A composite reinforced tungsten wire substrate and a method of making the same

Abstract

The application discloses a composite reinforced tungsten wire base material and a preparation method thereof, and the composite reinforcement is realized through integrated reinforcement of fine-grain reinforcement, solid solution reinforcement and second-phase reinforcement. The fine-grain reinforcement is realized through high and low two-stage sintering processes based on high grain boundary migration activation energy inflection point temperature and nanometer dispersion phase grain growth inhibition synergy of a base phase; the solid solution reinforcement is realized through tungsten-molybdenum solid solution formation; and the second-phase reinforcement is realized through zirconium-containing nanometer dispersion phase and rare earth oxide nanometer dispersion phase synergy. The nanometer dispersion phase in the tungsten wire base material has a particle size of less than 50 nm, the tungsten-molybdenum solid solution base phase has a grain size of less than 1 micrometer, and the tungsten wire base material has the remarkable characteristics of high wire drawing production efficiency, high product yield, high wire strength and low production cost.

Description

A composite reinforced tungsten wire substrate and its preparation method Technical Field

[0001] This invention relates to composite reinforced tungsten wire substrates and their preparation methods, belonging to the fields of powder metallurgy and metallic materials. Background Technology

[0002] As a sustainable green economy industry and a strategic emerging industry, the photovoltaic industry is receiving increasing attention. Crystalline silicon solar cells are a crucial type of cell within the photovoltaic industry. Reducing the cost of crystalline silicon raw materials is a pressing issue for the widespread application of solar cells. Reducing the thickness of silicon wafers and their manufacturing costs is an effective way to lower the overall cost of solar cells. Achieving the goals of larger and thinner silicon wafers depends on the continuous improvement of diamond wire saw quality and the continuous reduction of wire diameter; therefore, replacing high-carbon steel wire with high-strength, high-toughness tungsten wire has become an inevitable trend in the cutting and processing of ultra-thin monocrystalline silicon wafers.

[0003] Ultrafine tungsten-coated diamond wire typically refers to diamond wire made from a tungsten substrate with a diameter of 35 μm or less. The related invention patents, "An Alloy Wire and Its Preparation Method and Application" (application numbers 202110482229.3, 202110686165.9, 202110744773.0, 202110687610.3), involve tungsten alloys composed of oxides of tungsten and lanthanum, oxides of tungsten and yttrium, oxides of tungsten and cerium, and oxides of tungsten and zirconium. These tungsten alloys also contain a metallic element M, selected from at least one of potassium, rhenium, molybdenum, iron, and cobalt. The aforementioned patent claims only specify the content of lanthanum oxide, yttrium oxide, cerium oxide, or zirconium oxide (0.15wt%–2.0wt%, 0.25wt%–1.5wt%, 0.25wt%–1.5wt%, and 0.2wt%–1.5wt%, respectively) and potassium content (less than 80ppm), without specifying the content of other mentioned elements. The aforementioned claims specify the powder particle size as follows: for solid-solid doping, tungsten powder with a Fisher particle size of 1.0–4.0μm and lanthanum oxide, yttrium oxide, cerium oxide, or zirconium oxide with a particle size distribution D90 < 2.0μm are used as raw materials; after solid-liquid doping, the resulting material is reduced to alloy powder with an average Fisher particle size of 1.0–4.0μm. The aforementioned claims describe the particle size of lanthanum oxide, yttrium oxide, cerium oxide, or zirconium oxide in the sintered billet as follows: particle size less than 2.5μm. Although the preparation methods in the above claims involve doping powder preparation, pressing, sintering, and blanking, they do not involve the preparation process of the mixture and the sintering process of the tungsten alloy.

[0004] The materials and preparation method involved in the claims of the invention patent "A Super-Strong Tungsten Wire and Its Preparation Method" (application number 202211378053.8) are as follows: The tungsten alloy preparation involves tungsten, a dispersed second phase, and a solid solution strengthening phase; the dispersed second phase is one or more of rare earth oxides, zirconium oxide, and titanium oxide; the solid solution strengthening phase is one or more of rhenium, molybdenum, niobium, hafnium, iron, and cobalt; the content of the dispersed second phase in the tungsten alloy is 0.1-5.0 wt%; the content of the solid solution strengthening phase is 0.1-1.4 wt%; the raw material of the tungsten is blue tungsten; the raw material of the dispersed second phase is the nitrate or other salt corresponding to the dispersed second phase; the raw material containing the solid solution strengthening phase is the ammonium acid or metal powder corresponding to the solid solution strengthening phase; the pressed blank is pre-sintered at 1000-1400℃ in a hydrogen atmosphere for 1 hour; the pre-sintered pressed blank is densified at 1500-2700℃ in a hydrogen atmosphere for 2-10 hours.

