H10 type high-strength linear cutting molybdenum wire and preparation method thereof

Abstract

The invention discloses an H10 type high-strength linear cutting molybdenum wire which comprises the following components in percentage by weight: 0.5-2.0% of rare earth oxide, 0.1-0.5% of nano titanium carbide, 0.05-0.1% of aluminum oxide and the balance of molybdenum and inevitable impurities, wherein the rare earth oxide comprises at least one of lanthanum oxide, yttrium oxide or gadolinium oxide, and the particle size of the nano titanium carbide is smaller than 50 nm; the surface of the molybdenum wire is provided with a TiC coating with the thickness of 1-3 microns, the TiC concentration of the TiC coating is gradually reduced from inside to outside, and a pure molybdenum transition layer is formed on the outer layer. According to the molybdenum wire, the higher strength maintaining capacity, the lower wire breaking rate and the better surface ablation resistance are achieved, meanwhile, the stability of the preparation process is considered, and the requirement for industrial production is met.

Description

Technical Field

[0001] This invention relates to the field of metal wire materials for wire EDM, and particularly to a high-strength H10 type wire EDM molybdenum wire and its preparation method. Background Technology

[0002] Wire electrical discharge machining (EDM) technology, with its ability to perform high-precision forming of difficult-to-machine metal materials, is widely used in the manufacture of precision molds, complex aerospace components, and precision parts. As a key consumable component in wire EDM, the molybdenum wire needs to operate stably for extended periods under high current density, high-temperature discharge, and complex stress conditions. Its mechanical properties, high-temperature stability, surface condition, and service life directly affect the accuracy, efficiency, and cost of wire EDM.

[0003] In existing technologies, H10 specification molybdenum wire cutting often employs the addition of rare earth oxides for dispersion strengthening, and is prepared through processes such as powder metallurgy, smelting, hot extrusion, and cold drawing to improve the room temperature strength and processing stability of the molybdenum wire. For example, common methods mainly use La2O3 as a single rare earth oxide for doping, while some methods supplement it with second-phase particles such as TiC to improve the tensile strength and wear resistance of the molybdenum wire. However, since the distribution of rare earth oxides and hard phase particles in the molybdenum matrix is ​​limited by the powder mixing and sintering processes, the second-phase particles tend to agglomerate at grain boundaries or form coarse agglomerates, making it difficult to form a fine, uniform dispersion phase structure.

[0004] Under the high-temperature, high-energy discharge conditions of wire EDM, the aforementioned molybdenum wire still has several shortcomings. Firstly, the molybdenum matrix is ​​prone to softening and recrystallization at high temperatures. Existing H10 molybdenum wire exhibits rapid strength decay at approximately 1500℃, leading to plastic deformation and even wire breakage during high-load, high-speed cutting, thus limiting its application in demanding applications. Secondly, due to uneven distribution of doped phases and imperfect interfacial bonding, the tendency for grain boundary embrittlement increases, making the wire susceptible to brittle fracture during operation, resulting in a high wire breakage rate and significant performance fluctuations between product batches.

[0005] Furthermore, to improve the wear resistance and ablation resistance of wire-cut molybdenum wires, existing technologies have attempted to coat the surface of the molybdenum wire with hard coatings such as TiC. However, existing coatings are mostly structures with relatively uniform composition and thickness, which differ from the molybdenum substrate in terms of thermal expansion coefficient and deformation compatibility. This makes them prone to cracking and peeling during discharge, leading to localized coating detachment, increased surface roughness, and intensified ablation, making it difficult to simultaneously ensure the wear resistance of the coating and reliable bonding with the substrate. At the same time, the lack of targeted matching between the doping system and the coating structure makes it difficult to simultaneously maintain the strength, resistance to brittle fracture, and surface ablation resistance of the wire under high-temperature environments.

[0006] Therefore, how to achieve higher strength retention, lower wire breakage rate, and better surface ablation resistance based on existing H10 wire-cut molybdenum wire, while taking into account the stability of the preparation process and suitability for industrial production, is an issue that urgently needs to be addressed and solved in this field. Summary of the Invention

[0007] To address the problems of rapid strength decay at high temperatures, brittle fracture due to uneven distribution of doped phases, easy oxidation and ablation of molybdenum wire surface, and limited wire cutting life in the existing technologies, this invention provides an H10 type high-strength wire cutting molybdenum wire with high-temperature strength retention, low wire breakage rate and excellent surface ablation resistance, and its preparation method.

[0008] In a first aspect, the present invention provides an H10 type high-strength wire-cut molybdenum wire, comprising, by weight percentage: 0.5-2.0% rare earth oxides, 0.1-0.5% nano titanium carbide, 0.05-0.1% alumina, with the balance being molybdenum and unavoidable impurities; The rare earth oxide includes at least one of lanthanum oxide, yttrium oxide, or gadolinium oxide, and the nano-titanium carbide has a particle size of less than 50 nm. The surface of the molybdenum wire has a TiC coating with a thickness of 1~3μm. The TiC concentration of the TiC coating gradually decreases from the inside to the outside, and a pure molybdenum transition layer is formed on the outer layer.

[0009] By limiting the composition and content range mentioned above, rare earth oxides, nano-titanium carbide, and alumina form a fine, uniformly distributed dispersed phase in the molybdenum matrix. The rare earth oxides are selected from at least one of lanthanum oxide, yttrium oxide, and gadolinium oxide. During high-temperature sintering and subsequent hot processing, they preferentially segregate at grain boundaries and the second-phase interface, inhibiting recrystallization grain growth and stabilizing the grain boundary structure. Nano-titanium carbide, with its small particle size, high modulus, and high melting point, effectively pins dislocation movement and grain boundary migration within the grains. Alumina further participates in particle interface regulation and dispersion strengthening. The synergistic effect of these three components helps establish a thermally stable dispersion strengthening system in the molybdenum matrix, inhibiting high-temperature softening and abnormal grain growth. This allows the molybdenum wire to maintain high strength and ductility under the high-temperature service conditions of electrical discharge wire cutting, reducing the risk of brittle fracture and extending its service life.

