DEFORMATION PROCESSING OF CERAMICS.
Description
- Language(s)
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English
- Published
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1991, c1991.
- Summary
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The demonstration of successful forming of a variety of ceramics under several deformation modes with improvement to microstructures and properties suggests that deformation processing of ceramics should be technically feasible.
investigated and analyzed with an approximate analytical model and with a numerical method.
A high-temperature punch-stretching test was developed, in which a flat disk can be stretched into a hemispherical dome. Large biaxial tensile strains ($\varepsilon\sb{\rm eff}$ $>$ 0.5) were achieved for several fine-grained ceramics (zirconia with or without dopants, $\alpha\sp\prime$-Si$\sb3$N$\sb4$, MgO-doped Al$\sb2$O$\sb3$, and composites of zirconia:alumina and of zirconia:mullite in different ratios.) The strain distribution, load-displacement response, and location of fracture origins were
modeled based on grain rotation, without impingement, and the stress-strain behavior was predicted. Surprisingly such a texture enhanced the ductility.
Tensile superplasticity was found in a liquid-phase containing $\beta\sp\prime$-Si$\sb3$N$\sb4$ at 1535-1580$\sp\circ$C and at strain rates below 3 $\times$ 10$\sp{-4}$ s$\sp{-1}$, and elongations above 230% were achieved. Microstructures and XRD indicated that the anisotropic grain growth was accelerated by deformation, with the long axes of the grains, which are parallel to their c-axes, becoming highly aligned in the tension direction. This strain-enhanced texture/microstructural development was
mechanics was analyzed by a combined upper-bound/slab analysis. It was discovered that during hot-extrusion of Bi$\sb2$(Sr,Ca)$\sb3$Cu$\sb2$O$\sb{\rm 8+x}$ a strong texture was developed with the basal plane aligned along the extrusion direction. Since the basal plane is superconducting, such a texture is beneficial for current transportation.
Two dense ceramics, Bi$\sb2$(Sr,Ca)$\sb3$Cu$\sb2$O$\sb{\rm 8+x}$ and 2Y-TZP:10wt% Al$\sb2$O$\sb3$, were hot-extruded through conical dies under a wide range of conditions. Extrusion of Bi$\sb2$(Sr,Ca)$\sb3$Cu$\sb2$O$\sb{\rm 8+x}$ was performed at 775 to 825$\sp\circ$C and speeds of 0.0005 to 0.2 mm/s, with the die semi-angles from 30$\sp\circ$ to 60$\sp\circ$ and extrusion ratios from 4 to 9. Extrusion of 2Y-TZP:10wt% Al$\sb2$O$\sb3$ was performed at 1650$\sp\circ$C and 0.017 mm/s. The extrusion
This dissertation provides an initial assessment of the feasibility of deformation processing of ceramics.
- Physical Description
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215 p.
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