Electromagnetic induction-based EB-PVD molten pool height monitoring system and monitoring method

Abstract

The invention relates to an EB-PVD molten pool height monitoring system and method based on electromagnetic induction. The system comprises a water-cooled copper crucible, a coaxial annular coil array arranged in a water-cooled layer of the water-cooled copper crucible, an electronic measuring unit and a data processing system. According to the method, based on the principle that solid-state and molten-state electromagnetic characteristics of 8YSZ and other ceramic materials are remarkably different, an alternating magnetic field is applied through a coil array, and complex impedance of the alternating magnetic field is monitored; when a molten pool interface moves to different coil heights, impedance jump of the corresponding coil is caused, and the height of the molten pool is inversed in real time by analyzing a jump sequence. The built-in coil design is adopted, electromagnetic shielding of the copper crucible can be effectively overcome in combination with matched selection of the thickness of the inner wall of the water-cooled copper crucible and the excitation frequency, complete non-contact and high-reliability real-time monitoring under the EB-PVD high-vacuum, high-temperature and intense-radiation environment is achieved, and a key technical means is provided for process stability and coating quality control.

Description

Technical Field

[0001] This invention relates to the field of physical vapor deposition process monitoring and equipment technology, and in particular to an EB-PVD melt pool height monitoring system and monitoring method based on electromagnetic induction. Background Technology

[0002] Electron beam physical vapor deposition (EB-PVD) is a key technology for preparing high-performance thermal barrier coatings (TBCs) for aero-engine and gas turbine blades. This process utilizes a high-energy electron beam to bombard and melt a ceramic target (such as 8 wt.% yttrium-stabilized zirconium oxide, or 8YSZ) placed in a water-cooled copper crucible, generating a stable ceramic vapor flow that deposits a TBC with a columnar crystal structure on the blade surface. Process stability and coating quality directly depend on the stability of the evaporation source, and the core of evaporation source stability lies in the height and state of the target molten pool. On one hand, the height of the 8YSZ target decreases under electron beam bombardment, causing electron beam defocusing. Therefore, it is necessary to maintain the target liquid level at a relatively fixed height to fix the electron beam focal length and the distance between the target and the evaporation substrate. On the other hand, the temperature distribution in the molten pool directly affects the evaporation rate, the uniformity of the vapor flow, and the controllability of the process. If the molten pool experiences localized overheating, it will lead to unstable evaporation and splattering. Therefore, real-time and accurate monitoring of the molten pool height and state is one of the core challenges in ensuring the reproducibility of the EB-PVD process and the quality of the coating.

[0003] In existing technologies, the monitoring methods for EB-PVD melt pools mainly fall into the following categories, but all of them have significant limitations: (1) Contact temperature / position measurement method: For example, US Patent US20070141233A1 discloses an EB-PVD system equipped with automatic melt pool height control; the main disadvantage of this scheme is that the sensor must work in an extreme high temperature and strong radiation environment close to 2700°C, which is easily damaged, has a short lifespan, and may contaminate high-purity target materials, resulting in poor practicality and reliability.

[0004] (2) Optical and radiometric measurement methods: These include visual or video monitoring through an observation window, infrared thermometry, and radiometer measurement. These methods are severely limited by the harsh environment inside the EB-PVD process chamber: strong ceramic vapor flow can contaminate the observation window; X-rays, stray electrons, and plasma glow generated by high-energy electron beams can cause severe optical interference and signal distortion; in addition, drastic temperature changes on the surface of the molten pool and the presence of spatter can make it difficult to interpret optical signals stably, resulting in low reliability of measurement results.

[0005] (3) Indirect methods based on changes in material properties: Studies have shown that when oxide ceramics such as YSZ change from a solid state to a molten state, their electrical properties (such as ionic conductivity and dielectric constant) undergo a sudden change of several orders of magnitude. This provides a physical basis for using electromagnetic means to identify the state. However, in the actual EB-PVD device, the water-cooled copper crucible, as a good conductor with high conductivity, will produce a strong skin effect and electromagnetic shielding to the alternating electromagnetic field, making it difficult for the induction coil arranged outside the crucible to establish effective electromagnetic coupling with the target material inside, resulting in extremely weak signals or even complete shielding.