[0005] Traditional tungsten materials typically require high-temperature (usually above 1900℃) sintering processes to achieve high density (relative density ≥95wt%). However, high-temperature sintering easily leads to rapid tungsten grain growth, and the production process is energy-intensive and costly. Existing technologies for tungsten wire substrates used in ultrafine diamond wire do not focus on controlling the fine microstructure of tungsten alloys and do not involve integrated strengthening technologies that combine fine grain strengthening, solid solution strengthening, and second-phase strengthening.

[0006] Existing technologies generally suffer from problems such as low yield of ultrafine tungsten wire with a drawn wire diameter ≤35μm (the yield of tungsten wire products of 100,000 meters / roll is usually less than 60%) and low wire strength (usually around 5600MPa). Summary of the Invention

[0007] One objective of this invention is to provide a tungsten wire substrate for ultrafine diamond wire with high yield, high wire strength, and low manufacturing cost for ultrafine tungsten wires with a drawn wire diameter ≤35μm.

[0008] To achieve the above objectives, this invention provides a composite-strengthened tungsten wire substrate, which achieves composite strengthening of the tungsten wire substrate through integrated strengthening of fine grain strengthening, solid solution strengthening, and second-phase strengthening. The fine grain strengthening is achieved through nanoparticle raw materials, a two-stage sintering process based on the inflection point temperature of grain boundary migration activation energy, and the synergistic effect of nano-dispersed phases inhibiting the growth of matrix phase grains. The solid solution strengthening is achieved through the formation of a tungsten-molybdenum solid solution. The second-phase strengthening is achieved through the synergistic effect of zirconium-containing nano-dispersed phases and rare earth oxide nano-dispersed phases. Using the mass of tungsten in the tungsten wire substrate as a benchmark, the molybdenum / tungsten mass fraction ratio is 6-8%. The zirconium / tungsten mass fraction ratio is 0.2-0.5%, and the rare earth oxide / tungsten mass fraction ratio is 0.5-1.5%. The rare earth oxide is at least one of lanthanum, yttrium, cerium, praseodymium, and neodymium oxides, with preference given to at least one of lanthanum, yttrium, and cerium oxides. The composite reinforced tungsten wire substrate has the microstructure characteristics of a tungsten-molybdenum solid solution matrix phase and a nano-dispersed reinforcing phase. The grain size of the tungsten-molybdenum solid solution matrix phase is <1μm. The nano-dispersed reinforcing phase includes zirconium-containing nano-dispersed phases and rare earth oxide nano-dispersed phases, which are uniformly distributed in the grain boundaries and grain interiors of the tungsten-molybdenum solid solution phase, with a grain size <50nm.

[0009] The strength of grain boundaries and phase boundaries determines the toughness of a material. Only when the binding force between grain boundaries and phase boundaries is sufficiently high can dislocation sliding be activated within the grains, leading to plastic deformation, before the material fails due to intergranular fracture. In stark contrast to zirconium oxide, the addition of zirconium carbide (ZrC) and / or zirconium hydride (ZrH2) allows zirconium to capture impurity oxygen, purify and strengthen grain boundaries, and form composite carbon oxides of zirconium and tungsten or composite oxides of zirconium and rare earth elements that have a coherent or semi-coherent relationship with the tungsten-molybdenum solid solution matrix. Rare earth oxides have the function of purifying the alloy and its grain and phase boundaries. The combined addition of optimized proportions of zirconium carbide and / or zirconium hydride and rare earth oxides allows zirconium and rare earth elements to interact and restrain each other, hindering the growth of zirconium- and rare earth-containing dispersed phases and enhancing their dispersion strengthening function. The highly dispersed zirconium-containing nano-dispersion phase and rare earth oxide nano-dispersion in the tungsten alloy of this invention not only enhance the strength of grain boundaries and phase boundaries, but also strongly inhibit grain growth during sintering and refine the grains of the tungsten-molybdenum solid solution matrix, thus significantly improving the strength and toughness of the alloy. Both nano-dispersion phase strengthening and grain refinement can significantly improve the strength of the tungsten wire substrate. During wire drawing, the rare earth nano-dispersion strengthening phase in the tungsten alloy also reduces the coefficient of friction, achieving a dual effect of significantly improving the wire drawing yield. Since tungsten and molybdenum can form a continuous solid solution throughout the entire composition range, the optimized amount of molybdenum exists in the tungsten matrix lattice in the form of substitutional solid solution atoms, forming solid solution strengthening, which significantly improves the plastic deformation capacity of the alloy during pressure processing and wire drawing, and significantly improves the strength of the tungsten wire. This invention provides a tungsten wire substrate for ultrafine diamond wire, achieving a yield of over 90% for 35μm drawn wire diameters, and a tensile strength of over 6800MPa for 35μm tungsten alloy wires.

