JPH0879893A - Gradient function material and its manufacture - Google Patents

Abstract

PURPOSE: To provide the gradient function material in which powdered raw material is laminated in the order of particle diameters and solidified, especially the one useful for a rear material of an ultrasonic sensor probe and its manufacture. CONSTITUTION: The gradient function material featured by arranging metallic powder having particle diameters of a prescribed range depending on the particle diameter is formed by applying perptization uniformly to metallic powder having the particle diameter of a prescribed range with a sintering aid material and a peptization agent, putting the metallic powder subject to peptization into an agar sol solution in which the metallic powder is classified depending on the particle diameter, applying gel processing to the agar solution, pressing and dehydrating the solution to form a metallic powder classified compression material and sintering the metallic powder classified compression material.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a functionally graded material in which raw material powders are layered in the order of particle size and solidified, and in particular, a functionally graded material useful as a backing material for an ultrasonic sensor probe and a method for producing the same. Regarding More specifically, the present invention relates to a backing material for increasing the resolution of an ultrasonic sensor probe and a method for manufacturing the backing material. A functionally graded material is a type of material that has been drawing attention in recent years, and is a material that can simultaneously satisfy multiple functions that were not possible with conventional materials with the same material. For example,
Heat resistance temperature of iron-based alloy metal alone is 1,200-1,30
Although it is around 0 ° C and is heavy due to its large specific gravity, it is excellent in ductility and rigidity, has flexibility, and is strong against impact. On the other hand, ceramics have a heat resistant temperature of 1,500-
It is around 1,600 degrees C, so it is light because of its small specific gravity,
Very brittle and vulnerable to shock. However, when a material having high heat resistance and high impact resistance is desired, it is naturally conceivable that a combination of alloy metal and ceramic appears. However, although a joining method and a thermal spraying method have been developed as a method for compounding an alloy metal and a ceramic, the strength is not always satisfactory. Therefore, the surface layer at one end is made of alloy metal 100
%, The surface layer at the other end is 100% ceramic, and the middle part is made of a material with satisfactory heat resistance and impact resistance when the ratio of alloy metal and ceramic is continuously changed stepwise. You can do it. That is, a material having a new function can be obtained by continuously changing the ratio of the two-component system in an inclined manner. This is a functionally graded material.
It should be noted that the material that is continuously graded is not limited to a two-component system, and the physical property value of a one-component system, for example, the grain size, is continuously graded so that it is not possible to consider it with a conventional material of the same component system. It can also be expected to exhibit the desired function.
Such materials are also functionally graded materials.

[0002]

2. Description of the Related Art In ultrasonic sensors, importance is attached to detection sensitivity and distance resolution. The detection sensitivity is determined by the oscillator material, while the distance resolution is said to depend on the degree of suppression of free oscillation of the oscillator. The back surface material is used for the purpose of suppressing free vibration of the vibrator, but the ultrasonic waves emitted from the vibrator not only travel toward the flaw detection target but also toward the back material. The ultrasonic waves that have propagated to the backing material become reflected waves from the bottom surface of the backing material, which causes a reduction in resolution. Therefore, it is ideal that the backing material has a large ultrasonic attenuation characteristic.

Up to now, however, epoxy resin mixed with fine powder of tungsten has been used as a backing material.

[0004]

However, in a backing material obtained by mixing fine particles of tungsten with such an epoxy resin and hardening it, the damping characteristic value is 0.21 to 0.
It is about 37 dB / mm. Furthermore, since it is hardened with an epoxy resin, it is bonded to the vibrator by an adhesive, and it cannot be used in a high temperature range above the softening temperature of the adhesive or the epoxy resin.

In order to improve the measurement accuracy of the ultrasonic sensor, there has been a demand for a backing material having a high attenuation characteristic which enhances the resolution as well as the development of a vibrator having excellent detection sensitivity. In addition, it is necessary to develop vibrators and backing materials with high heat resistance for the purpose of use in the high temperature range. Further, there is a need for a backing material capable of stronger bonding between the vibrator and the backing material, for example, a backing material suitable for brazing, diffusion bonding or pressure bonding.

[0006]

In order to solve the above-mentioned various problems, the present invention intends to utilize a functionally graded material, which is a sintered product of ceramics or metal powder having high heat resistance, as a backing material. To do. The back material made of the functionally graded material, which is a sintered product, and the vibrator can be joined by a known means such as brazing, diffusion joining or pressure joining. However, in the conventional powder metallurgy method and ceramics sintering method, the entire backing material is uniform and a dense sintered product is completed.
The attenuation characteristic will be low. Therefore, as a means for developing a backing material having a large damping property and excellent bonding property, a ceramic or metal powder having a wide particle size distribution, for example, 0.2 to 300 microns is precipitated in a liquid medium to form a powder. Are sequentially stacked from the one having a large particle size to the one having a small particle size. By sintering this laminated powder molded product, a functionally gradient material useful as a target backing material can be obtained.

