Dental News - Application of electric field during formation increases plasticity of dental ceramics

Dental Tribune International

Thu. 7. June 2018

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WEST LAFAYETTE, Ind., U.S.: While inherently strong, most ceramics tend to fracture suddenly when just slightly strained under a load unless this is done under high temperatures. Structural ceramic components also require high temperatures to form through a lengthy process called sintering, in which a powdered material coalesces into a solid mass. Researchers from Purdue University in West Lafayette have found that the brittle nature of ceramics as they sustain heavy loads can be overcome, resulting in more resilient structures that could be used for many applications, including dental implants.

The study demonstrated that applying an electric field during the formation of yttria-stabilized zirconia (YSZ)—a typical thermal barrier ceramic—makes the material shapeable at room temperature, almost like metal. In their experiments, the researchers at the university's School of Materials Engineering could also see cracks sooner, since they started to slowly form at a moderate temperature as opposed to higher temperatures, giving them time to rescue a structure.

Prior studies have shown that applying an electric field, or “flash,” significantly accelerates the sintering process that forms YSZ and other ceramics, and at much lower furnace temperatures than conventional sintering. Flash-sintered ceramics also have very little porosity, which makes them denser and therefore easier to deform. The ability of flash-sintered ceramics to change shape at room temperature or increasingly higher temperatures, had not previously been tested.

What allows metals to be fracture-resistant and shapeable is the presence of “defects,” or dislocations—extra planes of atoms that shuffle during deformation to make a material simply deform rather than break under a load. “These dislocations will move under compression or tension, such that the material doesn’t fail,” said lead author Jaehun Cho, a graduate student at the university.

Ceramics normally do not form dislocations unless deformed at very high temperatures. Flash-sintering them, however, introduces these dislocations and creates a smaller grain size in the resulting material. “Smaller grains, such as nanocrystalline grains, may slide as the ceramic material deforms, helping it to deform better,” said Dr. Haiyan Wang, Basil S. Turner Professor of Engineering at the university’s School of Materials Engineering.

Improved plasticity results in greater stability during operation at relatively low temperatures. The next steps would be using these principles to design even more resilient ceramic materials.

The study, titled “High temperature deformability of ductile flash-sintered ceramics via in-situ compression,” was published online in Nature Communications on 25 May 2018. The research was conducted in collaboration with the Oak Ridge National Laboratory in Oak Ridge, the University of California, Davis and the Colorado State University in Fort Collins.

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