[0010] Another objective of this invention is to provide a low-cost method for preparing tungsten wire substrate for ultrafine diamond wire that can significantly improve the yield of ultrafine tungsten wire with a drawn wire diameter ≤35μm and significantly improve the strength of tungsten alloy wire.

[0011] To achieve the above objectives, the present invention provides a method for preparing a composite reinforced tungsten wire substrate, characterized in that:

[0012] The alloy raw materials include: tungsten-molybdenum nanocomposite powder with an average specific surface area particle size of <150nm, zirconium carbide and / or zirconium hydride nanopowder with an average specific surface area particle size of <50nm, and rare earth oxide powder with an average specific surface area particle size of <50nm; the mass fraction ratio of molybdenum / tungsten in the tungsten-molybdenum nanocomposite powder is 6-8%; the rare earth oxide is at least one of lanthanum, yttrium, cerium, praseodymium, and neodymium oxides, with at least one of lanthanum, yttrium, and cerium oxides preferred; the tungsten and molybdenum raw material powders can also be tungsten nanopowder and molybdenum nanopowder with an average specific surface area particle size of <150nm, and preferably, tungsten-molybdenum nanocomposite powder with an average specific surface area particle size of <150nm;

[0013] The alloy composition is as follows: based on the mass of tungsten in the tungsten wire substrate, the molybdenum / tungsten mass fraction ratio is 6-8%, the zirconium / tungsten mass fraction ratio is 0.2-0.5%, and the rare earth oxide / tungsten mass fraction ratio is 0.5-1.5%; the amount of zirconium-containing nanopowder added is determined according to the zirconium / tungsten mass fraction ratio, wherein the zirconium-containing nanopowder is zirconium carbide nanopowder and / or zirconium hydride nanopowder;

[0014] The alloy preparation steps include: wet milling mixture preparation, wet milling mixture drying and granulation, billet forming, removal of forming agent in the pressed billet and pre-firing of the pressed billet, and high and low two-stage sintering based on the inflection point temperature of grain boundary migration activation energy.

[0015] The preparation of the wet-milled mixture refers to: placing raw material powder that meets the requirements of alloy composition ratio and raw material particle size and a forming agent accounting for 2.0-2.3% of the total mass fraction of the powder into a ball mill for wet ball milling and mixing; preferably, the amount of forming agent added is 2.3%;

[0016] Drying and granulation of wet milled mixtures refers to spray drying and granulation of wet milled mixtures in a spray drying granulation tower to prepare spherical mixtures with an average particle size of <120μm.

[0017] Preform forming refers to the process of forming spray-dried granulated mixtures under a forming pressure of 220-250 MPa using a cold isostatic pressing process.

[0018] The removal of forming agent from the pressed blank and the pre-firing of the pressed blank refer to the following: after the forming agent is removed from the pressed blank, the blank is pre-firing in high-purity hydrogen gas. The pre-firing temperature is 1050-1150℃ and the holding time is 160-200 minutes, followed by furnace cooling.

[0019] The high-low two-stage sintering based on the inflection point temperature of grain boundary migration activation energy refers to: heating the pre-sintered blank to 1350-1450℃ and holding it for 40-60 minutes; cooling it to 1250-1350℃ and holding it for 8-10 hours, followed by furnace cooling; the "high" and "low" in the high-low two-stage sintering are relative comparisons of high and low temperatures, that is, the low temperature used here is lower than the high temperature used.

[0020] The medium for wet ball milling and mixing is alcohol; polyethylene glycol and paraffin wax forming agent are added together during wet ball milling and mixing, with a polyethylene glycol / paraffin wax forming agent mass ratio of 3:7 or 1:1; preferably, the polyethylene glycol / paraffin wax forming agent mass ratio is 3:7; the mass ratio of grinding balls to mixture is 1:1 or 2:1, the ball milling time is 15-20 hours, the grinding ball material is W-Co, and the Co mass fraction in the alloy balls is 1-3%; preferably, polyethylene glycol is type 4000 (i.e., PEG4000), the mass ratio of grinding balls to mixture is 2:1, and the Co mass fraction in the alloy balls is 2%.

[0021] The removal of the forming agent is carried out in high-purity hydrogen at four different temperatures: 180–220°C, 260–300°C, 360–400°C, and 460–500°C, with each temperature holding time being 100–150 minutes.

[0022] The cold isostatic pressing is either dry bag cold isostatic pressing or wet bag cold isostatic pressing, with dry bag cold isostatic pressing being preferred; the high and low stage sintering is carried out in a vacuum sintering furnace; the dew point of the high-purity hydrogen is below -60°C.