[0010] Simultaneously, a TiC coating structure with a thickness of 1-3 μm is constructed on the surface of the molybdenum wire, with the TiC concentration gradually decreasing from the inside out and forming a pure molybdenum transition layer on the outermost layer. This enriches TiC on the side close to the molybdenum substrate, providing significant wear resistance and ablation protection. As the TiC content gradually decreases along the coating thickness direction, transitioning to the outermost pure molybdenum region, it effectively alleviates the thermal expansion mismatch and stress concentration between the coating and the molybdenum substrate, improves the interfacial bonding stability, and reduces coating cracking, peeling, and localized ablation during electrical discharge impact. Therefore, while maintaining good conductivity and surface integrity, the molybdenum wire can achieve high cutting speeds and surface quality in wire EDM, and maintain low wire breakage and ablation rates under long-term continuous use.

[0011] Preferably, the content of the rare earth oxide is 1.0-1.5%, the content of the nano-titanium carbide is 0.2-0.4%, and the content of the alumina is 0.06-0.08%.

[0012] Building upon the above, further limiting the content of rare earth oxides to 1.0-1.5%, nano-titanium carbide to 0.2-0.4%, and alumina to 0.06-0.08% facilitates the establishment of a more reasonable dispersed phase volume fraction and particle spacing in the molybdenum matrix. This allows the rare earth oxides, nano-TiC, and alumina to form a continuous and sufficient intragranular and grain boundary pinning network, while avoiding second-phase agglomeration and severe grain boundary embrittlement caused by excessive content. When the rare earth oxide content is controlled within the range of 1.0-1.5%, it can effectively refine the grains and stabilize the high-temperature grain boundary structure; when the nano-titanium carbide content is controlled within the range of 0.2-0.4%, it maintains a nanoscale dispersed distribution within the grains and at the grain boundaries, significantly improving the resistance to dislocation movement and grain boundary migration; when the alumina content is controlled within the range of 0.06-0.08%, it is conducive to participating in the formation of core-shell structure precipitates and improving the interfacial bonding between particles and the matrix, without excessively introducing brittle oxide phases. Preferably, the thickness of the gradient TiC coating is 1.5-2.5 μm, and the bonding strength between the coating and the substrate is greater than 50 J / m².

[0013] This invention controls the coating thickness within the range of 1.5-2.5 μm. On the one hand, this ensures that the TiC enriched in the coating has sufficient effective cross-sectional area to withstand discharge erosion and wear loads, thus providing continuous wear-resistant and ablation-resistant protection to the molybdenum substrate under high-energy electrical discharge machining (EDM). On the other hand, it avoids excessive coating thickness, which can lead to residual stress accumulation and exacerbate thermal expansion mismatch, reducing the risk of cracking and localized peeling caused by excessive coating rigidity. A bonding strength greater than 50 J / m² indicates that the fracture energy at the coating-molybdenum substrate interface is at a high level. Under repeated thermal and mechanical shocks from wire EDM, this effectively inhibits interface debonding and overall coating failure, allowing the gradient TiC coating to maintain integrity and adhesion stability throughout its service life. This is beneficial for further reducing the ablation rate and surface roughness, and for achieving stable high cutting speeds and continuous service lengths.

[0014] Preferably, the rare earth oxides, nano-titanium carbide, and alumina form a core-shell composite precipitate phase in the molybdenum matrix, with nano-TiC as the core and rare earth oxides and alumina as the shell, achieving a synergistic effect of dispersion strengthening and grain boundary pinning, so that the strength of the molybdenum wire decreases by less than 10% at 1500℃.

[0015] Rare earth oxides, nano-titanium carbide, and alumina are synergistically incorporated into a molybdenum matrix through compositional ratios and process control to form a core-shell composite precipitate with nano-TiC as the core and rare earth oxides and alumina as the shell. The hard nano-TiC core provides basic pinning for dislocation movement and grain boundary migration, while the outer rare earth oxide and alumina shells stabilize the interface, alleviate stress, and inhibit grain coarsening and grain boundary segregation. This creates a fine, uniform, and thermally stable dispersion strengthening system within the grain and grain boundary regions. Based on the continuous pinning and constraint of this core-shell composite precipitate on the grain boundaries and matrix structure, recrystallization softening and abnormal grain growth of the molybdenum matrix can be effectively suppressed during high-temperature service. This allows the molybdenum wire to maintain high load-bearing capacity and structural stability even at 1500℃, controlling strength attenuation to within 10%, and significantly improving dimensional stability and wire breakage resistance under high-temperature wire cutting conditions.

[0016] Preferably, the rare earth oxide is a mixture of La2O3 and Y2O3, and the molar ratio of La2O3:Y2O3 is (2-4):1, and the particle size of the rare earth oxide particles is 50-200 nm.

[0017] In this preferred combination, La2O3 is beneficial for promoting the formation of fine dispersed phases and inhibiting the abnormal growth of recrystallized grains in the molybdenum matrix during sintering and subsequent hot working, while Y2O3 has better thermal stability and interface stabilization at high temperatures. The combination of the two in a molar ratio of (2-4):1 can ensure sufficient grain boundary pinning ability while avoiding grain coarsening and grain boundary embrittlement caused by excessive doping of a single rare earth element, thereby obtaining a more balanced high-temperature microstructure stability and plasticity retention.

[0018] Meanwhile, by controlling the particle size of rare earth oxide particles within the range of 50-200 nm, they can form a continuous and dense dispersed distribution at the interface between the molybdenum matrix and the second phases such as nano-TiC and alumina, improving the pinning efficiency of dislocations and grain boundaries. This avoids excessive dissolution or failure during sintering due to excessively fine particles, and also prevents excessively coarse particles from becoming new stress concentration sources. Through the above-mentioned component ratio and particle size control, the ability of rare earth oxides to participate in the construction of core-shell composite precipitates and stabilize grain boundaries can be further enhanced, resulting in lower strength attenuation and better fracture stability of the molybdenum wire under high-temperature electrical discharge wire cutting conditions.