[0006] In summary, the EB-PVD industry urgently needs a non-contact, highly reliable, real-time online molten pool interface monitoring technology capable of operating under harsh conditions of high vacuum, high temperature radiation, and strong metal shielding. Existing technologies cannot simultaneously meet these requirements. This invention addresses this technological gap by proposing an innovative solution. Summary of the Invention

[0007] The purpose of this invention is to overcome the above-mentioned shortcomings and provide an EB-PVD melt pool height monitoring system and method based on electromagnetic induction, thereby solving the problems in the prior art.

[0008] The objective of this invention is achieved as follows: An EB-PVD melt pool height monitoring system based on electromagnetic induction includes a water-cooled copper crucible, comprising a cylindrical receiving cavity arranged coaxially from the inside to the outside, an inner wall of the water-cooled copper crucible, and an outer wall of the water-cooled copper crucible, wherein an annular water-cooling layer is formed between the inner wall and the outer wall of the water-cooled copper crucible; a ceramic target is provided in the cylindrical receiving cavity at the center of the water-cooled copper crucible. A coaxial ring coil array, composed of multiple ring induction coils, is arranged along the axial direction of the water-cooled copper crucible and concentrically within the internal space of the ring-shaped water-cooling layer; the coaxial ring coil array is led out of the water-cooled copper crucible through a high-temperature signal harness. An electronic measurement unit, electrically connected to the coaxial ring coil array, is used to drive the coaxial ring coil array and provide it with alternating excitation signals, and to measure the complex impedance of each coil in real time. The data processing system is communicatively connected to the electronic measurement unit and is used to receive complex impedance data from the electronic measurement unit. By analyzing the changes in the complex impedance of each coil, the solid-liquid interface height of the ceramic target material in the water-cooled copper crucible is determined.

[0009] Furthermore, a crucible water inlet is provided on the lower part of one side of the outer wall of the water-cooled copper crucible, and a crucible water outlet is provided on the upper part of the other side. The crucible water inlet and crucible water outlet are respectively connected to the annular water-cooling layer and serve as the cooling water inlet and outlet.

[0010] Furthermore, the thickness of the inner wall of the water-cooled copper crucible is 2-5 mm; the thickness of the outer wall of the water-cooled copper crucible is 4-8 mm; and the internal width of the annular water-cooling layer is 35-45 mm.

[0011] Furthermore, the annular coil array is wound around the inner wall of the water-cooled copper crucible.

[0012] Furthermore, a sealing interface is provided on the lower part of the outer wall of the water-cooled copper crucible.

[0013] Furthermore, the signal harness of the coaxial ring coil array is connected to an external electronic measurement unit via a sealed interface.

[0014] A method for monitoring the height of an EB-PVD molten pool based on electromagnetic induction, employing the aforementioned EB-PVD molten pool height monitoring system based on electromagnetic induction, includes the following steps: S1. System initialization and baseline measurement: Before the EB-PVD process begins, the ceramic target is in a completely solid state; The monitoring system is activated, and the electronic measurement unit excites all coils at the selected frequency. The data processing system records the complex impedance value of each coil at this time and stores it as a "solid-state reference impedance". S2. Process Start-up and Molten Pool Formation: During the EB-PVD process, an electron beam is activated to heat the surface of the ceramic target. As heating proceeds, the ceramic target gradually melts from top to bottom, forming a molten pool. The solid-liquid interface moves downwards and gradually approaches the positions of the coils along each axis. Under relatively fixed conditions of electron beam power and heat dissipation environment, the molten state on the target surface will be maintained at a relatively fixed depth; S3. Real-time signal acquisition and feature extraction: During the electron beam heating process, the electronic measurement unit continuously and synchronously measures the real-time complex impedance of all coils; S4, Interface Height Calculation: The data processing system analyzes the changes in the real-time complex impedance of each coil relative to its reference complex impedance. S5. Determine the height of the molten pool: The solid-liquid interface height of the molten pool is determined based on the coil sequence in which the complex impedance changes significantly along the axial direction.

[0015] Further, in step S4, the data processing system compares the real-time impedance of each coil with its solid-state reference impedance; when the ceramic target material at a certain coil height changes from solid to molten, the impedance of the coil will change significantly due to the abrupt change in the electromagnetic properties of the material, especially the reactance component, and the data processing system detects this change event.

