Quartz resonance force sensor interface strengthening structure based on TiAl alloy transition layer and preparation method of quartz resonance force sensor interface strengthening structure

Abstract

The invention discloses a TiAl alloy transition layer-based quartz resonance force sensor interface strengthening structure and a preparation method thereof. The structure comprises a Fe-based substrate, a TiAl alloy transition layer, an epoxy resin packaging layer and a quartz resonance sheet, the TiAl alloy transition layer is deposited on the surface of the Fe-based substrate, and the epoxy resin packaging layer wraps the TiAl transition layer and packages the quartz resonance piece on the surface of the Fe-based substrate. The content of Al in the TiAl transition layer is 0-70 at.%, and the thickness of the TiAl transition layer is 50-1000 nm. Stable chemical bonding of the Fe-based substrate and the epoxy resin is achieved through the TiAl transition layer, and relative slippage of an interface is avoided; the cubic phase content in the transition layer is adjusted through the Al content, the lattice mismatching degree with Fe is reduced, and the interface stress is reduced. Through 10000 times of loading-unloading cycle tests, compared with a sensor without a transition layer, the indicating value error is reduced by 37.5%, the repeatability error is reduced by 57.2%, the hysteresis error is reduced by 78.3%, and the durability is remarkably improved while the sensing precision + / -0.2% FS is kept.

Description

Technical Field

[0001] This invention relates to the field of sensor packaging technology, and more specifically, to an interface reinforcement structure for a quartz resonant force sensor, particularly an interface reinforcement structure in which a titanium-aluminum (TiAl) alloy transition layer is introduced between an iron (Fe)-based substrate and an epoxy resin encapsulation layer, a method for preparing the structure, and a quartz resonant force sensor comprising the structure. Background Technology

[0002] A quartz resonant force sensor is a high-precision sensing device that utilizes the piezoelectric effect and resonant characteristics of quartz crystals to convert changes in external force into a frequency signal output. Due to its outstanding advantages such as high resolution, fast response speed, and good long-term stability, it is widely used in precision manufacturing, aerospace, robot joint force control, and high-end industrial automation. A typical packaging structure for this type of sensor usually includes a metal substrate as a support, a quartz resonator as the sensing element, and an encapsulation layer that fixes the quartz resonator to the metal substrate. The metal substrate is often made of an alloy material with a high iron (Fe) content (such as Q235 carbon steel) to ensure the overall structural strength and rigidity of the sensor; the encapsulation layer is often made of epoxy resin to achieve stress-free or low-stress fixation of the quartz resonator and to provide buffer protection. Therefore, the Fe substrate-epoxy resin-quartz resonator constitutes the core multi-layer interface system of the sensor packaging.

[0003] In existing technologies, the interfacial bonding between quartz resonators (SiO2 material) and epoxy resin generally exhibits good performance. This is due to the strong hydrogen bonds or chemical bonds formed between the polar groups (such as epoxy and hydroxyl groups) in the epoxy resin and the silanol groups on the quartz surface. However, the interfacial bonding between the Fe metal substrate and epoxy resin has always been a weak link in the encapsulation process. Because Fe metal has high surface energy and readily forms an oxide layer, while epoxy resin, as a polymer material, has relatively weak polarity, it is difficult for the two to form stable chemical bonds. The bonding mainly relies on physical forces such as mechanical locking forces (e.g., increasing the surface roughness of the substrate) and van der Waals forces. This physical bonding interface can meet basic requirements under static conditions, but during actual sensor service, especially under long-term cyclic alternating loads, the Fe-epoxy resin interface is prone to failure phenomena such as micro-slippage, fatigue debonding, and even complete delamination. Currently, common improvement solutions in the industry for this problem mainly include: optimizing the curing temperature and curing agent ratio of epoxy resin to adjust its internal stress, sandblasting or chemical etching on the Fe substrate surface to increase roughness, or doping epoxy resin with inorganic fillers to enhance its modulus, etc.

[0004] However, none of the aforementioned existing technical solutions have fundamentally solved the core problem of insufficient interfacial bonding strength between Fe and epoxy resin. The specific analysis is as follows: First, excessive control of the epoxy resin curing process or composition, while potentially reducing interfacial thermal stress to some extent, often comes at the cost of sacrificing the epoxy resin's own mechanical properties (such as toughness and modulus). This directly affects the efficiency of load transfer from the substrate to the quartz resonator, potentially introducing new sensor performance degradation problems. Second, simply increasing the surface roughness of the Fe substrate, while enhancing physical bonding to some extent through the "anchor effect," is a non-chemically bonded mechanical interlock. Under the continuous action of long-term cyclic shear force, the interface will still gradually experience fatigue wear and relative slippage, failing to fundamentally prevent failure. Furthermore, uneven roughness control can easily lead to localized stress concentration at the interface, becoming the starting point for crack initiation and accelerating interfacial damage. Therefore, existing technological improvements are limited to physical or process-level repairs of existing material systems (Fe and epoxy resin), failing to break free from the inherent technical framework that "Fe and epoxy resin are inherently difficult to chemically bond." This results in the inevitable performance degradation of sensors after long-term use due to interface failure, such as value drift, reduced repeatability, and increased hysteresis, severely restricting the long-term reliable application of quartz resonant force sensors in high-end fields.

