Mechanism Of Interfacial Wetting And Performance Of Ultrasonic-Assisted Brazing Of Alumina Ceramic

Sapphire(single crystal Al2O3) offer high strength, high hardness, wear resistance, corrosion resistance, high temperature resistance, good thermal conductivity and high light transmittance characteristics. So sapphire are usually used as the substrate material or window material in the micr oelectronics, semiconductor, photoelectric industry, aerospace industry. However, limited by its difficulty of large size sapphire molding and its high hardness and poor shaping performance, the sapphire are hardly applied in the field of large size and shape for complex components of application. One way to solve this problem is making different shapes of sapphire fittings by joining the small size of the sapphire. Based on this, this paper put forward a method of effective rapid brazing of sapphire ceramic with assisted ultrasonic under the atmospheric environment. By building simple ultrasonic brazing platform, this work systematacially studied the feasibility of ultrasonic assisted brazing sapphire, the mechanism of different ultrasonic effects of process parameters on the joint performance, the mechanism of ultrasonic on the microstructure of joint and morphology evolution of joint organizations, etc.The experimental results showed that, fast and reliable connection between the sapphires could be achieved by ultrasonic assisted brazing wih the use of Al and Al-12Si(wt.%) solder under the atmospheric environment. The shear strength of the joint increased with the increase of ultrasonic tim e and ultrasonic power. The incrasement of the ultrasonic time and power could effectively improve wetting of solder on ceramic, reduce defects such as porosity in the joint, and enhance the interfacial chemical reaction. However, when the ultrasonic time last too long(≥ 60 s) and ultrasonic power was too large(≥ 300 W), the joint strength declined instead. The study showed that long time and high intensity ultrasonic effect on the sapphire substrate could cause microcrack and thus reduce the shear strength. When Al acted as filler, the largestest joint shear strength could reach to 60.14 MPa when the ultrasonic time ranged from 5 s to 60 s. When Al-12 Si alloy acted as solder, largest shear strength could reach to 102.22 MPa under the ultrasonic time was 25 s.The achievemet of reliable connection of sapphire under the atmospheric condition relied on the ultrasonic cavitation and acoustic streaming effect. Oxide film on the surface of aluminum was broken with the aid of ultrasonic cavitation, and was removed with the acoustic streaming, so that the melting solder performanced good spreading and wetting o n sapphire surface. Meanwhile ultrasonic could promote the epitaxial growth of alumina on sapphire surface, which could accelerate the reaction wetting. Ultrasound also promoted the erosion of the substrate material, thus a large number of matrix alumina particles flowed into the seam, forming a tenon structure at the interfaces. In addition, when Al-12 Si was used as filler metal, ultrasound induced the element redistribution within the joint and promoted the formation of Al-Si-O ternary compound at the interfaces, and meanwhile formed self-supporting structure in the joint. The ultimate joint was formed by the particles from the spalling of the sapphire substrate which was prompted by ultrasound and the nano epitaxial growth ceramic phase on the surface of sapphire substrate.