Joining of silicon nitride ceramics for high-temperature applications

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Joining of silicon nitride ceramics for high-temperature applications Rong-Jun Xiea) and Mamoru Mitomo National Institute for Research in Inorganic Materials, Namiki 1-1, Ibaraki 305-0044, Japan

Li-Ping Huang and Xi-Ren Fu Shanghai Institute of Ceramics, Chinese Academy of Sciences, 1295 Dingxi Road, Shanghai 200050, People’s Republic of China (Received 29 January 1999; accepted 27 October 1999)

A refractory silicon nitride joint, which contains ␤–Si3N4 grains and grain boundary amorphous phase in the joined layer, was developed with the aid of a ceramic adhesive based on the system Si3N4–Y2O3–SiO2–Al2O3. The similarity in chemistry and microstructure between the parent ceramic and the joint zone indicates that the joining mechanism is the same as that involved in the sintering of Si3N4. The resultant joint exhibits a high bond strength of 550 MPa at 25 °C and retains a strength of 332 MPa at 1000 °C. Post-joining hot-isostatic pressing was applied to strengthen the joint, resulting in increased strengths of 668 MPa at room temperature and 464 MPa at 1000 °C.

I. INTRODUCTION

Ceramic joining, which can (i) provide a method for cost-effective fabrication of complex-shaped, largersized components, (ii) improve the reliability of ceramic parts, and (iii) repair cracked ceramic parts, is more attractive both for researchers and engineers.1,2 Laboratory studies have developed a wide range of technologies for producing silicon nitride ceramic joints such as active metal brazing,3–5 diffusion bonding,6,7 and recently, partial transient liquid-phase bonding.8–10 These joining methods can fabricate silicon nitride ceramic joints with sufficiently high strength at room temperature, but the joints cannot maintain their integrity and exhibit good environmental stability at high temperatures (>800 °C)7,11 due to the softening of the interlayer. In order to utilize the high-temperature potential of ceramic materials, two critical properties in terms of heat resistance and oxidation resistance of ceramic joints must be considered and required.7 This has led to extensive studies of refractory joining agents like oxynitrides and ceramics12–14 and new metallic braze alloys containing Au, Pd, Hf, etc. with higher solidus temperatures and better oxidation resistance.15,16 Ceramic adhesives in the system Si3N4–Y2O3–Al2O3– SiO2, first investigated by Walls and Ueki17,18 and then the present authors,19–21 are found to be suitable interlayer materials for joining silicon-nitride-based ceramics.

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Address all correspondence to this author. e-mail: [email protected]

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http://journals.cambridge.org

J. Mater. Res., Vol. 15, No. 1, Jan 2000 Downloaded: 14 Mar 2015

During joining, the ceramic adhesives densify in the presence of liquid phases produced at the joining temperature and are finally converted to ceramics. By comparing ceramic adhesives to pure glass adhesives, it is found that the joint bonded with ceramic adhesives primarily contains Si3N4 ceramic materials rather than glass i