Ultrasonic probe and ultrasonic probe manufacturing method

Abstract

To provide an ultrasonic probe that can be used in a high temperature environment.SOLUTION: An ultrasonic probe includes: an electrode; a vibrator that emits ultrasonic when voltage is applied to the electrode and converts the reflected wave of the ultrasonic into electric signals to output it; and a protective member that contacts an object to be inspected. A melting metallization layer is formed on both sides of the vibrator in a thickness direction. The ultrasonic probe further includes: a first joint member that joins the electrode and the vibrator through the melting metallization layer; and a second joint member that joins the vibrator and the protective member through the melting metallization layer. The first joint member and the second joint member are made of a material with a higher melting point than Al.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an ultrasonic probe that can be used in a high-temperature environment and a method for manufacturing the same.

Background Art

[0002] Conventionally, an ultrasonic probe is known that transmits ultrasonic waves from a piezoelectric vibrator to an object to be inspected and detects the internal state of the object to be inspected based on the time until the reflected wave returns. Such an ultrasonic probe is generally configured by laminating, for example, an electrode, a piezoelectric vibrator that transmits and receives ultrasonic waves, and a protective shoe interposed between the piezoelectric vibrator and the object to be inspected.

[0003] In recent years, as an ultrasonic probe that can be used in a high-temperature environment, there is one in which a piezoelectric vibrator is constituted by lithium niobate (LiNbO3) having a high Curie point (see, for example, Patent Documents 1 to 3).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in order to use an ultrasonic probe in a high-temperature environment, it is necessary not only to improve the heat resistance of the piezoelectric element but also to firmly bond a ceramic piezoelectric vibrator, a metal electrode, and a protective shoe. However, in the configurations of Patent Documents 1 to 3, the bonding strength between the ceramic and the metal is not sufficient, particularly in a fast reactor that uses liquid sodium as a coolant.

[0006] The present invention is made to solve such problems of the prior art, and its object is to provide an ultrasonic probe that can be used in a high-temperature environment.

Means for Solving the Problems

[0007] In order to solve the above problems, the present invention provides an ultrasonic probe comprising an electrode, a vibrator that transmits ultrasonic waves when a voltage is applied to the electrode and converts a reflected wave of the ultrasonic waves into an electric signal and outputs it, and a protective member that contacts an object to be inspected. In the ultrasonic probe, melting metallization layers are formed on both surfaces in the thickness direction of the vibrator, and a first joining member that joins the electrode and the vibrator via the melting metallization layer, and a second joining member that joins the vibrator and the protective member via the melting metallization layer are further provided, and the first joining member and the second joining member are characterized in that they are formed of a material having a melting point higher than that of Al.

Effects of the Invention

[0008] According to the present invention, an ultrasonic probe that can be used in a high-temperature environment can be obtained.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

[0010] Hereinafter, the ultrasonic probe 1 according to the embodiment will be described with reference to the drawings. Note that the embodiments of the present invention described below are examples when embodying the present invention, and do not limit the scope of the present invention to the scope of the description of the embodiments. Therefore, the present invention can be implemented with various modifications to the embodiments.

[0011] [Structure of Ultrasonic Probe 1] The ultrasonic probe 1 is a sensor that transmits ultrasonic waves to an object to be inspected and detects the internal state of the object to be inspected based on the reflected waves of the transmitted ultrasonic waves. In this way, since the ultrasonic probe 1 can grasp the internal state without destroying the object to be inspected, for example, it can be used as a sensor for detecting the state of a fluid passing through the inside of a pipe. The ultrasonic probe 1 is, for example, attached to a pipe through which liquid sodium, which is a coolant of a nuclear reactor, passes in a fast breeder reactor, and is used to measure the state (for example, flow velocity, flow rate, temperature) of the liquid sodium passing through the pipe. The ultrasonic probe 1 used for such applications is required to operate appropriately in a high-temperature environment of 850 ° C or higher assuming a severe accident. However, the use of the ultrasonic probe 1 is not limited to this.

