Metal grain boundary distinguishing method and device based on laser ultrasonic spectrum analysis

Abstract

The invention discloses a metal grain boundary distinguishing method and device based on laser ultrasonic spectrum analysis, and the method comprises the steps: carrying out the spatial modulation of laser acting on the surface of a sample through an excitation laser part, enabling the laser to be converted into linear array laser, controlling the excitation laser to cross a metal grain boundary through a stepping motor, and exciting an ultrasonic surface wave signal; the detection laser part is used for collecting excited ultrasonic surface wave signals; and the ultrasonic signal processing part is used for carrying out frequency spectrum refining and waveform decomposition processing on the surface wave signal, and determining the relationship between the stepping distance of the linear array laser relative to the grain boundary and the grain characteristic frequency intensity after the result is sorted, so that the distinguishing of the metal grain boundary is realized. Compared with a traditional metallographic method, the method has the advantages of being high in detection speed, low in cost, free of damage to samples and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of laser ultrasonic nondestructive testing, and in particular relates to a metal grain boundary resolution method and device based on laser ultrasonic spectrum analysis. Background Art

[0002] Metal materials play a vital role in modern industry, particularly in precision machining, high-end medical treatment, and aerospace. The grain size of metal materials, also known as metal grain size, is a crucial parameter when studying the microscopic characteristics of metal materials. In industrial production, grain size influences many physical properties of the material, such as elastic constants, density, fatigue strength, and toughness. During the manufacturing process of metal parts, problems such as process design, inappropriate heating temperatures, and external interference can cause the grain size of the metal material to fail to meet application requirements. Excessively large grains can lead to reduced strength, poor corrosion resistance, and increased susceptibility to damage, significantly reducing the material's expected service life. If the grain size of metal materials can be determined promptly during manufacturing, adjustments can be made to the manufacturing process to reduce the occurrence of substandard products. Therefore, the precise detection of metal grain size has high research value.

[0003] Currently, there are two common grain inspection techniques: destructive testing and non-destructive testing. Destructive testing primarily involves metallography and EBSD techniques, which are generally highly accurate but can damage the surface of the sample, resulting in low efficiency and high costs. Non-destructive testing primarily involves ultrasonic velocity and ultrasonic attenuation methods, which offer good cost-effectiveness and accuracy, but are contact-based, significantly reducing flexibility and efficiency. Summary of the Invention

[0004] The purpose of the present invention is to propose a metal grain boundary resolution method and device based on laser ultrasonic spectrum analysis, which has the advantages of fast detection speed, low cost and no damage to the sample.

[0005] The technical solution for implementing the present invention is: a metal grain boundary resolution method based on laser ultrasonic spectrum analysis, comprising:

[0006] The laser acting on the sample surface is spatially modulated to convert it into a linear array laser. The laser is excited to cross the metal grain boundary and stimulate ultrasonic surface wave signals through stepper motor control.

[0007] Collecting the excited ultrasonic surface wave signal;

[0008] The surface wave signal is subjected to spectrum refinement and waveform decomposition processing to determine the relationship between the distance of the linear array laser step relative to the grain boundary and the intensity of the grain characteristic frequency, thereby achieving the resolution of the metal grain boundary.

[0009] Furthermore, the excitation laser part first outputs a pulsed laser from an Nd:YAG laser. The light passes through a spatial modulation module and is focused by a cylindrical mirror to generate a linear array laser. The excitation light is reflected by a dichroic mirror and then passes through a convex lens to finally irradiate the surface of the material being tested to excite ultrasonic waves.

[0010] Furthermore, the Nd:YAG laser outputs pulsed laser, and its output frequency is 1 KHz.

[0011] Furthermore, the excitation laser wavelength is 1064 nm, and the detection laser wavelength is 632 nm.

[0012] Furthermore, the spatial modulation module includes a diffraction optical element and two convex lenses to perform beam splitting, beam expansion and collimation on the excitation laser.