[0007]

When powder having a wide particle size distribution is gently settled from the upper end of a container containing a liquid medium such as alcohol, water or propylene glycol, powder particles having a large particle size are converted into powder particles having a small particle size. Sequential sedimentation and continuous classification are performed to obtain a continuous gradient according to particle size. The classification accuracy and speed of the continuous slant depend on the viscosity of the liquid medium. That is, in a highly viscous medium, the sedimentation speed becomes slow and the classification accuracy improves.

It is extremely difficult to take out the continuous inclined body obtained in the above liquid medium as it is,
It can be easily taken out by using a solidifying material showing a sol-gel reversible reaction, for example, agar which is a natural polysaccharide as a medium. That is, agar is dissolved in hot water to become a sol-state liquid, and if kept at a temperature above the gel point, the sol-state is maintained. Further, the viscosity of the sol can be freely changed depending on the concentration to be dissolved and the temperature to be held. When a powder material having a wide particle size distribution is diffused in the liquid medium in the sol state, the powder particles having a large particle size are sequentially settled into the powder particles having a small particle size to form a continuous inclined body. Next, when the liquid in the sol state is cooled to a temperature not higher than the gelation point, the liquid is gelled and solidified, so that the continuous gradient according to the particle size can be easily taken out.

By applying pressure to the agar gel, the retained water can be easily separated to obtain a compressed body. 30 to 5 per square centimeter on the above-mentioned continuous inclined body
By applying a pressure of 0 kg, the continuous gradient body is compressed, and the packing density of the continuous gradient body can be arbitrarily changed depending on the pressure holding time.

If this compressed continuous inclined body is sintered by a known method, a continuously inclined sintered body depending on the grain size can be obtained.
It is well known that the sintering strength of powder particles depends on the particle size of the particles and the contact state between the particles. That is, when a continuous inclined body as shown in FIG. 1 is sintered, one end, which is an aggregate of small particles, has a small particle gap and has a very large specific surface area, so that the surface activity is high and the bonding strength between particles is high. Higher and more precise. On the other hand, the other end, which is an aggregate of large particles, has a large particle gap and a small specific surface area of the particles, so that the surface activity is low and the bonding strength between the particles is low,
It becomes a so-called porous state.

It is easy to join the dense one end of the back body made of the continuous inclined coupling body to the piezoelectric element which is the vibrator. Particularly when the raw material powder is a metal backing material, brazing with the piezoelectric element is easy. On the other hand, when the raw material powder is a ceramic backing material, electroless plating is applied to one dense end of the backing material and brazing is performed, or the backing material and the piezoelectric element are bonded by diffusion bonding or pressure welding.

The ultrasonic pulse emitted from the piezoelectric element is input from the dense one end of the bonding material or the back material, and the particles are vibrated by the energy derived from the ultrasonic pulse. However, since the bonding surface between the piezoelectric element and the backing material and the particles at one end of the dense and fine backing material are firmly bonded, their amplitude can be almost ignored and the ultrasonic pulse is not attenuated. The further advanced pulse propagates while consuming energy by vibrating the particles as the bond strength of the particles gradually increases and vibrates. The pulse arriving at the other open end of the backing material becomes a reflected pulse there, but its energy is attenuated to a small extent.

The electrical capacitance of the piezoelectric element, the electromechanical coupling coefficient, the specific acoustic impedance of the piezoelectric element, and the specific impedance of the backing material are selected according to the detection sensitivity and resolution of the desired ultrasonic sensor. The damping characteristics of the backing material also have a large effect. The raw material for producing the backing material, the range of particle size, the particle size distribution, the packing density, the sintering temperature, and other manufacturing conditions and the shape of the backing material may be selected according to the respective conditions.

[0014]

EXAMPLE A backing material is prepared according to the following procedures (1) to (10).

(1) 240 g of partially stabilized zirconia powder having a particle size of 0.2 to 300 μm and containing 8 mol% Y ₂ O ₃ as a sintering aid, 2.5 g of peptizing / decomposing agent and 100 ml. Add water and deflocculate and disperse with a ball mill.

(2) As shown in FIG.
2 has a classification medium tank 14 at the bottom, and both tanks 12, 1
The classification medium tank 14 of the functionally graded material manufacturing apparatus 10 in which 4 is partitioned by the shutter 16 is filled with an agar sol solution having a concentration of 2 wt%. Then, hot water is passed through the heat retention / cooling jacket 18 arranged around the classification medium tank 14 to keep the classification medium tank 14 at a temperature of 60 to 80 ° C., and the classification tank 14 and the peptization tank 12 are separated. The shutter 16 between them is closed.

(3) The deflocculating / dispersing liquid of the zirconia powder described above is put into the deflocculating tank 12 and sufficiently stirred so that large particles of zirconia powder do not settle.