[0012] FIG. 1 is a schematic cross-sectional view of the ultrasonic probe 1 according to the present embodiment. FIG. 2 is a table showing candidates for materials that can form the vibrator 4 (A), the protective shoe 5 (B), and the joining members 6 and 7 (C) and their physical properties. As shown in FIG. 1, the ultrasonic probe 1 mainly includes a housing 2, an electrode 3, a vibrator 4, a protective shoe 5 (protective member), joining members 6 and 7, and a signal line 8. In FIG. 1, each member is drawn thickly to clarify the laminated structure of each member, but it is different from the actual thickness.

[0013] The housing 2 is a box-shaped member that houses the components 3 to 8 of the ultrasonic probe 1. One surface (the lower surface in FIG. 1) of the housing 2 is open. Then, the housing 2 exposes the contact surface of the protective shoe 5 with the object to be inspected to the outside through the opening surface. Further, the electrode 3, the joining member 6, the vibrator 4, the joining member 7, and the protective shoe 5 are laminated in this order inside the housing 2.

[0014] The electrode 3 is a metal flat plate (disk) connected to the control device 9 by the signal line 8. The electrode 3 is formed of, for example, Pt. However, since the melting metallization method is adopted for the material constituting the electrode 3 and the end face of the vibrator 4 is metallized, the material is not limited to the above example, and Ti, Mo, Cr, Ta, W, etc. can also be adopted, but Pt is most desirable for the reason of preventing oxidation at high temperatures.

[0015] The vibrator 4 transmits ultrasonic waves when a voltage is applied, and generates a voltage by receiving ultrasonic waves (reflected waves of the transmitted ultrasonic waves). The vibrator 4 is, for example, a flat plate (disk)-shaped member made of ceramic. The vibrator 4 is formed of, for example, LiNbO3 as shown in FIG. 2(A). However, since the material constituting the vibrator 4 only needs to be a material that satisfies the use limit temperature at which performance can be maintained, it is not limited to the above example, and AlN, Ca2Al2SiO7, GaPO, La3Ga5SiO 14 etc. may be used, and they may be appropriately selected.

[0016] On both sides in the thickness direction of the vibrator 4 (the upper and lower surfaces in FIG. 1), melting metallization layers 4a and 4b are formed. The melting metallization layers 4a and 4b are metal films formed on the surface of the ceramic by the melting metallization method. The melting metallization layers 4a and 4b are formed by applying metal powder to the surface of the vibrator 4 and heating it. Examples of the material constituting the melting metallization layers 4a and 4b include metals (alloys) containing Ti. However, the material constituting the melting metallization layers 4a and 4b is not limited to the above example, and Zr may also be used. A combination in which the acoustic impedance satisfies vibrator 4 > metal brazing material > protective shoe 5 is most desirable.

[0017] The protective shoe 5 is a flat metal plate (disc) interposed between the vibrator 4 and the object to be inspected. The protective shoe 5 is formed of a material containing at least one element among W, Ta, Mo, and Nb, for example, as shown in FIG. 2(B). A property required for the protective shoe 5 is that the melting point is sufficiently higher than the use limit temperature of the vibrator 4. Another property required for the protective shoe 5 is that the acoustic impedance is close to that of the vibrator 4 (that is, Nb is most desirable). FIG. 2(B) lists elements with higher acoustic impedance than the vibrator 4, but the magnitude relationship between the acoustic impedances of the vibrator 4 and the protective shoe 5 is not particularly limited.

[0018] The joining members 6 and 7 are so-called "metal brazes" for joining metals. The joining member 6 (the first joining member) joins the electrode 3 and the vibrator 4 via the melting metallization layer 4a. The joining member 7 (the second joining member) joins the vibrator 4 and the protective shoe 5 via the melting metallization layer 4b. The joining members 6 and 7 are formed of a material containing at least one element among Ag, Ni, Ti, Zr, Au, and Cu. That is, the joining members 6 and 7 are formed of a material with a melting point higher than that of Al. Note that the joining members 6 and 7 may be composed of the same material or different materials.