[0016] Furthermore, in step S5, by identifying the coil sequence that undergoes impedance jumps sequentially from top to bottom along the axial direction, the movement trajectory and current height of the solid-liquid interface can be determined; for example, when the Nth coil undergoes a jump while the N+1th coil has not yet changed, it can be determined that the molten pool interface is located between these two coils, and the height of the molten pool can be deduced.

[0017] Furthermore, it also includes the following: S6. Combining multi-frequency excitation data: By leveraging the differences in penetration depth and sensitivity at different frequencies, the accuracy and anti-interference capability of interface positioning can be optimized. S7. Process Feedback and Control: The calculated real-time molten pool height is compared with the target height set by the process to generate a control signal, dynamically adjusting the power, focus point, or scanning mode of the electron beam to stabilize the molten pool height within the ideal range, thus achieving closed-loop control.

[0018] Compared with the prior art, the beneficial effects of the present invention are: This invention provides an EB-PVD melt pool height monitoring system and method based on electromagnetic induction, which has the following specific advantages: (1) Truly non-contact and pollution-free: The sensing coil does not come into direct contact with the high-temperature molten pool, which completely avoids the problems of sensor ablation and target material contamination, and there is no need for an easily contaminated observation window, resulting in extremely high reliability.

[0019] (2) Strong anti-interference capability: Based on the principle of electromagnetic induction, it is not affected by typical optical interference factors such as strong light radiation, vapor flow, and plasma glow in the EB-PVD cavity, and the signal is stable and reliable.

[0020] (3) Effectively overcome electromagnetic shielding: By controlling the thickness of the inner wall of the water-cooled copper crucible and by using a unique structural design that integrates the coil into the water-cooled interlayer and optimizing the excitation frequency, the problem of shielding the magnetic field by the high conductivity copper crucible is cleverly solved, and the effective sensing of the internal medium state is realized in a strong conductor environment.

[0021] (4) Strong real-time performance and fast response: The response speed of electromagnetic induction is much faster than that of heat conduction, which can quickly capture the dynamic changes of the molten pool interface and meet the needs of real-time process monitoring.

[0022] (5) Easy to integrate and industrial applications: The system has a compact structure and can be directly modified or integrated into existing standard water-cooled copper crucibles without changing the main process layout of EB-PVD. The sensing part is in a water-cooled environment, with low operating temperature, long life, and convenient maintenance, making it very suitable for long-term stable operation in industrial applications.

[0023] (6) Functional expandability: It can not only monitor the height of the molten pool and analyze the detailed characteristics of the impedance change of multiple coils, but also has the potential to evaluate the morphology and uniformity of the molten pool. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the structure of an EB-PVD melt pool height monitoring system based on electromagnetic induction according to the present invention.

[0025] Figure 2 This is a schematic diagram of the structure of the water-cooled copper crucible of the present invention.

[0026] in: 1. Ceramic target; 2. Water-cooled copper crucible; 201. Inner wall of water-cooled copper crucible; 202. Outer wall of water-cooled copper crucible; 203. Annular water-cooling layer; 204. Water inlet of crucible; 205. Water outlet of crucible; 3. Coaxial annular coil array; 4. Electronic measurement unit; 5. Signal harness; 6. Sealed interface; 7. Data processing system. Detailed Implementation

[0027] To better understand the technical solution of the present invention, a detailed description will be provided below in conjunction with relevant illustrations. It should be understood that the specific embodiments described below are not intended to limit the specific implementation of the technical solution of the present invention, but are merely possible implementations of the technical solution of the present invention. It should be noted that the descriptions of the positional relationships of the components herein, such as component A being located above component B, are based on the relative positions of the components in the illustrations and are not intended to limit the actual positional relationships of the components. Example 1

[0028] See Figure 1-2 , Figure 1 A schematic diagram of an EB-PVD melt pool height monitoring system based on electromagnetic induction according to Embodiment 1 is shown. As shown in the figure, the EB-PVD melt pool height monitoring system based on electromagnetic induction according to Embodiment 1 includes: Water-cooled copper crucible 2: As the main mechanical structure of the evaporation source carrier and system, it includes a cylindrical receiving cavity arranged coaxially from the inside to the outside, as well as an inner wall 201 and an outer wall 202 of the water-cooled copper crucible. An annular water-cooling layer 203 is formed between the inner wall 201 and the outer wall 202 of the water-cooled copper crucible. The water-cooled copper crucible has a crucible inlet 204 on the lower part of one side of the outer wall 202 and a crucible outlet 205 on the upper part of the other side. The crucible inlet 204 and the crucible outlet 205 are respectively connected to the annular water-cooling layer 203 and serve as the cooling water inlet and outlet. The water-cooled copper crucible 2 has a ceramic target 1 in its central cavity to ensure structural strength and cooling effect while also meeting the electromagnetic field penetration requirements mentioned later.