[0005] In summary, how to overcome the limitations of existing material systems and construct a transition layer between an Fe-based substrate and epoxy resin that can form a stable chemical bond, thereby fundamentally solving the problems of interfacial slippage and delamination failure, while also ensuring sensor accuracy and long-term durability, has become a technical challenge that urgently needs to be addressed by those skilled in the art.

[0006] It should be noted that the information disclosed in this background section is intended only to enhance the understanding of the overall background of the present invention, and should not be construed as an admission or in any way implying that the information constitutes prior art known to those skilled in the art. Summary of the Invention

[0007] This invention aims to address the aforementioned problems in the prior art by providing an interface strengthening structure for a quartz resonant force sensor based on a TiAl alloy transition layer, its fabrication method, and a quartz resonant force sensor incorporating this structure. The purpose of this invention is to overcome the technical defects in existing quartz resonant force sensors where the interface bonding strength between the Fe-based substrate and the epoxy resin encapsulation layer is insufficient due to only physical bonding. This leads to relative slippage and delamination failure under long-term cyclic loading, resulting in increased sensor indication error, poor repeatability, and increased hysteresis error, thus degrading the sensor's performance. This invention provides an interface strengthening solution that achieves stable chemical bonding between the Fe-based substrate and epoxy resin, good interface lattice matching, and significantly improves the long-term durability of the sensor.

[0008] To achieve the above-mentioned objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides an interface reinforcement structure for a quartz resonant force sensor based on a TiAl alloy transition layer, comprising an Fe-based substrate, a TiAl alloy transition layer, an epoxy resin encapsulation layer, and a quartz resonator. The TiAl alloy transition layer is deposited on at least a portion of the surface of the Fe-based substrate; the epoxy resin encapsulation layer covers the surface of the TiAl alloy transition layer opposite to the Fe-based substrate; and the quartz resonator is encapsulated and fixed to the surface of the Fe-based substrate by the epoxy resin encapsulation layer.

[0009] In the aforementioned interface strengthening structure, the atomic percentage content of Al in the TiAl alloy transition layer is from 0 at.% to 70 at.%. Preferably, the atomic percentage content of Al is from 10 at.% to 40 at.%. By controlling the Al content, the content of the cubic phase in the transition layer can be adjusted, thereby reducing the lattice mismatch between the TiAl transition layer and the Fe-based substrate and effectively reducing interfacial stress.

[0010] In the aforementioned interface reinforcement structure, the thickness of the TiAl alloy transition layer is from 50 nm to 1000 nm. Preferably, the thickness of the TiAl alloy transition layer is from 100 nm to 500 nm. This thickness range ensures that the transition layer can fully exert its chemical bonding function without significantly affecting the overall size and weight of the sensor.

[0011] In the aforementioned interface strengthening structure, the TiAl alloy transition layer can be a single-layer structure or a multi-layer structure containing at least two sub-layers. When a multi-layer structure is used, the composition of each sub-layer can be the same or different to adapt to different interface matching requirements.

[0012] In the above-described interface reinforcement structure, the Fe-based substrate is a metal substrate with an Fe element atomic percentage content ≥40 at.%, preferably a carbon steel substrate (e.g., Q235 carbon steel). The raw material for the epoxy resin encapsulation layer is selected from bisphenol A type epoxy resin, bisphenol F type epoxy resin, or combinations thereof.

[0013] Secondly, the present invention provides a method for preparing the above-mentioned interface-strengthened structure, comprising the following steps: Step S1: Pre-treat the Fe-based substrate to remove surface impurities and oxide layers; Step S2: A TiAl alloy transition layer is deposited on the pretreated Fe-based substrate surface using physical vapor deposition. Step S3: Apply epoxy resin to the surface of the TiAl alloy transition layer, attach the quartz resonator to the epoxy resin coating, and cure to form an epoxy resin encapsulation layer, thereby obtaining an interface-strengthened quartz resonator force sensor.

[0014] In the above preparation method, the physical vapor deposition process in step S2 is preferably a magnetron sputtering process. Specifically, it includes: under a vacuum of 1×10⁻⁶... -3 Pa to 5×10 -3 In an argon atmosphere of Pa, DC pulse magnetron sputtering is used with a sputtering power of 100 W to 600 W. The deposition thickness of the TiAl alloy transition layer is controlled by adjusting the sputtering time.

[0015] In the above preparation method, the target material used for magnetron sputtering in step S2 can be a TiAl alloy target, or a pure Ti target and a pure Al target. When using a pure Ti target and a pure Al target, the atomic percentage content of Al element in the TiAl alloy transition layer can be precisely controlled by co-sputtering and adjusting the sputtering power of the Ti target and the Al target.

[0016] In the above preparation method, the pretreatment in step S1 includes polishing the Fe-based substrate, followed by ultrasonic cleaning with acetone, anhydrous ethanol, and deionized water in sequence, with each ultrasonic cleaning lasting 10 to 30 minutes, and drying after cleaning. The curing treatment in step S3 is performed at a temperature of 60°C to 150°C for 2 to 4 hours.

[0017] Thirdly, the present invention also provides a quartz resonant force sensor, wherein the sensor comprises the quartz resonant force sensor interface reinforcement structure based on the TiAl alloy transition layer as described in any of the above technical solutions, or is prepared by the preparation method described in any of the above technical solutions.

