungsten alloys prepared in Examples 1 to 4 of the present invention. It can be clearly seen from the diagrams that the tungsten-based solid solution particles in the tungsten alloys of the present invention have a spherical particle morphology and a bimodal distribution characteristic, wherein the large particles have a particle size of 10 to 20 μm and the small particles have a particle size of 1 to 5 μm.

[0074] Figure 2 (a) to (b) are transmission electron microscope photographs of the microstructure and high-resolution atomic image of the interface between the tungsten-based solid solution particles and the five-element bonding phase of the two-phase deeply alloyed tungsten alloy obtained in Example 1, respectively. It can be seen from the figure that the alloyed tungsten-based solid solution particles are tightly combined with the five-element bonding phase and have a semi-coherent interface.

[0075] Figure 3(a) to (c) are respectively the transmission electron microscope high-resolution atomic images of the short-range ordered structure of the dual-phase deeply alloyed tungsten alloy prepared in Example 1 of the present invention, and the distribution results of tungsten and refractory elements. It can be seen from the figure that the tungsten-based solid solution particles have a short-range ordered B2 structure, in which the tungsten element occupies the corner positions of the cubic unit cell and the refractory elements occupy the body center positions of the cubic unit cell.

[0076] Comparative Example 1

[0077] All other conditions are the same as those in Example 1, except that the ratio of tungsten powder to vanadium powder is changed in the step of preparing the alloy tungsten mixed powder by mechanical mixing: 800 g of tungsten powder with an average particle size of 3-5 μm and a purity greater than 99.8%; 100 g of vanadium powder with an average particle size of 3-5 μm and a purity greater than 99.5%.

[0078] The dual-phase deeply alloyed tungsten alloy prepared in Comparative Example 1 has a relative density of 97.23%, a tensile strength of 647 MPa, and an elongation after fracture of 9.38%.

[0079] Experiments have noted that because refractory elements undergo a eutectic reaction with nickel, increasing their content leads to excessive nickel consumption in the alloy, preventing the formation of a structurally complete, compositionally matched face-centered cubic multinary solid solution binder phase. Furthermore, excessive addition of refractory elements leads to the formation of large amounts of nickel-based intermetallic compounds, iron-based intermetallic compounds, and refractory element oxides in the binder phase. These factors significantly reduce the strength of the binder phase and the interfacial bonding strength in the alloy, causing cracking along the interface and tearing of the binder phase, resulting in a rapid decrease in the alloy's tensile strength and elongation after fracture.

[0080] Comparative Example 2

[0081] All other conditions are the same as those in Example 1, except that the copper powder is completely replaced with nickel powder in the step of preparing the alloy tungsten mixed powder by mechanical mixing: 94 g of nickel powder is taken, with an average particle size of 3-5 μm and a purity greater than 99.9%; no copper powder is added.

[0082] The dual-phase deeply alloyed tungsten alloy prepared in Comparative Example 2 has a relative density of 96.87%, a tensile strength of 831 MPa, and an elongation after fracture of 12.59%.

[0083] The experiment noted that due to the sensitivity of refractory elements to nickel and iron, the content of nickel and iron must be maintained in a certain special ratio. The amounts of vanadium powder, nickel powder, and iron powder in this comparative example are 50g, 94g, and 6g, respectively. Due to the substantial increase in the nickel content, the chemical concentration of nickel in the binder phase is greatly increased, breaking through the critical conditions of the eutectic reaction and generating a large amount of nickel-based intermetallic compounds. In addition, the remaining nickel powder and iron powder are unable to meet the 7:3 composition ratio in the classic tungsten-based alloy, and their interface compatibility with the tungsten-based solid solution particles is reduced. Therefore, the generation of a large amount of intermetallic compounds and the reduction in interface compatibility cause a significant decrease in the strength and toughness of the alloy.

[0084] Comparative Example 3

[0085] Other conditions are the same as those in Example 1, except that the holding temperature of sintering A is changed in the step of preparing tungsten alloy by liquid phase sintering: the temperature is increased to 800° C. at a heating rate of 10° C. / min and held for 0.5 h.

[0086] The dual-phase deeply alloyed tungsten alloy prepared in Comparative Example 3 has a relative density of 95.36%, a tensile strength of 451 MPa, and an elongation after fracture of 6.59%.