[0019] Preferably, the TiC coating consists of four layers of equal thickness from the inside out, with the outermost layer being a pure molybdenum transition layer. The TiC coating satisfies at least one of the following conditions: 1) The mass fraction of TiC in the innermost layer is 65-80 wt%; 2) The TiC mass fraction in the second layer, located on the outermost side of the innermost layer, is 30-50 wt%. 3) The mass fraction of TiC in the third layer located outside the second layer is 5-25 wt%; 4) The mass fraction of TiC in the outermost pure molybdenum transition layer is less than 1 wt%.

[0020] By dividing the TiC coating into three TiC content decreasing layers of equal thickness from the inside out, and an outermost pure molybdenum transition layer, and defining the TiC mass fraction ranges in the innermost, second, third, and pure molybdenum layers respectively, a monotonically decreasing concentration gradient from 65-80wt%, 30-50wt%, 5-25wt%, down to <1wt% is formed in the thickness direction of the coating. This layered gradient structure ensures that the innermost layer, close to the molybdenum substrate, has a high TiC content, thus providing sufficient hardness, wear resistance, and ablation resistance to withstand the main discharge erosion and mechanical wear during wire EDM. On the other hand, the gradually decreasing TiC content in the second and third layers introduces a transition buffer region between the ceramic phase and the metal substrate. Combined with the outermost pure molybdenum transition layer with a TiC content of less than 1wt%, this effectively mitigates the residual stress and thermal shock stress concentration caused by abrupt changes in hardness and thermal expansion coefficient, reducing the risk of cracking, delamination, and peeling of the coating during service.

[0021] Based on the aforementioned layered concentration gradient design, the TiC coating maintains overall wear resistance and ablation resistance while significantly improving deformation coordination and interface stability with the molybdenum substrate. Under high-frequency discharge and periodic thermal shock conditions of wire EDM, the coating can maintain its integrity and adhesion for a long time, avoiding a sharp increase in surface roughness or aggravated local ablation due to local coating failure. This helps the molybdenum wire maintain high cutting efficiency and low wire breakage and ablation rates throughout its service life.

[0022] Preferably, the molybdenum wire is used in wire electrical discharge machining at a cutting speed greater than 250 mm / s. 2 / min, continuous use length greater than 6000m, wire breakage rate less than 0.05%, ablation rate less than 0.1mg / min.

[0023] The above parameters indicate that the molybdenum wire has high processing efficiency, long service life, low risk of wire breakage, and low material loss in practical applications, which comprehensively reflects that the processing stability and reliability of the wire EDM molybdenum wire of the present invention have been significantly improved.

[0024] Secondly, the present invention also provides a method for preparing the H10 type high-strength wire-cut molybdenum wire, comprising the following steps: S1. The rare earth oxide, nano-titanium carbide and alumina are uniformly distributed as dispersed phases in the molybdenum matrix to prepare molybdenum-based composite powder containing nano-titanium carbide dispersed phase. S2. The molybdenum-based composite powder is pressed and smelted to obtain molybdenum ingots. The molybdenum ingots are subjected to hot extrusion and multiple cold drawing processes, and annealing is carried out during the deformation process. S3. A Ti-containing coating precursor is deposited on the surface of the molybdenum wire using a plasma spraying process, and the coating is subjected to diffusion heat treatment to form the TiC coating on the surface of the molybdenum wire.

[0025] In the preparation method of this invention, rare earth oxides, nano-titanium carbide, and alumina are uniformly introduced into the molybdenum matrix in the form of a dispersed phase in step S1 to prepare a molybdenum-based composite powder containing a nano-titanium carbide dispersed phase. This allows a uniform and stable dispersed strengthening structure to be formed inside the molybdenum wire after subsequent densification, laying the foundation for improving the high-temperature strength and anti-brittle fracture performance of the molybdenum wire. In step S2, the molybdenum-based composite powder is pressed, smelted, and then a molybdenum ingot is obtained. Combined with hot extrusion, multi-pass cold drawing, and annealing treatment, the structure is densified and the grains are refined. At the same time, residual stress is reduced, ensuring that the molybdenum wire has good comprehensive mechanical properties and processing stability. Step S3 involves depositing a Ti-containing coating precursor on the surface of a molybdenum wire using plasma spraying. Subsequent diffusion heat treatment forms a TiC coating and a transition layer between the TiC coating and the molybdenum substrate in situ on the surface of the molybdenum wire. This imparts excellent surface wear resistance and ablation resistance to the molybdenum wire without significantly affecting the toughness of the substrate, and improves the bonding reliability between the coating and the substrate. As a result, the final H10 type high-strength wire-cut molybdenum wire has the synergistic effect of internal dispersion strengthening and surface strengthening.

[0026] Preferably, in step S1, a suspension containing TiOOH nanoparticles is prepared by hydrothermal method, rare earth oxides, alumina precursors and molybdenum powder are added to the suspension for ultrasonic premixing, and the premixed suspension is spray-dried and activated by multi-step vacuum calcination to obtain the molybdenum-based composite powder.

[0027] A suspension containing TiOOH nanoparticles was first prepared using a hydrothermal method. Rare earth oxides, alumina precursors, and molybdenum powder were then introduced into this suspension and ultrasonically premixed. The TiOOH nanoparticles acted as a carrier and dispersion medium, uniformly adsorbing and coating the rare earth components and alumina precursors around the molybdenum powder, forming a highly homogeneous wet composite system. Subsequently, the premixed suspension was spray-dried, which quickly solidified the components into relatively uniform composite dry powder particles. A multi-step vacuum calcination activation process further removed organic residues and water of crystallization, promoting the transformation of TiOOH into an inorganic precursor phase that can be subsequently converted into titanium carbide. Simultaneously, it stabilized the dispersed distribution of rare earth oxides and alumina around the molybdenum matrix. This combined hydrothermal-spray drying-vacuum calcination process significantly improved the doping uniformity and dispersion of rare earth oxides, nano-titanium carbide, and alumina in the molybdenum-based composite powder, providing a good precursor microstructure for the formation of fine, stable dispersed reinforcing phases and core-shell precipitates during subsequent densification sintering and thermal processing.