[0018] Compared with the prior art, the present invention has the following beneficial effects: Achieving stable chemical bonding fundamentally solves the interfacial failure problem: This invention, through density functional theory (DFT) simulations, confirms that Ti and Al atoms in the TiAl alloy transition layer can form stable chemical bonds with Fe atoms in the Fe-based substrate (adsorption energy can reach -6.32 J / m). 2 Furthermore, it can undergo charge redistribution with active groups such as epoxy groups, benzene rings, and amino groups in epoxy resin, forming chemisorption. The resulting Fe-TiAl-epoxy resin bilayer stable bonding structure effectively counteracts the interfacial shear force under cyclic loading, fundamentally avoiding the technical problem of relative slippage and delamination failure that easily occurs at the interface of traditional Fe-epoxy resin due to only weak physical bonding.

[0019] By optimizing interface matching through compositional control, this invention reduces interfacial stress: By limiting the Al content in the TiAl transition layer to the range of 0-70 at.%, the cubic phase content in the transition layer is controlled. Since Fe-based materials typically contain both body-centered cubic (bcc) and face-centered cubic (fcc) phases, appropriately increasing the Al content can promote the transformation of the hexagonal close-packed (hcp) phase in TiAl to the cubic phase, thereby reducing the lattice mismatch between the TiAl transition layer and the Fe substrate, decreasing residual interfacial stress, and further improving the mechanical stability and long-term reliability of the interface.

[0020] Significantly improved sensor durability and long-term stability: Durability tests with a 21N load and 10,000 load-unload cycles demonstrate that the sensor with the introduced TiAl transition layer (Al content 10 at.%, thickness 500 nm) exhibits significantly improved performance compared to the sensor without the transition layer: indication error decreased by 37.5% (from 0.181% to 0.113%), repeatability error decreased by 57.2% (from 0.355% to 0.152%), and hysteresis error decreased by 78.3% (from 0.557% to 0.121%). Simultaneously, the dispersion of test data was significantly reduced, indicating that the interface reinforcement structure not only improved the average performance level but also significantly enhanced the sensor's consistency. More importantly, these performance improvements were achieved while maintaining the sensor's original sensing accuracy (±0.2% FS), demonstrating the outstanding advantage of this invention in improving durability without sacrificing accuracy.

[0021] The process offers strong controllability and compatibility with existing packaging technologies: The preparation method of this invention employs magnetron sputtering to deposit a TiAl transition layer. This mature and stable process allows for precise control over the composition (Al content) and thickness (50 nm-1000 nm) of the transition layer, with good repeatability. Furthermore, this process is highly compatible with existing sensor packaging technologies, requiring no significant modifications to existing production lines and facilitating industrial-scale application.

[0022] The ultra-thin transition layer design does not affect the original structure of the sensor: The thickness of the TiAl transition layer of this invention is controlled in the submicron range of 50nm-1000nm, which belongs to the thin film category. It will not significantly increase the size and weight of the sensor, and will not affect the structural design and miniaturization requirements of the sensor. It can be widely used in various specifications of quartz resonant force sensors. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the interface reinforcement structure of the quartz resonant force sensor of the present invention; Figure 2The diagram shows a comparison of load transfer between the Fe-epoxy resin interface and the Fe-TiAl-epoxy resin interface; where (a) is a schematic diagram of the unstable Fe-epoxy resin interface without the TiAl transition layer, and (b) is a schematic diagram of the stable Fe-TiAl-epoxy resin interface with the TiAl transition layer. Figure 3 This is a step test diagram of the thickness of the pure Ti transition layer deposited on the surface of the Fe-based substrate in Example 1 (step meter test). Figure 4 This is a step test diagram (step tester) of the thickness of the TiAl alloy transition layer (Al content 10 at.%) deposited on the surface of the Fe-based substrate in Example 2. Figure 5 This is a thickness step test diagram (step meter test) of the TiAl alloy transition layer (Al content 10 at.%, thickness 100 nm) deposited on the surface of the Fe-based substrate in Example 3. Figure 6 This is a step test diagram (step meter test) of the thickness of the TiAl alloy transition layer (Al content 40 at.%) deposited on the surface of the Fe-based substrate in Example 4. Figure 7 The graph shows the change in indication error of the sensors in Examples 1-4 and Comparative Example 1 during 10,000 load-unload cycle tests. Figure 8 The graph shows the repeatability error variation of the sensors in Examples 1-4 and Comparative Example 1 during 10,000 load-unload cycle tests. Figure 9 The graph shows the hysteresis error variation curves of the sensors in Examples 1-4 and Comparative Example 1 during 10,000 load-unload cycle tests.

[0024] Explanation of reference numerals in the attached figures: 1 - Fe-based substrate; 2 - TiAl alloy transition layer; 3 - Epoxy resin encapsulation layer; 4 - Quartz resonator; 5 - Interfacial shear force; 6 - Relative displacement. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. However, it should be understood that the specific embodiments of this invention are only for explaining the invention and are not intended to limit the scope of protection of this invention. Any modifications, equivalent substitutions, improvements, etc., made under the premise of the inventive concept should be included within the scope of protection of this invention.