[0029] In this embodiment, the thickness of the inner wall 201 of the water-cooled copper crucible is 2-5mm, the thickness of the outer wall 202 of the water-cooled copper crucible is 4-8mm, and the annular water-cooling layer 203 has an annular width of about 40mm. The water-cooled copper crucible 2 not only undertakes the temperature regulation of the evaporation area of ​​the ceramic target material 1, but also provides a solid structural support for the system.

[0030] Coaxial ring coil array 3: As the core sensor component, it consists of multiple ring induction coils encapsulated by high-temperature resistant insulating materials. These ring induction coils are evenly arranged at a certain interval along the axial direction of the water-cooled copper crucible 2 and are concentrically arranged within the ring water-cooling layer 203, that is, sandwiched between the inner wall 201 and the outer wall 202 of the water-cooled copper crucible. In this embodiment, the annular coil array 3 is wound around the inner wall 201 of the water-cooled copper crucible; The coaxial ring coil array 3 is led out of the water-cooled copper crucible 2 through the high-temperature signal harness 5. The lower part of the outer wall 202 of the water-cooled copper crucible 2 is provided with a vacuum-sealed interface 6. The coaxial ring coil array 3 is connected to the outside through the signal harness 5 via the sealed interface 6.

[0031] Electronic measurement unit 4: used to drive the coaxial ring coil array 3 and acquire signals; the electronic measurement unit 4 generates an alternating current with a specific frequency range as an excitation signal and applies it to the coaxial ring coil array 3; in this embodiment, the frequency range generated by the electronic measurement unit 4 is preferably 0.2kHz to 2kHz; At the same time, it measures the complex voltage and complex current across each coil in real time and synchronously, and calculates the complex impedance of each coil, including the resistance and reactance components.

[0032] Data processing system 7: Receives real-time impedance data from electronic measurement unit 4. It internally stores the "reference impedance" of each coil measured when the target material is completely solid, thereby pre-establishing a physical property and impedance mapping model; it fuses and analyzes the impedance jump information of multiple coils, and outputs the height and morphology information of the solid-liquid interface of the target material, so as to realize the accurate perception of the molten state and the position of the solid-liquid interface. The data processing system 7 analyzes the changes in impedance of each coil relative to the reference value in real time through signal processing algorithms such as threshold judgment, trend analysis, and spatial sequence matching, especially the "sudden change". Based on the position and sequence of the coils where impedance changes occur, the system can infer the height of the current molten pool interface. The system can also feed back the calculated molten pool height information to the electron beam power controller or scanning controller of EB-PVD to realize closed-loop adjustment of process parameters.

[0033] This embodiment 1 relates to an EB-PVD molten pool height monitoring method based on electromagnetic induction. Applying the aforementioned EB-PVD molten pool height monitoring system based on electromagnetic induction, the method includes the following steps: S1. System initialization and baseline measurement: Before the EB-PVD process begins, the ceramic target is in a completely solid state; The monitoring system is activated, and the electronic measurement unit excites all coils at the selected frequency. The data processing system records the complex impedance value of each coil at this time and stores it as a "solid-state reference impedance". S2. Process Start-up and Molten Pool Formation: The electron beam is activated to heat the surface of the ceramic target. As heating proceeds, the ceramic target gradually melts from top to bottom, forming a molten pool. The solid-liquid interface moves downwards and gradually approaches the positions of the coils along each axis. S3. Real-time signal acquisition and feature extraction: During the electron beam heating process, the electronic measurement unit continuously and synchronously measures the real-time complex impedance of all coils; S4, Interface Height Calculation: The data processing system compares the real-time impedance of each coil with its "solid-state reference impedance". When the ceramic target material at a certain coil height changes from solid to molten, the impedance of the coil will jump significantly due to the abrupt change in the electromagnetic properties of the material, especially the reactance component. The data processing system detects this jump event. S5. Determine the height of the molten pool: By identifying the sequence of coils that undergo impedance jumps sequentially from top to bottom along the axial direction, the movement trajectory and current height of the solid-liquid interface can be determined. For example, when the Nth coil undergoes a jump while the (N+1)th coil has not yet changed, it can be determined that the molten pool interface is located between these two coils, and the height of the molten pool can be deduced.

