A method and system for plasma atomization regeneration of titanium alloy coarse powder based on powder rolling

Abstract

This invention discloses a plasma atomization regeneration method and system for titanium alloy coarse powder based on powder rolling, belonging to the field of titanium alloy powder remanufacturing technology. The method involves constructing a coarse powder, after screening and purification, into an outer stable powder layer, an intermediate transition powder layer, and an inner liquid-releasing powder layer. This is then differentially compacted and rolled to form a gradient dense powder strip, followed by surface embossing and roll forming to obtain a hollow feed body with axial degassing channels. After low-temperature activation and shaping, the powder is continuously fed into a plasma atomization zone, with inert gas being blown internally simultaneously. This causes the ends to form annular molten liquid films, which are then broken and sphericalized to obtain regenerated spherical titanium alloy powder. This method improves the target particle size yield, sphericity, and flowability, and reduces the proportion of bubbly, hollow, and satellite powders. It is suitable for continuous high-value regeneration of titanium alloy coarse powder and is applicable to additive manufacturing, hot isostatic pressing, and powder metallurgy powder supply fields.

Description

Technical Field

[0001] This invention relates to the field of titanium alloy powder remanufacturing technology, specifically to a method and system for the plasma atomization regeneration of titanium alloy coarse powder based on powder rolling. Background Technology

[0002] Titanium alloy powders possess high specific strength, excellent corrosion resistance, and superior high-temperature performance, and have been widely used in additive manufacturing, hot isostatic pressing, metal injection molding, and high-end powder metallurgy forming. These applications place high demands on the sphericity, particle size distribution, flowability, bulk density, oxygen content, and inclusion levels of the powder raw materials. Particularly in laser selective melting, electron beam forming, and high-density near-net-shape forming processes, powder particle size stability and powder feeding stability directly affect the forming quality, density, and mechanical properties. Therefore, the preparation and recycling of high-quality titanium alloy spherical powders has become an important technological direction in the field of titanium alloy powder manufacturing.

[0003] Existing methods for preparing titanium alloy powder mainly include gas atomization, plasma atomization, plasma rotating electrode atomization, and spheroidization after mechanical crushing. In actual production and use, a large amount of coarse powder, oversized powder, recycled powder, and irregularly shaped powder are generated. These powders typically have characteristics such as large particle size, sharp edges, thick surface oxide layer, satellite powder adhesion, localized agglomeration, and internal gas carrying capacity, making it difficult to directly meet the requirements of high-end forming processes for powder flowability and particle size distribution. If such coarse powder is used directly as product powder, it easily leads to uneven powder distribution, powder feeding fluctuations, unstable molten pool, and increased forming defects; if it is treated as a low-value raw material, it results in waste of metal resources and increased production costs.

[0004] For the reuse of coarse powder, existing processing routes mainly include direct remelting and ingot casting followed by reprocessing, coarse powder briquetting followed by remelting, screening followed by downgrading for reuse, and ordinary spheroidizing treatment. Direct remelting and ingot casting followed by reprocessing is a long process with high energy consumption and large metal loss, and requires re-billing or rod making, resulting in poor overall economic efficiency; although coarse powder briquetting followed by remelting shortens some processes, the random distribution of pores inside the briquettes makes them prone to collapse and melt after heating, making it difficult to form a stable and uniform liquid flow; screening followed by downgrading for reuse cannot solve the problem of high-value reuse; ordinary spheroidizing treatment usually only improves the particle shape and cannot simultaneously solve problems such as gas carrying capacity inside the coarse powder, discontinuous feeding, and low yield of target particle size.

[0005] In plasma atomization regeneration, using coarse powder directly as feed presents even more significant process challenges. Due to the large size, loose packing, and irregular morphology of coarse powder particles, direct feeding into the high-temperature zone often results in discontinuous feeding, local bridging, uneven heating, random enlargement of end-melt nodules, and significant fluctuations in droplet size. Simultaneously, residual gases inside and between coarse powder particles are rapidly released at high temperatures, easily forming bubbling and cracking at the molten ends, leading to an increased proportion of hollow powder, satellite powder, and abnormally coarse particles. While replacing loose coarse powder with ordinary high-density solid compacted material improves feeding continuity, the end-melting behavior easily changes from discrete particle melting to overall large-scale melting, forming large liquid nodules or unstable liquid columns, which is still not conducive to obtaining high-quality regenerated powder with concentrated particle size. Summary of the Invention

[0006] Technical problems to be solved

[0007] To address the shortcomings of existing technologies, this invention provides a method and system for the plasma atomization regeneration of titanium alloy coarse powder based on powder rolling, which solves the problems of existing technologies.

[0008] Technical solution

[0009] To achieve the above objectives, the present invention provides the following technical solution: 1. A method for regenerating titanium alloy coarse powder by plasma atomization based on powder rolling, comprising the following:

[0010] S1. The titanium alloy coarse powder to be recycled is screened, graded and purified. The titanium alloy coarse powder includes at least one of the following: recycled coarse powder, sieve residue coarse powder, ultra-large particle powder or irregular return powder. The purification process includes at least one of the following: dehumidification, degassing and impurity removal.

[0011] S2. In a vacuum environment or an inert atmosphere, titanium alloy powder with smaller particle size is laid as the outer layer of susceptible powder, mixed titanium alloy powder consisting of coarse and fine powder is laid as the middle transition powder layer, and coarse titanium alloy powder with larger particle size is laid as the inner layer of liquid release powder, so as to form a layered powder strip preform with at least three layers.

[0012] S3. The layered powder strip preform is fed into the powder rolling device for differential compaction rolling, so that the layered powder strip preform forms a gradient dense structure with the density gradually decreasing from the outside to the inside along the thickness direction, and a gradient compacted powder strip is obtained.

[0013] S4. The gradient compacted powder belt is textured to form axial microgrooves extending along the feeding direction on its surface, and the gradient compacted powder belt is rolled into a hollow feeding body to form a continuous axial degassing channel inside the hollow feeding body.

[0014] S5. The hollow feeder is subjected to low-temperature activation and shaping treatment to make the surface particles connect to maintain the conveying strength, while retaining the controlled interconnected pores inside the hollow feeder.

[0015] S6. The hollow feed body is continuously fed into the high-temperature action zone of the plasma atomization device, and inert gas is introduced simultaneously through the axial degassing channel, so that an annular molten liquid film is formed at the end of the hollow feed body. Under the combined action of plasma heat flow and atomization gas flow, the annular molten liquid film is broken into droplets and cooled and sphericalized to obtain recycled titanium alloy powder.

[0016] S7. Collect and sieve the recycled titanium alloy powder, and adjust at least two of the following parameters based on the annular stable state of the molten tip at the end of the hollow feeder: feeding speed of the hollow feeder, plasma power, inert gas internal blowing flow rate, and atomizing gas flow rate, in order to maintain the stable formation of the annular molten liquid film.

[0017] Preferably, in S2, the outer layer of stabilizing powder is composed of titanium alloy powder with a particle size of 15-80 μm, the middle transition powder layer is composed of titanium alloy powder with a particle size of 50-200 μm, and the inner layer of releasing powder is composed of titanium alloy coarse powder with a particle size of 80-400 μm.

[0018] Furthermore, the outer stabilizing powder layer, the intermediate transition powder layer, and the inner liquid-releasing powder layer are multi-layered structures arranged symmetrically about the middle surface of the powder belt.

[0019] Preferably, the differentiated compaction rolling in S3 is as follows: a unit compaction load higher than that in the middle region is applied to the outer region of the layered powder strip preform, so that the relative density of the outer layer of stable powder layer is greater than that of the middle transition powder layer, and the relative density of the middle transition powder layer is greater than that of the inner layer of liquid-releasing powder layer.

[0020] The relative density of the outer stabilizing powder layer is 88%–97%, the relative density of the intermediate transition powder layer is 75%–88%, and the relative density of the inner liquid-releasing powder layer is 55%–75%.

[0021] Preferably, the axial microgroove in S4 has a groove shape of any one of V-shaped groove, U-shaped groove or trapezoidal groove, a groove depth of 50 to 300 μm and a groove spacing of 0.5 to 3 mm;

[0022] The hollow feed body can be any of the following: tubular, open-ended rolled-edge tubular, or Ω-shaped hollow structure, and the equivalent pore size of the axial degassing channel is 0.5–3 mm.

[0023] Preferably, the low-temperature activation and shaping treatment in S5 is carried out in a vacuum environment or a high-purity inert atmosphere, and the treatment temperature is lower than the sintering and densification temperature of titanium alloy coarse powder, so that the surface of the hollow feed body forms a particle neck connection without completely sealing and densifying the inner liquid-releasing powder layer.