[0026] Detailed Description of the Technical Solution of the Invention: The present invention provides an interface reinforcement structure for a quartz resonant force sensor based on a TiAl alloy transition layer. For example... Figure 1As shown, the structure includes an Fe-based substrate 1, a TiAl alloy transition layer 2, an epoxy resin encapsulation layer 3, and a quartz resonator 4. The TiAl alloy transition layer 2 is deposited on the surface of the Fe-based substrate 1; the epoxy resin encapsulation layer 3 covers the surface of the TiAl alloy transition layer 2 facing away from the Fe-based substrate 1; and the quartz resonator 4 is encapsulated and fixed to the surface of the Fe-based substrate 1 by the epoxy resin encapsulation layer 3, forming a complete sensor encapsulation structure.

[0027] This invention aims to solve the problem of insufficient interfacial bonding strength in traditional Fe-epoxy resins by introducing a TiAl alloy transition layer 2 between the Fe-based substrate 1 and the epoxy resin encapsulation layer 3. Figure 2 As shown, in the traditional structure without a TiAl transition layer ( Figure 2 (a) The Fe-based substrate 1 is in direct contact with the epoxy resin encapsulation layer 3, and there is only a weak physical adsorption effect between them (such as van der Waals forces and mechanical locking forces). When the sensor is subjected to cyclic loads, shear force 5 is generated at the interface. Since the interface bonding force is insufficient to resist this shear force, relative displacement 6 easily occurs between the Fe-based substrate 1 and the epoxy resin encapsulation layer 3, leading to interface slippage or even delamination failure. However, in the structure of the present invention with the introduction of TiAl alloy transition layer 2 ( Figure 2 (b) The TiAl transition layer 2 forms stable chemical bonds with the Fe-based substrate 1 and the epoxy resin encapsulation layer 3, respectively, constructing a stable bilayer bonding interface of Fe-TiAl-epoxy resin. This structure can effectively counteract the interfacial shear force 5 under cyclic loading, fundamentally avoiding the occurrence of relative displacement 6, and achieving efficient and stable load transfer.

[0028] This invention optimizes the composition and thickness of the TiAl alloy transition layer 2. Regarding composition, the atomic percentage of Al in the TiAl alloy transition layer 2 is controlled to be between 0 at.% and 70 at.%, preferably between 10 at.% and 40 at.%. Through density functional theory (DFT) simulations, the inventors discovered that Ti and Al atoms in the TiAl alloy can form stable chemical bonds with Fe atoms in the Fe-based substrate, with an adsorption energy reaching -6.32 J / m². Furthermore, appropriately increasing the Ti content enhances the adsorption stability between TiAl and Fe. On the other hand, Fe-based materials typically contain both body-centered cubic (bcc) and face-centered cubic (fcc) phases, while the crystal structure of the TiAl alloy changes with Al content. When the Al content is low, TiAl mainly exists as a hexagonal close-packed (hcp) phase; as the Al content increases, the proportion of the cubic phase in TiAl gradually increases. By controlling the Al content, the crystal structure of the TiAl transition layer can be better matched with the dominant crystalline phase in the Fe substrate, thereby reducing the lattice mismatch between the two, decreasing interfacial residual stress, and improving the mechanical stability of the interface. If the Al content exceeds 70 at.%, too many brittle intermetallic compound phases may form in the TiAl alloy. At the same time, too low a Ti content will also reduce the interfacial adsorption stability between TiAl and the Fe substrate, adversely affecting the long-term reliability of the sensor. Therefore, controlling the Al content within the range of 0-70 at.% ensures good chemical bonding while reducing interfacial stress through lattice matching optimization.

[0029] Regarding thickness, the thickness of the TiAl alloy transition layer 2 is controlled between 50 nm and 1000 nm, preferably between 100 nm and 500 nm. If the transition layer is too thin (less than 50 nm), it is difficult to form a continuous and uniform covering layer on the Fe substrate surface, and there may be local exposed areas, resulting in direct contact between Fe and epoxy resin, which cannot fully utilize the bonding effect of the transition layer. If the transition layer is too thick (greater than 1000 nm), on the one hand, it will increase the time cost of sputtering deposition, and on the other hand, a thicker metal layer may introduce greater internal stress, and there is a risk of fatigue cracking under long-term cyclic loading. Controlling the thickness within the range of 50-1000 nm ensures sufficient coverage and effective bonding of the transition layer to the Fe substrate, while avoiding the adverse effects of an excessively thick metal layer. In addition, this thickness range belongs to the submicron level thin film, which will not significantly increase the size and weight of the sensor, and will not affect the miniaturization design and engineering application of the sensor.

[0030] In this invention, the TiAl alloy transition layer 2 can be a single-layer structure or a multi-layer structure containing at least two sublayers. When a multi-layer structure is used, the interfacial stress distribution or specific functions (such as gradient transition) can be further optimized by alternately depositing TiAl alloy layers of different compositions (e.g., alternating Ti-rich layers and Al-rich layers). The compositions of each sublayer in the multi-layer structure can be the same or different to adapt to different interfacial matching requirements.