[0019] The material forming the protective shoe 5 (Fig. 2(B)) and the material forming the joining members 6 and 7 (Fig. 2(C)) can be combined arbitrarily. However, the joining member 7 for joining the vibrator 4 and the protective shoe 5 is preferably formed of a material having an acoustic impedance between that of the vibrator 4 and the protective shoe 5 (more specifically, equal to or greater than that of the vibrator 4 and equal to or less than that of the protective shoe 5). As an example, when any one of W, Ta, and Mo is selected as the material forming the protective shoe 5, it is preferable to select Ag, Ni, Ti, Zr, Au, or Cu as the material forming the joining member 7. As another example, when Nb is selected as the material forming the protective shoe 5, it is preferable to select Ti or Zr as the material forming the joining member 7.

[0020] The signal line 8 connects the electrode 3 and the vibrator 4 to the control device 9. The control device 9 applies a voltage (high-frequency pulsed voltage) to the electrode 3 using the power of a commercial power source or a battery. As a result, a potential difference is generated between the electrode 3 and the vibrator 4, causing the vibrator 4 to transmit ultrasonic waves. The ultrasonic waves transmitted by the vibrator 4 propagate through the protective shoe 5 to the object to be inspected, and return to the vibrator 4 as reflected waves. Further, the vibrator 4 converts the received reflected waves into electrical signals (voltages) and outputs them to the control device 9 through the signal line 8. Then, the control device 9 identifies the internal state of the object to be inspected based on the electrical signals received from the vibrator 4. The specific operation of the ultrasonic probe 1 is the same as that of the prior art.

[0021] [Method for manufacturing the ultrasonic probe 1] Fig. 3 is a diagram showing the manufacturing process of the ultrasonic probe 1 according to the present embodiment. Fig. 4 is a schematic diagram of a jig 11 for restraining the laminated structure 10 that becomes the ultrasonic probe 1.

[0022] First, a brazing material for the electrode 3, the vibrator 4, the protective shoe 5, and the joining members 6 and 7 is formed into a predetermined shape (S1). Next, the electrode 3, the brazing material for the joining member 6, the metal powder for the molten metallization layer 4a, the vibrator 4, the metal powder for the molten metallization layer 4b, the brazing material for the joining member 7, and the protective shoe 5 are laminated in this order to form a laminated structure 10 (S2). Next, as shown in FIG. 4, the laminated structure 10 is restrained by a jig 11 (S3).

[0023] The jig 11 restrains the laminated structure 10 so as to limit thermal expansion in the lamination direction and allow thermal expansion in a direction orthogonal to the lamination direction. Here, "limiting thermal deformation in the lamination direction" does not mean completely preventing thermal deformation, but may mean allowing thermal deformation within a minute range (for example, within the elastic range of the spring washers 16a and 16b described later). The jig 11 includes, for example, a plurality of screws 12a and 12b, a pair of clamping plates 13a and 13b, a pair of ceramic plates 14a and 14b, a plurality of nuts 15a, 15b, 15c, 15d, 15e, and 15f, and a plurality of spring washers 16a and 16b.

[0024] The screws 12a and 12b are each extended in the lamination direction (vertical direction) at positions surrounding the laminated structure 10. Although two screws 12a and 12b are shown in FIG. 4, the laminated structure 10 may be surrounded by four screws.

[0025] The clamping plates 13a and 13b are flat metal plates. Through holes through which the screws 12a and 12b are inserted are formed in the clamping plates 13a and 13b. Then, the clamping plates 13a and 13b are disposed on both sides of the laminated structure 10 in the lamination direction, and the screws 12a and 12b are inserted through the through holes. Then, the clamping plates 13a and 13b clamp the laminated structure 10 from both sides in the lamination direction to restrain (position the components) the laminated structure 10.

[0026] The ceramic plates 14a and 14b are flat ceramic plates made of, for example, alumina (AlO3). The ceramic plates 14a and 14b are disposed between the laminated structure 10 and the clamping plates 13a and 13b. More specifically, the ceramic plate 14a is disposed between the electrode 3 and the clamping plate 13a. The ceramic plate 14b is disposed between the protective shoe 5 and the clamping plate 13b. Note that the ceramic plates 14a and 14b are arranged to absorb thermal deformation (expansion, contraction) of the electrode 3 and the protective shoe 5, which have a larger coefficient of linear expansion compared to the ceramic vibrator 4. Also, the ceramic plates 14a and 14b are made of a material with a lower heat transfer rate than the electrode 3 and the protective shoe 5. Further, it is desirable that the surface roughness of the ceramic plates 14a and 14b be made rough (for example, to a roughness of rough finish (Ra: 25 μm) to parallel finish (Ra: 6.3 μm) or more) to prevent sticking to the electrode 3 and the protective shoe 5.