[0087] The experiment noted that in Comparative Example 3, the holding temperature of Sintering A was too low (800°C), which failed to promote the formation of sintering necks within the tungsten particles. This restricted the coalescence and growth of the tungsten particles, resulting in incomplete spheroidization of the tungsten particles. The alloy was prone to fracture along the interface, and overall performance deteriorated. Furthermore, at this holding temperature and time, tungsten, vanadium, and copper were unable to enter the Ni-Fe solid solution phase through substitutional solid solution to form a stable quinary solid solution phase, preventing the alloy from achieving binder phase alloying.

[0088] Comparative Example 4

[0089] Other conditions are the same as those in Example 1, except that the holding temperature of sintering B is changed in the step of preparing tungsten alloy by liquid phase sintering: the temperature is increased to 1600° C. at a heating rate of 5° C. / min and held for 0.5 h.

[0090] The dual-phase deeply alloyed tungsten alloy prepared in Comparative Example 4 has a relative density of 98.94%, a tensile strength of 532 MPa, and an elongation after fracture of 8.16%.

[0091] The experiment noted that since sintering B was kept warm at 1600°C, this temperature is much higher than the eutectic temperature of nickel and refractory metal elements, and a large amount of nickel-based intermetallic compounds will be formed in the bonding phase. In addition, at this temperature, nickel, iron, and copper can all liquefy to form a liquid phase. The large amount of liquid phase in the alloy promotes the dissolution of tungsten and refractory metal elements into the liquid phase, and eventually forms a multi-component solid solution bonding phase melt with supersaturated tungsten dissolution. Although this process can promote the homogenization and densification of the alloy structure to a certain extent, due to the supersaturated dissolution of tungsten, the precipitation and growth of tungsten-based solid solution particles will be aggravated in the subsequent cooling process, and the grain size will increase rapidly. The above factors will cause the strength and toughness of the alloy to be much lower than that of Example 1.

[0092] Comparative Example 5

[0093] Other conditions are the same as those in Example 1, except that the holding time of sintering C in the cooling stage is changed in the step of preparing tungsten alloy by liquid phase sintering: the temperature is cooled to 1100°C at a cooling rate of 15°C / min and kept at this temperature for 3h.

[0094] The dual-phase deeply alloyed tungsten alloy prepared in Comparative Example 5 has a relative density of 98.67%, a tensile strength of 657 MPa, and an elongation after fracture of 11.39%.

[0095] Experimental observations indicate that when the holding time during the cooling phase is increased to 3 hours, the large tungsten-based solid solution particles, originally formed by tungsten precipitation from the supersaturated binder phase due to liquid solidification and subsequent deposition on the surfaces of existing large particles, leading to significant secondary growth, further grow, eventually exceeding the optimal size range of 10-20 μm. Furthermore, as the holding time increases, the elemental diffusion behavior within the binder phase intensifies with time. The fine, newly precipitated tungsten-based solid solution particles, originally formed due to restricted diffusion, as well as the medium-sized tungsten-based solid solution particles that were not fully dissolved, also grow significantly, resulting in a bimodal structure of tungsten-based solid solution particles in the tungsten alloy exceeding the optimal large and small particle size ranges. Furthermore, with increasing holding time, the diffusion time of nickel and refractory metal elements in the melt increases. This leads to the formation of nickel-based intermetallic compounds within the binder phase upon complete solidification of the multicomponent melt to form the multicomponent solid solution binder phase. Consequently, the abnormally large tungsten-based solid solution particles and the formation of intermetallic compounds significantly reduce the strength and toughness of the alloy.

[0096] Comparative Example 6

[0097] The other conditions are the same as those in Example 1, except that the holding temperature or holding time of sintering D in the cooling stage is changed in the step of preparing alloy tungsten by liquid phase sintering: cooling to 400°C at a cooling rate of 15°C / min and holding for 3 hours; or cooling to 650°C at a cooling rate of 15°C / min and holding for 1 hour.

[0098] The dual-phase deeply alloyed tungsten alloy prepared by Comparative Example 6 has a relative density of 97.82%, a tensile strength of 661 MPa, and an elongation after fracture of 13.28%; or a relative density of 98.19%, a tensile strength of 723 MPa, and an elongation after fracture of 19.31%.