[0024] After low-temperature activation and shaping treatment, a continuous and stable molten shell layer is formed on the surface of the hollow feed body, while the interior retains a network of venting pores that are connected to the axial degassing channel.

[0025] Preferably, the inert gas introduced through the axial degassing channel in S6 is argon or an argon-helium mixture. The inert gas flows along the axial direction of the hollow feed body in an internal blowing manner to guide the residual gas inside the hollow feed body to be discharged preferentially along the axial degassing channel and to suppress the internal gas from laterally breaking through the end molten liquid film.

[0026] The plasma atomization device uses a single-gun, double-gun, or multi-gun plasma torch to form a circumferential thermal field at the end of the hollow feed body.

[0027] Preferably, the annular stable state in S7 is characterized by the tip annular stability index K, which is determined based on at least three of the following parameters: tip annular roundness, neck length fluctuation, droplet detachment frequency fluctuation, tip brightness distribution variance, and axial degassing channel internal blowing pressure fluctuation.

[0028] When the molten tip ring stability index K is lower than the set threshold, the control system will adjust at least two of the following parameters in conjunction: the feeding speed of the hollow feed body, the plasma power, the plasma torch angle, the internal blowing inert gas flow rate, and the atomizing gas pressure, in order to restore a stable annular molten liquid film.

[0029] Preferably, a plasma atomization regeneration system for titanium alloy coarse powder based on powder rolling includes:

[0030] The raw material grading and purification unit is used to screen, classify, dehydrate, degas, and remove impurities from the coarse titanium alloy powder to be recycled.

[0031] The layered powder laying unit is used to lay out the layered powder strip preform in the order of outer stabilizing powder layer, intermediate transition powder layer and inner liquid releasing powder layer;

[0032] The gradient rolling unit is used to perform differentiated compaction rolling on the layered powder strip preform to form a gradient compacted powder strip with density decreasing from the outside to the inside along the thickness direction;

[0033] Embossing unit, used to form axial microgrooves on the surface of gradient compacted powder belt;

[0034] The tape is rolled into a hollow unit, which is used to roll the gradient compacted powder tape into a hollow feed body with a continuous axial degassing channel inside;

[0035] The activation and shaping unit is used to perform low-temperature activation and shaping treatment on the hollow feed body;

[0036] The coaxial feeding internal blowing unit is used to introduce inert gas into the hollow feed body through the axial degassing channel while feeding the hollow feed body to the plasma atomizing device.

[0037] The plasma atomization unit is used to heat and melt the end of the hollow feed body to form an annular molten liquid film, and then break the annular molten liquid film into recycled titanium alloy powder.

[0038] The powder collection and sieving unit is used to collect and classify the particle size of recycled titanium alloy powder.

[0039] The closed-loop control unit is used to adjust the feeding speed, plasma power, internal inert gas flow rate, and atomizing gas flow parameters according to the annular stable state of the melting tip at the end of the hollow feed body.

[0040] Preferably, the gradient rolling unit includes a roll group for achieving differentiated compaction, wherein the roll surface pressure distribution, roll gap profile, or roll surface texture of the roll group is configured to make the outer layer of the layered powder strip preform more compacted than the inner layer.

[0041] The hollow unit formed by the tape roll includes an edge-rolling module and a seam fixing module. The seam fixing module is used to maintain the continuous conveying strength of the hollow feed body and retain the internal interconnecting pores by means of mechanical edge-pinning, local hot-pressing consolidation or local sintering consolidation.

[0042] Preferably, the closed-loop control unit is connected to a melt tip visual monitoring component, a brightness monitoring component, an internal blowing pressure monitoring component, and a powder particle size detection component. The closed-loop control unit is configured to generate a melt tip ring stability index K based on the melt tip annular roundness, melt droplet shedding frequency, melt tip brightness field change, and internal blowing pressure fluctuation, and to perform coordinated control of the coaxial feeding internal blowing unit and the plasma atomization unit according to the melt tip ring stability index K, so as to maintain the annular molten liquid film atomization state at the end of the hollow feed body.

[0043] Beneficial effects

[0044] This invention provides a method and system for the plasma atomization regeneration of titanium alloy coarse powder based on powder rolling. It has the following beneficial effects:

[0045] 1. This invention constructs titanium alloy coarse powder into an outer stable melting powder layer, an intermediate transition powder layer, and an inner liquid-releasing powder layer, and forms a gradient dense structure with gradually decreasing density from the outside to the inside through differentiated compaction and rolling. This allows the feed body to form a controlled melting sequence after entering the plasma high-temperature zone, with the outer layer melting preferentially, the intermediate layer buffering and conducting heat, and the inner layer gradually releasing liquid. This avoids the problem of large liquid nodules forming by the overall collapse of ordinary solid compacted bodies, thereby improving the stability of the melt tip and the yield of the target particle size.

[0046] 2. This invention forms axial microgrooves on the surface of a gradient compacted powder belt and rolls it into a hollow feeder with a continuous axial degassing channel. This allows the molten metal on the surface to be redistributed circumferentially at the ends to form an annular molten liquid film. At the same time, it allows residual gas inside to be preferentially discharged axially, reducing bubbling, splashing, and cracking caused by gas breaking through the liquid film laterally. Therefore, it can significantly reduce the proportion of hollow powder and satellite powder, and improve the sphericity and flowability of the powder.

[0047] 3. This invention implements internal blowing inert gas guidance during plasma atomization and performs closed-loop adjustment of feeding speed, plasma power, internal blowing flow rate and atomizing gas parameters based on the stable annular state of the molten tip. This allows the feeding end to maintain a stable annular molten liquid film atomization state for a long time, reducing the fluctuation of liquid film thickness and droplet shedding frequency, improving the stability of continuous process operation, and is suitable for continuous and high-value recycling of titanium alloy coarse powder. Attached Figure Description

[0048] Figure 1 This is a process flow diagram of the present invention;

[0049] Figure 2 This is a system composition diagram of the present invention. Detailed Implementation

[0050] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Specific Implementation Example 1:

[0052] like Figures 1 to 2 As shown,

[0053] A method for regenerating coarse titanium alloy powder based on powder rolling by plasma atomization includes the following:

[0054] S1. The titanium alloy coarse powder to be recycled is screened, graded and purified, wherein the titanium alloy coarse powder includes at least one of the following: recycled coarse powder, sieve residue coarse powder, ultra-large particle size powder or irregular return powder; wherein the purification treatment includes at least one of dehumidification, degassing and impurity removal.

[0055] S2. In a vacuum environment or an inert atmosphere, titanium alloy powder with smaller particle size is laid as the outer layer of susceptible powder, mixed titanium alloy powder consisting of coarse and fine powder is laid as the middle transition powder layer, and coarse titanium alloy powder with larger particle size is laid as the inner layer of liquid release powder, so as to form a layered powder strip preform with at least three layers.

[0056] S3. The layered powder strip preform is fed into a powder rolling device for differential compaction rolling, so that the layered powder strip preform forms a gradient dense structure with the density gradually decreasing from the outside to the inside along the thickness direction, and a gradient compacted powder strip is obtained.

[0057] S4. The gradient compacted powder belt is textured to form axial microgrooves extending along the feeding direction on its surface, and the gradient compacted powder belt is rolled into a hollow feeding body to form a continuous axial degassing channel inside the hollow feeding body.

[0058] S5. The hollow feed body is subjected to low-temperature activation and shaping treatment to make the surface particles connect to maintain the conveying strength, while retaining the controlled interconnected pores inside the hollow feed body.

[0059] S6. The hollow feed body is continuously fed into the high-temperature action zone of the plasma atomizing device, and inert gas is introduced simultaneously through the axial degassing channel, so that an annular molten liquid film is formed at the end of the hollow feed body. The annular molten liquid film is broken into droplets and cooled and spherical under the combined action of plasma heat flow and atomizing gas flow to obtain recycled titanium alloy powder.

[0060] S7. Collect and sieve the recycled titanium alloy powder, and adjust at least two of the following parameters based on the annular stable state of the molten tip at the end of the hollow feeder: feeding speed of the hollow feeder, plasma power, inert gas internal blowing flow rate, and atomizing gas flow rate, in order to maintain the stable formation of the annular molten liquid film.

[0061] Steps S1 to S7 constitute a complete structural reconstruction coarse powder regeneration process chain, with clear material state inheritance relationships and process boundary constraints between each step. S1 outputs clean, graded powder that meets the requirements for layered use; S2 outputs a layered powder belt preform with functions of outer layer stabilization, middle layer controlled melting, and inner layer liquid release; S3 outputs a continuously compacted powder belt with a density gradient in the thickness direction; S4 outputs a hollow feeder with both surface flow guiding and internal gas guiding capabilities; S5 outputs a functionalized hollow feeder with a stable surface, internal connectivity, and continuous feeding capability; S6 outputs regenerated spherical titanium alloy powder formed after the annular molten liquid film is broken and cooled; and S7 maintains the stable liquid film atomization window required by S6 through melt tip state feedback.