(4) Stop the stirring device of the deflocculating tank 12 and pull the shutter 16 in the direction of the arrow 20 to completely open the space between both tanks to classify the deflocculating / dispersing liquid of the zirconia powder in the deflocculating tank 12. The medium tank 14 is brought into contact with the agar sol solution and left to stand.

(5) Peptization of the zirconia powder transferred to the classifying tank 14: The zirconia powder having the largest particle size in the liquid is settled downward and laminated on the bottom of the classifying medium tank 14. Meanwhile, the temperature of the classification medium tank is maintained at 60 to 80 ° C. until the sedimentation is completed.

(6) After the sedimentation is completed, the classification medium tank 14
Cooling water is caused to flow through the heat retaining / cooling jacket 18 to gelate the agar solution.

(7) The shutter 16 between the deflocculating tank 12 and the classifying medium tank 14 is closed again, and the pressure cylinder 22 constituting the floor surface of the classifying medium tank 14 is pushed up to gradually increase the applied pressure. Pressurized dehydration is performed while increasing the pressure to 30 to 50 kg per square centimeter to make a compressed body. The water dewatered in the classification medium tank 14 flows out from between the classification medium tank 14 and the shutter 16 or the pressurizing cylinder 22.

(8) After removing the deflocculating tank 12 and the shutter 16, the pressure cylinder 22 is pushed up to take out a predetermined compressed body from the classification medium tank 14 and punch it into a predetermined shape to take out a molded product.

(9) 1,200-
A sintered body as shown in FIG. 1 is obtained by holding at 1,600 ° C. for 1 to 2 hours.

(10) The dense surface of the sintered body 1 is ground and finished with a known diamond grindstone to obtain a predetermined backing material.

The following is a comparison of the damping characteristics of the backing material made by the above method and the backing material made by the conventional method of solidifying tungsten powder with an epoxy resin.

[0026]

[0027]

According to the present invention, it is possible to provide a functionally graded material suitable for a back surface material having a high attenuation characteristic for improving resolution. This makes it possible to significantly improve the measurement accuracy of the ultrasonic sensor. Further, according to the present invention, powder having a wide particle size distribution is gently settled from the upper end of the container containing the liquid medium into the agar medium, whereby the powder particles having a large particle size are sequentially settled to the powder particles having a small particle size. Then, continuous classification can be carried out, and a continuous inclined body depending on the particle size can be obtained very easily. In addition, by controlling the temperature of the agar, the sedimentation rate can be adjusted, which can improve the classification accuracy.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a continuous grain size graded material classified according to grain size formed according to the present invention.

FIG. 2 is a cross-sectional view of an apparatus for forming a particle size classified continuous particle size graded material of the present invention.

[Explanation of symbols]

1: Functionally Gradient Material 10: Functionally Gradient Material Manufacturing Equipment 12: Peptization Tank 14: Classification Medium Tank 16: Shutter 18: Insulation Cooling Jacket 22: Pressurizing Cylinder

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI Technical indication location G01N 29/24 G10K 11/162 (72) Inventor Yasuyuki Nakamura 1-16 Kasugacho, Takatsuki City, Osaka 72) Inventor Satoshi Watanabe 3-3, 1362 Taio-cho, Kohoku-ku, Yokohama-shi, Kanagawa

Claims (5)

[Claims] 1. A functionally gradient material, characterized in that metal powder and ceramic powder having a grain size within a predetermined size range are arranged in a gradient according to the grain size. 2. A metal powder and a ceramic powder having a particle size within a predetermined size range are uniformly deflocculated and dispersed together with a sintering aid and a deflocculating dispersant, and the deflocculated and dispersed metal powder in a sol-like agar solution. By classifying the metal powder classified according to the particle size, gelating the agar solution and dehydrating it under pressure to form a compressed metal powder compact, and sintering the compressed metal powder compact. Method of forming functionally graded material. 3. A material constituting a backing material for an ultrasonic sensor probe is composed of ceramics and metal powder having a particle diameter of 0.2 to 300 μm, and further, this raw material powder is provided from one end of the backing material to another material. A backing material for an ultrasonic sensor probe, which shows a particle size distribution having a gradient function depending on the particle size at one end and solidifies a raw material powder having this gradient function. 4. An appropriate viscosity for causing the raw material powder of the backing material for an ultrasonic sensor probe to settle in the order of the particle size of 0.2 to 300 microns, and a function of adhering the raw material powder particles to each other. A method for producing a backing material for an ultrasonic sensor probe, which is solidified by diffusing into a medium and settling in order of particle size, and then removing excess medium from the raw material powder settling in order of particle size . 5. A backing material for an ultrasonic sensor probe, which is 0.2 to
300 μm raw material powder is classified according to a certain particle size range, the classified raw material powder is kneaded with a binder having a function of adhering powder particles to each other, and then the raw material powder kneaded with the binder is laminated in the order of particle size, A method of manufacturing a solidified backing material for an ultrasonic sensor probe.