High-temperature-resistant coating type magnetostrictive ultrasonic transducer

Abstract

The invention discloses a high-temperature-resistant coating type magnetostrictive ultrasonic transducer, and belongs to the field of ultrasonic nondestructive testing. The transducer is composed of a high-temperature-resistant ceramic coil and a high-temperature-resistant magnetostrictive coating prepared on the basis of Fe3O4 / AlNiCo composite powder. The method comprises the following steps: firstly, spraying Fe3O4 / AlNiCo composite powder to the surface of a to-be-detected workpiece to form a magnetostrictive coating tightly combined with the surface of the workpiece as a sensing unit for exciting and receiving ultrasonic waves; then carrying out magnetization treatment on the coating by utilizing a magnetization device, and establishing a stable static bias magnetic field; removing the magnetizing device, and applying a pulse current signal in the ceramic coil to generate a dynamic alternating magnetic field; finally, based on the magnetostrictive effect, ultrasonic waves are excited and received in the coating, and detection of defects in the to-be-detected workpiece is achieved. The transducer has the advantages of high temperature resistance and high signal-to-noise ratio, and is suitable for rapid spot check detection and long-term online monitoring of structures such as high-temperature pipelines and high-temperature pressure vessels.

Description

Technical Field

[0001] The invention belongs to the technical field of ultrasonic nondestructive testing, and in particular relates to a high temperature resistant coating type magnetostrictive ultrasonic transducer. Background Art

[0002] In the petrochemical, nuclear power, thermal power and other industries, key hot end components (such as high temperature pipelines, pressure vessels, etc.) are usually used in high temperature environments of 300℃ to 600℃. As the service time increases, these components may have defects such as cracks, corrosion, and pores. If these defects are not discovered in time, they will cause major hidden dangers to the safe operation of the equipment and even cause catastrophic accidents. Therefore, the demand for non-destructive testing of hot end components in high temperature environments is becoming more and more urgent.

[0003] Piezoelectric ultrasonic transducers and magnetostrictive ultrasonic transducers are the two mainstream technologies in the field of internal defect detection of materials. However, in high-temperature detection, conventional piezoelectric ultrasonic transducers and patch-type magnetostrictive ultrasonic transducers still face the problem of performance degradation. Especially in high-temperature environments above 300°C, the acoustic coupling agent will evaporate at high temperatures, causing the transducer performance to degrade or even fail. Therefore, how to achieve long-term stable and efficient ultrasonic excitation and reception in high-temperature environments has become an important challenge in current high-temperature non-destructive testing technology.

[0004] Some scholars have proposed a method of spraying a magnetostrictive coating on the surface of the workpiece to be tested to improve the performance of the patch-type magnetostrictive ultrasonic transducer. Compared with the patch-type magnetostrictive ultrasonic transducer, the coated magnetostrictive ultrasonic transducer can effectively overcome the dependence on the acoustic coupling agent. At present, the research on the coated magnetostrictive ultrasonic transducer is still in its infancy, mainly focusing on the selection of magnetostrictive coating materials, the preparation process of the coating, and the defect detection performance of the transducer at room temperature. However, there are no relevant literature reports on the high temperature resistance of magnetostrictive coatings and the conversion efficiency of magnetostrictive ultrasound in high temperature environments.

[0005] Commonly used magnetostrictive materials such as pure nickel metal, iron-cobalt alloy, iron-gallium alloy and iron-aluminum alloy have relatively excellent magnetostrictive properties at room temperature, but their magnetostrictive properties degrade significantly in high temperature environments above 300°C. For example, the magnetostrictive strain coefficient of pure nickel metal decreases significantly with increasing temperature, while iron-cobalt alloy, iron-gallium alloy and iron-aluminum alloy are prone to oxidation in high temperature environments, causing their magnetostrictive properties to gradually degrade or even completely fail. Therefore, designing a magnetostrictive coating material with high temperature stability has become the key to determining whether the coated magnetostrictive ultrasonic transducer can meet high-temperature non-destructive testing applications. Summary of the invention

[0006] The present invention proposes a high temperature resistant coating type magnetostrictive ultrasonic transducer, which uses Fe3O4 / AlNiCo composite powder to prepare a high temperature resistant magnetostrictive coating as a sensing unit for magnetostrictive ultrasonic excitation and reception. Compared with the prior art, the transducer of the present invention has the advantages of high temperature resistance and high signal-to-noise ratio, and can effectively overcome the problem of performance degradation of the patch type magnetostrictive ultrasonic transducer in a high temperature environment.