[0099] The experiment noted that, because the holding temperature of sintering D in Comparative Example 6 was too low (400°C), deep alloying of the tungsten particles with the refractory elements to form tungsten-based solid solution particles was not achieved. At this temperature, the concentration gradient and chemical potential difference between the binder phase and the tungsten particles were unable to drive the directional migration of the refractory elements from the binder phase to the tungsten particles, preventing the formation of tungsten-based solid solution particles. As a result, the tungsten particles maintained the "strong but not tough" state of the pure tungsten structure, resulting in no synergistic improvement in alloy toughness. When the holding time of sintering D was too short (1h), the refractory element atoms in the binder phase and the displaced tungsten atoms in the tungsten particles could not achieve synchronous interdiffusion, making the lattice parameters of the tungsten-based particles incompatible with the binder phase. A semi-coherent interface could not be maintained between the tungsten-based particles and the binder phase, and the accumulated interfacial mismatch stress became a fatigue crack source, leading to strength degradation.

[0100] Comparative Example 7

[0101] Other conditions are the same as those in Example 1, except that the original powder composition is changed in the step of preparing the alloy tungsten mixed powder by mechanical mixing: the tungsten element powder and the vanadium element powder are replaced with an equal amount of tungsten-vanadium pre-alloyed powder.

[0102] The dual-phase deeply alloyed tungsten alloy prepared in Comparative Example 7 has a relative density of 93.95%, a tensile strength of 534 MPa, and an elongation after fracture of 15.42%.

[0103] Experimental observations indicate that when tungsten-vanadium pre-alloyed powder is used in place of elemental tungsten and vanadium powders, the alloy fails to form a bimodal distribution and a short-range ordered structure. This is because pre-alloying completely disrupts the step-by-step diffusion-controlled dynamic phase transformation process. Under the same process conditions, the use of tungsten-vanadium pre-alloyed powder presents the following challenges. First, due to the direct use of pre-alloyed powder, the tungsten particles are initially converted into tungsten-based solid solution particles. At the holding temperature (900°C) and holding time (0.5h) of Sintering A, numerous sintering necks appear, directly connecting the tungsten-based solid solution particles and forming a tungsten-based skeleton. Pre-alloying locks the refractory metal atoms within the tungsten lattice. At this stage, the refractory metal atoms primarily reside in the tungsten-based solid solution particles, with only a small amount entering the binder phase through substitutional solid solution along with tungsten. Due to the low solubility of tungsten in the binder phase, the refractory metal elements solid-solutioned into the binder phase in this manner are far lower than those in Example 1. Therefore, the quinary binder phase seen in Example 1 cannot form during this stage. Secondly, at the holding temperature (1350°C) and holding time (0.5h) of sintering B, the nickel, iron, and copper powders in the alloy form a large liquid phase, partially dissolving the tungsten-based solid solution particles formed by the pre-alloyed powder. The solid solution binder phase melts to form a binder phase melt. However, due to the low content of refractory metal elements in the binder phase, the diffusion process is unable to be slowed, resulting in rapid dissolution of small particles and rapid growth of large particles, exceeding the size range of the tungsten-based solid solution particles. This results in the inability to achieve bimodal structure control of the tungsten-based solid solution particles in sintering C. Finally, at the holding temperature and holding time of sintering D, due to the initial direct use of pre-alloyed powder, the refractory metal elements dissolve the tungsten particles at random lattice sites, resulting in a disordered tungsten-based solid solution structure. Combined with the low amount of refractory metal elements dissolved in the binder phase during sintering A and B, diffusion conditions are difficult to meet. Consequently, the short-range ordered structure of the tungsten-based solid solution particles cannot be constructed. The lack of bimodal structure and short-range ordered structure of tungsten-based solid solution particles in the alloy leads to a significant decrease in its strength and toughness.