[0034] As a preferred implementation, based on the above method, further step S6 can be adopted, combining multi-frequency excitation data: By leveraging the differences in penetration depth and sensitivity at different frequencies, the accuracy and anti-interference capability of interface positioning can be further optimized.

[0035] As a preferred embodiment, based on the above method, further steps can be taken, including S7, process feedback and control: The calculated real-time molten pool height is compared with the target height set by the process to generate a control signal, dynamically adjusting the power, focus point, or scanning mode of the electron beam to stabilize the molten pool height within the ideal range, thus achieving closed-loop control. Example 2

[0036] An alternative implementation of the EB-PVD melt pool height monitoring system based on electromagnetic induction, as described in Embodiment 1 above, differs from Embodiment 1 in that: The excitation signal of the electronic measurement unit 4 can be a single fixed frequency, dual frequency, or a small-range frequency scan to obtain richer spectral information, which can be used to compensate for temperature drift or improve the signal-to-noise ratio.

[0037] Arrangement of coaxial ring coil array 3: The coil spacing of the coaxial ring coil array 3 can be adjusted according to the required measurement accuracy and melt pool depth range; for more accurate morphology measurement, the coil density can be increased.

[0038] The structure of the water-cooled copper crucible 2: The area on the inner wall 201 of the water-cooled copper crucible directly opposite the coaxial annular coil array 3 is locally thinned or replaced with a high-temperature resistant insulating material, such as alumina ceramic, to form an electromagnetic window, thereby further enhancing the magnetic field penetration capability and improving detection sensitivity. This area requires a reinforced structural design to ensure safety.

[0039] The signal processing algorithm of the data processing system 7, in addition to the simple threshold method, can also use algorithms such as pattern recognition and neural networks to more accurately and robustly invert the state of the molten pool by utilizing the impedance change patterns of multiple coils and multiple frequencies.

[0040] The above embodiment is applied to a molten pool height monitoring system for the EB-PVD process of 8YSZ sputtering targets. The specific implementation process is as follows: (1) Monitoring system construction: A standard water-cooled copper crucible is used, with an inner wall thickness of 3 mm and an outer wall thickness of 6 mm, forming an annular water-cooling layer with a width of 35 mm.

[0041] In the middle of the annular water-cooling layer, eight annular induction coils are coaxially embedded along the crucible axis at 10mm intervals to form a coil array. The coils are made of an alumina ceramic tube skeleton and high-temperature resistant enameled wire, and the whole is sealed with high-temperature insulating glue.

[0042] After the signal lines of each coil converge, they are led out to the outside of the vacuum chamber through a specially designed vacuum feedthrough sealed interface.

[0043] The cable leads to an electronic measurement unit, which uses an impedance analyzer module to generate excitation signals at two frequencies, 0.5 kHz and 1.0 kHz, and simultaneously measures the complex impedance of eight channels.

[0044] The electronic measurement unit is connected to a host computer with a data processing system via a data bus. The host computer runs dedicated software responsible for data acquisition, storage, analysis, and interface display.

[0045] (2) Monitoring method and process: Installation and initialization: Place the 8YSZ ceramic ingot into the crucible; close the EB-PVD chamber and evacuate; turn on the crucible cooling water; start the monitoring system before the electron beam is turned on; the host computer software controls the electronic measurement unit to scan all coils at frequencies of 0.5 kHz and 1.0 kHz, and records the reference impedance Z_solid of each coil at the two frequencies.

[0046] Process Start-up and Monitoring: Start the electron beam and heat the target material according to the preset program; the host computer software begins to collect the impedance data Z_real-time of all coils at two frequencies in real time.

[0047] Signal processing and height calculation: The software calculates the impedance change ΔZ = Z_real-time - Z_solid for each coil in real time; a threshold is set: for example, the reactance change exceeds 20% of the reference value; when the ΔZ of the Nth coil from top to bottom exceeds the threshold, while the ΔZ of the (N+1)th coil does not exceed the threshold, the software determines that the current solid-liquid interface is located between the Nth and (N+1)th coils; the specific interface height value H_pool can be estimated through linear interpolation.