[0062] In S1, the raw material is selected from any one of the following titanium alloy coarse powders: TC4, TA15, TC11, Ti-6Al-2Sn-4Zr-2Mo, and industrial pure titanium. The raw material particle size range is set to 53–400 μm, the main working particle size range is set to 80–300 μm, the raw material moisture content is controlled below 0.015 wt%, the oxygen content is controlled below 0.25 wt%, the hydrogen content is controlled below 0.012 wt%, the magnetic foreign matter content is controlled below 20 ppm, and the non-metallic inclusion particle size is controlled below 30 μm. After purification, the adsorbed water on the powder surface and the residual gas in the pores are removed, and the gas disturbance sources in the subsequent winding and atomization stages are significantly reduced.

[0063] In S2, the total thickness of the layered powder strip is set to 1.2–2.4 mm, the thickness of the outer stabilizing powder layer on one side is set to 0.12–0.28 mm, the thickness of the intermediate transition powder layer on one side is set to 0.18–0.42 mm, and the thickness of the inner liquid-releasing powder layer at its center is set to 0.35–0.90 mm. The oxygen content in the powder spreading environment is controlled below 100 ppm, the working value is controlled below 30 ppm, and the relative humidity is controlled below 3%. After layering, the strip forms a continuous particle size gradient and pore size gradient in the thickness direction, which is a prerequisite for obtaining a dense outer and loose inner structure after subsequent compaction.

[0064] In S3, the rolling reduction rate is set to 25%–50%, the total number of rolling passes is set to 2–4, the rolling line speed is set to 0.3–2.0 m / min, and the unit compaction load is set to 40–150 MPa. After rolling, a highly dense and stable melt shell layer is formed on the outer layer of the strip, a heat flow and liquid seepage transition zone is formed in the middle layer, and the gas release and liquid release pore network is retained in the inner layer.

[0065] In S4, the axial microgrooves and hollow structure together determine the melting method at the end of the feed body. The axial microgrooves are responsible for redistributing the initial molten liquid along the axial and circumferential directions, suppressing local liquid accumulation; the axial degassing channel is responsible for guiding gas in the center, suppressing bubbling below the liquid film. After rolling, the outer diameter of the feed body is set to 2.5–5.0 mm, the wall thickness is set to 0.45–1.10 mm, and the equivalent aperture of the central channel is set to 0.8–1.8 mm.

[0066] The S5 low-temperature activation and setting temperature is set to 560–680℃, the holding time is set to 25–50 min, and the vacuum degree is set to the level of 10^-3 Pa or the purity of the inert gas is set to 99.999%. After processing, a continuous particle neck connecting layer is formed on the surface of the feed body, the joint is stable, no powder is shed or the edges crack during feeding, and the internal pore network remains connected with the axial degassing channel.

[0067] In S6, the plasma power is set to 55–95 kW, the atomizing gas pressure to 0.8–1.4 MPa, the internal inert gas flow rate to 2.0–4.5 L / min, the feeding speed to 0.45–0.95 m / min, and the oxygen content in the atomizing chamber to be controlled below 30 ppm. After the feed body enters the hot zone, the outer stable molten shell layer preferentially forms a continuous liquid film, the middle layer restricts the advance of the thermal front, the inner coarse powder skeleton gradually collapses and melts and replenishes the liquid film, the central channel discharges the internal residual gas and establishes an internally blown stable flow field, and an annular molten liquid film with an average thickness of 80–220 μm is formed at the end.

[0068] After powder collection in S7, the particles are sieved into three product ranges: 15–53 μm, 45–105 μm, and 53–150 μm. The sphericity acceptance index is set at no less than 0.95, the proportion of satellite powder is controlled below 5%, the proportion of hollow powder is controlled below 2%, and the powder oxygen increment is controlled below 0.015 wt%. The target particle size yield is 12%–28% higher than that of the solid compaction process without hollow channels. If the stable state of the molten tip ring deviates from the set threshold, the control system will synchronously adjust at least two of the following: feeding speed, plasma power, internal blowing flow rate, and atomizing gas pressure, so that the fluctuation range of liquid film thickness is controlled within ±15% of the average liquid film thickness, and the fluctuation coefficient of droplet detachment frequency is controlled within 8%.

[0069] The outer stabilizing powder layer in S2 is composed of titanium alloy powder with a particle size of 15-80 μm, the intermediate transition powder layer is composed of titanium alloy powder with a particle size of 50-200 μm, and the inner liquid-releasing powder layer is composed of titanium alloy coarse powder with a particle size of 80-400 μm.

[0070] Furthermore, the outer stabilizing powder layer, the intermediate transition powder layer, and the inner liquid-releasing powder layer are multi-layer structures arranged symmetrically about the middle surface of the powder belt.

[0071] The outer stabilizing powder layer uses 15–80 μm titanium alloy powder, with a main working range of 15–53 μm. This particle size range exhibits high powder spreading uniformity, high surface continuity after compaction, and dense and uniformly distributed melting initiation points, resulting in a short critical time for forming a continuous liquid film. The intermediate transition powder layer uses 50–200 μm mixed powder, with a main working range of 53–150 μm. Fine powder fills the gaps between coarse powder, while coarse powder provides skeletal support, enabling this layer to function as both a heat conduction buffer and a liquid replenishment / throttling layer. The inner liquid-releasing powder layer uses 80–400 μm coarse powder, with a main working range of 150–300 μm. This layer maintains skeletal collapse and gradual liquid replenishment characteristics after heating, without forming an overall instantaneous liquid core.

[0072] The three-layer structure is symmetrically arranged about the top and bottom of the powder strip, with the specific layer sequence set as follows: outer layer stabilizing powder layer / intermediate transition powder layer / inner layer releasing powder layer / inner layer releasing powder layer / intermediate transition powder layer / outer layer stabilizing powder layer. This symmetrical layer sequence ensures that the rolling strain, coiling springback, and melting front are consistent in the vertical direction. After coiling, the circumferential wall thickness deviation of the hollow feed body is controlled within ±8%, the eccentricity of the central air guide channel is controlled within 5%, and the circumferential brightness difference of the end liquid ring is controlled within 12%.

[0073] The thickness proportions of each layer are fixed as follows: the outer layer of stabilizing powder accounts for 18% to 26% of the total, the middle transition powder layer accounts for 24% to 34% of the total, and the inner layer of releasing powder accounts for 40% to 56% of the total. Under this thickness proportion, the feed body has three functional zones: a continuous outer shell, a controllable transition zone, and an effective central skeleton, thus achieving a balance between the heat input, liquid replenishment rate, and gas conduction capacity required to form a stable liquid film.

[0074] The differentiated compaction rolling described in S3 is as follows: a unit compaction load higher than that in the middle region is applied to the outer region of the layered powder strip preform, so that the relative density of the outer layer of stable powder is greater than that of the middle transition powder layer, and the relative density of the middle transition powder layer is greater than that of the inner layer of liquid-releasing powder layer.

[0075] The relative density of the outer stabilizing powder layer is 88%–97%, the relative density of the intermediate transition powder layer is 75%–88%, and the relative density of the inner liquid-releasing powder layer is 55%–75%.

[0076] After differentiated compaction rolling, the relative density of the outer stable melt powder layer is set at 91%–95%, the relative density of the intermediate transition powder layer is set at 79%–85%, and the relative density of the inner liquid-releasing powder layer is set at 60%–70%. This density combination directly determines the melting sequence and liquid supply method of the feed material in the hot zone. When the outer layer density reaches 91%–95%, a continuous stable melt shell is formed on the surface, the surface powder loss rate during the feeding process is controlled below 0.3%, and the initial melting time at the end is controlled at 0.12–0.35 s; when the intermediate layer density reaches 79%–85%, the interlayer bonding is stable and the liquid replenishment rate is controlled, and the hot front advance speed is controlled at 55%–78% of the initial melting advance speed of the outer layer; when the inner layer density reaches 60%–70%, the central skeleton maintains air-conducting connectivity and gradual liquid release characteristics, and the internal blowing pressure is controlled within a stable range of 0.02–0.06 MPa.

[0077] The rolling process is set to three passes, with the first pass pre-compacting reduction rate set at 8%–15%, the second pass main compaction reduction rate set at 12%–25%, and the third pass shaping reduction rate set at 5%–12%. The roll inlet tension is set at 3–12 N, the outlet tension at 5–18 N, and the roll surface roughness Ra is controlled at 0.6–2.0 μm. The unit compaction load of the outer layer is 18%–35% higher than that of the middle layer, thereby forming a stable density gradient.

