A duplex deep-alloyed alloy tungsten and a preparation method thereof

Abstract

The application discloses a kind of duplex deep alloyed alloy tungsten and preparation method thereof, belong to tungsten-based material preparation field.The method is mixed to the metal element powder used by mechanical stirring, obtain duplex deep alloyed alloy tungsten by cold isostatic pressing forming, combined four-step sintering method;The alloy tungsten system prepared in the method, successfully alloyed the body-centered cubic structure single-phase tungsten particle in traditional tungsten alloy into body-centered cubic short-range order structure tungsten-based solid solution particle, the particle size of tungsten-based solid solution particle presents bimodal distribution, alloyed the face-centered cubic structure ternary solid solution binder phase in traditional tungsten alloy into face-centered cubic structure multielement solid solution binder phase, while maintaining the semi-coherent interface relationship of tungsten-based solid solution particle and binder phase;Duplex deep alloyed alloy tungsten prepared has tensile strength of 1100MPa or more and elongation of 25% or more after breaking, effectively solve the double problems of "brittle dominant failure" and "strength-plasticity inversion" of traditional tungsten alloy, promote the development and progress of tungsten-based material.

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 application, the construction of the body-centered cubic short-range ordered B2 structure inside the tungsten-based solid solution particles is another key factor for achieving the synergistic improvement of the strength and toughness of the alloy tungsten. The construction of the short-range ordered B2 structure formed by the refractory elements inside the body-centered cubic tungsten particles has an ordered energy barrier of strong chemical bonds, which improves the strength of the alloy tungsten. At the same time, the short-range ordered B2 structure can activate secondary slip systems, promote cross-slip and multiple slip deformation, and thus improve the toughness. If only the refractory elements are solid-solved in the tungsten particles, a random substitutional disordered structure is formed instead of the short-range ordered B2 structure, and the strengthening mainly depends on the elastic interaction between the solute atoms and dislocations, which has a low strengthening efficiency and sharply deteriorates the toughness with the increase of the solute concentration.

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

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

[0013] It is found in experiments that, due to the high eutectic reaction sensitivity of the refractory elements to the nickel elements and iron elements during the sintering process, in combination with the above composition regulation for the tungsten elements and refractory elements, it is required to simultaneously realize the alloying of the tungsten particles to form short-range ordered structure tungsten-based solid solution particles and the alloying of the binder phase to form a quaternary binder phase solid solution in the alloy tungsten, and to ensure that no intermetallic compound is generated inside the binder phase. Therefore, the content of the nickel elements and iron elements must be maintained at a certain special ratio. However, the ratio of the nickel and iron inside the quaternary binder phase solid solution after alloying cannot meet the seven-three component ratio in the classical tungsten-based alloy, and the interface matching between the tungsten-based solid solution particles and the binder phase is inevitably reduced, thereby greatly reducing the toughness of the alloy. However, the addition of the copper elements or cobalt elements can perfectly solve the above problems. The copper elements and cobalt elements belong to the fourth period elements, and some of their properties are similar. Copper and cobalt can be infinitely solid-solved with nickel, so the addition of copper powder and cobalt powder can replace part of the role of nickel in the binder phase and does not react with the refractory elements. Therefore, by adding and regulating the content of the copper powder and cobalt powder, the interface matching can be optimized while ensuring the dual-phase alloying and the short-range ordered structure of the tungsten-based solid solution particles, and the strength and toughness of the alloy can be improved.

