JPH06300550A - Layer thickness measurement method for layer structure material using ultrasonic wave - Google Patents

Abstract

PURPOSE:To provide a layer thickness measurement method using an ultrasonic wave for performing the non-destructive measurement of the layer thickness of a material having a layer structure, and inspecting and evaluating the layer thickness. CONSTITUTION:Probes 4 and 5 having a two-probe system to transmit and receive an ultrasonic wave via an ultrasonic wave angle beam method are used, and the probe 5 for receiving the wave is made to linearly scan along the direction of the probe 4 for transmitting the wave. Then, interface echo from a specimen 7 and the rear scattered wave thereof are processed via a gate to concurrently measure a mixture signal of the rear scattered wave and the interface echo. Data obtainable therefrom is sent to a computer 6 and subjected to a fast Fourier transform process, thereby being resolved into a frequency spectrum. Also, a component along a scan axis direction is added to the spectrum for three-dimensional indication and a comparison is made between the specimen 7 and a material with known layer thickness in terms of three-dimensional form, thereby finding the layer thickness of the specimen 7.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a layer thickness measuring method using ultrasonic waves for nondestructively measuring the layer thickness of a material having a layer structure, and inspecting and evaluating the layer thickness.

[0002]

2. Description of the Related Art In recent years, in order to improve the toughness, arrestability, wear resistance and corrosion resistance of various materials, different materials are combined according to the purpose of use, and functionally graded materials in which the elastic coefficients are one-dimensionally distributed or the same material. , Research on high-performance materials that have a two-layer, three-layer or more layer structure by combining materials that differ only in their particle size on the surface and inside, and by combining different materials.
Being developed. Correspondingly, non-destructive layer thickness measurement is required.

In the above high-performance materials, the layer thickness has a great influence on the performance of the material, and if the layer thickness is too thin, these performances cannot be exhibited. Therefore, the layer thickness is required to be above a certain level. Also, from the standpoint of reliability with respect to user requirements, it is inconvenient if the layer thickness is not constant within the plate. Therefore, the layer thickness control is very important.

As a non-destructive method for measuring the layer thickness, a vertical flaw detection method using a longitudinal wave by ultrasonic waves has been conventionally known as a known technique. For example, the description of the clad steel by the ultrasonic flaw detection method (1974 edition) edited by Japan Society for the Promotion of Science, Steelmaking 19th Committee can be mentioned. This method measures the time difference between the ultrasonic wave reflected from the surface of the subject and the interface, and compares it with the speed of sound of the test piece that was measured in advance and converts it into a distance. is there.

[0005]

In the above-mentioned prior art, it is necessary to surely obtain the reflection echo from the layer interface, but in the above-mentioned high-performance material, the difference in acoustic impedance between the layers is often small. , The echo reflected from the interface is buried in the noise and the interface echo cannot be detected, or the interface echo and the noise may be erroneously recognized, which makes accurate layer thickness measurement difficult. To be

An object of the present invention is to use backscattered waves, which were previously treated as useless like noise, and when the difference in the acoustic impedance of the layer structure is small and the interface echo cannot be obtained as in the above materials. Another object is to provide a method for measuring the layer thickness with a good S / N ratio.

[0007]

To solve the above-mentioned problems, in the oblique angle method using ultrasonic waves, two transmitting and receiving probes are used, and the receiving probe is linearly arranged in the direction of the transmitting probe. Scan, and gate the interface echo and backscattered wave from the subject, measure those waves at the same time, take the data obtained by it into a computer and decompose it into a frequency spectrum by fast Fourier transform, By adding a component in the scan axis direction (tentatively referred to as the X-axis direction) and displaying it three-dimensionally, by comparing the three-dimensional shape of the subject and the one whose layer thickness is known in advance, This is achieved by the method of determining the layer thickness of the subject.

[0008]

The present invention, in measuring the layer thickness by ultrasonic waves,
Instead of measuring the time difference between the reflected wave from the surface of the subject and the interface, the backscattered wave, which was previously treated as useless like noise, and the signal mixed with the interface echo were subjected to frequency decomposition. It is characterized by being used.