[0027] The thickness dimensions of the ceramic plates 14a and 14b may be different from each other. More specifically, the larger the thickness dimensions of the components of the laminated structure 10 (that is, the electrode 3 and the protective shoe 5) in contact with the ceramic plates 14a and 14b, the larger the thickness dimensions of the ceramic plates 14a and 14b. Also, the larger the coefficient of linear expansion of the components of the laminated structure 10 (that is, the electrode 3 and the protective shoe 5) in contact with the ceramic plates 14a and 14b, the larger the thickness dimensions of the ceramic plates 14a and 14b. In the present embodiment, the thickness dimension of the ceramic plate 14b in contact with the protective shoe 5 is made larger than that of the ceramic plate 14a in contact with the electrode 3.

[0028] Nuts 15a to 15f are screwed onto screws 12a and 12b. Nuts 15a to 15f position the clamping plates 13a and 13b and adjust the restraining force of the laminated structure 10 by the clamping plates 13a and 13b. More specifically, nuts 15a, 15b, 15c, and 15d are screwed onto screws 12a and 12b so as to sandwich the clamping plate 13b in the lamination direction, thereby positioning and fixing the clamping plate 13b. Nuts 15e and 15f are screwed onto screws 12a and 12b above the clamping plate 13a and press the clamping plate 13a downward so that the components of the laminated structure 10 are restrained with a force that prevents displacement.

[0029] Spring washers 16a and 16b are formed by cutting a part of the circumferential direction of a washer, with a pair of cut surfaces being displaced in the thickness direction. Examples of the material constituting the spring washers 16a and 16b include Cu, Ni, and SUS. The spring washers 16a and 16b are inserted through the screws 12a and 12b between the clamping plate 13a and the nuts 15e and 15f. The spring washers 16a and 16b serve to adjust the restraining force of the clamping plates 13a and 13b as the laminated structure 10 thermally expands due to heating (S4) of the laminated structure 10 described later. More specifically, the spring washers 16a and 16b weaken the restraining force of the clamping plates 13a and 13b as the laminated structure 10 thermally expands, preventing the laminated structure 10 from being excessively compressed.

[0030] As shown in FIG. 4, by restraining the laminated structure 10 with the jig 11, the thermal expansion of the laminated structure 10 in the lamination direction is limited within the elastic range of the spring washers 16a and 16b. Note that the restraining force by the clamping plates 13a and 13b may be a weak force that can prevent displacement of the components of the laminated structure 10. On the other hand, since the jig 11 does not restrain the laminated structure 10 in the direction orthogonal to the lamination direction (the horizontal direction in FIG. 4), thermal expansion of the laminated structure 10 in the horizontal direction is allowed.

[0031] Next, the laminated structure 10 restrained by the jig 11 is accommodated in a vacuum furnace (not shown), heated at a heating rate in the range of about 8 °C / min to 10 °C / min or less at a predetermined temperature (750 °C to 1,000 °C) according to the joining target for about 3 to 5 hours, and then naturally cooled in the vacuum furnace (S4). As a result, the metal powder melts and melting metallization layers 4a and 4b are formed on both surfaces of the vibrator 4, and the metal brazing material melts and the electrodes 3, the vibrator 4, and the protective shoe 5 are joined by the joining members 6 and 7. Further, the electrodes 3 and the vibrator 4 and the control device 9 are connected by the signal line 8 and housed in the housing 2, whereby the ultrasonic probe 1 is completed (S5).

[0032] Note that the predetermined temperature varies depending on the material of the vibrator 4. For example, for Ca2Al2SiO7 and GaPO, it is 750 °C, for La3Ga5SiO 14 it is set to 800 °C to 900 °C or less, and for AlN and LiNbO3, it is 1,000 °C (850 °C in this embodiment) or less. Also, from the viewpoint of working efficiency, the heating rate is preferably in the range of about 8 °C / min to about 10 °C / min. However, if the heating rate exceeds 10 °C / min, there is a risk of joining defects such as cracking of the vibrator 4 due to a rapid temperature change.