[0031] In this invention, the Fe-based substrate 1 is a metal substrate with an Fe atomic percentage content ≥40 at.%, preferably a carbon steel substrate, such as Q235 carbon steel. This type of substrate has good mechanical and processing properties and is a commonly used substrate material for quartz resonant force sensors. The epoxy resin encapsulation layer 3 can be made from bisphenol A type epoxy resin, bisphenol F type epoxy resin, or a combination thereof. These epoxy resins have excellent adhesion and process adaptability, and bond well with the quartz resonator.

[0032] The preparation method provided by this invention includes the following steps: Step S1: Fe-based substrate pretreatment First, the Fe-based substrate is polished, for example, using metallographic sandpaper to gradually polish it to a mirror finish, to remove macroscopic defects and oxide layers from the substrate surface, obtaining a smooth and clean surface. After polishing, the substrate is ultrasonically cleaned sequentially with acetone, anhydrous ethanol, and deionized water, each ultrasonic cleaning time being 10 to 30 minutes, to thoroughly remove oil, polishing residue, and other impurities from the substrate surface. After cleaning, the substrate surface is dried with high-purity nitrogen gas, resulting in a clean and dry pretreated Fe-based substrate. The purpose of this pretreatment step is to obtain an atomically clean surface, providing a good adhesion base for the subsequent deposition of the TiAl transition layer and preventing impurities and oxide layers from affecting the interfacial bonding quality between TiAl and Fe.

[0033] Step S2: Deposition of TiAl alloy transition layer A TiAl alloy transition layer was deposited on a pretreated Fe-based substrate using physical vapor deposition (PVD), preferably DC pulsed magnetron sputtering. The deposition process was carried out in an argon atmosphere with a vacuum level controlled at 1 × 10⁻⁶. -3 Pa to 5×10 -3Pa is used to ensure the stability of the sputtering process and the purity of the film. The sputtering power is controlled from 100 W to 600 W, and the sputtering rate and film density can be changed by adjusting the sputtering power. There are two options for the deposition target: one is to use a TiAl alloy target to obtain a TiAl alloy transition layer with a specific composition by sputtering with a single target; the other is to use a pure Ti target and a pure Al target for co-sputtering. By adjusting the sputtering power of the Ti target and the Al target separately, the atomic percentage content of Al in the TiAl alloy transition layer can be flexibly and precisely controlled, and the composition can be continuously adjusted.

[0034] Before deposition begins, the substrate can be cleaned by bias ion bombardment, that is, by bombarding the substrate surface with argon ions at a bias power of 30-100 W, in order to further remove any thin oxide layer that may exist on the substrate surface and enhance the bonding force between the TiAl transition layer and the substrate.

[0035] By adjusting the sputtering time, the deposition thickness of the TiAl alloy transition layer can be precisely controlled to achieve the desired range of 50 nm to 1000 nm. The relationship between sputtering time and thickness can be determined through preliminary process calibration. For example, under fixed sputtering power and gas pressure conditions, by preparing samples with different sputtering times and performing thickness tests (such as profilometry), a sputtering time-thickness relationship curve can be established, thereby achieving precise thickness control.

[0036] When it is necessary to prepare a multi-layered TiAl alloy transition layer, a multi-target alternating sputtering method can be used. For example, two targets (such as a TiAl alloy target and a pure Al target, or TiAl alloy targets with different compositions) can be used, and by controlling the alternating on and off of the targets and the sputtering time, a sublayer structure with alternating composition can be deposited.

[0037] Step S3: Encapsulation and Curing Epoxy resin (such as bisphenol A or bisphenol F type epoxy resin) is uniformly coated onto the surface of an Fe-based substrate with a deposited TiAl alloy transition layer. Coating methods can include spin coating, spraying, brushing, or dispensing, depending on the production scale and precision requirements. The coating thickness should be appropriate, ensuring sufficient coverage of the TiAl transition layer while avoiding excessive thickness that could lead to excessive stress within the encapsulation layer or affect sensor sensitivity.

[0038] Gently attach the AT-cut quartz resonator to the uncured epoxy resin coating, adjusting its position to align it with the substrate. Avoid introducing air bubbles during the attachment process to ensure tight contact between the quartz resonator and the epoxy resin layer.

[0039] The bonded components are placed in an oven and cured at 60℃ to 150℃ for 2 to 4 hours. The curing temperature and time depend on the type of epoxy resin and the curing agent system selected. It is essential to ensure that the epoxy resin is fully cross-linked and cured to form an encapsulation layer with sufficient strength and toughness, while avoiding excessively high temperatures that could negatively impact the performance of the quartz resonator. After curing, the components are allowed to cool naturally to room temperature, resulting in an interface-strengthened quartz resonator force sensor.

[0040] To make the technical solution and beneficial effects of the present invention clearer, a detailed description is provided below through specific embodiments and comparative examples. However, it should be noted that the following embodiments are for illustrative purposes only and should not be construed as limiting the present invention. All equivalent modifications or substitutions made based on the technical solution of the present invention fall within the protection scope of the present invention.