[0023] This invention employs a comprehensive approach combining thermodynamic calculations, kinetic calculations, phase-field simulations, finite element simulations, and experimental verification to achieve integrated and synergistic design of raw material properties, alloy composition, and preparation processes. Based on the intrinsic properties of nanomaterials, the suppression of grain growth through pre-solidification and interdiffusion full solid solution during sintering of tungsten-molybdenum nanocomposite powders, the suppression of grain growth through zirconium-containing nano-dispersed phases and rare earth oxide nano-dispersions, and a two-stage low-temperature sintering method developed based on the inflection point temperature characteristics of grain boundary migration activation energy, this invention achieves grain refinement strengthening of the alloy through multi-factor synergy. Utilizing the intrinsic properties of the tungsten-molybdenum homogeneous phase diagram, molybdenum-tungsten solid solution strengthening is achieved through co-reduction pre-solidification and interdiffusion solid solution during sintering, while reducing the sintering temperature required to achieve near-full densification of the alloy system. PEG400, which functions as both a dispersant and a forming agent, is used. 0. Utilizing the protective effect of paraffin on highly active powders, and through the control of the wet milling process, uniform dispersion of nanoparticles and protection of the intrinsic properties of raw materials are achieved. This promotes the uniform dispersion of zirconium-containing nanophases and rare earth oxide nanophases in the tungsten matrix, enhancing the dispersion strengthening effect of nano-dispersion phases on the alloy. High-flow-rate spherical powders are obtained through spray drying granulation, promoting uniform filling of the forming mold cavity, significantly increasing the density and uniformity of the isostatic pressed compact, and promoting low-temperature sintering densification. Through a two-stage low-temperature sintering design based on the compatibility of nanomaterials and alloy composition, sintering energy consumption and production costs are significantly reduced. The low-temperature sintering refers to a sintering temperature significantly lower than the traditional sintering temperature of 1900℃. Attached Figure Description

[0024] Figure 1 shows the X-ray diffraction pattern and analysis results of the composite reinforced tungsten wire substrate prepared in Example 1 of the present invention. The substrate composition is W-5.57wt%Mo-0.21wt%ZrC-1.39wt%La2O3.

[0025] Figure 2 is an electron backscatter diffraction image of the composite reinforced tungsten wire substrate prepared in Example 1 of the present invention. The substrate composition is W-5.57wt%Mo-0.21wt%ZrC-1.39wt%La2O3.

[0026] As shown in Figure 1, the tungsten wire substrate contains a tungsten-molybdenum solid solution matrix phase with the same crystal structure as tungsten and a reinforcing phase with the same crystal structure as La2O3, exhibiting a two-phase structure of matrix and reinforcing phase. Due to the low amount of zirconium added and the fact that zirconium can form compounds with rare earth elements and / or tungsten, no zirconium-containing reinforcing phase was detected.

[0027] As shown in Figure 2, fine dot-like dispersed phases exist within the tungsten-molybdenum solid solution grains and at the grain boundaries in the alloy. Using ImageJ software, the average grain size of the tungsten-molybdenum solid solution grains in the alloy was measured to be 0.7 micrometers using the intercept method, and the grain size of the dispersed phase was measured to be ~40 nm. Detailed Implementation

[0028] The present invention will be further described below with reference to embodiments and comparative examples.

[0029] Example 1:

[0030] The alloy raw materials include: tungsten-molybdenum nanocomposite powder with an average specific surface area particle size of 138 nm, zirconium carbide (ZrC) powder with an average specific surface area particle size of 45 nm and containing 88.34 wt% Zr, lanthanum oxide (La2O3) powder with an average specific surface area particle size of 40 nm, and a molybdenum / tungsten mass fraction ratio of 6% in the tungsten-molybdenum nanocomposite powder.

[0031] The alloy composition is: W-5.57wt% Mo-0.21wt% ZrC-1.39wt% La2O3, corresponding to a molybdenum / tungsten mass fraction ratio of 6%, a zirconium / tungsten mass fraction ratio of 0.2%, and a lanthanum oxide / tungsten mass fraction ratio of 1.5%.

[0032] The alloy preparation process is as follows:

[0033] A. Preparation of wet-milled mixture: Raw material powder that meets the requirements of alloy composition ratio and raw material particle size, and PEG4000 and paraffin composite forming agent accounting for 2.3% of the total mass fraction of powder are put into a ball mill for wet ball milling and mixing; the wet milling medium is alcohol; in the PEG4000 and paraffin composite forming agent, the mass ratio of PEG4000 / paraffin is 3:7; the mass ratio of W-2wt%Co alloy grinding balls to the mixture is 2:1, and the ball milling time is 20 hours.