[0048] Data display and alarms: The real-time molten pool height H_pool is displayed in the software interface as a curve and numerical value; the height safety range can be set to 20-30mm. When H_pool exceeds the range, the system will issue an audible and visual alarm.

[0049] Closed-loop control: H_pool is used as a process variable and compared with the set value. A control signal is generated through a PID algorithm to automatically adjust the filament current of the electron beam, so that the height of the molten pool is stabilized near the set value.

[0050] Working principle: This invention provides an EB-PVD melt pool height monitoring system and method based on electromagnetic induction, which specifically solves the following problems: (1) Realize non-contact real-time monitoring: A method is provided to obtain the height and morphology information of the solid-liquid interface of ceramic target material in real time and quantitatively without direct contact with the high-temperature molten pool or relying on an easily contaminated optical window.

[0051] (2) Overcoming strong electromagnetic shielding: Solving the problem of how to effectively transmit the excitation magnetic field to the target area and sensitively detect the attenuation of electromagnetic response signal caused by changes in the state of the target in the strong conductor shielding environment of water-cooled copper crucible.

[0052] (3) Ensure long-term stable operation of the system: Design a monitoring device whose core sensor can withstand the high heat flux, strong radiation and high vacuum environment of the EB-PVD source area, and whose structure is easy to integrate into existing equipment, and has long-term reliability and maintainability for industrial applications.

[0053] The present invention provides an EB-PVD melt pool height monitoring system and method based on electromagnetic induction, which is based on the following design principles: (1) Physical basis: It utilizes the characteristic that there are orders of magnitude differences in electromagnetic parameters such as conductivity and dielectric constant between the solid state (high resistance insulator) and the molten state (high temperature ionic conductor) of ceramic materials such as 8YSZ. This sudden change in physical properties will significantly change its response to an applied alternating magnetic field.

[0054] (2) Anti-shielding structure design: Placing the induction coil within a water-cooling layer is a key innovation. Cooling water is a low-conductivity medium, having minimal impact on magnetic field penetration. This position allows the coil to be as close as possible to the target material, separated only by a thin copper inner wall, while water cooling effectively protects the coil from high-temperature damage. By optimizing the excitation frequency and calculating the skin depth δ, the alternating magnetic field can partially penetrate the copper inner wall and couple with the target material without excessive attenuation. Specifically: Electromagnetic coupling working mechanism: 8YSZ ceramic targets are high-resistance insulators in the solid state, but transform into high-temperature ionic conductors upon melting, with conductivity typically increasing by 1 to 3 orders of magnitude and dielectric constant also changing significantly. This abrupt change in physical properties provides a theoretical basis for non-contact real-time monitoring based on electromagnetic coupling of alternating magnetic fields. Alternating magnetic fields in metallic conductors are affected by the skin effect, with the magnetic field mainly concentrated within a certain depth of the conductor surface. The skin depth δ is given by the following formula (1): Formula (1) Where ω is the angular frequency, μ is the permeability, and σ is the electrical conductivity. The skin effect indicates that the penetration depth of a magnetic field is inversely proportional to the excitation frequency; the higher the frequency, the shallower the penetration. The copper wall of the target material has high electrical conductivity (approximately 5.8 × 10⁻⁶). 7 With a relative permeability close to 1 (S / m), magnetic field penetration is limited. A reasonable selection of the excitation frequency needs to balance penetration and detection sensitivity, ensuring that the magnetic field can partially penetrate the copper inner wall of the induction melting target while avoiding excessive shielding effects.

[0055] The surface impedance model is used to describe the response of a metal to an alternating magnetic field, and can be expressed by the following formula (2): Formula (2) Among them, R s , where is the surface resistance, represents eddy current loss, and increases with the square root of the excitation frequency. Skin depth decreases with the square root of the frequency; both together determine the coupling and shielding balance of the system.

[0056] In this detection system, the detection coil is located outside the inner wall of the copper. An alternating current is applied to generate a magnetic field, forming closed eddy currents on the surface of the copper inner wall. The absorption and reflection of the magnetic field by the copper wall are equivalent to the reflection impedance Z at the coil port. r Its increment is approximately given by the following formula (3): Formula (3) Among them, mutual inductance M This represents the electromagnetic coupling strength between the coil and the target material. When the 8YSZ target material transitions from a solid to a molten liquid state, its conductivity increases significantly, leading to a higher surface resistance R. s As the impedance decreases, both the real and imaginary parts of the reflected impedance change significantly. Simultaneously, changes in the morphology and height of the molten liquid surface alter the mutual inductance. M The change in impedance causes fluctuations. Together, these factors allow the coil port impedance to dynamically reflect the molten state of the target material and changes in the liquid level, enabling non-contact online monitoring.