[0033] The degree of vacuum inside the vacuum furnace is appropriately selected according to the material constituting the laminated structure 10. For example, when Nb is used for the protective shoe 5, it is desirable to set a high degree of vacuum to prevent oxidation. Also, the heating temperature (predetermined temperature) is a temperature equal to or higher than the melting points of the metal powder that becomes the melting metallization layers 4a and 4b and the metal brazing material that becomes the joining members 6 and 7. For example, when Ti is used for the metal powder and Ag is used for the metal brazing material, it is about 850 °C. Further, the heating time (predetermined time) is appropriately selected according to the thickness dimension of the metal brazing material, etc.

[0034] [Consideration of the jig 11] FIG. 5 is a table showing the bonding results when the presence or absence of the ceramic plates 14a and 14b and the spring washers 16a and 16b and the material of the protective shoe 5 are changed. In the columns of the ceramic plates 14a and 14b and the spring washers 16a and 16b in FIG. 5, an "x" indicates that the member is omitted, and a "o" indicates that the member is used. In the column of the bonding results in FIG. 5, an "x" indicates that bonding was not possible, a "Δ" indicates that bonding was possible to the same extent as in the prior art, and a "o" indicates that bonding was possible to a higher quality (higher strength) than in the prior art.

[0035] As shown in Patterns A to D, when any of the ceramic plates 14a and 14b and the spring washers 16a and 16b were omitted, proper bonding could not be achieved. More specifically, problems such as cracking of the vibrator 4 and sticking of the electrodes 3 and the protective shoe 5 to the clamping plates 13a and 13b occurred. From this, it was found that it is desirable for the surface roughness of the ceramic plates 14a and 14b to be rougher. The surface roughness of the ceramic plates 14a and 14b is preferably rough finish (Ra: 25 μm) to finish (Ra: 6.3 μm) or more.

[0036] However, when the spring washers 16a and 16b were used (Pattern B), the frequency of cracking of the vibrator 4 decreased. In particular, the lower the Mohs hardness of the material (SUS > Ni > Cu) of the spring washers 16a and 16b, the lower the frequency of cracking of the vibrator 4. That is, it is considered that during the process of heating the laminated structure 10, the thermal expansion of the electrodes 3 and the protective shoe 5 is absorbed by the elasticity of the spring washers 16a and 16b. From this, it was found that the Mohs hardness of the spring washers 16a and 16b is important, and it was found that Cu is desirable.

[0037] Also, when using the ceramic plates 14a (Pattern C), sticking between the electrodes 3 and the protective shoes 5 and the clamping plates 13a, 13b could be prevented. Furthermore, when using both of the ceramic plates 14a, 14b (Pattern D) and changing the combination of the thickness dimensions (thin, medium, thick) of the ceramic plates 14a, 14b, when the ceramic plate 14b was made thicker than the ceramic plate 14a, the crack of the vibrator 4 was the least. That is, it is considered that by bringing the ceramic plates 14a, 14b with low heat transfer coefficients into contact with the electrodes 3 and the protective shoes 5, a rapid drop in the temperature of the electrodes 3 and the protective shoes 5 during cooling can be prevented. The thicknesses of the ceramic plates 14a, 14b may be set, for example, according to the thicknesses of the electrodes 3 and the protective shoes 5 and the ratio of the coefficients of thermal expansion.

[0038] On the other hand, as shown in Patterns E to F, when using all of the ceramic plates 14a, 14b and the Cu spring washers 16a, 16b, the frequency of the vibrator 4 became extremely low, and the electrodes 3, the vibrator 4, and the protective shoes 5 were properly joined via the joining members 6, 7. Regarding the vibrator 4, when using the protective shoe 5 made of Ti (Pattern E), cracks occurred at about the same level as in the prior art, whereas when using the protective shoe 5 made of Nb with a lower coefficient of thermal expansion than Ti (Pattern F), no cracks were confirmed. That is, it was confirmed that by forming the protective shoe 5 with a material having a low coefficient of thermal expansion (in other words, a material having a linear expansion coefficient close to that of the vibrator 4), cracks in the vibrator 4 can be effectively prevented.