By incorporating the backscattered wave and the interface echo at the same time, the backscattering can be performed even when the reflection echo from the interface, which has been difficult to measure in the past, is small, or when the echo is too small to be distinguished from noise. By measuring the shape of the intensity distribution of the frequency spectrum of the signal in which the wave and the interface echo are mixed, it is possible to measure the layer thickness with a good S / N ratio.

This is because the shape of the intensity distribution of the frequency spectrum of the signal in which the backscattered wave and the interface echo are mixed is dependent on the viscosity coefficient of the attenuation of the ultrasonic waves, and the ultrasonic impedance due to the change in the acoustic impedance in each layer of the subject. This is because the difference in the layer thickness depends on the influence on the change of the reflectance and the transmittance and the dependence of the attenuation of the scattered wave on the size of the crystal grain.

From the above, the frequency spectrum is affected by the difference in layer thickness, and the characteristics such as the viscosity coefficient, acoustic impedance, and particle size peculiar to the subject are reflected in its shape, so that the layer thickness is known in advance. By comparing the frequency spectrum shape of the reference object and the shape of the object and finding the most similar shape, noise, interface echo,
It makes it possible to measure the layer thickness without any particular attention to the backscattered waves.

When the backscattered wave is used, it is necessary to average the measurement results at a large number of measurement points because of its coherence and scattering property. However, in this method, the oblique flaw detection method is used. By scanning only the receiving probe by using, the information at one measurement point can be obtained in a manner that takes into account the effect of scattered waves that have spread, so that it can be performed more accurately without complicated averaging. Enables layer thickness measurement.
Further, by using the water immersion method oblique-angle flaw detection longitudinal wave, it is possible to gain scattering intensity and obtain high reproducibility and high stability.

Further, by using a computer in the analysis for measuring the layer thickness from the data measured by the above-mentioned mechanism, it becomes possible to decompose those data into a frequency spectrum. Also, since the intensity distribution of this frequency spectrum reflects the crystal grain size of the lower layer of the layer to be measured, it is possible to optimize the frequency that should be used to obtain the reception gain by measuring those frequency spectra. to enable.

Further, the data can be visually recognized as having a three-dimensional shape. As a result, in the layer thickness measurement, the object and the referenced data are formed into a shape having a three-dimensional spread, which is visually easy to understand, enables easy and highly accurate comparison, and makes it difficult to obtain an interface echo. This makes it possible to easily and highly accurately measure the layer thickness of a subject.

[0015]

EXAMPLES The details of the present invention will be described below based on examples. In this example, the reference test piece was made of the same material for both the surface layer and the lower layer, and the surface layer thickness was 1.4 mm,
1.5 mm ... 2.2 mm, 2.3 mm, lower layer thickness is 40 mm, crystal grain size in the surface layer is about 10 μm, lower layer 1
Ten pieces of steel plates having different grain sizes of 00 μm in the surface layer and the lower layer are used. The subject has a surface layer thickness of 1.4 mm to 2.
Up to 3 mm, the lower layer thickness is 40 mm, the grain size in the surface layer portion is about 10 μm, and the steel plate of the same kind as the referenced test piece of the lower layer portion 100 μm is the measurement target. Also, as a probe,
A wide band with a center frequency of 50 MHz is used.

In FIG. 1, the pulse generated by the pulse generator 1 is converted into ultrasonic waves by the transmitting probe 4. At this time, the wavelength of the ultrasonic waves is set to be about the particle size of the layer (second layer 12) for which the interface echo is desired to be obtained, so that the interface echo can be easily obtained. In addition, the transmission / reception probes 4 and 5 and the subject 7
In order to keep the contact condition with the constant, the water immersion method is used here, and the subject 7 is submerged in the water tank 9. The ultrasonic waves emitted from the transmitting probe 4 travel through the water like a path 10. The ultrasonic waves that have reached the subject 7 return echoes from the surface of the first layer 11, echoes from the interface, backscattered waves, and echoes from the bottom surface, and are received by the receiving probe 5. This signal is synchronized from the pulse generator 1 through the cable 3 and measured by the oscilloscope 2. At this time, the receiving probe 5 scans 30 mm in the X-axis direction at a pitch of 1 mm. The received signal obtained here is sent to the computer 6.