[0057] (3) Arraying and differential measurement: Axial coil arrays are used to extend single-point measurement to one-dimensional spatial measurement. The interface is located by detecting "jump propagation", eliminating the ambiguity of single-coil measurement. Multi-frequency and differential technology helps to suppress common-mode noise caused by temperature drift, small changes in coil parameters, etc., and improves signal-to-noise ratio and stability.

[0058] Despite the extremely high conductivity of the copper crucible, this invention achieves effective electromagnetic coupling through geometric design. First, the coaxial structure ensures that the coil and the return current path of the copper crucible are strictly coaxial, resulting in a ring-shaped magnetic field distribution. The leakage magnetic field is concentrated in the radially inner region, which is beneficial for effective magnetic field coupling to the target material. Second, the water-cooling layer, as a low-conductivity medium, provides an ideal window for magnetic field penetration, isolating the coil from the effects of high temperature and preventing direct contact between the coil and the metal surface. Finally, the multi-coil array captures impedance transitions at different coil heights, effectively eliminating the ambiguity of single-coil depth positioning. This enables measurement of the molten pool depth and solid-liquid interface position, as well as suppression of multi-source interference, ensuring stable system response and accurate measurement. Therefore, the coil exhibits a stable response to the target material's condition.

[0059] The present invention discloses an EB-PVD molten pool height monitoring system based on electromagnetic induction. In use, after the vacuum chamber is evacuated, the electron beam heats the surface of the target material to form a molten pool. As the molten pool deepens, the solid-liquid interface contacts coils of different axes in sequence. The system collects the impedance changes of multiple coils in real time, calculates the solid-liquid interface morphology information, and feeds back the molten pool depth to the electron beam power and scanning trajectory control system to realize closed-loop adjustment of power and trajectory, ensuring the stability and reliability of the melting process.

[0060] This invention discloses an EB-PVD molten pool height monitoring system and method based on electromagnetic induction. The system includes a water-cooled copper crucible, a coaxial ring coil array placed inside its water-cooled layer, an electronic measurement unit, and a data processing system. The method is based on the principle that the electromagnetic properties of ceramic materials such as YSZ differ significantly between their solid and molten states. An alternating magnetic field is applied through the coil array, and its complex impedance is monitored. When the molten pool interface moves to different coil heights, it causes a jump in the impedance of the corresponding coil. The molten pool height is then inverted in real time by analyzing the jump sequence. This invention employs an internal coil design, combined with the appropriate selection of the inner wall thickness of the water-cooled copper crucible and the excitation frequency, effectively overcoming the electromagnetic shielding of the copper crucible. This achieves completely non-contact, highly reliable real-time monitoring in the high vacuum, high temperature, and strong radiation environment of EB-PVD, providing a key technical means for process stability and coating quality control.

[0061] The above are merely specific application examples of the present invention and do not constitute any limitation on the scope of protection of the present invention. All technical solutions formed by equivalent transformations or substitutions fall within the scope of protection of the present invention.

Claims

1. A system for monitoring the height of an EB-PVD molten pool based on electromagnetic induction, characterized in that, Includes the following: The water-cooled copper crucible (2) includes a cylindrical receiving cavity arranged coaxially from the inside to the outside, as well as an inner wall (201) and an outer wall (202) of the water-cooled copper crucible, with an annular water-cooling layer (203) formed between the inner wall (201) and the outer wall (202); a ceramic target (1) is provided in the cylindrical receiving cavity at the center of the water-cooled copper crucible (2). The coaxial ring coil array (3) is composed of multiple ring induction coils. The coaxial ring coil array (3) is arranged along the axial direction of the water-cooled copper crucible (2) and concentrically arranged in the internal space of the ring water-cooling layer (203). The coaxial ring coil array (3) is led out of the water-cooled copper crucible (2) through a high-temperature signal harness (5). The electronic measurement unit (4) is electrically connected to the coaxial ring coil array (3) for driving the coaxial ring coil array (3) and providing it with alternating excitation signals, and measuring the complex impedance of each coil in real time; The data processing system (7) is connected in communication with the electronic measurement unit (4) to receive complex impedance data from the electronic measurement unit (4) and to determine the solid-liquid interface height of the ceramic target (1) in the water-cooled copper crucible (2) by analyzing the changes in the complex impedance of each coil.