[0013] Furthermore, the detection laser part collects the excited ultrasonic surface wave signal, and the He-Ne laser outputs a continuous laser. The laser light intensity is first adjusted by a half-wave plate, and then the laser light passes through the polarization beam splitter prism PBS;

[0014] The propagation direction of the P-polarized light remains unchanged after transmission, while the S-polarized light is reflected perpendicular to the direction of the P-polarized light. The transmitted P-polarized light is converted into circularly polarized light by a quarter-wave plate and reflected by a reflector. It is coupled with the excitation light on the dichroic mirror and transmitted through the dichroic mirror. After passing through the convex lens, it is irradiated onto the surface of the horizontally placed material being tested.

[0015] The detection laser is reflected on the surface of the material and returns along the original optical path. When the reflected light passes through the quarter-wave plate, the reflected light is converted from circularly polarized light to S-polarized light and reflected to another perpendicular direction by the beam splitter prism PBS. A knife edge is placed in the direction of light propagation. When the light passes through the knife edge, the position of the knife edge is adjusted to block half of the reflected light intensity.

[0016] The remaining reflected light is focused by a convex lens, and then the stray light is filtered out using blue light glass, and then the detection light is received by the photodetector;

[0017] After the linear array laser excites ultrasonic surface waves on the sample surface, the surface waves cause the detection laser to deflect during the propagation along the sample surface, causing the light intensity received by the photodetector to change, thereby obtaining surface wave information.

[0018] Furthermore, the ultrasonic signal processing part first performs Fourier transform on the surface wave signal to obtain the signal spectrum, then uses the complex modulation refinement algorithm to improve its resolution, and finally uses the Gaussian waveform decomposition algorithm to obtain the amplitude of the grain characteristic center frequency.

[0019] Furthermore, the grain boundaries of the sample grains are scanned across to determine the relationship between the characteristic frequency intensity corresponding to the grains in the linear array scanning direction and the linear array laser stepping distance; the relative position of the grain boundaries of the sample grains is judged based on the intensity of the characteristic frequency in the collected ultrasonic surface wave data.

[0020] A metal grain boundary resolution device based on laser ultrasonic spectrum analysis is used to implement the above method, and the device includes:

[0021] The excitation laser module is used to spatially modulate the laser acting on the sample surface, converting it into a linear array laser. The stepper motor controls the excitation laser to cross the metal grain boundary and stimulate the ultrasonic surface wave signal.

[0022] A detection laser module is used to collect the excited ultrasonic surface wave signal;

[0023] The ultrasonic signal processing module is used to refine the spectrum and decompose the waveform of the surface wave signal. After sorting the results, an expression for the relationship between the distance of the linear array laser relative to the grain boundary and the intensity of the grain characteristic frequency is established to achieve the resolution of the metal grain boundary.

[0024] An electronic device includes a memory, a processor, and a computer program stored in the memory and runnable on the processor, wherein the processor implements the above-mentioned metal grain boundary resolution method based on laser ultrasonic spectrum analysis when executing the program.

[0025] Compared with the existing technology, the significant advantages of the present invention are: ultrasonic waves are excited and detected through the interaction between laser and target material. Compared with traditional ultrasonic detection, laser ultrasonic detection does not require coupling agent and can achieve non-contact excitation and detection; the system can work in harsh environments; the optically modulated laser spot radius is small, and complex curved surfaces can be detected; the frequency of ultrasonic waves excited by the laser on the material surface is higher than that of traditional ultrasonic detection, and its wavelength is shorter, which makes laser ultrasound have higher detection accuracy, thereby realizing low-cost and rapid non-destructive detection of metal grains. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Schematic diagram of the metal grain boundary resolution device for laser ultrasonic spectrum analysis.

[0027] Figure 2 This is the result of ultrasonic surface waves excited by linear array laser. DETAILED DESCRIPTION

[0028] The specific implementation of the present invention will be further described below with reference to the accompanying drawings.

[0029] The present invention proposes a metal grain boundary resolution method and device based on laser ultrasonic spectrum analysis, which can more accurately determine the size of metal grains.