[0039] [Comparison with the conventional manufacturing method (hot stamping)] As a conventional method for joining the laminated structure 10, there is a so-called "hot press". The hot press is a method of heating in an Ar environment while pressing the laminated structure 10 with a predetermined force (a force greater than the restraining force by the jig 11) in the lamination direction. When joining the laminated structure 10 by hot stamping, the vibrator 4 is likely to crack, and there is a limit (for example, about 1 mm to 2 mm) to the thickness dimension of the vibrator 4. On the other hand, in the jig 11 according to the present embodiment, since it only restrains with a weak force that prevents the positional deviation of the components of the laminated structure 10, even if the thickness dimension of the vibrator 4 is greatly changed, it is possible to appropriately join without causing cracks.

[0040] Here, the frequency of the ultrasonic wave generated by the vibrator 4 depends on the thickness dimension of the vibrator 4. More specifically, the smaller the thickness dimension, the higher the frequency of the ultrasonic wave is generated, and the larger the thickness dimension, the lower the frequency of the ultrasonic wave is generated. Therefore, the thickness dimension of the vibrator 4 according to the present embodiment may be selected in the range of 0.1 mm to 30 mm according to the use of the ultrasonic probe 1, for example, as follows.

[0041] As an example, when the ultrasonic probe 1 is used for inspecting damage to a pipe, the thickness dimension of the vibrator 4 is set to 0.1 mm to 0.5 mm (more preferably, 0.1 mm to 0.2 mm), and ultrasonic waves of 33 MHz to 6.6 MHz (more preferably, 33 MHz to 16.5 MHz) may be generated. As another example, when the ultrasonic probe 1 is used for measuring the flow velocity of a fluid in a pipe, the thickness dimension of the vibrator 4 is set to 1 mm to 2 mm, and ultrasonic waves of 3.3 MHz to 1.65 MHz may be generated. As still another example, when the ultrasonic probe 1 is used for detecting a rupture sound in a pipe (that is, used as an AE (Acoustic Emission) sensor), the thickness dimension of the vibrator 4 is set to 5 mm to 30 mm (more preferably, 10 mm to 30 mm), and ultrasonic waves of 0.66 MHz to 0.11 MHz (more preferably, 0.33 MHz to 0.11 MHz) may be generated.

[0042] [Consideration of the state of the joint surface] FIG. 6 is a table showing the configurations and the states of the joint surfaces of Comparative Examples 1 and 2 and Examples 1 and 2. FIG. 7 is a diagram showing the results of ultrasonic flaw detection of the joint surface (A) between the electrode 3 and the vibrator 4 and the joint surface (B) between the vibrator 4 and the protective shoe 5 in Comparative Example 1. FIG. 8 is a diagram showing the results of ultrasonic flaw detection of the joint surface (A) between the electrode 3 and the vibrator 4 and the joint surface (B) between the vibrator 4 and the protective shoe 5 in Comparative Example 2. FIG. 9 is a diagram showing the results of ultrasonic flaw detection of the joint surface (A) between the electrode 3 and the vibrator 4 and the joint surface (B) between the vibrator 4 and the protective shoe 5 in Example 1. FIG. 10 is a diagram showing the results of ultrasonic flaw detection of the joint surface (A) between the electrode 3 and the vibrator 4 and the joint surface (B) between the vibrator 4 and the protective shoe 5 in Example 2.

[0043] In FIGS. 7 to 10, the non-uniformity of the joint surface is represented as a color change. FIG. 7 shows the state of the joint surface of the conventional (Comparative Example 1) when the operating temperature is about 500°C. This state of the joint surface serves as a reference. FIG. 8 shows the state of the joint surface when the active Ag solder is adopted for the joining method and the heating temperature is set to 850°C (Comparative Example 2). As shown in FIG. 8, when the active Ag solder is adopted for the joining method and the heating temperature is increased, the non-uniformity of the joint surface increases as compared with FIG. 7.