Claims

1. A dual-phase deeply alloyed tungsten alloy, characterized by: The invention comprises alloyed tungsten-based solid solution particles and a multicomponent solid solution binder phase, wherein the particle sizes of the alloyed tungsten-based solid solution particles present a bimodal distribution; The preparation process of the tungsten alloy is as follows: at least one of copper powder and cobalt powder is mixed with metal element powder including tungsten powder, refractory metal element powder, nickel powder and iron powder to obtain a mixed element powder; after the mixed element powder is pressed into shape, it is sintered A at 850-1050°C with a holding time of ≤1h, and then sintered B at 1300-1550°C with a holding time of ≤1.5h, and then first cooled to 1000-1200°C for sintering C with a holding time of ≤2h, and then cooled to 600-800°C for sintering D with a holding time of ≥3h to obtain the obtained powder; wherein the refractory metal element powder is selected from any one or two of vanadium powder, niobium powder, molybdenum powder, tantalum powder and rhenium powder.

2. The dual-phase deeply alloyed tungsten alloy according to claim 1, characterized in that: The tungsten-based solid solution particles have a body-centered cubic short-range ordered structure, wherein the short-range ordered structure is specifically a B2 ordered structure, wherein the tungsten element occupies the corner positions of the cubic unit cell and the refractory element occupies the body center position of the cubic unit cell; The multi-component solid solution binder phase has a face-centered cubic structure, wherein the elemental components are specifically tungsten, refractory metal, nickel, iron and copper; and / or; The multi-component solid solution binder phase has a face-centered cubic structure, wherein the elemental components are specifically tungsten, refractory metal, nickel, iron and cobalt.

3. The dual-phase deeply alloyed tungsten alloy according to claim 1, characterized in that: A semi-coherent interface is formed between the alloyed tungsten-based solid solution particles and the multicomponent solid solution binder phase.

4. The dual-phase deeply alloyed tungsten alloy according to claim 3, characterized in that: The tungsten-based solid solution particles are nearly spherical, the large particle size is 10-20 μm, and the small particle size is 0.5-5 μm.

5. The dual-phase deeply alloyed tungsten alloy according to any one of claims 1 to 4, characterized in that: The mixed element powder is composed of tungsten powder, refractory metal element powder, nickel powder, iron powder and copper powder in a mass ratio of (80-97): (0.5-7.5): (1-12): (0.5-5): (1-3); and / or; The mixed element powder is composed of tungsten powder, refractory metal element powder, nickel powder, iron powder and cobalt powder in a mass ratio of (80~97): (0.5~7.5): (1~12): (0.5~5): (0.1~1).

6. The dual-phase deeply alloyed tungsten alloy according to claim 5, characterized in that: The tensile strength of the tungsten alloy is ≥1100 MPa, and the elongation after fracture is ≥25%.

7. The method for preparing a dual-phase deeply alloyed tungsten alloy according to any one of claims 1 to 6, characterized in that: A mixed element powder is obtained by mixing at least one of copper powder and cobalt powder with metal element powders including tungsten powder, refractory metal element powder, nickel powder and iron powder; after the mixed element powder is pressed into shape, it is sintered A at 850-1050°C with a holding time of ≤1h, and then sintered B at 1300-1550°C with a holding time of ≤1.5h, and then first cooled to 1000-1200°C for sintering C with a holding time of ≤2h, and then cooled to 600-800°C for sintering D with a holding time of ≥3h to obtain the mixed element powder; wherein the refractory metal element powder is selected from any one or two of vanadium powder, niobium powder, molybdenum powder, tantalum powder and rhenium powder.

8. The method for preparing a dual-phase deeply alloyed tungsten alloy according to claim 7, characterized in that: The mixing is carried out using a three-dimensional mixer, and the mixing time is 8 to 12 hours; The pressing method is cold isostatic pressing, and the pressure of the cold isostatic pressing is 250-300 MPa.

9. The method for preparing a dual-phase deeply alloyed tungsten alloy according to claim 8, characterized in that: The conditions for sintering A are: a heating rate of 10-20°C / min, a temperature of 900-1000°C, and a holding time of 0.5-1h; the conditions for sintering B are: a heating rate of 5-15°C / min, a temperature of 1350-1500°C, and a holding time of 0.5-1.5h.

10. The method for preparing a dual-phase deeply alloyed tungsten alloy according to claim 8 or 9, characterized in that: The conditions for sintering C are: temperature of 1050-1150°C, holding time of 1-2 hours, and cooling rate of 10-20°C / min; the conditions for sintering D are: temperature of 650-750°C, holding time of 3-5 hours, and cooling rate of 10-20°C / min.

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