[0014] As a preferred scheme, the tungsten-based solid solution particles are near-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 application makes full use of the melting point characteristics and solid solution characteristics between the high-melting-point tungsten powder, the refractory element powder and the low-melting-point nickel powder, iron powder and copper powder or cobalt powder, and promotes the stable formation of the tungsten skeleton and the multi-element solid solution by adopting short-time holding at 850-1050 DEG C; short-time holding at 1300-1550 DEG C promotes the formation of the multi-element melt and the dissolution of the small-size tungsten particles and the moderate growth of the large-size tungsten particles, so as to homogenize the alloy organization and densify the alloy; short-time holding at 1000-1200 DEG C solidifies and precipitates small-size tungsten particles to form a bimodal distribution structure, and long-time holding at 600-800 DEG C promotes the diffusion of the refractory elements in the binder phase to the inside of the tungsten particles, converts the tungsten particles into body-centered cubic short-range ordered structure tungsten-based solid solution particles by substitutional solid solution, realizes the semi-coherent interface between the tungsten-based solid solution and the binder phase, realizes the deep alloying of the alloy tungsten in two phases, and has the advantages of simple process flow, remarkable effect and the like. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 For the organizational morphology of the deep alloyed alloy tungsten in two phases obtained in examples 1-4, Figure 1 (a) in the figure is the organizational morphology scanning electron microscope photo of the deep alloyed alloy tungsten in two phases obtained in example 1; Figure 1 (b) in the figure is the organizational morphology scanning electron microscope photo of the deep alloyed alloy tungsten in two phases obtained in example 2; Figure 1 (c) in the figure is the organizational morphology scanning electron microscope photo of the deep alloyed alloy tungsten in two phases obtained in example 3; Figure 1 (d) in the figure is the organizational morphology scanning electron microscope photo of the deep alloyed alloy tungsten in two phases obtained in example 4.

[0031] Figure 2 (a) in the figure is the organizational morphology transmission electron microscope photo of the tungsten-based solid solution particle and the multi-element binder phase interface of the deep alloyed alloy tungsten in two phases obtained in example 1; Figure 2 (b) in the figure is the transmission electron microscope high-resolution atomic image photo of the tungsten-based solid solution particle and the multi-element binder phase interface of the deep alloyed alloy tungsten in two phases obtained in example 1.

[0032] Figure 3 (a) in the figure is the transmission electron microscope high-resolution atomic image photo of the short-range ordered structure tungsten-based solid solution particle of the deep alloyed alloy tungsten in two phases obtained in example 1; Figure 3 (b) in the figure is the tungsten element distribution result of the short-range ordered structure tungsten-based solid solution particle of the deep alloyed alloy tungsten in two phases prepared by the method in example 1; Figure 3 (c) in the figure is the refractory element distribution result of the short-range ordered structure tungsten-based solid solution particle of the deep alloyed alloy tungsten in two phases prepared by the method in 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 were the same as those in Example 1, except that the holding temperature of sintering A was changed in the step of preparing tungsten alloy by liquid phase sintering: the temperature was increased to 800° C. at a heating rate of 10° C. / min and kept at that temperature 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 relative density of the dual-phase deep-alloyed alloy tungsten prepared by Comparative Example 6 was 97.82%, the tensile strength was 661 MPa, and the elongation after fracture was 13.28%; or the relative density was 98.19%, the tensile strength was 723 MPa, and the elongation after fracture was 19.31%.

[0099] It was noticed in the experiment that, in Comparative Example 6, the holding temperature of sintering D was too low (400°C), and the deep alloying of refractory elements to tungsten particles to form tungsten-based solid solution particles could not be achieved. At this temperature, the concentration gradient and chemical potential difference between the binder phase and the tungsten particles could not drive the directional migration of refractory elements from the binder phase to the tungsten particles, and tungsten-based solid solution particles could not be formed, resulting in the tungsten particles maintaining the "only strong not tough" state of pure tungsten structure, which led to the inability to synergistically improve the alloy toughness. When the holding time of sintering D was too short (1h), the refractory element atoms in the binder phase and the tungsten atoms displaced from the tungsten particles could not realize synchronous interdiffusion, so that the tungsten-based particle lattice parameters could not match the binder phase, the tungsten-based particles and the binder phase could not maintain a semi-coherent interface, and the interface mismatch stress accumulated to become a fatigue crack source, leading to strength decay.

[0100] Comparative Example 7

[0101] The other conditions were the same as in Example 1, and only the composition of the original powder was changed in the step of preparing the alloy tungsten mixed powder using a mechanical mixing method: the tungsten element powder and the vanadium element powder were replaced with an equal amount of tungsten-vanadium pre-alloyed powder.

[0102] The relative density of the dual-phase deep-alloyed alloy tungsten prepared by Comparative Example 7 was 93.95%, the tensile strength was 534 MPa, and the elongation after fracture was 15.42%.

