[Image above] Purdue University researchers recently developed a patent-pending high-temperature mechanical deformation method to introduce dislocations into ceramics. Pictured are ACerS Fellow Haiyan Wang (left) and graduate student Chao Shen (right), two of the Purdue researchers, as they work on a transmission electron microscope. Credit: Yifan Zhang, Purdue University
As demonstrated by our guests on ACerS podcast Ceramic Tech Chat, ceramic engineers must be flexible to handle working with such brittle materials. But in a creative twist, in recent years, ceramic materials have instead been the ones bending to the will of researchers thanks to the growing field of dislocations in ceramics.
Dislocations are one-dimensional line defects that are the main carriers of plastic deformation in crystalline solids. Metallic materials have traditionally been the focus of research on dislocation-mediated plastic deformation, but ceramics are gaining ground with the development of methods to engineer dislocations into ceramics in a simple and controllable manner.
The importance of this emerging research field was recognized in August 2023 when the editors of Journal of the American Ceramic Society named Xufei Fang as the journal’s inaugural 2nd Century Trailblazer. The Trailblazers initiative aimed to raise the profile of early-career ceramic and glass scientists and engineers, and Fang’s open-access paper on tailoring dislocations in ceramics at room temperature was selected as the final winner out of 50+ published submissions.
While Fang’s paper briefly discussed several methods for introducing dislocations into ceramics, the focus was on dislocation engineering via mechanical deformation. Mechanical deformation offers the opportunity to deform samples from bulk to sub-microscales, plus it can introduce dislocations into both single crystals and polycrystalline samples.
A challenge with mechanical deformation, however, is tuning plasticity while suppressing crack formation. As Fang notes, “The mechanical deformation boundary conditions play a crucial role in determining whether or not the deformed sample will survive or just fracture.”
Temperature typically is a key parameter in mechanical deformation methods. Above a ceramic’s brittle-to-ductile transition temperature, additional slip systems can be activated, allowing for greater plastic deformation. On the other hand, higher temperatures open the door to high-temperature creep, dislocation climb, recovery, and grain boundary sliding, which add to the complexity of deformation mechanisms.
Finding the right balance between temperature and mechanical loading, then, is essential to successfully deforming ceramics through this method. In a recent open-access paper, researchers at Purdue University describe the development and validation of their patent-pending high-temperature mechanical deformation method.
The researchers are led by ACerS Fellow Haiyan Wang and ACerS member Xinghang Zhang and also include ACerS Fellow R. Edwin Garcia. While details of their patent-pending method are limited, they report that it resulted in micropillars of single-crystal titanium dioxide and aluminum oxide achieving strains of 10% and 6–7.5%, respectively, at room temperature.
In a Purdue press release, the researchers say they plan to collaborate with industry on large-scale demonstrations of their method in various ceramics systems, including bulk polycrystalline ceramics.
The open-access paper, published in Science Advances, is “Achieving room temperature plasticity in brittle ceramics through elevated temperature preloading” (DOI: 10.1126/sciadv.adj4079).