[0078] The feed prepared according to this density gradient exhibits the following characteristics during the atomization stage: the liquid film thickness fluctuation is less than 70% of that using a uniform high-density solid strip process, the standard deviation of the de-drip frequency is reduced by 22% to 38%, and the yield of the target particle size is increased by 12% to 24%.

[0079] The axial microgroove described in S4 has a groove shape of any one of V-shaped groove, U-shaped groove or trapezoidal groove, a groove depth of 50 to 300 μm and a groove spacing of 0.5 to 3 mm;

[0080] The hollow feed body is any one of tubular, open-ended rolled-edge tubular, or Ω-shaped hollow structure, and the equivalent pore size of the axial degassing channel is 0.5 to 3 mm.

[0081] The axial microgroove adopts a trapezoidal groove structure, with a groove depth of 100–180 μm, a groove spacing of 0.9–1.6 mm, a groove top width of 120–260 μm, and a groove bottom width of 40–120 μm. Under these microgroove geometric parameters, the outer layer of liquid at the end of the feed body migrates synchronously along the groove direction and between the grooves during the initial melting stage, the circumferential liquid redistribution time is controlled within 8–20 ms, and the probability of local liquid nodule formation is significantly reduced.

[0082] The hollow feed body adopts a tubular structure with an outer diameter of 3.0–4.2 mm, a wall thickness of 0.55–0.95 mm, and an equivalent aperture of 1.1–1.6 mm for the axial degassing channel. Within these dimensions, the feed body possesses sufficient axial stiffness and circumferential liquid storage capacity, while the central air guiding channel exhibits low flow resistance. The average axial flow velocity of the internally blown gas is controlled within 0.8–4.0 m / s, and the pressure fluctuation amplitude is controlled within ±6%.

[0083] With this combination of microgroove and hollow dimensions, the circumferential thickness difference of the annular liquid film formed at the end of the feed body is controlled within ±12% of the average liquid film thickness, the droplet drop direction deviation angle is controlled within ±7°, and the hollow powder ratio is controlled below 2%.

[0084] The low-temperature activation and shaping treatment described in S5 is carried out in a vacuum environment or a high-purity inert atmosphere. The treatment temperature is lower than the sintering and densification temperature of the titanium alloy coarse powder, so that the surface of the hollow feed body forms a particle neck connection without completely sealing and densifying the inner liquid-releasing powder layer.

[0085] After the low-temperature activation and shaping treatment, a continuous and stable shell layer is formed on the surface of the hollow feed body, while the interior retains a network of venting pores that communicate with the axial degassing channel.

[0086] The low-temperature activation and shaping treatment employs a vacuum heat treatment method. The treatment temperature is set at 620℃, the holding time at 40 min, the vacuum degree at 8×10^-4 Pa, the heating rate at 8℃ / min, and the cooling method is furnace cooling to 300℃ followed by inert gas cooling. Under these conditions, a continuous particle neck connecting layer is formed in the fine powder zone on the surface of the feed body. The effective connecting thickness of the surface layer is controlled between 80 and 220 μm, the continuity of the joint area meets the feeding requirements, and the three-point bending load reaches 1.8 to 2.4 times that of the untreated state.

[0087] Under these heat treatment conditions, the inner liquid-releasing powder layer maintains a connected pore network, with the central connected porosity controlled at 18%–34%, the intermediate transition layer's connected porosity controlled at 9%–18%, and the outer molten shell layer's open porosity controlled below 3%. After treatment, the surface powder shedding rate during the feeding process is controlled below 0.2%, and the pressure drop in the axial air guide channel is maintained within ±8% of the set value.

[0088] This structural state directly corresponds to the thermal response sequence in S6: the surface layer first forms a continuous liquid film, the middle layer restricts the advance of the thermal front, the inner layer maintains the functions of gas release and liquid replenishment, and the entire cross-section does not collapse at the feeding end.

[0089] The inert gas introduced through the axial degassing channel in S6 is argon or an argon-helium mixture. The inert gas flows along the axial direction of the hollow feed body in an internal blowing manner to guide the residual gas inside the hollow feed body to be discharged preferentially along the axial degassing channel and to suppress the internal gas from laterally breaking through the end molten liquid film.

[0090] The plasma atomizing device uses a single-gun, double-gun, or multi-gun plasma torch to form a circumferential thermal field at the end of the hollow feed body.

[0091] The internally blown inert gas is high-purity argon with a purity of 99.999%, a flow rate of 3.2 L / min, an inlet pressure of 0.038 MPa, and a supply temperature of room temperature. After the internally blown gas flows along the axial degassing channel, a central exhaust flow field is formed at the end of the feed body. The residual gas inside is preferentially discharged along the central channel, and the gas residence time below the liquid film is controlled to be less than 15 ms.

[0092] The plasma atomizing device employs a dual-gun plasma torch arrangement with the torch shaft angle set to 36°–52°, the operating power set to 72–88 kW, argon as the working gas, an atomizing gas pressure set to 1.05 MPa, and a nozzle-to-feed body distance set to 9–18 mm. Under this thermal field arrangement, the circumferential heat input difference of the feed body is controlled within 10%, and the circumferential brightness difference of the melt tip is controlled within 12%.

[0093] Under these internal blowing and thermal field parameters, the average thickness of the annular molten liquid film was set to 110–190 μm, the film closure degree reached above 0.90, the droplet shedding frequency was stable within the range of 420–900 Hz, and the frequency fluctuation coefficient was controlled within 8%. Compared with the solid feed process without internal blowing, the number of bubbling cycles was reduced by 40%–65%, the proportion of hollow powder was reduced by 35%–55%, and the yield of the target particle size was increased by 15%–28%.

[0094] The annular stable state described in S7 is characterized by the tip annular stability index K, which is determined based on at least three of the following parameters: tip annular roundness, neck length fluctuation, droplet detachment frequency fluctuation, tip brightness distribution variance, and axial degassing channel internal blowing pressure fluctuation.

[0095] When the molten tip ring stability index K is lower than the set threshold, the control system adjusts at least two of the following parameters in conjunction: the feeding speed of the hollow feeder, the plasma power, the plasma torch angle, the internal blowing inert gas flow rate, and the atomizing gas pressure, in order to restore a stable annular molten liquid film.

[0096] The tip ring stability index K is defined by the following formula:

[0097] K=0.30C+0.20(1-Ln)+0.20(1-Fn)+0.15(1-Bn)+0.15(1-Pn),

[0098] Where C is the roundness of the melt tip ring, Ln is the relative fluctuation coefficient of the liquid neck length, Fn is the relative fluctuation coefficient of the droplet detachment frequency, Bn is the normalized value of the variance of the melt tip brightness field, and Pn is the normalized value of the internal blowing pressure fluctuation. The stability threshold of K is set to 0.78, the warning threshold is set to 0.70, and the instability threshold is set to 0.60.

[0099] When 0.70≤K<0.78, Level 1 adjustment is executed: the feed speed correction range is within ±0.08m / min, the plasma power correction range is within ±5kW, and the internal blowing flow rate correction range is within ±0.5L / min; when 0.60≤K<0.70, Level 2 adjustment is executed: the feed speed correction range is within ±0.15m / min, the plasma power correction range is within ±10kW, the atomizing gas pressure correction range is within ±0.15MPa, and the gun position angle correction range is within ±3°; when K<0.60 persists for more than 2 seconds, the system performs protective speed reduction and alarm.

[0100] Under stable operating conditions, C is controlled above 0.92, Ln below 0.12, Fn below 0.08, Bn below 0.10, and Pn below 0.10. Following this control strategy, the median particle size D50 fluctuation is controlled within ±6%, and the yield fluctuation of the 15–53 μm target particle size is controlled within ±4%.

[0101] A plasma atomization regeneration system for titanium alloy coarse powder based on powder rolling includes:

[0102] The raw material grading and purification unit is used to screen, classify, dehydrate, degas, and remove impurities from the coarse titanium alloy powder to be recycled.

[0103] The layered powder laying unit is used to lay out the layered powder strip preform in the order of outer stabilizing powder layer, intermediate transition powder layer and inner liquid releasing powder layer;

[0104] A gradient rolling unit is used to perform differentiated compaction rolling on the layered powder strip preform to form a gradient compacted powder strip with density decreasing from the outside to the inside along the thickness direction.