[0034] B. Drying and granulation of wet milled mixture: The wet milled mixture is spray-dried and granulated in a spray drying granulation tower. The granulated material is passed through a 120-mesh sieve to meet the requirement that the average particle size of the spherical mixture is <120μm.

[0035] C. Billet forming: A dry bag cold isostatic press is used to form the spray-dried granulated mixture under a forming pressure of 250MPa;

[0036] D. Forming agent removal and pre-firing of the compact: Forming agent removal and pre-firing of the compact in cold isostatic pressing are carried out in a hydrogen furnace with a hydrogen dew point of -65℃. The heating rate for forming agent removal is 3℃ / min, and the holding temperatures are 180℃, 280℃, 360℃ and 460℃ respectively, with a holding time of 150 minutes at each stage. The heating rate from 460℃ to the pre-firing temperature is 5℃ / min, and the holding temperature for pre-firing is 1150℃ for 160 minutes, followed by furnace cooling.

[0037] E. Sintering: Stage 1 sintering: The pre-fired blank is heated to 1400℃ in a vacuum sintering furnace at a heating rate of 10℃ / min and held for 50 minutes; Stage 2 sintering: After the first stage holding period, the temperature is lowered to 1300℃ at a cooling rate of 10℃ / min and held for 9 hours, followed by furnace cooling. The highest vacuum level in the sintering furnace during the sintering process is 25 Pa.

[0038] Figure 1 shows the X-ray diffraction pattern and analysis results of the composite-reinforced W-5.57wt%Mo-0.21wt%ZrC-1.39wt%La2O3 tungsten wire substrate of Example 1. As shown in Figure 1, the tungsten wire substrate contains a tungsten-molybdenum solid solution matrix phase with the same crystal structure as tungsten and a reinforcing phase with the same crystal structure as La2O3, exhibiting a two-phase structure of matrix and reinforcing phase. Due to the low amount of zirconium added and the fact that zirconium can form compounds with rare earth elements and / or tungsten, no zirconium-containing reinforcing phase was detected.

[0039] Figure 2 is an electron backscattering diffraction (ESD) image of the W-5.57wt%Mo-0.21wt%ZrC-1.39wt%La2O3 tungsten wire substrate reinforced in Example 1. As shown in Figure 2, fine dot-like dispersed phases exist within the tungsten-molybdenum solid solution grains and at the grain boundaries in the alloy. Using ImageJ software, the average grain size of the tungsten-molybdenum solid solution grains in the alloy was measured to be 0.7 μm using the intercept method, and the grain size of the dispersed phase was found to be ~40 nm.

[0040] Example 2:

[0041] The alloy raw materials include: tungsten-molybdenum nanocomposite powder with an average specific surface area particle size of 141 nm, zirconium carbide powder with an average specific surface area particle size of 45 nm and containing 88.34 wt% Zr, zirconium hydride (ZrH2) powder with an average specific surface area particle size of 47 nm and containing 97.75 wt% Zr, and yttrium oxide (Y2O3) powder with an average specific surface area particle size of 45 nm. The molybdenum / tungsten mass fraction ratio in the tungsten-molybdenum nanocomposite powder is 8%.

[0042] The alloy composition is: W-7.34wt% Mo-0.31wt% ZrC-0.19% ZrH2-0.46wt% Y2O3, corresponding to a molybdenum / tungsten mass fraction ratio of 8%, a zirconium / tungsten mass fraction ratio of 0.5%, and a yttrium oxide / tungsten mass fraction ratio of 0.5%.

[0043] The alloy preparation process is as follows:

[0044] A. Preparation of wet-milled mixture: Raw material powder that meets the requirements of alloy composition ratio and raw material particle size, and PEG4000 and paraffin composite forming agent accounting for 2.3% of the total mass fraction of powder are put into a ball mill for wet ball milling and mixing; the wet milling medium is alcohol; in the PEG4000 and paraffin composite forming agent, the mass ratio of PEG4000 / paraffin is 3:7; the mass ratio of W-2wt%Co alloy grinding balls to the mixture is 2:1, and the ball milling time is 15 hours.

[0045] B. Drying and granulation of wet milled mixture: The wet milled mixture is spray-dried and granulated in a spray drying granulation tower. The granulated material is passed through a 120-mesh sieve to meet the requirement that the average particle size of the spherical mixture is <120μm.

[0046] C. Billet forming: A dry bag cold isostatic press is used to form the spray-dried granulated mixture under a forming pressure of 220MPa;

[0047] D. Forming agent removal and pre-firing of the compact: Forming agent removal and pre-firing of the compact in cold isostatic pressing are carried out in a hydrogen furnace with a hydrogen dew point of -65℃. The heating rate for forming agent removal is 3℃ / min, and the holding temperatures are 220℃, 300℃, 400℃ and 500℃ respectively, with a holding time of 100 minutes at each stage. The heating rate from 500℃ to the pre-firing temperature is 5℃ / min, and the holding temperature for pre-firing is 1050℃, with a holding time of 200 minutes, followed by furnace cooling.