2. The EB-PVD melt pool height monitoring system based on electromagnetic induction according to claim 1, characterized in that: The water-cooled copper crucible has a crucible inlet (204) on the lower part of one side of the outer wall (202) and a crucible outlet (205) on the upper part of the other side. The crucible inlet (204) and crucible outlet (205) are respectively connected to the annular water-cooling layer (203) and serve as the cooling water inlet and outlet.

3. The EB-PVD melt pool height monitoring system based on electromagnetic induction according to claim 1, characterized in that: The thickness of the inner wall (201) of the water-cooled copper crucible is 2-5 mm; the thickness of the outer wall (202) of the water-cooled copper crucible is 4-8 mm; and the internal width of the annular water-cooling layer (203) is 35-45 mm.

4. The EB-PVD melt pool height monitoring system based on electromagnetic induction according to claim 1, characterized in that: The annular coil array (3) is wound on the inner wall (201) of the water-cooled copper crucible.

5. The EB-PVD melt pool height monitoring system based on electromagnetic induction according to claim 1, characterized in that: The water-cooled copper crucible (2) has a sealing interface (6) at the lower part of the outer wall (202) of the water-cooled copper crucible (2).

6. The EB-PVD melt pool height monitoring system based on electromagnetic induction according to claim 5, characterized in that: The signal harness (5) of the coaxial ring coil array (3) is connected to the external electronic measurement unit (4) via the sealed interface (6).

7. A method for monitoring the height of an EB-PVD molten pool based on electromagnetic induction, employing an EB-PVD molten pool height monitoring system based on electromagnetic induction as described in any one of claims 1-6, characterized in that, Includes the following steps: S1. System initialization and baseline measurement: Before the EB-PVD process begins, the ceramic target is in a completely solid state; The monitoring system is activated, and the electronic measurement unit excites all coils at the selected frequency. The data processing system records the complex impedance value of each coil at this time and stores it as a "solid-state reference impedance". S2. Process Start-up and Molten Pool Formation: During the EB-PVD process, an electron beam is activated to heat the surface of the ceramic target. As heating proceeds, the ceramic target gradually melts from top to bottom, forming a molten pool. The solid-liquid interface moves downwards and gradually approaches the positions of the coils along each axis. S3. Real-time signal acquisition and feature extraction: During the electron beam heating process, the electronic measurement unit continuously and synchronously measures the real-time complex impedance of all coils; S4, Interface Height Calculation: The data processing system analyzes the changes in the real-time complex impedance of each coil relative to its reference complex impedance. S5. Determine the height of the molten pool: The solid-liquid interface height of the molten pool is determined based on the coil sequence in which the complex impedance changes significantly along the axial direction.

8. The method for monitoring the height of an EB-PVD molten pool based on electromagnetic induction according to claim 7, characterized in that: In step S4, the data processing system compares the real-time impedance of each coil with its solid-state reference impedance. When the ceramic target material at a certain coil height changes from solid to molten, the impedance of the coil will change significantly due to the abrupt change in the electromagnetic properties of the material, especially the reactance component. The data processing system detects this change event.

9. The method for monitoring the height of an EB-PVD molten pool based on electromagnetic induction according to claim 7, characterized in that: In step S5, by identifying the coil sequence that undergoes impedance jumps sequentially from top to bottom along the axial direction, the movement trajectory and current height of the solid-liquid interface can be determined. For example, when the Nth coil changes direction but the (N+1)th coil has not yet changed direction, it can be determined that the molten pool interface is located between these two coils, and the height of the molten pool can be deduced from this.

10. The method for monitoring the height of an EB-PVD molten pool based on electromagnetic induction according to claim 7, characterized in that: Also includes the following: S6. Combining multi-frequency excitation data: By leveraging the differences in penetration depth and sensitivity at different frequencies, the accuracy and anti-interference capability of interface positioning can be optimized. S7. Process Feedback and Control: The calculated real-time molten pool height is compared with the target height set by the process to generate a control signal, dynamically adjusting the power, focus point, or scanning mode of the electron beam to stabilize the molten pool height within the ideal range, thus achieving closed-loop control.

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