Sonocapillary and wetting mechanism during ultrasonic brazing porous Si3N4 ceramics in air

Abstract

In this work, porous Si3N4 ceramics are directly brazed in air using ZnAl filler with the assistance of ultrasonic vibration. The results show that good wetting of ceramic is realized within 10 s at low temperature of 450 °C. Under ultrasonic, high pressure of 7.5 MPa occurs near the entrance of ceramic micro-hole, which helps to overcome the energy barrier (1.09–2.18 MPa) to initiate sonocapillary. The capillary action of the filler is rapid, and then the infiltrated filler tightly bonds with the ceramic. The microstructure analysis reveals that Al element of the filler and O element that pre-dissolved in the filler are the main wetting elements, and the bonding interface is amorphous. It is the high temperature (1500 K) and pressure (4.87 × 108 MPa) caused by the collapse of the cavitation bubbles that cause the rapid wetting of the ceramics, which is proved by simulation. Ultrasonic power higher than Mode II produces joint stronger than the ceramic substrate, showing the potential of ultrasonic brazing.