[0048] E. Sintering: Stage 1 sintering: The pre-fired blank is heated to 1350℃ in a vacuum sintering furnace at a heating rate of 10℃ / min and held for 60 minutes; Stage 2 sintering: After the first stage holding period, the temperature is lowered to 1250℃ at a cooling rate of 10℃ / min and held for 10 hours, followed by furnace cooling. The highest vacuum level in the sintering furnace during the sintering process is 25 Pa.

[0049] Analysis results show that the tungsten wire substrate of this embodiment (W-7.34wt%Mo-0.31wt%ZrC-0.19%ZrH2-0.46wt%Y2O3) contains a tungsten-molybdenum solid solution matrix phase with the same crystal structure as tungsten and a reinforcing phase with the same crystal structure as Y2O3, exhibiting a two-phase structure of matrix and reinforcing phase. Since zirconium can form compounds with rare earth elements and / or tungsten, no zirconium-containing reinforcing phase was detected. Fine, dot-like dispersed phases exist within the tungsten-molybdenum solid solution grains and at grain boundaries in the alloy. Using ImageJ software, the average grain size of the tungsten-molybdenum solid solution grains in the alloy was measured to be 0.7 micrometers using the intercept method, and the grain size of the dispersed phase was measured to be ~40 nm.

[0050] Example 3:

[0051] The alloy raw materials include: tungsten-molybdenum nanocomposite powder with an average specific surface area particle size of 140 nm, zirconium hydride powder with an average specific surface area particle size of 47 nm and containing 97.75 wt% Zr, lanthanum oxide powder with an average specific surface area particle size of 40 nm, cerium oxide (CeO2) powder with an average specific surface area particle size of 42 nm, and a molybdenum / tungsten mass fraction ratio of 7% in the tungsten-molybdenum nanocomposite powder.

[0052] The alloy composition is: W-6.46wt% Mo-0.38wt% ZrH2-0.5wt% La2O3-0.42wt% CeO2, corresponding to a molybdenum / tungsten mass fraction ratio of 7%, a zirconium / tungsten mass fraction ratio of 0.4%, and a (lanthanum oxide + cerium oxide) / tungsten mass fraction ratio of 1.0%.

[0053] The alloy preparation process is as follows:

[0054] A. Preparation of wet-milled mixture: Raw material powder that meets the requirements of alloy composition ratio and raw material particle size, and PEG4000 and paraffin composite forming agent accounting for 2.3% of the total mass fraction of powder are put into a ball mill for wet ball milling and mixing; the wet milling medium is alcohol; in the PEG4000 and paraffin composite forming agent, the mass ratio of PEG4000 / paraffin is 3:7; the mass ratio of W-2wt%Co alloy grinding balls to the mixture is 2:1, and the ball milling time is 18 hours.

[0055] B. Drying and granulation of wet milled mixture: The wet milled mixture is spray-dried and granulated in a spray drying granulation tower. The granulated material is passed through a 120-mesh sieve to meet the requirement that the average particle size of the spherical mixture is <120μm.

[0056] C. Billet forming: A dry bag cold isostatic press is used to form the spray-dried granulated mixture under a forming pressure of 240MPa;

[0057] D. Forming agent removal and pre-firing of the compact: Forming agent removal and pre-firing of the compact in cold isostatic pressing are carried out in a hydrogen furnace with a hydrogen dew point of -65℃. The heating rate for forming agent removal is 3℃ / min, and the holding temperatures are 200℃, 260℃, 380℃ and 480℃ respectively, with a holding time of 120 minutes at each stage. The heating rate from 480℃ to the pre-firing temperature is 5℃ / min, and the holding temperature for pre-firing is 1100℃, with a holding time of 180 minutes, followed by furnace cooling.

[0058] E. Sintering: Stage 1 sintering: The pre-fired blank is heated to 1450℃ in a vacuum sintering furnace at a heating rate of 10℃ / min and held for 40 minutes; Stage 2 sintering: After the first stage holding period, the temperature is lowered to 1350℃ at a cooling rate of 10℃ / min and held for 8 hours, followed by furnace cooling. The highest vacuum level in the sintering furnace during the sintering process is 25 Pa.