[0007] A high temperature resistant coating type magnetostrictive ultrasonic transducer is composed of a high temperature resistant ceramic coil and a high temperature resistant magnetostrictive coating prepared based on Fe3O4 / AlNiCo composite powder.

[0008] The magnetostrictive coating is prepared by uniformly mixing Fe3O4 powder and AlNiCo powder, and then spraying the Fe3O4 / AlNiCo composite powder onto the surface of the workpiece to be tested by thermal spraying, thereby forming a magnetostrictive coating that is tightly combined with the workpiece to be tested and serves as a sensing unit for ultrasonic excitation and reception.

[0009] The Fe3O4 powder is a soft magnetic material with low coercivity and significant magnetostrictive effect, and is used as a magnetostrictive sensing unit to generate and receive ultrasonic waves; the AlNiCo powder is a hard magnetic material with high coercivity, which is initially non-magnetic but easy to magnetize, and after magnetization, is used to provide the static bias magnetic field required in the magnetostrictive ultrasonic transduction process.

[0010] After the coating is magnetized, a stable static bias magnetic field strength of 100 to 5000 Oe is established.

[0011] The mass ratio of the Fe3O4 powder to the AlNiCo powder is 10:1, and the particle sizes of the two powder materials are 10-100 μm.

[0012] The coating has a thickness of 0.1 to 1 mm, a Curie temperature of 600 to 860° C., and has magnetostrictive properties and mechanical bonding strength that are stable in a high temperature environment below 600° C.

[0013] The maximum operating temperature of the transducer is 600° C., and the signal-to-noise ratio of the received signal is 20-100 dB.

[0014] The present invention provides a high-temperature resistant coated magnetostrictive ultrasonic transducer. The transducer does not require the use of an acoustic coupling agent during the detection process, has the advantages of high temperature resistance and high signal-to-noise ratio, can maintain excellent magnetostrictive performance and mechanical bonding strength in a high-temperature environment below 600°C, is suitable for rapid spot checks and long-term online monitoring of structures such as high-temperature pipelines and pressure vessels, and shows broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1It is a structural schematic diagram of a high temperature resistant coating type magnetostrictive ultrasonic transducer.

[0016] Figure 2 This is a photo of the cross section of a high-temperature resistant magnetostrictive coating.

[0017] Figure 3 It is the waveform diagram of the receiving signal measured at different temperatures of the coated magnetostrictive ultrasonic transducer. DETAILED DESCRIPTION

[0018] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0019] like Figure 1 As shown, the high temperature resistant coating type magnetostrictive ultrasonic transducer proposed by the present invention is composed of a high temperature resistant ceramic coil and a high temperature resistant magnetostrictive coating prepared based on Fe3O4 / AlNiCo composite powder.

[0020] The preparation of high temperature resistant magnetostrictive coating includes: powder selection and mixing, workpiece surface pretreatment, thermal spray coating formation and magnetization treatment. First, Fe3O4 powder and AlNiCo powder are uniformly mixed in a mass ratio of 10:1, wherein Fe3O4 powder is a soft magnetic material with low coercivity and has a significant magnetostrictive effect, which is used for the generation and reception of ultrasonic waves; AlNiCo powder is a hard magnetic material with high coercivity, which is initially non-magnetic but easy to magnetize, and provides a stable static bias magnetic field after magnetization. The particle size of the two powders is controlled between 10 and 100 μm to ensure mixing uniformity and spraying performance.

[0021] The above powders are placed in a ball mill for dry ball milling to form composite powders.

[0022] The surface of the workpiece to be tested is then pretreated by sandblasting to remove surface oxides and oil stains, and to form appropriate roughness to enhance the adhesion of the coating. Finally, compressed air is used to remove residual particles.

[0023] The coating is formed by atmospheric plasma thermal spraying technology, and the evenly mixed composite powder is sprayed layer by layer on the surface of the workpiece to be tested through the spraying equipment, and finally a coating with a thickness of 0.8mm is formed. During the spraying process, the spraying parameters are set including: spraying power 30kW, powder flow rate 25g / min, spraying distance 100mm, and the surface temperature of the workpiece is kept stable to avoid cracking or peeling caused by thermal stress.

[0024] The actual cross-section photo after coating spraying is as follows Figure 2 shown.