[0044] FIG. 9 shows the state of the joint surface when the melting metallization method and Ag solder are adopted for the joining method and the heating temperature is set to 850°C (Example 1). FIG. 10 shows the state of the joint surface when Nb is adopted for the protective shoe 5 instead of Ti in Example 1 (Example 2). Note that FIGS. 9 and 10 are photographed with higher resolution as compared with FIGS. 7 and 8. The states of the joint surfaces shown in FIGS. 9 and 10 have sufficient uniformity even when used in an environment of 800°C or higher.

[0045] And it can be confirmed that when Nb is adopted for the protective shoe 5 (FIG. 10), the state of the joint surface is more uniform as compared with the case where Ti is adopted for the protective shoe 5 (FIG. 9). And the uniformity of the joint surface indicates that the electrode 3 and the vibrator 4, and the vibrator 4 and the protective shoe 5 are firmly joined.

[0046] [Operation Confirmation] The ultrasonic probes according to Comparative Example 1 and Example 2 were used in environments at room temperature, 200°C, and 400°C. As a result, it was confirmed that the ultrasonic probes according to Comparative Example 1 and Example 2 output the same electrical signals in any environment. That is, it was confirmed that the ultrasonic probe according to Example 2 did not lose its function even when heated to 850°C at S4 in FIG. 3.

[0047] [Advantages and Effects of the Present Embodiment] According to the above embodiment, by forming the joint members 6 and 7 from a material having a melting point higher than that of Al, the operable temperature of the ultrasonic probe 1 can be increased. Further, by joining the ceramic vibrator, the metal electrodes 3, and the protective shoe 5 via the molten metallization layers 4a, 4b, and the joint members 6, 7, the joint surface can be made uniform (i.e., strong). As a result, an ultrasonic probe 1 that can be used in a high-temperature environment can be obtained.

[0048] In particular, it is desirable to employ Nb as the material of the protective shoe 5 because the joining result is the best (i.e., the joining strength is the highest). When LiNbO3 is employed for the vibrator 4, it is desirable to form the joint member 7 from Ti or Zr having an acoustic impedance equal to or higher than that of the vibrator 4 and equal to or lower than that of the protective shoe 5. By making the magnitude relationship of the acoustic impedances of the vibrator 4, the joint member 7, and the protective shoe 5 as described above, the detection accuracy of the ultrasonic probe 1 can be improved. This is due to the reflection and transmission properties of ultrasonic waves at the interface between adjacent members (i.e., the vibrator 4 and the joint member 7, the joint member 7 and the protective shoe 5). More specifically, when the difference in acoustic impedance between adjacent members is large, the reflectance at the interface is improved and the transmittance is decreased, resulting in a decrease in detection accuracy. On the other hand, when the difference in acoustic impedance between adjacent members is small, the reflectance at the interface is decreased and the transmittance is improved, resulting in an improvement in detection accuracy. This can be explained by Snell's law.

[0049] Further, according to the above manufacturing method, even when Nb is selected as the material of the protective shoe 5 by heating the laminated structure 10 in a vacuum furnace, it is possible to prevent the protective shoe 5 from being oxidized during the manufacturing process. Furthermore, according to the above manufacturing method, the formation of the molten metallized layers 4a and 4b and the joining of the electrodes 3, the vibrator 4, and the protective shoe 5 by the joining members 6 and 7 can be performed simultaneously. As a result, the manufacturing process of the ultrasonic probe 1 can be simplified.

[0050] Further, according to the above manufacturing method, since the laminated structure 10 is heated using the jig 11 that restrains the laminated structure 10 only in the lamination direction, it is possible to prevent misalignment of the respective components constituting the laminated structure 10 while allowing horizontal deformation due to thermal expansion. Also, by interposing the ceramic plates 14a and 14b between the electrodes 3 and the protective shoe 5 and the clamping plates 13a and 13b, it is possible to prevent the electrodes 3 and the protective shoe 5 from sticking to the clamping plates 13a and 13b and the vibrator 4 from cracking. Furthermore, by interposing the spring washers 16a and 16b between the clamping plate 13a and the nuts 15e and 15f, it is possible to prevent the vibrator 4 from cracking due to thermal expansion of the electrodes 3 and the protective shoe 5.

