Effect of interface design on high-temperature failure of laminated composites
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Effect of interface design on high-temperature failure of laminated composites Z. Chena) and J. J. Mecholsky, Jr. Department of Materials Science and Engineering, University of Florida, Gainesville, Florida 32611
S. Hu NRC Associate, Air Force Materials, Directorate, Wright-Patterson Air Force Base, Ohio 45433 (Received 29 September 1994; accepted 1 April 1996)
The fracture strength and toughness of alumina can be increased by lamination with strategically placed nickel layers and with a modified NiyAl2 O3 interface through tape casting. In order to examine the potential of this type of laminated composite in high temperature applications, the laminates were tested at elevated temperatures. This paper describes how a modified tortuous interface, instead of a smooth interface, increases the creep resistance of the laminates. Interface modification can control high temperature laminate behavior and is critical to successful composite design.
I. INTRODUCTION
Covalent or ionic-bonds give ceramics high chemical stability, high strength, high wear-resistance, and high temperature stability. However, their low temperature brittleness (low toughness) limits their application as structural materials. Research1–3 has shown that the toughness can be improved by adding additional phases, e.g., fibers, to reinforce or toughen the brittle matrix at room temperature. One of the earliest of these additional phase toughened composites was a metal phase toughened ceramic composite.4 The toughening mechanisms for ductile particles in a brittle matrix involve crack deflection (including bowing), ductile particle bridging, crack blunting, and particle debonding. The residual stresses around these particles can deflect cracks out of their primary paths, cause them to bow between obstacles, and result in bifurcation. Ductile particles can cause blunting of the crack tip, or ductile particle bridging in well bonded particulate composites.5 Since small size ductile phases are highly constrained by the surrounding stiff ceramic matrix, the ductility that absorbs energy by plastic deformation during fracture is limited.1 Thus, the ductile bridging role in this type of composite is much less than had been expected.6 Recently, the use of continuous ductile lamina to toughen ceramic matrix composites (multilayer composites) was studied.7–9 Chen and Mecholsky10–12 used Ni lamina to toughen the alumina layers in Al2 O3yNi tape cast laminated composites. The toughness, strength, and reliability of alumina are greatly improved with the addition of ductile lamina. The contribution of these improvements was attributed to thermal residual stress, ductile layer crack deflection, and ductile bridging. The ductile layer bridging a)
Now with the Space Power Institute, Auburn, Alabama 36849. J. Mater. Res., Vol. 11, No. 8, Aug 1996
http://journals.cambridge.org
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contributes a major part of toughening in this type of composite. The interaction of brittle and ductile layers in the la
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