[0025] After spraying, the coating is magnetized by a strong permanent magnet, and a magnetic field strength of 10000Oe is applied for 10 minutes to ensure that the AlNiCo powder in the coating is fully magnetized, thereby establishing a static bias magnetic field with a strength of 1000Oe.

[0026] The wound ceramic coil is placed on the magnetized coating. The coil is wound with nickel wire, has 30 turns and an outer diameter of 15 mm.

[0027] The coil surface is coated with a high temperature resistant insulating ceramic layer to prevent electrical failure in high temperature environments.

[0028] The non-contact lift-off distance between the ceramic coil and the coating is 2 mm, forming a complete high-temperature resistant coated magnetostrictive ultrasonic transducer.

[0029] The ultrasonic transmitting device applies a Tone-Burst pulse signal with a center frequency of 4MHz and a peak current of 10A to the ceramic coil, generating a dynamic alternating magnetic field around the coil and exciting ultrasonic waves in the coating based on the magnetostrictive effect.

[0030] The ultrasonic wave is reflected by the bottom surface of the workpiece and propagates into the coating, causing a change in the magnetic field. The ultrasonic echo signal is received through the electromagnetic induction of the coil.

[0031] The ultrasonic receiving device amplifies and filters the signal received by the ceramic coil and transmits it to the oscilloscope.

[0032] By analyzing the ultrasonic echo signal, it is possible to determine whether the workpiece to be tested has defects.

[0033] like Figure 3 The experimental test results shown in the figure show that within the temperature range of 25°C to 600°C, the measured signal-to-noise ratio of the received signal is in the range of 50 to 60 dB.

[0034] The experimental results verify that the transducer of the present invention has the advantages of high temperature resistance and high signal-to-noise ratio.

[0035] When detecting defects in high-temperature pipelines and pressure vessels, the transducer of the present invention directly forms a coating on the target surface by thermal spraying, and detection can be performed without an acoustic coupling agent; the transducer has wide application value in rapid spot checks and long-term online monitoring of high-temperature equipment in the petrochemical, nuclear power and thermal power industries.

[0036] The above embodiments are only for detailed description of the implementation process of the present invention, but not for limiting the implementation of the present invention. For ordinary technicians in the relevant field, any obvious changes or modifications derived from the technical solution of the present invention are still within the scope of protection of the present invention.

Claims

1. A high temperature resistant coating type magnetostrictive ultrasonic transducer, characterized in that: The transducer consists of a high-temperature resistant ceramic coil and a high-temperature resistant magnetostrictive coating prepared based on Fe3O4 / AlNiCo composite powder.

2. The high temperature resistant coating type magnetostrictive ultrasonic transducer according to claim 1, characterized in that: The magnetostrictive coating is prepared by uniformly mixing Fe3O4 powder and AlNiCo powder, and then spraying the Fe3O4 / AlNiCo composite powder onto the surface of the workpiece to be tested by thermal spraying, thereby forming a magnetostrictive coating that is tightly combined with the workpiece to be tested and serves as a sensing unit for ultrasonic excitation and reception.

3. The high temperature resistant coating type magnetostrictive ultrasonic transducer according to claim 1, characterized in that: The Fe3O4 powder is a soft magnetic material with low coercivity and significant magnetostrictive effect, and is used as a magnetostrictive sensing unit to generate and receive ultrasonic waves; the AlNiCo powder is a hard magnetic material with high coercivity, which is initially non-magnetic but easy to magnetize, and after magnetization, is used to provide the static bias magnetic field required in the magnetostrictive ultrasonic transduction process.

4. The high temperature resistant coating type magnetostrictive ultrasonic transducer according to claim 1, characterized in that: After the coating is magnetized, a stable static bias magnetic field strength of 100 to 5000 Oe is established.

5. The high temperature resistant coating type magnetostrictive ultrasonic transducer according to claim 1, characterized in that: The mass ratio of the Fe3O4 powder to the AlNiCo powder is 10:1, and the particle sizes of the two powder materials are 10-100 μm.

6. The high temperature resistant coating type magnetostrictive ultrasonic transducer according to claim 1, characterized in that: The coating has a thickness of 0.1 to 1 mm, a Curie temperature of 600 to 860° C., and has magnetostrictive properties and mechanical bonding strength that are stable in a high temperature environment below 600° C.

7. The high temperature resistant coating type magnetostrictive ultrasonic transducer according to claim 1, characterized in that: The maximum operating temperature of the transducer is 600° C., and the signal-to-noise ratio of the received signal is 20-100 dB.

Images