Mechanical behavior of active brazed silicon-nitride joints
Within the group of engineering ceramics, silicon-nitride (Si{sub 3}N{sub 4}) has the most interesting features regarding its technological performance in joints to be exposed to high mechanical loads and high temperatures. However, owing to its very low coefficient of thermal expansion combining it with other materials, such as steels, can be a difficult task. The objective of the research presented is to assess the mechanical properties of silicon-nitride joints applying four-point bending and uniaxial shear tests. AgCu-based active filler metals have been employed as brazes. In four-point bending tests of Si{sub 3}N{sub 4}-Si{sub 3}N{sub 4}-joints, it becomes obvious that there is a correlation between the bending strength, the filler metal composition, and the brazing parameters applied. Joining silicon nitride to steel is very critical due to the large mismatch in physical properties. In order to assess this influence, Si{sub 3}N{sub 4}-austenitic stainless steel (AISI316)-joints have been brazed and tested. A possible way to reduce thermally induced stresses in silicon-nitride/steel-joints is the application of interlayers either ductile or adapted in thermal expansion to the ceramic parent material. An excellent agreement between calculation and experiments has been found for such joints, where tugsten (W) as an expansion-adapted material has been employed as stress-reducing interlayer. W-interlayers of a thickness of 4--6 mm have reduced thermally induced stresses in the Si{sub 3}N{sub 4}-steel joint significantly. These results contradict the theoretical results that predicted lower stresses in the ceramic by employing a ductile interlayer in the joint. As the metallographic analysis reveals, metallurgical interactions between Ni or Cu as interlayer and the AgCuTi-braze are responsible for this phenomenon.
- OSTI ID:
- 115517
- Report Number(s):
- CONF-9404233-; TRN: 95:002927-0096
- Resource Relation:
- Conference: 75. American Welding Society (AWS) annual meeting, Philadelphia, PA (United States), 10-15 Apr 1994; Other Information: PBD: 1994; Related Information: Is Part Of 75th Diamond anniversary American Welding Society annual meeting; PB: 273 p.
- Country of Publication:
- United States
- Language:
- English
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