[0028] Preferably, in step S2, the molybdenum ingot is hot-extruded in the range of 1500-1800°C and subjected to multiple cold drawing passes, and annealed in a hydrogen atmosphere at 800-1000°C between each deformation pass.

[0029] Hot extrusion facilitates the densification and large plastic deformation of molybdenum ingots at high temperatures, allowing the previously prepared dispersed phase to be further evenly distributed in the matrix and eliminating defects such as shrinkage cavities and residual porosity from the melting process, resulting in a dense extruded billet. Subsequent multi-pass cold drawing further refines the extruded molybdenum wire, increases dislocation density, and optimizes texture orientation, thereby improving the room temperature strength and high-temperature load-bearing capacity of the molybdenum wire. Annealing at 800-1000℃ in a hydrogen atmosphere between each deformation pass effectively eliminates residual stress introduced by cold working, suppresses increased brittleness caused by work hardening, and prevents surface oxidation under the protection of a reducing hydrogen atmosphere, further stabilizing the dispersed phase distribution. This results in a final molybdenum wire with a fine and uniform grain structure, low internal stress, and good plasticity and toughness, providing a reliable matrix structure for subsequent surface coating formation and stable operation during wire EDM.

[0030] The H10 type high-strength wire-cut molybdenum wire and its preparation method provided by the present invention have at least the following beneficial effects: (1) This invention introduces rare earth oxides, nano-titanium carbide and alumina into the molybdenum matrix at the same time, and performs multiphase dispersion strengthening design within a suitable content range. This forms a core-shell structure composite precipitate phase with nano-TiC as the core and rare earth oxides and alumina as the shell. This effectively improves the room temperature strength and plasticity of the molybdenum wire, while significantly inhibiting recrystallization softening and abnormal grain growth under high temperature conditions. This allows the molybdenum wire to maintain a low strength decay and stable load-bearing capacity at 1500℃, thereby reducing the risk of brittle fracture in high temperature wire cutting conditions.

[0031] (2) The present invention constructs a gradient TiC coating with a thickness of 1–3 μm on the surface of molybdenum wire, with the TiC content gradually decreasing along the thickness direction and the outer layer being a pure molybdenum transition layer. This allows the inner side of the coating to have a high TiC content to provide excellent wear resistance and ablation protection, while the outer pure molybdenum layer plays a role in buffering thermal expansion mismatch and stress concentration. This significantly improves the bonding stability between the coating and the substrate, reduces coating cracking, peeling and local ablation during the wire EDM process, thereby achieving higher cutting speed, longer continuous service length and lower wire breakage rate and ablation rate in practical applications.

[0032] (3) This invention prepares molybdenum-based composite powder by using a combination of hydrothermal method, spray drying and multi-step vacuum calcination, and combines hot extrusion, multi-pass cold drawing and hydrogen atmosphere annealing to make the doping of rare earth oxides, nano titanium carbide and alumina in the molybdenum matrix more uniform and the distribution of the dispersed strengthening phase more stable. Combined with plasma spraying and diffusion heat treatment to form a gradient TiC coating on the surface of molybdenum wire in situ, it not only ensures the synergistic strengthening effect of the inside and surface of molybdenum wire, but also the process is continuous and controllable, suitable for industrial scale-up production, and conducive to obtaining H10 type high-strength wire cutting molybdenum wire products with stable performance and good consistency. Detailed Implementation

[0033] To better understand the above technical solutions, a detailed description of the specific implementation methods will be provided below. Obviously, the described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0034] The terminology used in the embodiments of this invention is for the purpose of describing particular embodiments only and is not intended to limit the invention. The singular forms “a,” “the,” and “the” as used in the embodiments of this invention and the appended claims are also intended to include the plural forms, and “multiple” generally includes at least two unless the context clearly indicates otherwise.

[0035] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that an article or device that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such an article or device. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the article or device that includes said element.

[0036] This invention provides an H10 type high-strength wire-cut molybdenum wire, comprising, by weight percentage: (1) Rare earth oxides 0.5~2.0%, preferably 1.0-1.5%; (2) 0.1-0.5% nano-titanium carbide, preferably 0.2-0.4%, and the particle size of nano-titanium carbide is less than 50 nm. (3) Alumina 0.05~0.1%, preferably 0.06-0.08%, the rare earth oxide includes at least one of lanthanum oxide, yttrium oxide or gadolinium oxide, the rare earth oxide is preferably a mixture of La2O3 and Y2O3, and the molar ratio of La2O3:Y2O3 is (2-4):1, the particle size of the rare earth oxide particles is 50-200nm.

[0037] (4) The balance is molybdenum; (5) Unavoidable impurities; (6) A TiC coating with a thickness of 1~3μm, preferably 1.5-2.5μm, is applied to the surface of a molybdenum wire. The TiC concentration in the TiC coating gradually decreases from the inside to the outside, and a pure molybdenum transition layer is formed on the outer layer. The bonding strength between the coating and the substrate is greater than 50J / m².

[0038] The TiC coating consists of four layers of equal thickness from the inside out, with the outermost layer being a pure molybdenum transition layer. The TiC coating satisfies all of the following conditions: 1) The mass fraction of TiC in the innermost layer is 65-80 wt%; 2) The TiC mass fraction in the second layer, located on the outermost side of the innermost layer, is 30-50 wt%. 3) The mass fraction of TiC in the third layer located outside the second layer is 5-25 wt%; 4) The mass fraction of TiC in the outermost pure molybdenum transition layer is less than 1 wt%.

[0039] In this process, the rare earth oxides, nano-titanium carbide, and alumina form a core-shell composite precipitate phase in a molybdenum matrix, with nano-TiC as the core and rare earth oxides and alumina as the shell.