[0105] An embossing unit is used to form axial microgrooves on the surface of the gradient compacted powder belt;

[0106] The tape is wound into a hollow unit, which is used to roll the gradient compacted powder tape into a hollow feed body with a continuous axial degassing channel inside;

[0107] An activation and shaping unit is used to perform low-temperature activation and shaping treatment on the hollow feed body;

[0108] The coaxial feeding internal blowing unit is used to introduce inert gas into the hollow feed body through the axial degassing channel while feeding the hollow feed body to the plasma atomizing device.

[0109] The plasma atomization unit is used to heat and melt the end of the hollow feed body to form an annular molten liquid film, and then break and spheroidize the annular molten liquid film into recycled titanium alloy powder.

[0110] The powder collection and sieving unit is used to collect and classify the particle size of recycled titanium alloy powder.

[0111] The closed-loop control unit is used to adjust the feeding speed, plasma power, internal inert gas flow rate, and atomizing gas flow parameters according to the annular stable state of the melting tip at the end of the hollow feed body.

[0112] The raw material grading and purification unit consists of a sealed raw material silo, a double-layer vibrating screen, an air classifier, a magnetic separator, a vacuum degassing chamber, and an inert atmosphere drying chamber. The raw material output particle sizes correspond to the outer layer powder, middle layer powder, and inner layer powder, respectively. The layered powder spreading unit consists of a three-compartment metering feeder, a bidirectional powder spreading head, a carrier belt conveyor mechanism, a layer thickness monitor, and a sealed inert atmosphere hood, with a layer thickness control accuracy of ±0.03mm. The gradient rolling unit consists of a pre-pressure roller group, a main pressure roller group, a tension control module, a guide width limiting module, and an online thickness monitoring module, with a finished strip thickness control accuracy of ±0.04mm. The embossing unit consists of a micro-textured embossing roller, a servo embossing pressure mechanism, and a contour detection module, with a groove depth control accuracy of ±15μm. The coiling and hollow forming unit consists of a three-stage edge-rolling die, a sizing die, a central mandrel, a seam alignment mechanism, and a seam fixing mechanism, with the outer diameter deviation of the feed material after coiling controlled within ±0.05mm. The activation and shaping unit consists of a vacuum heat treatment furnace, a temperature control module, a heat preservation module, and a slow cooling module, with a furnace temperature control accuracy of ±3℃. The coaxial feeding and internal blowing unit consists of a servo feeding roller, a coaxial air supply connector, a sealing guide sleeve, a mass flow controller, and a pressure monitor. The plasma atomization unit consists of a dual-gun plasma torch, a gun position adjustment mechanism, atomizing nozzles, a cavity, an observation window, and an atmosphere control module. The powder collection and sieving unit consists of a cooling settling tower, a cyclone separator, a powder collection tank, a multi-stage sieve, and a tail powder return channel. The closed-loop control unit consists of an industrial controller, an image acquisition module, a pressure acquisition module, a brightness acquisition module, an actuator control module, and a data storage module.

[0113] The entire production line operates in the following sequence: "raw material processing - layering and belt construction - gradient compaction - surface embossing - belt winding into hollow - low temperature activation - coaxial feeding and internal blowing - annular liquid film atomization - powder collection and sieving - status feedback". Each unit is connected by a closed transition, and the oxygen content of the entire line is controlled below 30 ppm.

[0114] The gradient rolling unit includes a roll group for achieving differentiated compaction, wherein the roll surface pressure distribution, roll gap profile, or roll surface texture of the roll group is configured to make the outer layer of the layered powder strip preform more compacted than the inner layer.

[0115] The hollow unit formed by the tape roll includes an edge-rolling module and a seam fixing module. The seam fixing module is used to maintain the continuous conveying strength of the hollow feed body and retain the internal interconnecting pores by means of mechanical edge-pinching, local hot-pressing consolidation or local sintering consolidation.

[0116] The roll assembly adopts a combination structure of zoned loading rolls and crown-shaped roll gaps. The contact stress in the outer region is 25%–32% higher than that in the middle region. The roll gap curvature radius is set according to the thickness of the finished strip and the interlayer compression ratio. The roll surface roughness Ra is controlled between 0.8 and 1.5 μm. This roll structure ensures that three states—stable compaction in the outer layer, transitional compaction in the middle layer, and porosity-preserving compaction in the inner layer—are formed simultaneously.

[0117] The edge-rolling module adopts a three-stage progressive edge-rolling structure. The first-stage edge-rolling angle is set to 25°–40°, the second-stage edge-rolling angle is set to 55°–75°, and the third-stage edge-rolling angle is set to 85°–110°. Finally, the sizing die stabilizes the cross-section of the feed body to the target outer diameter. The joint fixing module adopts a local hot-pressing consolidation method. The width of the hot-pressing zone is set to 0.25–0.50 mm, the hot-pressing temperature is set to 420–560℃, and the hot-pressing time is set to 0.5–2.0 s. This joint fixing zone ensures axial conveying strength while not blocking the internal air guide path. The circumferential proportion of the joint zone is controlled below 8%, preventing the feed body from opening or collapsing during continuous feeding.

[0118] The closed-loop control unit is connected to a melt tip visual monitoring component, a brightness monitoring component, an internal blowing pressure monitoring component, and a powder particle size detection component. The closed-loop control unit is configured to generate a melt tip ring stability index K based on the melt tip annular roundness, melt droplet shedding frequency, melt tip brightness field change, and internal blowing pressure fluctuation. Based on the melt tip ring stability index K, the coaxial feeding internal blowing unit and the plasma atomization unit are coordinated to maintain the annular molten liquid film atomization state at the end of the hollow feed body.

[0119] The fused tip visual monitoring component uses a high-speed camera with a sampling frequency set to 2000fps and an image resolution set to no less than 1024×1024; the brightness monitoring component has a sampling frequency set to 500Hz; the internal blowing pressure monitoring component has a sampling frequency set to 1000Hz; the particle size detection module outputs D10, D50, D90, and the target particle size ratio for each batch or continuous sampling cycle. The closed-loop control unit performs K-value calculation and control decision every 100ms and trend analysis every 500ms.

[0120] The control outputs include: feed speed adjustment resolution of 0.01 m / min, plasma power adjustment resolution of 1 kW, internal blowing flow rate adjustment resolution of 0.1 L / min, atomizing gas pressure adjustment resolution of 0.02 MPa, and gun position angle adjustment resolution of 0.5°. During steady-state operation, K is controlled above 0.78, the visually detected liquid ring eccentricity is controlled within 6%, the circumferential variance of the brightness field is controlled below 0.10, and the pressure pulsation is controlled below 0.10.

[0121] After the closed-loop control is executed, the end of the feed body maintains a continuous atomized state of annular molten liquid film, the particle size distribution concentration is improved, the target particle size yield is stable, the process fluctuation is reduced, and the continuous running time reaches more than 4 hours without continuous instability of the melt tip. Specific Implementation Example 2:

[0123] Preparation of 15-53μm Spherical Powder for Additive Manufacturing Based on TC4 Coarse Powder Regeneration using Gradient Compacted Hollow Feed Body: This case study uses TC4 titanium alloy coarse powder as the recycled raw material, with the target product being 15-53μm spherical powder for additive manufacturing. The focus is on verifying the effect of the complete structural chain of "layered powder belt preform + gradient compaction + axial microgroove + hollow feed body + internal blowing guide + annular molten liquid film steady-state atomization" on improving fine powder yield, liquid film stability, and spherical powder quality.

[0124] Raw material conditions and pretreatment parameters: The raw material used was the same batch of TC4 coarse powder recovery material, which was a mixture of residue from previous plasma atomization sieving and additive manufacturing recovered ultra-large particle size material. After mixing, the particle size distribution of the raw material was 53-300μm, of which 81.4% was in the 80-250μm range. The original oxygen content was 0.182wt%, hydrogen content was 0.0081wt%, nitrogen content was 0.021wt%, moisture content was 0.011wt%, loose density was 2.14g / cm³, and irregular particles and slightly agglomerated particles accounted for 17.6%. After being processed by a double-layer vibrating screen and air classifier, the raw material was divided into three parts: 15-53μm fine powder, 53-150μm transition powder, and 150-300μm coarse powder. After vacuum degassing and inert atmosphere drying, the moisture content of the powder was reduced to 0.003 wt%, the oxygen content was stabilized at 0.186 wt%, the hydrogen content was reduced to 0.0053 wt%, the magnetic foreign matter content was controlled at 12 ppm, and the median size of non-metallic inclusions was controlled within 18 μm. This treatment ensures stable powder surface conditions during subsequent powder spreading, rolling, and winding processes, and significantly reduces bubbling sources in the high-temperature zone.