[0051] Further, according to the ultrasonic probe 1, it can be attached to a pipe through which liquid sodium serving as a coolant of a nuclear reactor passes, and can be used to measure the state (e.g., flow velocity, flow rate, temperature) of the liquid sodium passing through the pipe. Moreover, application to fluid analysis in a high-temperature environment such as a combustion test in a spacecraft or an aircraft can also be expected. Furthermore, it can provide high frequencies exceeding 10 MHz required for flaw detection tests and monitoring in chemical plants, thermal power generation, etc., and can also provide low frequencies of 1 MHz or less required for monitoring such as breaking sounds like an AE sensor.

Explanation of Reference Numerals

[0052] 1…Ultrasonic probe, 2…housing, 3…electrode, 4…vibrator, 4a, 4b…molten metallized layer, 5…protective shoe, 6, 7…joint member, 8…signal line, 9…control device, 10…laminated structure, 11…fixture, 12a, 12b…screw, 13a, 13b…clamping plate, 14a, 14b…ceramic plate, 15a~15f…nut, 16a, 16b…spring washer

Claims

1. An electrode, a vibrator that transmits ultrasonic waves when a voltage is applied to the electrode, converts a reflected wave of the ultrasonic waves into an electrical signal, and outputs the electrical signal, and a protective member that contacts an object to be inspected, in an ultrasonic probe, wherein melting metallized layers are formed on both surfaces of the vibrator in the thickness direction, a first joining member that joins the electrode and the vibrator via the melting metallized layer, and a second joining member that joins the vibrator and the protective member via the melting metallized layer are further provided, wherein the first joining member and the second joining member are formed of a material having a melting point higher than that of Al, characterized ultrasonic probe.

2. In the ultrasonic probe according to Claim 1, the first joining member and the second joining member are formed of a material containing at least one element among Ag, Ni, Ti, Zr, Au, and Cu, characterized ultrasonic probe.

3. In the ultrasonic probe according to Claim 2, The vibrator is formed of LiNbO ３ and the protective member is formed of a material containing at least one element among W, Ta, Mo, and Nb, characterized ultrasonic probe.

4. In the ultrasonic probe according to Claim 3, the protective member is formed of a material containing Nb, the electrode is formed of a material containing Ti, and the first joining member and the second joining member are formed of a material containing Zr, characterized ultrasonic probe.

5. In the ultrasonic probe according to Claim 1, the second joining member is formed of a material having an acoustic impedance equal to or higher than that of the vibrator and equal to or lower than that of the protective member, characterized ultrasonic probe.

6. In a method for manufacturing the ultrasonic probe according to Claim 1, the electrode, a metal brazing material to be the first joining member, metal powder to be the melting metallized layer, the vibrator, metal powder to be the melting metallized layer, a metal brazing material to be the second joining member, and the protective member are laminated in this order to form a laminated structure, and the laminated structure is heated in a vacuum furnace at a temperature equal to or higher than the melting points of the metal brazing material and the metal powder, characterized method for manufacturing an ultrasonic probe.

7. In the method for manufacturing the ultrasonic probe according to Claim 6, the laminated structure is restrained by a jig that restricts thermal expansion in the lamination direction and allows thermal expansion in a direction orthogonal to the lamination direction, and heated in the vacuum furnace, characterized method for manufacturing an ultrasonic probe.

8. In the method for manufacturing an ultrasonic probe according to claim 7, the jig includes: a plurality of screws each extending in the stacking direction at positions surrounding the stacked structure; a pair of clamping plates inserted through the plurality of screws on both sides of the stacked structure in the stacking direction; a pair of ceramic plates disposed between the electrode and one of the clamping plates and between the protective member and the other clamping plate; a plurality of nuts screwed onto the plurality of screws respectively; and a method for manufacturing an ultrasonic probe, characterized in that the clamping force of the stacked structure by the pair of clamping plates is adjusted by pressing the clamping plates with the plurality of nuts.

9. In the method for manufacturing an ultrasonic probe according to claim 8, a method for manufacturing an ultrasonic probe, characterized in that the pair of ceramic plates have different thickness dimensions in the stacking direction.

10. In the method for manufacturing an ultrasonic probe according to claim 8, a method for manufacturing an ultrasonic probe, characterized in that a spring washer is interposed between the clamping plate and the nut to adjust the clamping force.

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