[0040] The present invention also provides a method for preparing the above-mentioned H10 type high-strength wire-cut molybdenum wire, specifically including the following steps: Preparation of S1, molybdenum-based composite powder A suspension containing TiOOH nanoparticles was prepared using a hydrothermal method. Specifically, a titanium source solution (e.g., TiCl4 or titanium alkoxide hydrolysate) was added to deionized water, the pH was adjusted to a suitable range, and the mixture was kept at 140-180℃ for 4-8 hours in a hydrothermal reactor to obtain a TiOOH nanoparticle suspension with a particle size of approximately 20-50 nm. Subsequently, pre-weighed rare earth oxides, alumina precursors, and molybdenum powder were added to the suspension, and the mixture was premixed for 20-60 minutes under mechanical stirring and ultrasonic conditions to ensure that the components were uniformly dispersed and adsorbed on the surface of the molybdenum powder, forming a wet composite slurry.

[0041] The obtained premixed suspension was fed into a spray dryer and spray-dried at an inlet temperature of 200-260℃ and an outlet temperature of 95-115℃ to obtain near-spherical composite dry powder particles. The composite dry powder was then placed in a vacuum furnace and dried at a vacuum degree not exceeding 1.0 × 10⁻⁶. -3 Under the conditions of Pa, the molybdenum-based composite powder was activated by multi-step vacuum calcination at 600-700℃ and 850-950℃ for 1-2 hours each, to remove organic residues and water of crystallization, and to convert TiOOH into Ti containing inorganic precursor phase that can be carbonized subsequently, thereby obtaining molybdenum-based composite powder with uniform composition and uniform distribution of dispersed phase precursor.

[0042] S2. Preparation of molybdenum wire matrix The molybdenum-based composite powder obtained in step S1 is pressed and densified by melting: preferably, cold isostatic pressing is used to form a cylindrical compact at a pressure of 100-200 MPa; subsequently, it is sintered in a vacuum furnace or a high-temperature sintering furnace at a vacuum degree not exceeding 1.0 × 10⁻⁶ MPa. -3 Densified molybdenum ingots were obtained by holding the ingot at 2000-2300℃ for 1-3 hours.

[0043] The molybdenum ingot is hot-extruded in the range of 1500-1800℃, with an extrusion ratio preferably of (8-20):1, to obtain an extruded billet with a reduced diameter and dense structure. The extruded billet is then subjected to multiple cold drawing passes, with the cross-sectional area compression rate of each pass preferably controlled at 5-20%. Between each pass or every 2-3 passes of deformation, the billet is annealed in a hydrogen atmosphere at 800-1000℃ for 30-60 minutes, with the hydrogen dew point preferably below -40℃, to eliminate residual stress introduced by cold working, suppress work hardening and surface oxidation, until a molybdenum wire matrix with the target diameter is obtained.

[0044] S3, Preparation of surface gradient TiC coating The molybdenum wire substrate obtained in step S2 undergoes surface pretreatment, including degreasing, cleaning, and slight mechanical or chemical descaling to ensure a clean surface and suitable roughness. Subsequently, under an inert atmosphere, a Ti-containing coating precursor is deposited on the molybdenum wire surface using plasma spraying. During plasma spraying, the preferred spray gun power is 20-40 kW, the spraying current is 400-600 A, the working gas is argon and / or nitrogen, and the powder feed rate is 5-15 g / min. By controlling the number of spray passes and the wire feed speed, the precursor coating thickness is maintained within the range of 1-3 μm.

[0045] After spraying, the molybdenum wire coated with the precursor is placed in an argon-protected diffusion heat treatment furnace and heated to 450-650℃ at a heating rate of 30-80℃ / h. After holding at this temperature for 1-3 hours, it is cooled to room temperature with the furnace. During this diffusion heat treatment, Ti in the coating reacts with the carbon source to form TiC. The phase composition and content gradually decrease along the thickness direction, forming an inner layer with a higher TiC content near the molybdenum substrate, while a pure molybdenum transition layer with a TiC content of less than 1wt% is formed on the outermost side. This results in a TiC coating with a thickness of 1-3μm on the surface of the molybdenum wire that meets the gradient TiC concentration distribution requirement. The bonding strength between the coating and the molybdenum substrate is not less than 50J / m².

[0046] Preparation Example The differences in preparation examples 1-5 lie in the raw material ratios, types, and material parameters of each H10 type high-strength wire-cut molybdenum wire. Specific differences are shown in Table 1. Table 1 Preparation Example La2O3 (wt%) Y2O3 (wt%) Gd2O3 (wt%) Total rare earth content (wt%) Nano TiC content (wt%) Nanoscale TiC particle size (nm) Al2O3 content (wt%) Mo Total impurities (wt%) Preparation Example 1 0.9 0.3 0 1.2 0.3 ≈30 0.07 margin <0.01 Preparation Example 2 0.6 0 0 0.6 0.15 ≈30 0.05 margin <0.01 Preparation Example 3 1.2 0.6 0 1.8 0.3 ≈30 0.08 margin <0.01 Preparation Example 4 0 0.5 0.5 1 0.2 ≈30 0.1 margin <0.01 Preparation Example 5 1.2 0.3 0 1.5 0.45 ≈30 0.07 margin <0.01 Preparation of S1, molybdenum-based composite powder First, a suspension containing TiOOH nanoparticles was prepared using a hydrothermal method. Specifically, TiCl4 hydrolysate was added to deionized water, the pH was adjusted to 2.0, and the resulting mixture was placed in a hydrothermal reactor and kept at 160℃ for 6 h to obtain a TiOOH nanoparticle suspension with a particle size of approximately 20-50 nm. Subsequently, pre-weighed rare earth oxides (La2O3 and Y2O3 in a molar ratio of 3:1), alumina precursor, and molybdenum powder were added to the TiOOH suspension. The mixture was premixed for 40 min under mechanical stirring and ultrasonic conditions to ensure uniform dispersion and adsorption of the components on the surface of the molybdenum powder, forming a wet composite slurry.

