Creep characteristics of alumina, nickel aluminate spinel, zirconia composites
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Dong-Kyu Kim University of Illinois at Urbana–Champaign, Department of Materials Science and Engineering, Urbana, Illinois 61801
Joy E. Trujillo University of California, Irvine, Department of Chemical Engineering and Materials Science, Irvine, California 92697-2575
Waltraud M. Kriven University of Illinois at Urbana–Champaign, Department of Materials Science and Engineering, Urbana, Illinois 61801
Martha L. Mecartneya) University of California, Irvine, Department of Chemical Engineering and Materials Science, Irvine, California 92697-2575 (Received 14 September 2007; accepted 20 November 2007)
Fine grained, three-phase ceramic composites that exhibit favorable toughness, hardness, and high room-temperature strength were evaluated for high-temperature mechanical stability. A 50vol%Al2O3–25vol%NiAl2O4–25vol%3 mol%yttria-stabilized tetragonal zirconia polycrystal (3Y–TZP) and a 33vol%Al2O3–33vol%NiAl2O4– 33vol%3Y-TZP composite were compression creep tested at temperatures between 1350 and 1450 °C under constant stresses of 20–45 MPa. The three-phase microstructure effectively limited grain growth (average d0 ⳱ 1.3 m, average df ⳱ 1.6 m after 65% true strain). True strain rates were 10−4 to 10−6 s−1 with stress exponents n ⳱ 1.7 to 1.8 and a grain-size exponent p ⳱ 1.3. A method for compensating for grain growth is presented using stress jump tests. The apparent activation energy for high-temperature deformation for 50vol%Al2O3–25vol%NiAl2O4– 25vol%3Y–TZP was found to be 373 kJ/mol-K.
I. INTRODUCTION
Environmental concerns with respect to process waste and energy consumption have led the metal-working industry to consider process alternatives such as dry machining that are more environmentally and health friendly.1 Ceramic cutting tools have been proposed for dry machining1,2 because they have positive attributes such as high abrasion and corrosion resistance, a high hot hardness, and low chemical affinity.3 On the other hand, the same ceramic tools have currently limited use due to low toughness and low thermal-shock resistance due to low thermal conductivity, low fracture strength, and/or a high elastic modulus. Broader use of ceramic tooling may be achieved
a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2008.0071 556
http://journals.cambridge.org
J. Mater. Res., Vol. 23, No. 2, Feb 2008 Downloaded: 14 Mar 2015
through improved performance of ceramic tool materials via improved fracture toughness and strength. Improving the strength of ceramic-tool materials may be achieved by minimizing the grain size and strength-limiting flaw populations.4,5 Griffith flaws may be reduced through the reduction of grain size, d, with the relationship, f ⬀ d−1/2, where f is the flexural strength as derived from the Griffith crack criterion. Nanoscale and microscale ceramic materials have been used to create highhardness, high-strength materials by reducing residual porosity, reducing microcracking from crystallographic thermal-expansion anisotropy, and using finer surface finish
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