High-spatial-resolution magnetic Barkhausen noise MBN sensor and measurement method

Abstract

The invention discloses a high-spatial-resolution magnetic Barkhausen noise MBN sensor and a measurement method, and belongs to the technical field of micro-magnetic nondestructive testing. A magnetic Barkhausen noise (MBN) nondestructive testing method is adopted, lossy operations such as grinding and polishing on the surface of the material and acid pickling are avoided, and measurement of the grain boundary position and the grain boundary inclination angle of the material is achieved. Firstly, through an innovative horseshoe-shaped magnet yoke design, by optimizing a magnet yoke structure and accurately machining a tip air gap of the magnet yoke structure, preparation of a high-spatial-resolution MBN sensor is achieved. And then, by utilizing the difference between the grain boundary position of the ferromagnetic material and the internal magnetic signal of the grain, the internal and grain boundary areas of the grain can be accurately distinguished through plane scanning and characteristic value extraction, and the positioning of the grain boundary position is realized. Meanwhile, a magnetic field rotation method is introduced, and the inclination angle of the grain boundary is accurately measured by comparing and analyzing MBN signals in different magnetic field directions. According to the device and the method, the measurement efficiency of microstructures such as the ferromagnetic material grain boundary is effectively improved.

Description

Technical Field

[0001] The present application relates to the field of micro-magnetic non-destructive testing technology, and in particular to a method and device for measuring the position and inclination angle of grain boundaries of ferromagnetic materials. The method is based on magnetic Barkhausen noise detection technology, does not require material surface processing, and realizes the positioning of material grain boundaries and the detection of grain boundary inclination angles. Background Art

[0002] Importance of ferromagnetic materials. Grain boundaries, as key microstructural defects of materials, significantly affect the magnetic and mechanical properties of materials. Traditional methods of detecting grain boundary information include metallographic microscopes, magneto-optical Kerr microscopes, transmission electron microscopes, etc., but these methods all require grinding, polishing, and even pickling of the surface, which is a cumbersome process and a lossy measurement method. Magnetic Barkhausen noise (MBN) has been proven to be an effective detection method for the microstructure of ferromagnetic materials. It has the advantages of non-destructive detection and rapid detection, and is therefore widely used in the detection of ferromagnetic material properties.

[0003] However, the spatial resolution of traditional MBN sensors is poor, often in the millimeter range. The grain size of common ferromagnetic materials such as steel is in the micrometer range, so traditional MBN sensors cannot accurately measure the grain boundary information (including position and tilt angle, etc.) of ferromagnetic materials. Summary of the invention

[0004] Based on the above, the purpose of the present invention is to provide a MBN detection method with high spatial resolution, which cooperates with plane scanning and magnetic field rotation methods to achieve non-destructive detection of grain boundary positions and tilt angles of ferromagnetic materials.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] A nondestructive detection method for the position and tilt angle of grain boundaries of ferromagnetic materials is characterized in that: a high spatial resolution MBN sensor is designed, and then the MBN of the material is detected line by line and point by point through a plane scanning method, and appropriate magnetic features are selected to finally achieve plane magnetic imaging of the material. Based on the difference between the magnetic signals of the grain boundary and the inside of the grain, the magnetic imaging results are used to accurately identify the position of the grain boundary. The present invention also introduces a magnetic field rotation mechanism, and by comparing and analyzing the measurement results at the grain boundary after the magnetic field is rotated and the data inside the grain, the tilt angle of the grain boundary can be accurately measured.

[0007] The high spatial resolution MBN sensor adopts a horseshoe-shaped yoke design and precisely processes the tip air gap that determines the spatial resolution, achieving an air gap size of the micron level.

[0008] The method for detecting the grain boundary and the grain boundary inclination angle of the ferromagnetic material is as follows:

[0009] 1) Use a function generator to generate a 10Hz to 100Hz sinusoidal signal, which is then passed through a power amplifier and then into the excitation yoke to perform AC magnetization on the test piece;

[0010] 2) Fix the MBN sensor to the clamping device, and use a high-precision displacement device to fix the air gap of the MBN sensor to a position of 0.05mm to 0.1mm from the test piece;

[0011] 3) The signal measured by the MBN sensor is filtered and amplified by hardware and then passed to the acquisition card for transmission to the host computer;

[0012] 4) Change the measurement position and repeat steps 1) to 3) until the measurement process of the entire area to be measured including the grain boundary is completed;