[0103] It is noticed that when using tungsten-vanadium pre-alloyed powder to replace tungsten element powder and vanadium element powder, the alloy cannot form bimodal distribution and short-range ordered structure. This is because the pre-alloying completely destroys the step diffusion controlled dynamic phase transformation process. Under the same process conditions, using tungsten-vanadium pre-alloyed powder will bring the following problems. First, because the pre-alloyed powder is used directly, the tungsten particles have already been converted into tungsten-based solid solution particles in the initial stage. At the holding temperature (900℃) and holding time (0.5h) of sintering A, a large number of sintering necks appear, directly realizing a large number of connections between tungsten-based solid solution particles, forming a tungsten-based skeleton. Because pre-alloying causes refractory metal elements to be locked in the tungsten lattice, at this time, refractory metal elements mainly exist in tungsten-based solid solution particles, and only a small amount of refractory metal elements enter the binder phase by substitutional solid solution with tungsten. Because the solubility of tungsten in the binder phase is low, the amount of refractory metal elements entering the binder phase by this way will be much lower than that in Example 1. Therefore, the five-element binder phase cannot be formed in this stage. Second, at the holding temperature (1350℃) and holding time (0.5h) of sintering B, the nickel powder, iron powder and copper powder in the alloy will form a large amount of liquid phase, and the tungsten-based solid solution particles formed by the pre-alloyed powder will partially dissolve, and the solid solution binder phase will melt to form a binder phase melt. However, because the content of refractory metal elements in the binder phase is low, the diffusion process cannot be delayed, so that small particles are quickly dissolved and large particles are quickly grown, breaking through the size range of tungsten-based solid solution particles. This leads to the failure to realize the bimodal structure regulation of tungsten-based solid solution particles in sintering C. Finally, at the holding temperature and holding time of sintering D, because the pre-alloyed powder is used directly at the beginning, the solid solution of refractory metal elements to tungsten particles is random replacement of lattice sites, and the tungsten-based solid solution formed belongs to disordered structure. Combined with the low solid solution amount of refractory metal elements in the binder phase in the previous sintering A and sintering B stages, it is difficult to meet the diffusion conditions. Therefore, it is impossible to realize the construction of short-range ordered structure of tungsten-based solid solution particles. 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 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: one of copper powder and cobalt powder is mixed with tungsten powder, refractory metal element powder, nickel powder and iron powder to obtain a mixed element powder; after the mixed element powder is pressed and formed, it is subjected to sintering A at 850-1050° C. for a holding time of ≤1 hour, and then sintering B at 1300-1550° C. for a holding time of ≤1.5 hours, and then firstly cooled to 1000-1200° C. for a holding time of ≤2 hours, and then cooled to 600-800° C. for a holding time of ≥3 hours, and then sintered D 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; 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); 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).

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, in which 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; When the mixed element powder consists of tungsten powder, refractory metal element powder, nickel powder, iron powder and copper powder, the multi-component solid solution binder phase has a face-centered cubic structure, wherein the element components specifically include tungsten element, refractory metal element, nickel element, iron element and copper element; or; When the mixed element powder consists of tungsten powder, refractory metal element powder, nickel powder, iron powder and cobalt powder, the multi-component solid solution bonding phase is a face-centered cubic structure, wherein the element components are specifically tungsten, refractory metal, nickel, iron and cobalt.

3. The dual-phase deeply alloyed tungsten alloy according to claim 2, 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.

4. The dual-phase deeply alloyed tungsten alloy according to any one of claims 1 to 3, characterized in that: The tensile strength of the tungsten alloy is ≥1100 MPa, and the elongation after fracture is ≥25%.

5. The method for preparing a dual-phase deeply alloyed tungsten alloy according to any one of claims 1 to 4, characterized in that: A mixed element powder is obtained by mixing one of copper powder and cobalt powder with tungsten powder, refractory metal element powder, nickel powder and iron powder; after the mixed element powder is pressed and formed, it is subjected to sintering A at 850-1050°C with a holding time of ≤1 hour, then sintering B at 1300-1550°C with a holding time of ≤1.5 hours, and then first cooling it to 1000-1200°C for sintering C with a holding time of ≤2 hours, and then cooling it to 600-800°C for sintering D with a holding time of ≥3 hours 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; 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); 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 method for preparing a dual-phase deeply alloyed tungsten alloy according to claim 5, 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.

7. The method for preparing a dual-phase deeply alloyed tungsten alloy according to claim 6, 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.

8. The method for preparing a dual-phase deeply alloyed tungsten alloy according to claim 6 or 7, 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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