[0041] Example 1: Fabrication of a quartz resonant force sensor with a 500 nm pure Ti transition layer Substrate pretreatment: A Q235 carbon steel substrate with dimensions of 10 mm × 10 mm × 2 mm was used as the Fe-based substrate. It was successively polished to a mirror finish using 400#, 800#, 1200#, and 2000# metallographic sandpaper. After polishing, the substrate was sequentially placed in acetone, anhydrous ethanol, and deionized water, and ultrasonically cleaned for 15 minutes each at a cleaning power of 100 W. After cleaning, the substrate surface was dried with high-purity nitrogen gas to obtain the pretreated Fe-based substrate.

[0042] Transition layer deposition: Deposition was performed using a DC pulsed magnetron sputtering system. The pretreated Fe-based substrate was placed on a sample holder within the vacuum chamber, and a pure Ti target (99.99% purity) was used. The vacuum was evacuated to a background vacuum level better than 5 × 10⁻⁶. -4 After Pa, high-purity argon gas (99.999% purity) is introduced, and the gas flow rate is adjusted to stabilize the working vacuum at 2 × 10⁻⁶. -3 Pa. The substrate bias power supply was turned on, and the substrate was subjected to ion bombardment cleaning for 10 min at a bias power of 50 W to remove any possible oxide layer on the surface. Then, the bias power was turned off, and the Ti target sputtering power supply was turned on, with the sputtering power set to 200 W, for pre-sputtering for 5 min to remove contaminants from the target surface. After pre-sputtering, the substrate baffle was opened to begin deposition, with the deposition time controlled at 50 min. After deposition, the power supply and gas were turned off, and the sample was removed, yielding an Fe-based substrate with a deposited Ti transition layer. The thickness of the accompanying wafers prepared in the same batch was measured using a profilometer (e.g., ...). Figure 3 As shown in the figure, the thickness of the Ti transition layer was measured to be approximately 500 nm.

[0043] Encapsulation and Curing: Bisphenol A type epoxy resin (E-51 type) and curing agent (methyltetrahydrophthalic anhydride) were mixed evenly at a mass ratio of 100:80. After vacuum degassing, a small amount of epoxy resin was evenly coated onto the surface of the Ti transition layer using a dispensing machine. An AT-cut quartz resonator (8 mm in diameter and 0.2 mm in thickness) was gently attached to the epoxy resin coating, and air bubbles were gently pressed out and the position adjusted. The assembly was placed in a forced-air drying oven and cured at 90°C for 2 h, then allowed to cool naturally to room temperature to obtain a quartz resonator force sensor with a 500 nm pure Ti transition layer.

[0044] Example 2: Fabrication of a quartz resonant force sensor with a 500 nm TiAl alloy transition layer (Al content 10 at.%) The difference between this embodiment and Embodiment 1 lies in the deposition step of the transition layer. Specifically: Transition layer deposition: TiAl alloy target (Ti:Al atomic ratio 90:10, purity 99.9%) was selected. The sputtering power remained at 200 W, and the working vacuum was 2×10⁻⁶. -3 Pa, deposition time 50 min. Other sputtering parameters and procedures were the same as in Example 1. Post-deposition analysis was performed using a profilometer (e.g., ...). Figure 4 As shown in the figure, the thickness of the TiAl alloy transition layer was measured to be approximately 500 nm. Energy-dispersive X-ray spectroscopy (EDS) analysis of the transition layer composition confirmed that the Al content was approximately 10 at.%.

[0045] The remaining steps (substrate pretreatment and encapsulation curing) are exactly the same as in Example 1.

[0046] Example 3: Fabrication of a quartz resonant force sensor with a 100 nm TiAl alloy transition layer (Al content 10 at.%) The difference between this embodiment and Embodiment 2 lies in the deposition time of the transition layer. Specifically: Transition layer deposition: The same TiAl alloy target (Ti:Al atomic ratio 90:10) and sputtering parameters as in Example 2 were used, but the deposition time was shortened to 10 min. After deposition, the layer was tested using a step meter (e.g., ...). Figure 5 As shown in the figure, the thickness of the TiAl alloy transition layer was measured to be approximately 100 nm. The remaining steps were the same as in Example 2.

[0047] Example 4: Fabrication of a quartz resonant force sensor with a 500 nm TiAl alloy transition layer (Al content 40 at.%) The difference between this embodiment and Embodiment 2 lies in the composition of the transition layer. Specifically: Transition layer deposition: TiAl alloy target (Ti:Al atomic ratio 60:40, purity 99.9%) was selected. The sputtering power remained at 200 W, and the working vacuum was 2×10⁻⁶. -3 Pa, deposition time 50 min. Post-deposition was measured using a step profiler (e.g., ...). Figure 6 As shown in the figure, the thickness of the TiAl alloy transition layer was measured to be approximately 500 nm. EDS analysis confirmed that the Al content was approximately 40 at.%. The remaining steps were the same as in Example 2.

[0048] Comparative Example 1: Fabrication of a quartz resonant force sensor without a TiAl transition layer The difference between this comparative example and Example 1 is that the transition layer deposition step is omitted. Specifically: Substrate pretreatment: exactly the same as in Example 1.

[0049] Encapsulation and curing: The pretreated Fe-based substrate was directly used for encapsulation. Bisphenol A type epoxy resin (E-51 type) and curing agent were mixed in the same proportion and directly coated on the surface of the Fe-based substrate. Then, a quartz resonator was attached and cured under the same conditions (90℃, 2 h) to obtain a quartz resonator force sensor without a TiAl transition layer.