[0125] In this case, the layered powder strip preform adopts a six-layer structure symmetrical about the center plane, consisting of, from top to bottom, an outer stabilizing powder layer, an intermediate transition powder layer, an inner liquid-releasing powder layer, an inner liquid-releasing powder layer, an intermediate transition powder layer, and an outer stabilizing powder layer. The total thickness is set to 1.80 mm. The specific thickness of each layer is set as follows: 0.18 mm for each of the upper and lower outer stabilizing powder layers, 0.28 mm for each of the upper and lower intermediate transition powder layers, and a total thickness of 0.88 mm for the two intermediate liquid-releasing powder layers. The outer stabilizing powder layer uses 15–53 μm TC4 fine powder, the intermediate transition powder layer is formed by mixing 53–150 μm powder with 15–53 μm fine powder at a mass ratio of 7:3, and the inner liquid-releasing powder layer uses 150–300 μm coarse powder. The layering process is completed in a high-purity argon environment, with the oxygen content maintained at 22 ppm, the relative humidity maintained below 2%, and the layer thickness deviation controlled within ±0.02 mm. This layered structure ensures that the feed body forms a clear particle size gradient, packing gradient and subsequent compaction response gradient in the thickness direction, so that the outer layer has continuous melting stability, the middle layer has heat flow buffering and liquid replenishment and flow restriction capabilities, and the inner layer has skeleton collapse melting and gas-conducting and liquid-releasing capabilities.

[0126] Gradient compaction, microgroove forming, and hollow rolling parameters: The layered powder strip preform undergoes three passes of differentiated compaction rolling. The first pre-compaction reduction is 11%, the second main compaction reduction is 21%, and the third shaping reduction is 7%, for a total rolling reduction of 35.6%. The rolling speed is 0.85 m / min, the inlet tension is 6 N, the outlet tension is 11 N, and the roll surface roughness Ra is 1.1 μm. After rolling, the relative density of the outer stable powder layer reaches 93.2%, the relative density of the intermediate transition powder layer reaches 82.1%, and the relative density of the inner liquid-releasing powder layer reaches 66.4%.

[0127] Subsequently, trapezoidal axial microgrooves are machined on the surface of the strip, with a groove depth of 120 μm, a groove spacing of 1.20 mm, a groove top width of 210 μm, and a groove bottom width of 85 μm. The microgrooves are continuously distributed along the feeding direction, covering 83% of the effective feeding section of the feed body.

[0128] The embossed gradient compacted powder tape is rolled into a hollow tubular feed body using a three-stage edge-rolling die. The outer diameter of the rolled body is 3.60 mm, the wall thickness is 0.80 mm, and the equivalent aperture of the central axial degassing channel is 1.40 mm. The joints are fixed by local hot-pressing, with a hot-pressing zone width of 0.38 mm, a hot-pressing temperature of 505℃, and an action time of 1.1 s. After rolling, the axial straightness deviation of the feed body is controlled within 0.6 mm / m, the joint continuity is good, and the axial air pressure drop is 0.0048 MPa.

[0129] The rolled hollow feed body is placed in a vacuum heat treatment furnace for low-temperature activation and shaping. The vacuum level is maintained at 8×10^-4 Pa, the heating rate is 8℃ / min, the holding temperature is 620℃, and the holding time is 40min. After furnace cooling to 300℃, high-purity argon gas is switched for further cooling. After treatment, a continuous particle neck connecting layer is formed on the surface of the feed body, with an effective connecting thickness of approximately 160μm. The powder shedding rate on the outer surface is reduced to 0.14%, and the three-point bending limit load is increased to 2.13 times that of the untreated feed body. The central skeleton pore network remains connected, with an inner layer connected porosity of 26.8%, a middle layer connected porosity of 13.6%, and an outer layer open porosity of less than 2.2%. This condition ensures sufficient mechanical integrity of the feed body during feeding, while still maintaining central gas conduction and gradual liquid release capabilities.

[0130] The plasma atomization system employs a dual-gun plasma torch arrangement with an included angle of 44°. The total plasma power is 78kW, the working gas is high-purity argon, the atomizing gas pressure is 1.02MPa, and the distance from the nozzle to the end of the feed body is 13mm. The feeding speed of the hollow feed body is set to 0.75m / min, the internal argon flow rate is 3.2L / min, the internal inlet pressure is 0.038MPa, and the oxygen content in the atomization chamber is maintained at 27ppm. High-speed visual monitoring showed that a continuous annular molten liquid film was formed at the end of the feed body 0.42s after entering a stable working condition. The average thickness of the liquid film was 142μm, the circumferential thickness fluctuation range was ±11.8%, the liquid film closure degree was 0.93, the droplet shedding frequency was stable at 684Hz, the frequency fluctuation coefficient was 6.2%, the circumferential variance of the brightness field was 0.084, the normalized value of the internal blowing pressure fluctuation was 0.072, and the molten tip ring stability index K was stable in the range of 0.84 to 0.88.

[0131] This case study sets up four sets of experiments to verify the contribution of each key feature in the complete technical solution to the results. Group A is the complete solution group, which adopts a gradient layered hollow feed body, axial microgrooves, and internal air blowing; Group B omits the axial microgrooves, while keeping the other parameters the same as Group A; Group C is changed to a solid compacted body, eliminating the hollow channel and internal air blowing, while keeping the remaining layered structure and compaction density consistent; Group D is changed to a uniform high-density solid compacted body, with the relative density uniformly controlled between 93% and 95%, eliminating the layered structure, microgrooves, and hollow channels, while keeping the remaining atomization power and feeding speed as consistent as possible. Each group runs continuously for 45 minutes, recording the number of bubbling at the melt tip, liquid film closure, droplet detachment frequency fluctuation coefficient, 15–53 μm yield, 45–105 μm yield, sphericity, satellite powder ratio, hollow powder ratio, and oxygen increment.

[0132] Within 45 minutes of running the complete scheme in Group A, the number of bubbling at the melt tip was 6, the average liquid film closure was 0.93, the droplet detachment frequency fluctuation coefficient was 6.2%, the yield of 15-53μm particles was 41.8%, the yield of 45-105μm particles was 68.4%, the sphericity was 0.967, the proportion of satellite powder was 3.8%, the proportion of hollow powder was 1.5%, and the oxygen increment was 0.012wt%.

[0133] After removing the axial microgrooves in Group B, the number of bubbling at the melt tip increased to 11 times, the liquid film closure decreased to 0.88, the droplet detachment frequency fluctuation coefficient increased to 9.1%, the yield of 15–53 μm particles decreased to 37.2%, the yield of 45–105 μm particles was 64.7%, the sphericity was 0.953, the proportion of satellite powder was 5.1%, the proportion of hollow powder was 1.9%, and the oxygen increment was 0.013 wt%.

[0134] After adopting a solid compaction body without hollow channels in Group C, the number of bubbling at the melt tip increased to 19, the liquid film closure decreased to 0.76, the droplet detachment frequency fluctuation coefficient increased to 14.8%, the yield of 15–53 μm particles decreased to 33.9%, the yield of 45–105 μm particles was 59.8%, the sphericity was 0.942, the proportion of satellite powder was 6.9%, the proportion of hollow powder was 3.4%, and the oxygen increment was 0.017 wt%.

[0135] Group D, after using a uniform high-density solid compaction body, experienced 27 bubbling cycles at the melt tip, resulting in intermittent liquid nodules rather than a continuous liquid film. The liquid film closure degree was only 0.62, the droplet detachment frequency fluctuation coefficient reached 20.6%, the yield of 15–53 μm particles was 28.4%, the yield of 45–105 μm particles was 53.1%, the sphericity was 0.924, the satellite powder ratio was 9.2%, the hollow powder ratio was 5.8%, and the oxygen increment was 0.021 wt%.

[0136] The comparison between Group A and Group B shows that the introduction of axial microgrooves increased the liquid film closure from 0.88 to 0.93, improved the yield of 15-53 μm particles by 4.6 percentage points, and reduced the proportion of satellite powder by 1.3 percentage points. This indicates that the surface guiding structure directly affects the uniformity of annular liquid film formation and the stability of droplet peeling.

[0137] The comparison between Group A and Group C shows that the introduction of the hollow air guide channel and the internal blowing flow field reduced the number of bubbling cycles from 19 to 6, the proportion of hollow powder from 3.4% to 1.5%, and the yield of 15-53μm powder increased by 7.9 percentage points. This indicates that the central air guide plays a decisive role in suppressing bubbling below the liquid film and promoting the yield of fine powder.