[0013] 5) Rotate the excitation magnetic field and repeat steps 1) to 4);

[0014] 6) Extract characteristic values ​​from the measured MBN signals and correspond the characteristic values ​​to the measurement positions one by one. Since the grain boundary, as an important part of the microstructure, directly affects the magnetization process of the material and the characteristics of the MBN signal, there will be obvious differences in the characteristic values ​​at the grain boundary and inside the grain;

[0015] 7) The effect of grain boundary on micromagnetic signal is related to the angle of magnetic field. However, commonly used ferromagnetic materials, such as grain-oriented silicon steel, are also affected by rolling stress during the production process. In order to remove this influence and measure the inclination angle of grain boundary, it is necessary to subtract the average value of the local area inside the grain from the result measured at the grain boundary position:

[0016]

[0017] In the formula, MBN θ MBN represents the MBN characteristic value signal after removing the effect of rolling direction at the grain boundary position. gb Represents the original signal of the characteristic value measured at the same grain boundary position, MBN i Represents the MBN characteristic value signal measured inside the grain.

[0018] 8) MBN θ One-to-one correspondence with the measured positions of the grain boundaries is used to solve the inclination angle of the grain boundaries based on the principle that the characteristic value appears at an extreme value when the magnetic field is perpendicular to the grain boundaries.

[0019] The beneficial effects of the present invention are:

[0020] 1. The present invention utilizes the MBN measurement method, which does not require the sample surface to be destroyed, and obtains information such as the position and tilt angle of the grain boundary, thereby achieving non-destructive testing of the sample.

[0021] 2. The present invention proposes a high spatial resolution MBN sensor design method, which improves the spatial resolution of the MBN sensor by processing the air gap of the MBN sensor yoke. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Overall schematic diagram of the sensor measurement specimen;

[0023] Figure 2 Yoke air gap size measurement diagram;

[0024] Figure 3 Schematic diagram of the sensor scanning path;

[0025] Figure 4 Schematic diagram of the sensor's two-dimensional magnetic imaging;

[0026] Figure 5 Schematic diagram of magnetic field and grain boundary tilt angle;

[0027] Figure 6 Schematic diagram of solving the grain boundary tilt angle.

[0028] In the figure: 1-yoke 2-coil 3-Permalloy shell 4-epoxy resin layer 5-yoke air gap 6-test piece 7-excitation yoke 8-excitation coil 9-grain 1 10-grain boundary 11-grain 2. DETAILED DESCRIPTION

[0029] The present invention is further described below in conjunction with the accompanying drawings and the above embodiments. The specific implementation examples provided below are only descriptive and not restrictive, and cannot be used to limit the protection scope of the present invention.

[0030] Figure 1The figure shows the overall schematic diagram of the MBN sensor measuring the specimen. The high spatial resolution MBN sensor mainly includes a magnetic yoke, an enameled coil, a Permalloy shell and epoxy resin. The magnetic yoke 1 is made of Permalloy and has a similar appearance to a horseshoe. The size of the air gap at its tip determines the spatial resolution of the sensor. The air gap size is changed to a length of 1μm to 100μm and a width of 0.1μm to 5μm by cutting, grinding and polishing the air gap part of the magnetic yoke. The enameled coil 2 is wound on the left side of the magnetic yoke. When the material microstructure changes and generates magnetic field disturbances, the changing magnetic field signal is converted into a voltage signal. A layer of Permalloy shell 3 is wrapped around the outside of the magnetic yoke to reduce the influence of external noise on the collected signal. In order to reduce the leakage magnetic field generated during the operation of the sensor and increase the stability of the structure, epoxy resin 4 is added as a filler between the horseshoe-shaped magnetic yoke and the Permalloy shell to improve the detection performance and reliability of the sensor.

[0031] The size of the sensor yoke air gap 5 is measured using an optical microscope, and the results are as follows Figure 2 As shown. A function generator is used to generate a 50Hz, 1.5V sinusoidal excitation signal, which is amplified by a power amplifier and then input into coil 8 to excite the test piece. The sensor is fixed to the clamping device, and the movement of the sensor is controlled by a high-precision translation stage. The measurement path is as follows: Figure 3 As shown in the figure. The MBN signal collected by the sensor is band-pass filtered (10kHz~1MHz) and then pre-amplified 1000 times. The processed signal is then uploaded to the host computer via the PXIe6376 data acquisition card with a sampling rate of 2M / s. The measurement step size is set to 0.2mm during the experiment.