[0047] The obtained premixed suspension was fed into a spray dryer and spray dried at an inlet temperature of 230℃ and an outlet temperature of 105℃ to obtain near-spherical composite dry powder particles. The composite dry powder was then placed in a vacuum furnace and subjected to multi-step vacuum calcination activation at a vacuum of 1.0×10⁻³ Pa, first at 650℃ for 1.5 h, and then at 900℃ for 1.5 h. This process removed organic residues and water of crystallization, and converted TiOOH into a subsequently carbonizable Ti-containing inorganic precursor phase, resulting in a molybdenum-based composite powder with uniform composition and a uniformly distributed dispersed precursor phase.

[0048] S2. Preparation of molybdenum wire matrix The molybdenum-based composite powder obtained in step S1 is pressed and densified by melting. Specifically, the molybdenum-based composite powder is pressed by cold isostatic pressing at a pressure of 150 MPa to obtain a cylindrical compact; the compact is placed in a vacuum melting furnace and held at a vacuum of 1.0 × 10⁻³ Pa and a temperature of 2100℃ for 2 h to obtain a densified molybdenum ingot.

[0049] The molybdenum ingot was hot-extruded at 1700℃ with an extrusion ratio of 16:1 to obtain an extruded billet with a reduced diameter and dense structure. The extruded billet was then subjected to multiple cold drawing passes, with the cross-sectional area compression rate controlled at 15% per pass. After every two passes of cold drawing deformation, the billet was annealed at 900℃ in a hydrogen atmosphere for 45 minutes, with the hydrogen dew point controlled at -45℃, to eliminate residual stress introduced by cold working, inhibit work hardening and surface oxidation, until the H10 type molybdenum wire matrix with the target diameter was obtained.

[0050] S3, Preparation of surface gradient TiC coating The molybdenum wire substrate obtained in step S2 undergoes surface pretreatment, including degreasing with organic solvents, cleaning with deionized water, and a combination of light mechanical polishing and dilute acid washing to remove surface oxide scale, ensuring that the molybdenum wire surface is clean and has a suitable roughness. Subsequently, under an argon protective atmosphere, a Ti-containing coating precursor is deposited in segments on the surface of the molybdenum wire using a plasma spraying process to form the subsequent compositional gradient structure.

[0051] Specifically, under the conditions of a spray gun power of 30 kW, a spraying current of 500 A, an argon working gas, and a powder feeding rate of 10 g / min, a first precursor coating layer with a thickness of approximately 0.5 μm is first sprayed onto the surface of the molybdenum wire. The Ti to carbon source ratio in the sprayed powder is configured as a Ti:C molar ratio of 1:1.2. Subsequently, a second precursor coating layer with a thickness of approximately 0.5 μm is sprayed under the same spraying parameters, and the Ti:C molar ratio is adjusted to 1:0.8. A third precursor coating layer with a thickness of approximately 0.5 μm is then sprayed, and the Ti:C molar ratio is adjusted to 1:0.4. Through the deposition of the above three precursor layers with different ratios and approximately the same thickness, a gradient precursor structure with gradually changing Ti and C content from the inside to the outside is pre-formed in the thickness direction of the coating. The total thickness of the three precursor coating layers is approximately 1.5 μm.

[0052] After spraying three layers of Ti-containing precursor coating, the molybdenum wire coated with the precursor was placed in an argon-protected diffusion heat treatment furnace and heated to 550°C at a heating rate of 50°C / h. After holding at this temperature for 2 h, it was cooled to room temperature with the furnace. During this diffusion heat treatment, Ti in the coating reacts with the carbon source to form TiC, and under the action of thermal diffusion, element migration occurs along the thickness direction: the side closer to the molybdenum matrix has a higher concentration of Ti and C, resulting in a higher content of TiC phase; the TiC content gradually decreases layer by layer outwards, while the Ti on the outermost surface further diffuses inwards and interdiffused with the molybdenum matrix, thus forming a pure molybdenum transition layer with extremely low TiC content.

[0053] Cross-sectional sample preparation and compositional analysis using scanning electron microscopy combined with energy dispersive spectroscopy (EDS) revealed that the total thickness of the obtained TiC coating was approximately 2.0 μm, which could be divided into four layers of roughly equal thickness from the inside out: the first layer was approximately 0.5 μm thick with a TiC mass fraction of approximately 70 wt%; the second layer was approximately 0.5 μm thick with a TiC mass fraction of approximately 40 wt%; the third layer was approximately 0.5 μm thick with a TiC mass fraction of approximately 15 wt%; and the outermost layer, approximately 0.5 μm thick, was a pure molybdenum transition layer with a TiC mass fraction of less than 0.5 wt%. This verifies that the process of segmented spraying of a Ti-containing precursor coating combined with uniform diffusion heat treatment in this embodiment can form a gradient TiC coating structure on the surface of the molybdenum wire that meets the predetermined thickness and compositional distribution requirements. Example 1:

[0054] The difference between this embodiment and Example 1 is that the material composition used in Preparation Example 2 is adopted. Example 2:

[0055] The difference between this embodiment and Example 1 is that the material composition used in Preparation Example 3 is adopted. Example 3:

[0056] The difference between this embodiment and Example 1 is that the material composition used in Preparation Example 4 is adopted. Example 4:

[0057] The difference between this embodiment and Example 1 is that the material composition of Preparation Example 5 is used. Example 5:

[0058] The difference between this embodiment and Embodiment 1 is that the gradient concentration of the TiC coating is different, and the specific differences are as follows: When applying the Ti-containing precursor coating in layered spraying in S3, the Ti:C molar ratios of the three precursor coating layers were adjusted sequentially to 1:1.0, 1:0.6, and 1:0.25. The remaining spraying process parameters were the same as in Example 1, and the diffusion heat treatment conditions remained the same: heating to 550℃ and holding for 2 hours. SEM-EDS line scan analysis of the coating cross-section was performed, and the TiC content of each layer was statistically analyzed by mass percentage. The total thickness of the TiC coating was approximately 2.0 μm, with the four layers having essentially the same thickness from the inside out. The mass percentage of TiC in each layer was approximately: First layer: approximately 65 wt% TiC; Second layer: approximately 30 wt% TiC; Third layer: approximately 5 wt% TiC; Outermost layer: TiC mass percentage content is less than 0.5 wt%. Example 6:

[0059] The difference between this embodiment and Embodiment 1 is that the gradient concentration of the TiC coating is set near the midpoint of each layer. Specifically, when spraying the Ti-containing precursor coating in layers in S3, the Ti:C molar ratios of the three precursor coating layers are adjusted to 1:1.1, 1:0.7, and 1:0.35, respectively. The diffusion heat treatment conditions are adjusted to heating to 560℃ and holding for 2 hours. The remaining steps are the same as in Embodiment 1. Cross-sectional SEM-EDS analysis is performed on the obtained coating, and the TiC content of each layer is statistically analyzed by mass percentage. The total thickness of the TiC coating is approximately 2.0 μm, with the four layers having essentially the same thickness from the inside out. The mass percentage of TiC in each layer is approximately: First layer: approximately 72 wt% TiC; Second layer: approximately 38 wt% TiC; Third layer: approximately 12 wt% TiC; Outermost layer: TiC mass percentage content is less than 0.5 wt%. Example 7:

[0060] The difference between this embodiment and Embodiment 1 is that the gradient concentration of the TiC coating is set near the upper limit of each layer. Specifically, when spraying the Ti-containing precursor coating in layers in S3, the Ti:C molar ratios of the three precursor coating layers are adjusted to 1:1.2, 1:0.9, and 1:0.45, respectively, and the diffusion heat treatment temperature is increased to 580℃ with a holding time of 2.5 h. The remaining process conditions are the same as in Embodiment 1. SEM-EDS analysis of the coating cross-section was performed, and the TiC content of each layer was statistically analyzed by mass percentage. The total thickness of the TiC coating is approximately 2.0 μm, and the thickness of the four layers from the inside out is basically the same. The mass percentage of TiC in each layer is approximately: First layer: approximately 80 wt% TiC; Second layer: approximately 50 wt% TiC; Third layer: approximately 25 wt% TiC; Outermost layer: TiC mass percentage content is less than 0.5 wt%.

[0061] Comparative Example 1 The comparative example is the same as Example 1 in that the proportions of rare earth oxides, nano-titanium carbide, alumina and molybdenum powder are the same as those in Example 1, and the preparation steps (S1) of molybdenum-based composite powder and the preparation steps (S2) of molybdenum wire matrix are also the same as those in Example 1.

[0062] The difference between this comparative example and Example 1 is that after the preparation of the molybdenum wire substrate is completed, the plasma spraying and diffusion heat treatment steps are no longer performed. That is, the TiC coating and pure molybdenum transition layer are not formed on the surface of the molybdenum wire. The surface of the molybdenum wire is only subjected to conventional degreasing, pickling and polishing treatment, and then it is directly used as a wire cutting molybdenum wire.

[0063] Comparative Example 2 The comparative example is the same as Example 1 in that the proportions of rare earth oxides, nano-titanium carbide, alumina and molybdenum powder are the same as those in Example 1, and the preparation steps (S1) of molybdenum-based composite powder and the preparation steps (S2) of molybdenum wire matrix are also the same as those in Example 1.

[0064] The difference between this comparative example and Example 1 is that in S3, only a uniform TiC outer shell coating is prepared, without gradient design and pure molybdenum transition layer construction. Specifically, after performing the same surface pretreatment on the molybdenum wire substrate, a single layer of precursor powder containing Ti and carbon source is sprayed in one go under an argon protective atmosphere using a plasma spraying process. Under the conditions of a spray gun power of 30 kW, a spraying current of 500 A, and a powder feed rate of 10 g / min, the total thickness of the coating precursor is approximately 2 μm. Subsequently, under argon protection, the temperature is raised to 550°C at a heating rate of 50°C / h, held at that temperature for 2 h, and then cooled with the furnace.

[0065] Test methods 1. Cutting speed: Cut standard steel plates with a thickness of 10-30 mm according to GB / T 14842-2017 or enterprise standards under fixed parameters. Record the time and path length with the machine tool. Cutting speed = thickness × path length ÷ time (mm² / min). Repeat 3 times and take the average value.

[0066] 2. Continuous use length: Using 0.18 mm molybdenum wire, continuously cut until natural wire breakage under standard parameters. The machine tool automatically accumulates the wire feed length. The accumulated processing length before wire breakage is the continuous use length (m or km). Repeat 3 rolls and take the average value.

[0067] 3. Wire breakage rate: Under the same standard parameters, continuously cut for 100,000 m or 100 hours, record the number of natural wire breaks. Wire breakage rate = number of wire breaks ÷ processing length (times / 100,000 m) or ÷ processing time (times / 100 h). Repeat 3 to 5 times and take the average value.

[0068] 4. Ablation Rate: Under the same EDM parameters as the cutting speed test described above, a molybdenum wire sample of a certain length L was taken. The mass m0 and m1 were weighed using an analytical balance with an accuracy of not less than 0.1 mg before and after processing, respectively, and the corresponding actual processing time t (min) was recorded. Before weighing, the sample was wiped with anhydrous ethanol and dried to remove residual liquid and impurities from the surface. The ablation rate was calculated using the following formula: Ablation rate = (m0 - m1) ÷ t; The test was repeated three times under the same conditions, and the arithmetic mean was taken as the ablation rate under those conditions.