[0138] A comparison between Group A and Group D shows that, compared to traditional uniform high-density solid compacted materials, the complete structural scheme increases the yield of fine powder (15–53 μm) by 13.4 percentage points, improves sphericity by 0.043, reduces the proportion of hollow powder by 4.3 percentage points, reduces the proportion of satellite powder by 5.4 percentage points, and improves liquid film closure by 0.31. These results demonstrate that the inventiveness of this invention lies not in a single process step, but in the reconstruction of melting behavior by a complete structural system of "layered particle size functional distribution—gradient compaction—microgroove guidance—hollow gas guidance—internal blowing steady state—annular liquid film closed-loop atomization." Specific Implementation Example 3:

[0140] This study focuses on the regeneration of TA15 coarse powder using a gradient-dense hollow feedstock to prepare high-flowability spherical powder with a particle size of 53–150 μm for hot isostatic pressing. TA15 titanium alloy coarse powder is used as the regenerated raw material. The target product is a high-flowability spherical powder with a particle size of 53–150 μm, suitable for hot isostatic pressing and near-net-shape forming in powder metallurgy. The study primarily verifies the improvement effect of this technical solution on medium particle size yield, bulk density, flowability, and long-term steady-state operation capability under larger target particle size conditions.

[0141] The raw material selected was TA15 titanium alloy coarse powder, derived from a mixture of ultrafine particle residue from previous gas atomization sieves and recycled coarse particles from production. The original particle size range was 75–380 μm, with 76.8% in the 106–250 μm range. The original oxygen content was 0.149 wt%, the hydrogen content was 0.0062 wt%, and the original moisture content was 0.009 wt%. Irregular particles and satellite agglomerates accounted for 14.2% of the total. After multi-stage sieving and inert drying, three groups of raw materials were obtained: 20–63 μm fine powder, 63–180 μm transition powder, and 180–350 μm coarse powder. After degassing, the powder moisture content decreased to 0.002 wt%, the magnetic foreign matter content was 9 ppm, the oxygen content stabilized at 0.153 wt%, and the hydrogen content decreased to 0.0041 wt%.

[0142] In this case, the target particle size is relatively large, so the wall thickness of the feed body and the size of the central gas guiding channel are correspondingly increased to obtain a stronger medium-particle liquid supply capacity. The total thickness of the layered powder belt is set at 2.30 mm, and the layer sequence still adopts a six-layer structure symmetrical about the center plane. The upper and lower outer stabilizing powder layers are each 0.22 mm thick, using 20-63 μm TA15 fine powder; the upper and lower middle transition powder layers are each 0.36 mm thick, using a mixture of 63-180 μm transition powder and 20-63 μm fine powder at a mass ratio of 8:2; the middle double-layer liquid-releasing powder layer has a total thickness of 1.14 mm, using 180-350 μm coarse powder.

[0143] After three passes of differentiated rolling, the relative density of the outer stabilizing powder layer reaches 92.4%, the relative density of the middle transition powder layer reaches 80.6%, and the relative density of the inner liquid-releasing powder layer reaches 68.1%.

[0144] The surface axial microgrooves are U-shaped, with a groove depth of 150 μm, a groove spacing of 1.50 mm, and a groove opening width of 240 μm. They are rolled to form an open, rolled-edge, tubular hollow feed body with an outer diameter of 4.20 mm, a wall thickness of 0.96 mm, and an equivalent aperture of 1.62 mm for the central axial degassing channel. The joints are fixed using a combination of localized hot-pressing and mechanical edge-locking, with the joint area accounting for 6.8% of the circumferential area.

[0145] The rolled hollow feed body was subjected to low-temperature activation and shaping in a vacuum heat treatment furnace at a vacuum level of 6×10^-4 Pa, a heating rate of 7℃ / min, a holding temperature of 640℃, and a holding time of 48 min. It was then furnace cooled to 320℃ and subsequently cooled with high-purity argon. After treatment, a continuous, fusible shell layer with an effective connecting thickness of approximately 190 μm was formed on the outer layer of the feed body. The three-point bending limit load increased to 2.31 times that of the untreated feed body, the surface powder shedding rate decreased to 0.11%, and the seam cracking rate was zero. The central interconnected porosity was 23.4%, the intermediate layer interconnected porosity was 12.8%, and the pressure drop of the internal blowing channel at the rated flow rate was 0.0055 MPa.

[0146] The plasma atomization system employs a dual-gun plasma torch opposed structure, with a total power set at 86kW, atomizing gas pressure set at 0.92MPa, nozzle-to-feed body distance set at 15mm, feed rate set at 0.68m / min, internal high-purity argon flow rate set at 3.8L / min, inlet pressure set at 0.043MPa, and oxygen content in the atomization chamber controlled at 24ppm. After stable system operation, an annular molten liquid film with an average thickness of 176μm is formed at the melt tip, with a film closure degree of 0.91, circumferential thickness fluctuation range of ±13.2%, droplet shedding frequency of 512Hz, frequency fluctuation coefficient of 5.8%, normalized value of brightness variance of 0.079, normalized value of internal blowing pressure fluctuation of 0.067, and melt tip annular stability index K maintained in the range of 0.85–0.89.

[0147] This case study included three experimental groups. Group E was the complete scheme group, employing a gradient hollow feed body, U-shaped microchannels, and internal air blowing. Group F retained the hollow structure but eliminated the density gradient, uniformly compacting the outer, middle, and inner layers to 91%–93%. Group G retained the density gradient but eliminated internal blowing, utilizing only the central channel for natural venting. Each group was run continuously for 60 minutes, and the following parameters were measured: 53–150 μm yield, 106–180 μm yield, Hall flow rate, loose packing density, sphericity, satellite powder ratio, hollow powder ratio, number of melt tip bubbling events, dripping frequency fluctuation coefficient, and average K-value.

[0148] The complete E-group program ran for 60 minutes, with 7 bubbling cycles at the melt tip, an average K value of 0.87, a yield of 71.6% for the 53–150 μm particle size, an 83.2% yield for the 106–180 μm particle size, a Hall flow rate of 15.8 s / 50 g, a loose packing density of 2.56 g / cm³, a tapped density of 2.94 g / cm³, a sphericity of 0.962, a satellite powder ratio of 3.4%, a hollow powder ratio of 1.2%, and an oxygen increment of 0.010 wt%.

[0149] After the density gradient was removed in Group F, although the hollow channels and internal blowing still existed, the uniform high density of the outer, middle and inner layers caused the end liquid supply to change from gradual replenishment to intermittent overall collapse and melting. The number of bubbling times increased to 13, the average K value decreased to 0.76, the yield of 53-150μm particles decreased to 64.9%, the yield of 106-180μm particles decreased to 78.0%, the Hall flow rate became 17.2s / 50g, the loose packing density decreased to 2.47g / cm³, the sphericity decreased to 0.949, the proportion of satellite powder increased to 4.9%, the proportion of hollow powder increased to 2.3%, and the oxygen increment increased to 0.013wt%.

[0150] Group G retains the density gradient but eliminates internal blowing. The central channel can only passively ventilate, resulting in a significant increase in bubbling below the liquid film, with 18 bubbling cycles. The average K value is 0.73. The yield of particles in the 53–150 μm range is 66.1%, and the yield of particles in the 106–180 μm range is 79.4%. The Hall flow rate is 16.8 s / 50 g, the loose packing density is 2.49 g / cm³, the sphericity is 0.951, the proportion of satellite powder is 4.5%, the proportion of hollow powder is 2.8%, and the oxygen increment is 0.014 wt%.

[0151] To verify the actual operational capability of the scheme, a continuous 4-hour stability test was conducted on the complete scheme of Group E. During the test, samples were taken every 30 minutes to detect the yield of 53–150 μm particle size, Hall flow rate, sphericity, and K value. During the 4-hour operation, the K value remained above 0.82, the yield of 53–150 μm particle size fluctuated between 70.2% and 72.4%, the Hall flow rate fluctuated between 15.6 and 16.1 s / 50g, the sphericity fluctuated between 0.959 and 0.964, and the internal blowing pressure fluctuation remained below ±7%. No persistent melt tip deviance or seam instability occurred, indicating that the feed body structure and control logic are not only suitable for short-term verification but also possess process stability under continuous operation conditions.

[0152] A comparison between groups E and F shows that the central channel and internal blowing alone are insufficient to achieve optimal medium-sized particle size yield. Only when a density gradient exists do the liquid supply rate, liquid film thickness, and droplet cycle remain stable. Compared to group F, group E showed a 6.7 percentage point increase in the yield of 53–150 μm particles, a 1.4 s / 50 g improvement in Hall flow rate, and a 0.09 g / cm³ increase in loose packing density, indicating that gradient compaction has a direct effect on forming a stable liquid supply mechanism for medium-sized particles.

