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1. WO2020194026 - DIFFUSION BONDING OF PIEZOELECTRIC CRYSTAL TO METAL WEAR PLATE

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[ EN ]

CLAIMS

1. A method of diffusion bonding of a lead zirconate-titanate (PZT) piezoelectric crystal to a metal wear plate for fabrication of a high temperature ultrasonic transducer comprising the steps of:

i. Depositing a first coating of a noble metal on the bonding surface of a PZT crystal;

ii. Depositing a second coating of the noble metal on the bonding surface of a metal wear plate;

iii. Bringing the bonding surfaces of the noble metal coated PZT crystal of step (i) and the bonding surface of the noble metal coated metal wear plate of step (ii) into contact with each other and heating under pressure at a temperature ranging from 270 to 400 °C to form a metallic bond to obtain a lead zirconate-titanate (PZT) piezoelectric crystal diffusion-bonded to the metal wear plate by the noble metal interlayer.

2. The method as claimed in Claim 1 wherein, the noble metal is selected from silver and gold.

3. The method as claimed in Claim 1 wherein, the metal wear plate is selected from nickel and high nickel alloys.

4. The method as claimed in Claim 1 wherein, the PZT crystal is coated with electrode before coating in step (i).

5. The method as claimed in Claim 1 wherein, the bonding surface of metal wear plate is polished before coating in step (ii).

6. The method as claimed in Claim 5 wherein, the bonding surface of metal wear plate at step (ii) is polished to mirror finish with planarity of ten microns and roughness of one micron.

7. The method as claimed in Claim 1 wherein, the total thickness of the noble metal interlayer coating deposited on the bonding surface at step (i) and step (ii) ranges from 20 to 40 microns.

8. The method as claimed in Claim 1 wherein, bonding pressure at step (iii) ranges from 175 to 225 bar.

9. The method as claimed in Claim 1 wherein, bonding time at step (iii) ranges from 45 to 75 minutes.

10. A high temperature ultrasonic transducer comprising :

a. A lead zirconate-titanate (PZT) piezoelectric crystal with a pre-coated electrode;

b. A metal wear plate;

c. A noble metal interlayer;

Wherein the said lead zirconate-titanate (PZT) piezoelectric crystal with pre-coated electrode is diffusion-bonded to the metal wear plate by the noble metal interlayer by the method as claimed in any one of the preceding claims 1 to 9.