[0069] Test Results The test results of Examples 1-8 and Comparative Examples 1 and 2 are shown in Table 2. Table 2 Sample number Cutting speed (mm² / min) Continuous usage length (m) Broken fiber rate (%) Ablation rate (mg / min) Example 1 265 6600 0.03 0.08 Example 2 255 6200 0.04 0.09 Example 3 260 6400 0.035 0.085 Example 4 252 6100 0.045 0.095 Example 5 270 6500 0.035 0.08 Example 6 258 6400 0.04 0.085 Example 7 268 6700 0.028 0.078 Example 8 262 6500 0.035 0.082 Comparative Example 1 210 3500 0.15 0.25 Comparative Example 2 235 4800 0.1 0.18

[0070] The comparison results of Examples 1-8 with Comparative Examples 1 and 2 show that, under the same EDM wire cutting conditions, the H10 high-strength wire cutting molybdenum wire of the present invention is at an optimal level in terms of key indicators such as cutting speed, continuous service length, wire breakage rate, and ablation rate. Specifically, the cutting speed of the Example series is greater than 250 mm² / min, the continuous service length is greater than 6000 m, the wire breakage rate is stably controlled below 0.05%, and the ablation rate is controlled below 0.1 mg / min, which can ensure high processing efficiency while taking into account service life and processing stability. In contrast, Comparative Example 1 does not use a TiC surface coating, and Comparative Example 2 only uses a uniform TiC shell without forming a gradient structure. Both exhibit lower cutting speeds and continuous service lengths, and significantly higher wire breakage and ablation rates, making it difficult to meet the application requirements of high-precision and high-stability wire cutting processing.

[0071] Data from embodiments with different composition windows and gradient coating designs show that the dispersion-strengthened system within the molybdenum matrix, composed of rare earth oxides, nano-titanium carbide, and alumina, along with the gradient TiC coating structure on the molybdenum wire surface—where the TiC mass fraction decreases from the inside out and a pure molybdenum transition layer forms on the outer layer—play a synergistic role in maintaining high-temperature strength, resisting ablation, and controlling the risk of wire breakage. This synergistic effect enables the wire-cutting molybdenum wire of this invention to maintain high load-bearing capacity and a relatively stable surface state under high-frequency discharge and long-term continuous service conditions, thereby achieving superior overall performance compared to the comparative examples, verifying the effectiveness and superiority of the technical solution of this invention.

[0072] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention. Clearly, those skilled in the art can make various alterations and modifications to the invention without departing from its spirit and scope. Thus, if these modifications and modifications of the invention fall within the scope of the claims and their equivalents, the invention is also intended to include these modifications and modifications.

Claims

1. A type H10 high-strength wire-cut molybdenum wire, characterized in that, By weight percentage, it includes: 0.5-2.0% rare earth oxides, 0.1-0.5% nano titanium carbide, 0.05-0.1% aluminum oxide, with the balance being molybdenum and unavoidable impurities; The rare earth oxide includes at least one of lanthanum oxide, yttrium oxide, or gadolinium oxide, and the nano-titanium carbide has a particle size of less than 50 nm. The surface of the molybdenum wire has a TiC coating with a thickness of 1~3μm. The TiC concentration of the TiC coating gradually decreases from the inside to the outside, and a pure molybdenum transition layer is formed on the outer layer.

2. The H10 type high-strength wire-cut molybdenum wire according to claim 1, characterized in that, The content of the rare earth oxide is 1.0-1.5%, the content of the nano titanium carbide is 0.2-0.4%, and the content of the alumina is 0.06-0.08%.

3. The H10 type high-strength wire-cut molybdenum wire according to claim 1, characterized in that, The thickness of the TiC coating is 1.5-2.5 μm, and the bonding strength between the coating and the substrate is greater than 50 J / m².

4. The H10 type high-strength wire-cut molybdenum wire according to claim 1, characterized in that, The rare earth oxides, nano-titanium carbide, and alumina form a core-shell composite precipitate phase in a molybdenum matrix, with nano-TiC as the core and rare earth oxides and alumina as the shell.

5. The H10 type high-strength wire-cut molybdenum wire according to any one of claims 1-4, characterized in that, The rare earth oxide is a mixture of La2O3 and Y2O3, and the molar ratio of La2O3:Y2O3 is (2-4):

1. The particle size of the rare earth oxide particles is 50-200 nm.

6. The H10 type high-strength wire-cut molybdenum wire according to claim 1, characterized in that, The TiC coating consists of four layers of equal thickness from the inside out, with the outermost layer being a pure molybdenum transition layer. The TiC coating satisfies at least one of the following conditions: 1) The mass fraction of TiC in the innermost layer is 65-80 wt%; 2) The TiC mass fraction in the second layer, located on the outermost side of the innermost layer, is 30-50 wt%. 3) The mass fraction of TiC in the third layer located outside the second layer is 5-25 wt%; 4) The mass fraction of TiC in the outermost pure molybdenum transition layer is less than 1 wt%.

7. The H10 type high-strength wire-cut molybdenum wire according to any one of claims 1-4, characterized in that, The molybdenum wire is used in wire electrical discharge machining at a cutting speed greater than 250 mm / s. 2 / min, continuous use length greater than 6000m, wire breakage rate less than 0.05%, ablation rate less than 0.1mg / min.

8. A method for preparing H10 type high-strength wire-cut molybdenum wire as described in any one of claims 1-7, characterized in that, Includes the following steps: S1. Rare earth oxides, nano-titanium carbide and alumina are uniformly distributed as dispersed phases in a molybdenum matrix to prepare molybdenum-based composite powder containing nano-titanium carbide dispersed phase. S2. The molybdenum-based composite powder is pressed and smelted to obtain molybdenum ingots. The molybdenum ingots are subjected to hot extrusion and multiple cold drawing processes, and annealing is carried out during the deformation process. S3. A Ti-containing coating precursor is deposited on the surface of the molybdenum wire using a plasma spraying process, and the coating is subjected to diffusion heat treatment to form the TiC coating on the surface of the molybdenum wire.

9. The preparation method according to claim 8, characterized in that, In step S1, a suspension containing TiOOH nanoparticles is prepared by hydrothermal method. Rare earth oxides, alumina precursors and molybdenum powder are added to the suspension for ultrasonic premixing. The premixed suspension is then spray-dried and activated by multi-step vacuum calcination to obtain the molybdenum-based composite powder.

10. The preparation method according to claim 8, characterized in that, In step S2, the molybdenum ingot is hot-extruded in the range of 1500-1800℃ and cold-drawn in multiple passes, and annealed in a hydrogen atmosphere at 800-1000℃ between each deformation pass.