Estimation of Stress Exponent and Activation Energy for Rapid Densification of 8 mol% Yttria‐Stabilized Zirconia Powder. Issue 3 (24th December 2012)

• Record Type: Journal Article
• Authors: Kumagai, Tatsuo; Wakai, F.
• Is Part Of: Journal of the American Ceramic Society. Volume 96:Issue 3(2013)
• Page Start: 852
• Page End: 858
• Publication Date: 2012-12-24
• Subjects: Ceramics -- Periodicals; 620.1405
• DOI: 10.1111/jace.12117
• Languages: English
• ISSNs: 0002-7820

Abstract

<abstract abstract-type="main" xml:lang="en" id="jace12117-abs-0001"> <title> <x xml:space="preserve">Abstract</x> </title> <p>The rapid densification behavior of 8 mol% Y<sub>2</sub>O<sub>3</sub>‐stabilized ZrO<sub>2</sub> polycrystalline (8Y‐SZP) powder compacts at the initial stage of pressure sintering (relative density (<inline-graphic mimetype="image" xlink:href="ark:/27927/pgg1v9c5r8p" xlink:type="simple" xmlns:xlink="http://www.w3.org/1999/xlink" /><mml:math altimg="urn:x-wiley:00027820:media:jace12117:jace12117-math-0001" overflow="scroll" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mover><mml:mrow><mml:mi mathvariant="bold-italic">ρ</mml:mi></mml:mrow><mml:mo>·</mml:mo></mml:mover></mml:mrow></mml:math>) below 0.92) has been investigated using an electric current‐activated/assisted sintering (ECAS) system. Data points corresponding to a fixed heating rate were extracted from the densification rate (<inline-graphic mimetype="image" xlink:href="ark:/27927/pgg1v9c5r97" xlink:type="simple" xmlns:xlink="http://www.w3.org/1999/xlink" /><mml:math altimg="urn:x-wiley:00027820:media:jace12117:jace12117-math-0002" overflow="scroll" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mover><mml:mrow><mml:mi mathvariant="bold-italic">ρ</mml:mi></mml:mrow><mml:mo>·</mml:mo></mml:mover></mml:mrow></mml:math>) versus ρ and <inline-graphic mimetype="image" xlink:href="ark:/27927/pgg1v9c5rcb" xlink:type="simple" xmlns:xlink="http://www.w3.org/1999/xlink" /><mml:math altimg="urn:x-wiley:00027820:media:jace12117:jace12117-math-0003" overflow="scroll" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mover><mml:mrow><mml:mi mathvariant="bold-italic">ρ</mml:mi></mml:mrow><mml:mo>·</mml:mo></mml:mover></mml:mrow></mml:math> versus temperature (<italic>T</italic>) curves. These curves were obtained experimentally by consolidation at a fixed current. Under fixed current ECAS, the heating rate (<inline-graphic mimetype="image" xlink:href="ark:/27927/pgg1v9c5rff" xlink:type="simple" xmlns:xlink="http://www.w3.org/1999/xlink" /><mml:math altimg="urn:x-wiley:00027820:media:jace12117:jace12117-math-0004" overflow="scroll" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mover><mml:mrow><mml:mi mathvariant="bold-italic">T</mml:mi></mml:mrow><mml:mo>·</mml:mo></mml:mover></mml:mrow></mml:math>) decreases continuously over sintering time. Using a quasi‐ constant heating rate (CHR) method, data points were extracted to plot <inline-graphic mimetype="image" xlink:href="ark:/27927/pgg1v9c5rhj" xlink:type="simple" xmlns:xlink="http://www.w3.org/1999/xlink" /><mml:math altimg="urn:x-wiley:00027820:media:jace12117:jace12117-math-0005" overflow="scroll" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mover><mml:mrow><mml:mi mathvariant="bold-italic">ρ</mml:mi></mml:mrow><mml:mo>·</mml:mo></mml:mover></mml:mrow></mml:math> vs. ρ, <inline-graphic mimetype="image" xlink:href="ark:/27927/pgg1v9c5rkn" xlink:type="simple" xmlns:xlink="http://www.w3.org/1999/xlink" /><mml:math altimg="urn:x-wiley:00027820:media:jace12117:jace12117-math-0006" overflow="scroll" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mover><mml:mrow><mml:mi mathvariant="bold-italic">ρ</mml:mi></mml:mrow><mml:mo>·</mml:mo></mml:mover></mml:mrow></mml:math> vs. <italic>T</italic>, and ρ vs. <italic>T</italic> curves at a fixed <inline-graphic mimetype="image" xlink:href="ark:/27927/pgg1v9c5rnr" xlink:type="simple" xmlns:xlink="http://www.w3.org/1999/xlink" /><mml:math altimg="urn:x-wiley:00027820:media:jace12117:jace12117-math-0007" overflow="scroll" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mover><mml:mrow><mml:mi mathvariant="bold-italic">T</mml:mi></mml:mrow><mml:mo>·</mml:mo></mml:mover></mml:mrow></mml:math>. The stress exponent (<italic>n</italic>), estimated from a log‐log plot of grain size (<italic>d</italic>)‐corrected <inline-graphic mimetype="image" xlink:href="ark:/27927/pgg1v9c5rqv" xlink:type="simple" xmlns:xlink="http://www.w3.org/1999/xlink" /><mml:math altimg="urn:x-wiley:00027820:media:jace12117:jace12117-math-0008" overflow="scroll" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mover><mml:mrow><mml:mi mathvariant="bold-italic">ρ</mml:mi></mml:mrow><mml:mo>·</mml:mo></mml:mover></mml:mrow></mml:math>/ρ and effective stress (σ<sub>eff</sub>) at 1300–1400 K, shows an almost constant value of 1. In addition, the activation energy (<italic>Q</italic>) for rapid densification, estimated from an Arrhenius plot of <italic>d</italic>‐corrected <inline-graphic mimetype="image" xlink:href="ark:/27927/pgg1v9c5rsz" xlink:type="simple" xmlns:xlink="http://www.w3.org/1999/xlink" /><mml:math altimg="urn:x-wiley:00027820:media:jace12117:jace12117-math-0009" overflow="scroll" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mover><mml:mrow><mml:mi mathvariant="bold-italic">ρ</mml:mi></mml:mrow><mml:mo>·</mml:mo></mml:mover></mml:mrow></mml:math>/ρ also shows an almost constant value of 350 kJ/mol, which is considerably lower than the previously reported value of the activation energy for Zr<sup>4+</sup> lattice diffusion of about 440 kJ/mol. These results suggest that rapid densification of 8Y‐SZP by ECAS seems to proceed by diffusional creep controlled by grain‐boundary diffusion of Zr<sup>4+</sup> ions.</p> </abstract>