The high temperature mechanical characteristics of superplastic 3 mol% yttria stabilized zirconia

Journal Article · Mon Jan 05 04:00:00 EST 1998 · Acta Materialia

DOI:https://doi.org/10.1016/S1359-6454(97)00251-6· OSTI ID:616202

Owen, D M ^[1]; Chokshi, A H ^[2]

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1. California Inst. of Tech., Pasadena, CA (United States). Graduate Aeronautical Lab.
2. Indian Inst. of Science, Bangalore (India). Dept. of Metallurgy

A detailed study was undertaken to characterize the deformation behavior of a superplastic 3 mol% yttria-stabilized tetragonal zirconia (3YTZ) over a wide range of strain rates, temperatures and grain sizes. The experimental data were analyzed in terms of the following equation for high temperature deformation: SR {proportional_to} FS{sup n} d{sup {minus}p} exp({minus}Q/RT), where SR is the strain rate, FS is the flow stress, d is the grain size, Q is the activation energy, R is the gas constant, T is the absolute temperature, and n and p are constants termed the stress exponent and the inverse grain size exponent, respectively. The experimental data over a wide range of stresses revealed a transition in stress exponent. Deformation in the low and high stress regions was associated with n about 3 and p about 1, and n about 2 and p about 3, respectively. The transition stress between the two regions decreased with increasing grain size. The activation energy was similar for both regions with a value of about 550 kJ/mol. Microstructural measurements revealed that grains remained essentially equiaxed after the accumulation of large strains, and very limited concurrent grain growths occurred in most experiments. Assessment of possible rate controlling creep mechanisms and comparison with previous studied indicate that in the n=2 region, deformation occurs by a grain boundary sliding process whose rate is independent of impurity content. Deformation in the n=3 region is controlled by an interface reaction that is highly sensitive to impurity content. It is concluded that an increase in impurity content increases yttrium segregation to grain boundaries, which enhances the rate of the interface reaction, thereby decreasing the apparent transition stress between the n=2 and n=3 regions. This unified approach incorporating two sequential mechanisms can rationalize many of the apparently dissimilar results that have been reported previously for deformation of 3YTZ.

• OSTI ID: 616202
• Journal Information: Acta Materialia, Journal Name: Acta Materialia Journal Issue: 2 Vol. 46; ISSN 1359-6454; ISSN ACMAFD
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
DEFORMATION
MICROSTRUCTURE
PLASTICITY
YTTRIUM OXIDES
ZIRCONIUM OXIDES