The details will be described below with reference to the flowchart of FIG. 2 with reference to FIGS. 3 to 7. First, in order to obtain referenced data for layer thickness measurement, measurement is performed on a layer thickness of which is known in advance.

In FIG. 3, the X-axis represents the scanning direction, and each wavy solid line is an example of data acquisition by a computer at a certain X position using the measuring apparatus of FIG. Here, the gate 15 is applied to data from the rear of the surface echo 13 to the front of the bottom echo 14 in order to select a necessary data portion. To obtain the frequency spectrum of the obtained data, a fast Fourier transform is performed on the gated data at each X position. As a result, a three-dimensional graph having coordinate axes of the scan position, frequency, and ultrasonic intensity as shown in FIG. 4 is obtained.

This was carried out on 10 reference test pieces having different layer thicknesses whose layer thicknesses were previously known. The graph of FIG. 4 was obtained for each of the 10 test pieces. The volume and shape of this graph are measured for each of 10 test pieces in an X position of 0 mm to 30 mm and a frequency range of 10 MHz to 90 MHz and stored in a computer. This becomes the referenced data.

Here, by expressing the layer thickness as a function of volume, the layer thickness can be obtained by measuring the volume of the subject and substituting it into the function.

In addition to the above method, as shown in FIG.
Shape comparison is made possible by comparing the volumes of the overlapping portions. As shown in FIG. 7, a correlation graph of the common partial volume and the layer thickness is created, and the one having a large common partial volume is set as the layer thickness of the subject.

A more accurate layer thickness can be obtained by comparing and examining the above two methods.

[0023]

INDUSTRIAL APPLICABILITY The present invention makes it easy to measure the layer thickness of a material having a layered structure with similar acoustic characteristics in each layer, which has been difficult until now, by utilizing an ultrasonic interface echo and a backscattered wave. It also enables highly accurate measurement.

[Brief description of drawings]

FIG. 1 is a device schematic view showing an example of a measuring device for carrying out the method of the present invention.

FIG. 2 is a flowchart showing an operation and analysis procedure in the embodiment.

FIG. 3 is a diagram showing a display example of ultrasonic waves and a gate received by a reception probe.

FIG. 4 is a diagram showing a display example of a frequency spectrum of data.

FIG. 5 is a diagram showing an example of measurement of correlation between three-dimensional shape volume and layer thickness.

FIG. 6 is a conceptual diagram of a common partial volume.

FIG. 7 is a diagram showing an example of measuring a correlation between a common partial volume and a layer thickness.

[Explanation of symbols]

 1 Ultrasonic Generator 2 Oscilloscope 3 Sync Signal 4 Transmitting Probe 5 Receiving Probe 6 Computer 7 Subject 8 Water 9 Water Tank 10 Ultrasonic Path 11 1st Layer 12 2nd Layer 13 Surface Echo 14 Bottom Echo 15 Gate

Claims (1)

[Claims] 1. An ultrasonic oblique angle two-probe method is used to scan the receiving probe linearly in the transmitting probe direction,
The received signal obtained at each position of the subject is gated to simultaneously capture the interfacial echo and the backscattered wave, and then the signal is spectrally decomposed to determine the spectrum intensity as a function of the distance between the probes and the frequency. The three-dimensional display is performed, the frequency range to be adopted and the distance between the probes are set, and the volume and shape of the three-dimensionally displayed signal strength are obtained. A method for ultrasonically measuring the layer thickness of a layered material, which comprises comparing the data obtained in advance by the same method with respect to several known and different samples.