[0153] A comparison between Group E and Group G shows that by retaining only the hollow channel and eliminating internal blowing, the central gas discharge changes from active organization to passive release, local bubbling below the liquid film intensifies, the K value decreases, and the proportion of hollow powder increases. Compared to Group G, Group E shows a 1.6 percentage point decrease in the proportion of hollow powder, a 5.5 percentage point increase in the yield of 53–150 μm particles, and a 1.1 percentage point decrease in the proportion of satellite powder, indicating that the internal blowing flow field plays a decisive role in liquid film stability and the yield of medium-sized particles.

[0154] This case further demonstrates that the proposed technical solution has structural adaptability across different target particle sizes: for fine powder targets, it emphasizes liquid film closure and high-frequency stable droplet stripping; for medium-sized targets, it emphasizes gradual liquid supply, central gas delivery, and long-term continuous operation stability. This supports the argument that the innovation of this solution has a universal structural basis, rather than being effective only for a specific particle size window.

[0155] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising a reference structure" does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes the element.

[0156] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for regenerating titanium alloy coarse powder based on powder rolling by plasma atomization, characterized in that, Including the following: S1. The titanium alloy coarse powder to be recycled is screened, graded and purified. The titanium alloy coarse powder includes at least one of the following: recycled coarse powder, sieve residue coarse powder, ultra-large particle powder or irregular return powder. S2. In a vacuum environment or an inert atmosphere, titanium alloy powder with smaller particle size is laid as the outer layer of susceptible powder, mixed titanium alloy powder consisting of coarse and fine powder is laid as the middle transition powder layer, and coarse titanium alloy powder with larger particle size is laid as the inner layer of liquid release powder, forming a layered powder strip preform. S3. The layered powder strip preform is fed into the powder rolling device for differential compaction rolling, so that the layered powder strip preform forms a gradient dense structure with the density gradually decreasing from the outside to the inside along the thickness direction, and a gradient compacted powder strip is obtained. S4. The gradient compacted powder belt is textured to form axial microgrooves extending along the feeding direction on its surface, and the gradient compacted powder belt is rolled into a hollow feeding body to form a continuous axial degassing channel inside the hollow feeding body. S5. The hollow feeder is subjected to low-temperature activation and shaping treatment to make the surface particles connect to maintain the conveying strength, while retaining the controlled interconnected pores inside the hollow feeder. S6. The hollow feed body is continuously fed into the high-temperature action zone of the plasma atomization device, and inert gas is introduced simultaneously through the axial degassing channel, so that an annular molten liquid film is formed at the end of the hollow feed body. Under the combined action of plasma heat flow and atomization gas flow, the annular molten liquid film is broken into droplets and cooled and sphericalized to obtain recycled titanium alloy powder. S7. Collect and sieve the recycled titanium alloy powder to maintain the formation of annular molten liquid film.

2. The method for plasma atomization regeneration of titanium alloy coarse powder based on powder rolling according to claim 1, characterized in that, In S2, the outer layer of stabilizing powder is composed of titanium alloy powder with a particle size of 15–80 μm, the middle transition powder layer is composed of titanium alloy powder with a particle size of 50–200 μm, and the inner layer of releasing powder is composed of coarse titanium alloy powder with a particle size of 80–400 μm.

3. The method for plasma atomization regeneration of titanium alloy coarse powder based on powder rolling according to claim 1, characterized in that, In S3, the differentiated compaction rolling is as follows: a higher unit compaction load is applied to the outer region of the layered powder strip preform than to the middle region, so that the relative density of the outer stable powder layer is greater than the relative density of the middle transition powder layer, and the relative density of the middle transition powder layer is greater than the relative density of the inner liquid release powder layer. The relative density of the outer stabilizing powder layer is 88%–97%, the relative density of the intermediate transition powder layer is 75%–88%, and the relative density of the inner liquid-releasing powder layer is 55%–75%.

4. The method for plasma atomization regeneration of titanium alloy coarse powder based on powder rolling according to claim 1, characterized in that, The axial microgrooves in S4 have a groove shape of any one of V-shaped groove, U-shaped groove or trapezoidal groove, a groove depth of 50 to 300 μm and a groove spacing of 0.5 to 3 mm; The hollow feed body can be any of the following: tubular, open-ended rolled-edge tubular, or Ω-shaped hollow structure, and the equivalent pore size of the axial degassing channel is 0.5–3 mm.

5. The method for plasma atomization regeneration of titanium alloy coarse powder based on powder rolling according to claim 1, characterized in that, The S5 low-temperature activation and shaping treatment is carried out in a vacuum environment or a high-purity inert atmosphere, and the treatment temperature is lower than the sintering and densification temperature of titanium alloy coarse powder. After low-temperature activation and shaping treatment, a continuous and stable molten shell layer is formed on the surface of the hollow feed body, while the interior retains a network of venting pores that are connected to the axial degassing channel.

6. The method for plasma atomization regeneration of titanium alloy coarse powder based on powder rolling according to claim 1, characterized in that, The inert gas introduced through the axial degassing channel in S6 is argon or an argon-helium mixture. The inert gas flows along the axial direction of the hollow feed body in an internal blowing manner to guide the residual gas inside the hollow feed body to be discharged preferentially along the axial degassing channel and to suppress the internal gas from laterally breaking through the end molten liquid film. The plasma atomization device uses a single-gun, double-gun, or multi-gun plasma torch to form a circumferential thermal field at the end of the hollow feed body.

7. The method for plasma atomization regeneration of titanium alloy coarse powder based on powder rolling according to claim 1, characterized in that, In S7, the annular stable state is characterized by the tip annular stability index K, which is determined based on at least three of the following parameters: tip annular roundness, neck length fluctuation, droplet detachment frequency fluctuation, tip brightness distribution variance, and axial degassing channel internal blowing pressure fluctuation. When the molten tip ring stability index K is lower than the set threshold, the control system will adjust at least two of the following parameters in conjunction: the feeding speed of the hollow feed body, the plasma power, the plasma torch angle, the internal blowing inert gas flow rate, and the atomizing gas pressure, in order to restore a stable annular molten liquid film.

8. A plasma atomization regeneration system for titanium alloy coarse powder based on powder rolling, according to any one of claims 1-7, characterized in that, include: The raw material grading and purification unit is used to screen, classify, dehydrate, degas, and remove impurities from the coarse titanium alloy powder to be recycled. The layered powder laying unit is used to lay out the layered powder strip preform in the order of outer stabilizing powder layer, middle transition powder layer and inner liquid releasing powder layer; The gradient rolling unit is used to perform differentiated compaction rolling on the layered powder strip preform to form a gradient compacted powder strip with density decreasing from the outside to the inside along the thickness direction; Embossing unit, used to form axial microgrooves on the surface of gradient compacted powder belt; The tape is wound into hollow units, which are used to roll the gradient compacted powder tape into a hollow feed body with a continuous axial degassing channel inside; The activation and shaping unit is used to perform low-temperature activation and shaping treatment on the hollow feed body; The coaxial feeding internal blowing unit is used to introduce inert gas into the hollow feed body through the axial degassing channel while feeding the hollow feed body to the plasma atomizing device. The plasma atomization unit is used to heat and melt the end of the hollow feed body to form an annular molten liquid film, and then break the annular molten liquid film into recycled titanium alloy powder. The powder collection and sieving unit is used to collect and classify the particle size of recycled titanium alloy powder. The closed-loop control unit is used to adjust the feeding speed, plasma power, internal inert gas flow rate, and atomizing gas flow parameters according to the annular stable state of the melting tip at the end of the hollow feed body.

9. The plasma atomization regeneration system for titanium alloy coarse powder based on powder rolling according to claim 8, characterized in that, The gradient rolling unit includes a roll group for achieving differentiated compaction, wherein the roll surface pressure distribution, roll gap profile, or roll surface texture of the roll group is configured to make the outer layer of the layered powder strip preform more compacted than the inner layer. The hollow unit formed by the tape roll includes an edge-rolling module and a seam fixing module. The seam fixing module is used to maintain the continuous conveying strength of the hollow feed body and retain the internal interconnecting pores by means of mechanical edge-pinning, local hot-pressing consolidation or local sintering consolidation.

10. The plasma atomization regeneration system for titanium alloy coarse powder based on powder rolling according to claim 8, characterized in that, The closed-loop control unit is connected to a melt tip visual monitoring component, a brightness monitoring component, an internal blowing pressure monitoring component, and a powder particle size detection component. The closed-loop control unit is configured to generate a melt tip ring stability index K based on the melt tip annular roundness, melt droplet shedding frequency, melt tip brightness field change, and internal blowing pressure fluctuation. Based on the melt tip ring stability index K, the coaxial feeding internal blowing unit and the plasma atomization unit are coordinated to maintain the annular molten liquid film atomization state at the end of the hollow feed body.

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