ISSN:
1573-4803
Source:
Springer Online Journal Archives 1860-2000
Topics:
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
Notes:
Abstract Reproducible controlled surface flaws were introduced in reaction-bonded Si3N4 by Knoop microhardness indentation. Fracture was initiated at a single suitably oriented flaw on the tensile surface of a four-point bend specimen, and the stress required to propagate the controlled flaw catastrophically was used to calculate the critical stress intensity factor K IC from standard fracture-mechanics formulae for semi-elliptical surface flaws in bending. K IC was unchanged up to 1200° C, but values above this temperature together with those at room temperature after vacuum annealing were reduced approximately 25%. This reduction is thought to be due to reaction with oxygen concentrations present in the vacuum “atmosphere” rather than to a change in material properties. Although flaw “healing” was observed for annealing in air, it was accompanied by a decrease in fracture stress. It is suggested that this is due to volume mismatch between Si3N4 and the oxidation product, cristobalite, which introduces tensile stresses in the matrix material.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00545154
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