[0030] like Figure 1 As shown, the metal grain boundary resolution device includes: a detection laser 1, a half-wave plate 2, a PBS beam splitter prism 3, a quarter-wave plate 4, a reflector 5, an excitation laser 6, a diffraction optical element 7, a convex lens 8, a convex lens 9, a cylindrical mirror 10, a dichroic mirror 1, a convex lens 12, a detection sample 13, a knife edge 14, a convex lens 15, a blue light glass 16, a photodetector 17, a signal amplifier 18, an oscilloscope 19 and a computer 20.

[0031] Based on the above device, the detection method of the present invention comprises the following steps:

[0032] Step 1: The excitation laser part first uses an Nd:YAG laser to output a 1064nm pulsed laser with an output frequency of 1KHz. The light is split into 16 beams by a diffraction optical element. After being expanded and collimated by a lens, it is modulated into a laser linear array with a spacing of 100um using a cylindrical mirror. The linear array laser is reflected by a dichroic mirror, and then focused by a convex lens and finally irradiated on the surface of the material to be tested to excite ultrasonic waves;

[0033] Step 2: The detection laser part collects the excited ultrasonic surface wave signal. The He-Ne laser outputs a continuous laser. The laser intensity is first adjusted by a half-wave plate, and then the laser light passes through the polarization beam splitter prism PBS;

[0034] After the P-polarized light is transmitted, its propagation direction remains unchanged, while the S-polarized light is reflected perpendicular to the P-polarized light. The transmitted P-polarized light is converted into circularly polarized light by a quarter-wave plate and reflected by a reflector. It is then coupled with the excitation light on the dichroic mirror and transmitted through the dichroic mirror. After passing through a convex lens, it is irradiated onto the horizontal surface of the material being tested.

[0035] The detection laser is reflected on the surface of the material and returns along the original optical path. When the reflected light passes through the quarter-wave plate, the reflected light is converted from circularly polarized light to S-polarized light and reflected to another perpendicular direction by the beam splitter prism PBS. A knife edge is placed in the direction of light propagation. When the light passes through the knife edge, the position of the knife edge is adjusted to block half of the reflected light intensity.

[0036] The remaining reflected light is focused by a convex lens, and then the stray light is filtered out using blue light glass. The detection light is then received by a photodetector, amplified by a signal amplifier, and then collected using an oscilloscope. The waveform of a typical surface acoustic wave signal is shown in the figure below. Figure 2 As shown;

[0037] After the linear array laser excites ultrasonic surface waves on the sample surface, the surface waves cause the detection laser to deflect during the propagation along the sample surface, causing the light intensity received by the photodetector to change, thereby obtaining surface wave information.

[0038] Step 3: The ultrasonic signal processing part mainly uses a computer to refine the spectrum and decompose the waveform of the surface wave signal, and obtain the characteristic frequency amplitude corresponding to the sample grain.

[0039] Step 4: Use a metal grain boundary resolution device for laser ultrasonic spectrum analysis to scan across the grain boundaries of the sample grains and establish a mathematical expression for the relationship between the characteristic frequency intensity corresponding to the grain in the linear array scanning direction and the linear array laser step distance.

[0040] Step 5: Substitute the intensity of the characteristic frequency in the collected ultrasonic surface wave data to determine the relative position of the grain boundary of the sample.

Claims

1. A metal grain boundary resolution method based on laser ultrasonic spectrum analysis, characterized in that: include: The laser acting on the sample surface is spatially modulated to convert it into a linear array laser. The laser is excited to cross the metal grain boundary and stimulate ultrasonic surface wave signals through stepper motor control. Collecting the excited ultrasonic surface wave signal; The surface wave signal is subjected to spectrum refinement and waveform decomposition processing to determine the relationship between the distance of the linear array laser step relative to the grain boundary and the intensity of the grain characteristic frequency, thereby achieving the resolution of the metal grain boundary.

