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Lookup NU author(s): Emeritus Professor Derek Thompson
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Typical alpha-sialon starting compositions, of formula Ln(0.33)Si(9.3)Al(2.7)O(1.7)N(14.3), were densified by hot-pressing using Ln(2)O(3) as sintering additives, where Ln = Nd, Dy, and Yb. The as-sintered materials were heat-treated at 1450 degrees C for 96 hours and then re-sintered at 1800 degrees C for 1 hour to observe the overlapping effects of both Ln(2)O(3) and multiple heat-treatment on thermal stability of the Ln-alpha-sialon phase and also the change in microstructure. The kinds of grain boundary phases which occurred also affected the results. The hardness, fracture toughness and flexural strength of the materials were evaluated using indentation and three-point bending tests, respectively. Mechanical tests and detailed microstructural analysis have led to the conclusion that a multiple-mechanism is involved, with debonding, crack deflection, crack bridging, and elongated grain pull-out all making a significant contribution towards improving the fracture toughness. Nd-containing specimens were tough with a highest indentation fracture toughness K-1C of 7.0 MPa m(1/2). In contrast, Dy- and Yb-containing specimens were hard and brittle with a highest Vickers hardness H-V10 of 18.0 GPa. All re-sintered specimens underwent beta -->alpha transformation to some degree, leading to a degradation of mechanical properties as a consequence. (C) 2000 Kluwer Academic Publishers.
Author(s): Liu Q, Gao L, Yan DS, Thompson DP
Publication type: Article
Publication status: Published
Journal: Journal of Materials Science
Year: 2000
Volume: 35
Issue: 9
Pages: 2229-2233
ISSN (print): 0022-2461
ISSN (electronic): 1573-4803
Publisher: Springer New York LLC
URL: http://dx.doi.org/10.1023/A:1004722825366
DOI: 10.1023/A:1004722825366
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