[0050] The sensors prepared in Examples 1-4 and Comparative Example 1 were subjected to performance tests, and the test methods are as follows: Sensing accuracy test: A standard force value within the range of 0-100% FS (full scale) was applied to the sensor on a standard force source loading device. The sensor's frequency output was recorded, and its linearity and accuracy were calculated. The sensing accuracy was expressed as the percentage error of full scale (% FS). The test results show that the sensing accuracy of all embodiments and comparative examples of the sensor is within ±0.2% FS in the initial state, indicating that the introduction of the TiAl transition layer did not negatively affect the inherent sensing accuracy of the sensor.

[0051] Durability testing: The sensor was subjected to load-unload cyclic testing using an electromagnetic dynamic fatigue testing machine. Test conditions were: load amplitude 21 N (corresponding to approximately 10-90% FS), loading frequency 5 Hz, and 10,000 cycles. Cycling was paused before the start of each cycle and at 1000, 2000, 5000, 8000, and 10000 cycles for static calibration of the sensor. The three key performance indicators—indication error, repeatability error, and hysteresis error—were recorded.

[0052] The definitions of each performance indicator are as follows: Indication error: The percentage difference between the average value of multiple measurements at the same test point and the standard value, relative to the standard value, reflects the accuracy of the sensor.

[0053] Repeatability error: The degree of consistency between the results obtained from multiple measurements of the same measurand under the same conditions. It is usually expressed as a percentage of the difference between the maximum and minimum values ​​of the three measurements relative to the full-scale output, reflecting the precision of the sensor.

[0054] Hysteresis error: The percentage of the maximum deviation of the output corresponding to the same input quantity in the forward and reverse strokes of the sensor relative to the full-scale output, reflecting the sensor's elastic hysteresis and mechanical friction characteristics.

[0055] The final results after 10,000 cycles of testing are summarized in Table 1.

[0056] Table 1. Comparison of performance indicators after 10,000 cycles of testing under 21N load. sample Al content (at.%) TiAl thickness (nm) Indication error (%) Repeatability error (%) Hysteresis error (%) Example 1 0 500 0.136 0.173 0.258 Example 2 10 500 0.113 0.152 0.121 Example 3 10 100 0.166 0.236 0.296 Example 4 40 500 0.098 0.194 0.135 Comparative Example 1 - - 0.181 0.355 0.557 As can be seen from the data in Table 1: Comparative Example 1 (without transition layer) showed a significant increase in indication error, repeatability error, and hysteresis error after 10,000 cycles, especially the hysteresis error, which reached 0.557%, indicating that the Fe-epoxy resin interface had undergone significant performance degradation, with severe interfacial slippage and damage.

[0057] The errors in Example 1 (pure Ti transition layer) were all lower than those in Comparative Example 1, indicating that the introduction of the Ti transition layer improved the interfacial bonding to some extent, which is consistent with the principle analysis of this invention that Ti can form chemical bonds with Fe. However, the pure Ti transition layer had limited effect in reducing hysteresis error (0.258%), which was still higher than that of the Al-containing TiAl transition layer.

[0058] Example 2 (Al 10 at.%, 500 nm) showed significantly better performance than Example 1 and Comparative Example 1. Compared with Comparative Example 1, its indication error decreased by 37.5% (from 0.181% to 0.113%), repeatability error decreased by 57.2% (from 0.355% to 0.152%), and hysteresis error decreased by 78.3% (from 0.557% to 0.121%). This fully demonstrates the superiority of the TiAl alloy transition layer over the pure Ti transition layer and verifies the theoretical analysis that the introduction of an appropriate amount of Al helps to optimize interface matching, reduce stress, and enhance bonding.

[0059] Example 4 (Al 40 at.%, 500 nm) showed the lowest indication error (0.098%) and a low hysteresis error (0.135%), comparable to Example 2, but with a slightly higher repeatability error (0.194%). This suggests that a higher Al content may further optimize certain aspects (such as lattice matching), but may introduce new variations in other aspects (such as film uniformity or internal stress), although the overall performance is still far superior to Comparative Example 1.

[0060] Comparing Examples 2 and 3 (both with Al 10 at.%, but different thicknesses), it is evident that the 500 nm thick transition layer (Example 2) performs significantly better than the 100 nm thick transition layer (Example 3). While Example 3 exhibits better indication error (0.166%), repeatability (0.236%), and hysteresis (0.296%) than Comparative Example 1, it is inferior to Example 2. This indicates that the 100 nm thick transition layer may not completely cover the Fe substrate surface or may have insufficient interfacial stress release, validating the necessity of controlling the thickness to above 100 nm (preferably 100-500 nm).

[0061] Figures 7 to 9 The trends of indication error, repeatability error, and hysteresis error for each sample during 10,000 cycles are shown. The graphs clearly demonstrate that: (1) The error value of Comparative Example 1 increases sharply with the number of cycles, especially after 5000 cycles, the slope of the curve increases significantly, indicating that the interface damage accumulates faster.

[0062] (2) Although the error value of Example 1 is lower than that of Comparative Example 1, it still shows a significant upward trend as the number of cycles increases.