2. The metal grain boundary resolution method based on laser ultrasonic spectrum analysis according to claim 1, characterized in that: The excitation laser part first outputs a pulsed laser from an Nd:YAG laser. The light passes through a spatial modulation module and is focused by a cylindrical mirror to generate a linear array laser. The excitation light is reflected by a dichroic mirror and then passes through a convex lens to finally irradiate the surface of the material being tested to excite ultrasonic waves.

3. The metal grain boundary resolution method based on laser ultrasonic spectrum analysis according to claim 2, characterized in that: The Nd:YAG laser outputs pulsed laser with an output frequency of 1KHz.

4. The metal grain boundary resolution method based on laser ultrasonic spectrum analysis according to claim 2, characterized in that: The excitation laser wavelength is 1064 nm, and the detection laser wavelength is 632 nm.

5. The metal grain boundary resolution method based on laser ultrasonic spectrum analysis according to claim 2, characterized in that: The spatial modulation module includes a diffraction optical element and two convex lenses to split, expand and collimate the excitation laser.

6. The metal grain boundary resolution method based on laser ultrasonic spectrum analysis according to claim 1, characterized in that: The detection laser part collects the excited ultrasonic surface wave signal. The He-Ne laser outputs continuous laser light. The half-wave plate is used to adjust the laser light intensity, and then the laser light passes through the polarization beam splitter prism PBS. The propagation direction of the P-polarized light remains unchanged after transmission, while the S-polarized light is reflected perpendicular to the direction of the P-polarized light. The transmitted P-polarized light is converted into circularly polarized light by a quarter-wave plate and reflected by a reflector. It is coupled with the excitation light on the dichroic mirror and transmitted through the dichroic mirror. After passing through the convex lens, it is irradiated onto the surface of the horizontally placed material being tested. The detection laser is reflected on the surface of the material and returns along the original optical path. When the reflected light passes through the quarter-wave plate, the reflected light is converted from circularly polarized light to S-polarized light and reflected to another perpendicular direction by the beam splitter prism PBS. A knife edge is placed in the direction of light propagation. When the light passes through the knife edge, the position of the knife edge is adjusted to block half of the reflected light intensity. The remaining reflected light is focused by a convex lens, and then the stray light is filtered out using blue light glass, and then the detection light is received by the photodetector; After the linear array laser excites ultrasonic surface waves on the sample surface, the surface waves cause the detection laser to deflect during the propagation along the sample surface, causing the light intensity received by the photodetector to change, thereby obtaining surface wave information.

7. The metal grain boundary resolution method based on laser ultrasonic spectrum analysis according to claim 1, characterized in that: The ultrasonic signal processing part first performs Fourier transform on the surface wave signal to obtain the signal spectrum, then uses the complex modulation refinement algorithm to improve its resolution, and finally uses the Gaussian waveform decomposition algorithm to obtain the amplitude of the grain characteristic center frequency.

8. The metal grain boundary resolution method based on laser ultrasonic spectrum analysis according to claim 7, characterized in that: The grain boundaries of the sample grains are scanned across to determine the relationship between the characteristic frequency intensity corresponding to the grains in the linear array scanning direction and the linear array laser step distance; the relative position of the sample grain boundaries is determined based on the intensity of the characteristic frequency in the collected ultrasonic surface wave data.

9. A metal grain boundary resolution device based on laser ultrasonic spectrum analysis, characterized in that: For implementing the method according to any one of claims 1 to 8, the device comprises: The excitation laser module is used to spatially modulate the laser acting on the sample surface, converting it into a linear array laser. The stepper motor controls the excitation laser to cross the metal grain boundary and stimulate the ultrasonic surface wave signal. A detection laser module is used to collect the excited ultrasonic surface wave signal; The ultrasonic signal processing module is used to refine the spectrum and decompose the waveform of the surface wave signal. After sorting the results, the relationship between the distance of the linear array laser relative to the grain boundary and the intensity of the grain characteristic frequency is determined to achieve the resolution of the metal grain boundary.

10. An electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein: When the processor executes the program, the method according to any one of claims 1 to 8 is implemented.

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