[0059] Analysis results show that the tungsten wire substrate of this embodiment (W-6.46wt%Mo-0.38wt%ZrH2-0.5wt%La2O3-0.42wt%CeO2) contains a tungsten-molybdenum solid solution matrix phase with the same crystal structure as tungsten and a reinforcing phase with the same crystal structure as La2O3, exhibiting a two-phase structure of matrix and reinforcing phase. Since zirconium can form compounds with rare earth elements and / or tungsten, no zirconium-containing reinforcing phase was detected. Fine, dot-like dispersed phases exist within the tungsten-molybdenum solid solution grains and at grain boundaries in the alloy. Using ImageJ software, the average grain size of the tungsten-molybdenum solid solution grains in the alloy was measured to be 0.85 micrometers using the intercept method, and the grain size of the dispersed phase was measured to be ~40 nm.

[0060] The alloy substrates prepared in Examples 1 to 3 were drawn into wires using traditional processes: tungsten alloy rods → rotary forging → continuous rotary forging → electrolytic cleaning → high-frequency annealing → welding → continuous rotary forging → wire drawing. The tensile strength of tungsten alloy wires with a diameter of 35 μm was measured according to the national standard GB / T 4181-2017 "Tungsten Wire". The yield of 100,000 meters / roll ultrafine wires with a diameter of 35 μm and the test results of the tensile strength of tungsten alloy wires with a diameter of 35 μm using the above three sets of substrates are shown in Table 1. Table 1 shows that the alloy exhibits typical characteristics such as high yield of drawn wires and high tensile strength.

[0061] Table 1. Yield and tensile strength of alloy substrates drawn into wires for each embodiment.

[0062]

[0063] Comparative Example 1

[0064] Except for the sintering process (singling process in one stage), the raw materials, alloy composition and other process parameters for alloy preparation are the same as in Example 1.

[0065] The sintering process of alloy A is as follows: the pre-sintered blank is heated to 1300°C in a vacuum sintering furnace at a heating rate of 10°C / min, held for 10 hours, and then cooled with the furnace.

[0066] The sintering process of alloy B is as follows: the pre-sintered blank is heated to 1400°C in a vacuum sintering furnace at a heating rate of 10°C / min, held for 10 hours, and then cooled with the furnace.

[0067] Test results show that the relative densities of the sintered blanks of alloys A and B are 84% and 95%, respectively. Using ImageJ software, the average grain size of the tungsten-molybdenum solid solution grains in alloys A and B was measured to be 0.65 μm and 2 μm, respectively, using the intercept method.

[0068] Comparative Example 2

[0069] Except for the tungsten-molybdenum nanocomposite powder and alloy composition, the other alloy raw materials and preparation processes are the same as in Example 3.

[0070] Alloy C: W-3.84wt%Mo-0.1wt%ZrH2-0.19wt%CeO2, corresponding to a molybdenum / tungsten mass fraction ratio of 4%, a zirconium / tungsten mass fraction ratio of 0.1%, and a cerium oxide / tungsten mass fraction ratio of 0.2%; the tungsten-molybdenum nanocomposite powder with a molybdenum / tungsten mass fraction ratio of 4% has an average particle size of 140nm in terms of specific surface area.

[0071] Alloy D: W-10.48wt% Mo-0.63wt% ZrH2-1.0wt% La2O3-0.57wt% CeO2, corresponding to a molybdenum / tungsten mass fraction ratio of 12%, a zirconium / tungsten mass fraction ratio of 0.7%, and a (lanthanum oxide + cerium oxide) / tungsten mass fraction ratio of 1.8%; the tungsten-molybdenum nanocomposite powder with a molybdenum / tungsten mass fraction ratio of 12% has an average particle size of 180nm in terms of specific surface area.

[0072] Test results show that the relative densities of the sintered blanks of alloys C and D are 95% and 94%, respectively. Using ImageJ software, the average grain size of the tungsten-molybdenum solid solution grains in alloys C and D was measured to be 1.8 μm and 0.8 μm, respectively, using the intercept method. The yield and tensile strength of the wire drawn from alloy C were 77% and 5597 MPa, respectively; the yield and tensile strength of the wire drawn from alloy D were 79% and 5801 MPa, respectively.