[0063] (3) The error values ​​of Examples 2 and 4 remained stable throughout the entire cycle, with a very small increase and low data dispersion, indicating that the interface structure was stable and no significant performance degradation occurred. In particular, Example 2 maintained a low hysteresis error (0.121%) after 10,000 cycles, demonstrating excellent interface stability.

[0064] (4) The error value of Example 3 was higher than that of Example 2 in the early stage of the cycle, and showed a certain upward trend as the number of cycles increased, but it was still better than Comparative Example 1 overall.

[0065] Based on the above test results, the following conclusions can be drawn: This invention, by introducing a TiAl alloy transition layer between the Fe-based substrate and the epoxy resin encapsulation layer, and specifically controlling the Al content within the preferred range of 10-40 at.% and the thickness within the preferred range of 100-500 nm, can significantly enhance the interfacial bonding strength and greatly improve the durability and long-term stability of the sensor under cyclic loading while maintaining its original sensing accuracy. This technical solution effectively solves the technical problem of easy failure of the Fe-epoxy resin interface in the prior art, and has significant technical progress and practical value.

[0066] The interface reinforcement structure and fabrication method for a quartz resonant force sensor based on a TiAl alloy transition layer of this invention can be widely applied in the fabrication of various quartz resonant force sensors, pressure sensors, accelerometers, and other devices that require the encapsulation of quartz resonant elements on a metal substrate. This technical solution offers good process compatibility and significant performance improvements, making it particularly suitable for high-end applications requiring high long-term stability and reliability, such as aerospace structural health monitoring, force control in precision manufacturing processes, robot joint torque sensing, and high-speed rail wheel-rail force detection. With the development of intelligent manufacturing and the Industrial Internet, the demand for highly reliable sensors will continue to grow, and the technical solution of this invention has excellent industrial application prospects and promotional value.

[0067] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A quartz resonant force sensor interface reinforcement structure based on a TiAl alloy transition layer, characterized in that, include: Fe-based substrate; TiAl alloy transition layer, said TiAl alloy transition layer being deposited on at least a portion of the surface of said Fe-based substrate; An epoxy resin encapsulation layer, wherein the epoxy resin encapsulation layer covers the surface of the TiAl alloy transition layer opposite to the Fe-based substrate; and... A quartz resonator is encapsulated on the surface of the Fe-based substrate by the epoxy resin encapsulation layer.

2. The interface reinforcement structure for a quartz resonant force sensor based on a TiAl alloy transition layer according to claim 1, characterized in that, The atomic percentage content of Al in the TiAl alloy transition layer is 0 to 70 at.%.

3. The interface reinforcement structure for a quartz resonant force sensor based on a TiAl alloy transition layer according to claim 1, characterized in that, The thickness of the TiAl alloy transition layer is 50 nm to 1000 nm.

4. The interface reinforcement structure for a quartz resonant force sensor based on a TiAl alloy transition layer according to claim 1, characterized in that, The TiAl alloy transition layer is a single-layer structure or a multi-layer structure containing at least two sub-layers, wherein the composition of each sub-layer in the multi-layer structure is the same or different.

5. The interface reinforcement structure for a quartz resonant force sensor based on a TiAl alloy transition layer according to claim 1, characterized in that, The Fe-based substrate is a metal substrate with an Fe element atomic percentage content of ≥40 at.%; the raw material of the epoxy resin encapsulation layer is selected from bisphenol A type epoxy resin, bisphenol F type epoxy resin, or a combination thereof.

6. A method for preparing an interface reinforcement structure for a quartz resonant force sensor based on a TiAl alloy transition layer as described in any one of claims 1 to 5, characterized in that, Includes the following steps: Step S1: Pre-treat the Fe-based substrate to remove surface impurities and oxide layers; Step S2: A TiAl alloy transition layer is deposited on the pretreated Fe-based substrate surface using physical vapor deposition. Step S3: Apply epoxy resin to the surface of the TiAl alloy transition layer, attach the quartz resonator to the epoxy resin coating, and cure to form an epoxy resin encapsulation layer, thereby obtaining an interface-strengthened quartz resonator force sensor.

7. The preparation method according to claim 6, characterized in that, In step S2, the physical vapor deposition process is a magnetron sputtering process, specifically including: in an argon atmosphere with a vacuum of 1×10⁻³ Pa to 5×10⁻³ Pa, using DC pulse magnetron sputtering with a sputtering power of 100 W to 600 W, and controlling the deposition thickness of the TiAl alloy transition layer by adjusting the sputtering time.

8. The preparation method according to claim 7, characterized in that, In step S2, the target material used in the magnetron sputtering is a TiAl alloy target, or a pure Ti target and a pure Al target, and the atomic percentage content of Al element in the TiAl alloy transition layer is controlled by co-sputtering.

9. The preparation method according to claim 6, characterized in that, In step S1, the pretreatment includes polishing the Fe-based substrate, followed by ultrasonic cleaning with acetone, anhydrous ethanol, and deionized water in sequence, with each ultrasonic cleaning lasting 10 to 30 minutes, and drying after cleaning; in step S3, the curing temperature is 60°C to 150°C, and the curing time is 2 to 4 hours.

10. A quartz resonant force sensor, characterized in that, A quartz resonant force sensor interface reinforcement structure comprising a TiAl alloy transition layer as described in any one of claims 1 to 5.

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