[0032] The characteristic values ​​of the measured MBN signals, such as peak value, coercive force, etc., are extracted respectively, and they are matched one by one with the measurement points. The two-dimensional magnetic imaging is performed using data processing software. Since the grain boundary and the interior of the grain have different effects on the MBN signal, the characteristic values ​​of the MBN signal at the grain boundary will show a different change trend from that inside the grain. The parameters closely related to the grain boundary are selected, which can be used as the characteristic values ​​of grain boundary positioning, such as the MBN peak value. The schematic diagram of the two-dimensional magnetic imaging is shown in the figure. Figure 4 shown.

[0033] On the basis of grain boundary positioning, a coordinate system is established with the rolling direction as the horizontal axis and the horizontal direction as the vertical axis, such as Figure 5 Taking the characteristic value MBN peak as an example, the magnetic field rotation step is set to 10°, and the results at different magnetic field angles are measured, as shown in Figure 6 As shown in (a), it can be found that the overall characteristic value shows a downward trend. By removing the influence of rolling stress on the experimental results, Figure 6 (b) shows the result. Figure 6As shown in (c), it can be found that a peak appears when the magnetic field angle is 30°. Since the MBN peak is strongest when the angle is vertical, it means that the inclination angle of the measured grain boundary is 60°.

Claims

1. A high spatial resolution magnetic Barkhausen noise MBN sensor, characterized in that: include: The magnetic yoke is a horseshoe-shaped structure made of Permalloy, and the tip air gap is precisely processed to a length of 1μm to 100μm and a width of 0.1μm to 5μm through cutting, grinding and polishing steps to improve spatial resolution; An enameled coil, wound around the side of the magnetic yoke, is used to convert the magnetic field disturbance generated by the microstructure change of the material into a voltage signal; Permalloy shell, wrapped around the outside of the magnetic yoke, is used to reduce the impact of external noise on the collected signal; The epoxy resin filler is disposed between the magnetic yoke and the Permalloy housing to reduce magnetic leakage during operation of the magnetic Barkhausen noise sensor, i.e., the MBN sensor, and increase stability.

2. The high spatial resolution magnetic Barkhausen noise MBN sensor according to claim 1, characterized in that: The size of the air gap at the tip of the yoke determines the spatial resolution of the MBN sensor.

3. A method for detecting grain boundaries and grain boundary inclination angles of ferromagnetic materials using the high spatial resolution magnetic Barkhausen noise (MBN) sensor as claimed in claim 1 or 2, comprising the following steps: a) Use a function generator to generate a 10Hz to 100Hz sinusoidal signal, amplify it through a power amplifier, and pass it into the excitation coil to perform AC magnetization on the test piece; b) Fix the MBN sensor to the clamping device, and control the end of the MBN sensor to slightly contact the test piece; c) The MBN sensor measurement signal is filtered and amplified by hardware and then passed to the acquisition card for transmission to the host computer; d) changing the measuring position and repeating the above measuring steps a) to c) until the entire measuring area including the grain boundary is measured; e) rotating the excitation magnetic field and repeating the above measurement steps a) to d); f) extracting characteristic values ​​from the measured MBN signals, and making a one-to-one correspondence between the characteristic values ​​and the measurement positions, so as to distinguish the characteristic value differences between the grain boundary and the grain interior; g) MBN characteristic value signal MBN after removing the rolling direction effect by calculation θ : In the formula, MBN θ MBN represents the MBN characteristic value signal after removing the effect of rolling direction at the grain boundary position. gb Represents the original signal of the characteristic value measured at the same grain boundary position, MBN i Represents the MBN characteristic value signal measured inside the grain; h) MBN θ One-to-one correspondence with the measured positions of the grain boundaries is used to solve the inclination angle of the grain boundaries based on the principle that the characteristic value appears at an extreme value when the magnetic field is perpendicular to the grain boundaries.

4. The method for detecting grain boundaries and grain boundary inclination angles of ferromagnetic materials according to claim 3, characterized in that: By precisely machining the tip air gap size of the yoke, the spatial resolution of the MBN sensor is improved, thereby achieving simultaneous detection of the grain boundary position and grain boundary inclination angle in ferromagnetic materials.

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