Claims

1. A composite reinforced tungsten wire substrate, characterized in that: The composite reinforcement is achieved through the integrated reinforcement of grain refinement, solid solution reinforcement, and second-phase reinforcement. The grain refinement reinforcement is achieved through nanopowder raw materials, a two-stage sintering process based on the inflection point temperature of grain boundary migration activation energy, and the synergistic inhibition of matrix phase grain growth by nano-dispersed phases. The solid solution reinforcement is achieved through the formation of a tungsten-molybdenum solid solution. The second-phase reinforcement is achieved through the synergistic effect of zirconium-containing nano-dispersed phases and rare earth oxide nano-dispersed phases. Using the mass of tungsten in the tungsten wire substrate as a benchmark, the molybdenum / tungsten mass fraction ratio is 6-8%, and the zirconium / tungsten mass fraction ratio is 0. 0.2~0.5%, rare earth oxide / tungsten mass fraction ratio = 0.5~1.5%; the rare earth oxide is at least one of lanthanum, yttrium, cerium, praseodymium, and neodymium oxides; the composite reinforced tungsten wire substrate has the microstructure characteristics of a tungsten-molybdenum solid solution matrix phase and a nano-dispersed reinforcing phase; the grain size of the tungsten-molybdenum solid solution matrix phase is <1μm; the nano-dispersed reinforcing phase includes zirconium-containing nano-dispersed phase and rare earth oxide nano-dispersed phase, uniformly distributed in the grain boundaries and grain interiors of the tungsten-molybdenum solid solution phase, with a grain size <50nm; its preparation method is: alloy raw material package Includes: tungsten-molybdenum nanocomposite powder with an average specific surface area particle size <150nm, zirconium carbide and / or zirconium hydride nanopowder with an average specific surface area particle size <50nm, and rare earth oxide powder with an average specific surface area particle size <50nm; wherein the molybdenum / tungsten mass fraction ratio in the tungsten-molybdenum nanocomposite powder is 6~8%; wherein the rare earth oxide is at least one of lanthanum, yttrium, cerium, praseodymium, and neodymium oxides; the alloy composition is as follows: based on the mass of tungsten in the tungsten wire substrate, the molybdenum / tungsten mass fraction ratio is 6~8%, the zirconium / tungsten mass fraction ratio is 0.2~0.5%, and the rare earth... The oxide / tungsten mass fraction ratio is 0.5~1.5%; the amount of zirconium-containing nanopowder added is determined according to the zirconium / tungsten mass fraction ratio, wherein the zirconium-containing nanopowder is zirconium carbide nanopowder and / or zirconium hydride nanopowder; the alloy preparation steps include: wet milling mixture preparation, wet milling mixture drying and granulation, billet forming, removal of forming agent in the pressed billet and pre-firing of the pressed billet, and high and low two-stage sintering based on the inflection point temperature of grain boundary migration activation energy; wet milling mixture preparation refers to: adding raw material powder that meets the requirements of alloy composition ratio and raw material particle size and accounting for 2.0~2% of the total mass fraction of powder.3% of the forming agent is added to a ball mill for wet ball milling and mixing; drying and granulation of the wet-milled mixture refers to spray drying and granulation of the wet-milled mixture in a spray drying granulation tower to prepare spherical mixtures with an average particle size <120μm; billet forming refers to forming the spray-dried granulated mixture using a cold isostatic pressing process under a forming pressure of 220~250MPa; removal of the forming agent from the pressed billet and pre-firing of the pressed billet refer to pre-firing the billet in high-purity hydrogen after removing the forming agent from the pressed billet. The holding temperature for sintering is 1050~1150℃, and the holding time is 160~200 minutes, followed by furnace cooling. The high-low two-stage sintering based on the grain boundary migration activation energy inflection point temperature refers to: heating the pre-sintered blank to 1350~1450℃ and holding it for 40~60 minutes; then cooling it to 1250~1350℃ and holding it for 8~10 hours, followed by furnace cooling. The yield of 35μm drawn wire diameter tungsten wire substrates exceeds 90%, and the tensile strength of 35μm tungsten alloy wire reaches over 6800MPa.

2. The composite reinforced tungsten wire substrate according to claim 1, characterized in that: The medium for wet ball milling and mixing is alcohol; polyethylene glycol and paraffin wax forming agent are added together during wet ball milling and mixing, with a polyethylene glycol / paraffin wax forming agent mass ratio of 3:7 or 1:1; the mass ratio of grinding balls to mixture is 1:1 or 2:1, the ball milling time is 15-20 hours, the grinding ball material is W-Co, and the Co mass fraction in the alloy balls is 1-3%.

3. The composite reinforced tungsten wire substrate according to claim 1, characterized in that: The removal of the forming agent is carried out in high-purity hydrogen at four different temperatures: 180~220℃, 260~300℃, 360~400℃ and 460~500℃, with each stage lasting 100~150 minutes.

4. The composite reinforced tungsten wire substrate according to claim 1, characterized in that: The cold isostatic pressing is either dry bag cold isostatic pressing or wet bag cold isostatic pressing.

5. The method for preparing a composite reinforced tungsten wire substrate according to claim 1, characterized in that: The high and low stage sintering is carried out in a vacuum sintering furnace.

6. A composite reinforced tungsten wire substrate according to claim 1 or 3, characterized in that: The dew point of high-purity hydrogen is below -60°C.

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