Fractography of Reaction-Sintered Si3N4

[+] Author and Article Information
M. G. Mendiratta

Systems Research Laboratories, Inc., 2800 Indian Ripple Road, Dayton, OH 45440

P. L. Land, R. Ruh

Air Force Materials Laboratory, Wright-Patterson Air Force Base, OH 45433

R. W. Rice

Naval Research Laboratory, Washington, D. C. 20390

D. C. Larsen

IIT Research Institute, Chicago, Ill. 60616

J. Eng. Power 102(2), 244-248 (Apr 01, 1980) (5 pages) doi:10.1115/1.3230244 History: Received December 18, 1975; Online September 28, 2009


Fractography studies were accomplished on two reaction-sintered Si3 N4 materials (Norton NC-350 Si3 N4 and KBI (Kawecki-Berylco) Si3 N4 ) which had been tested in four-point bending at room temperature, 1200, 1350, and 1500°C in air. At room temperature NC-350 exhibited uniform planar features representing a transgranular fracture mode, uniformly distributed small pores having a size range of 1–2 μm or less, and a few isolated large pores of ∼10 μm. In contrast, the KBI Si3 N4 at room temperature exhibited nonuniform, diffuse, and ill-defined fracture features, small pores having a size range of 2–5 μm, and many large pores of ∼50 μm in size. At high temperatures, the fracture appearance of NC-350 Si3 N4 was ill defined and diffuse, indicating a change in fracture mode. The fracture originating flaws in NC-350 were primarily the large pores or pore agglomerates. At all temperatures, in the KBI material, it was not possible to observe the mirror and, therefore, the site of fracture initiation. For NC-350, KIC values were 1.2–1.6 MN/m3/2 at room temperature and 2.1–2.4 MN/m3/2 at high temperatures.

Copyright © 1980 by ASME
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