Ceramics made plastically deformable at room temperature

Plasticity or plastic deformability is a material’s ability to be deformed by compression, tension or shear into a specific shape or geometry without breaking. Typically, ceramic materials exhibit very limited plastic deformability under room temperature.

Now, Haiyan Wang and Xinghang Zhang from Purdue University’s College of Engineering have lead a team whose method is said to improve ceramic room-temperature plastic deformability by first introducing high-density defects in brittle ceramics under high temperatures. The research has been published in Science Advances.

“Such a strategy can prominently improve the room-temperature plastic deformability of ceramics, and holds the promise to inject ductility, or the ability to be drawn into near net shape, of ceramics in the near future,” Zhang said in a statement. 

Ceramic materials are used as structural materials in aerospace, transportation, power plants and manufacturing; and in applications such as bearings in engines and machines, capacitors, electrical insulating materials, electrodes in batteries and fuel cells, and thermal barrier coatings in high-temperature machines.

They are mechanically strong and chemically inert; resist wear and corrosion; insulate against heat and electricity; and are harder, and have higher melting points, than metals.

Ceramics are brittle at room temperature; they bend only at high enough temperatures when dislocation activity can be activated, whereas metals bend without breaking at room temperature.

Wang said ceramics have few dislocations - defects in materials that change the arrangement of atoms in a structure - causing their brittle nature.

“A dislocation can glide within crystals to enable plastic deformability at certain stress levels,” said Wang. “However, in ceramic materials, it is difficult to nucleate dislocations at room temperature, as the fracture stress in ceramics is much less than the stress to nucleate dislocations at such temperatures.”

“In contrast, metallic materials are ductile because they easily nucleate a very high density of dislocations,” said Zhang. “And dislocations are mobile in metals at room temperature, significantly improving their ductility. So the way to improve plasticity for ceramics is to nucleate abundant dislocations in ceramics before we start to deform them.”

Wang said extensive efforts have been made to enhance the deformability of ceramics, but with limited success. 

The Purdue team has introduced dislocations into ceramic materials by preloading them during deformation at high temperatures. Once the ceramic specimens are cooled, the dislocations improve the plasticity of ceramics at room temperature.

The technique has been tested and validated on various ceramic systems and ceramic pillars of different dimensions.

“After the preloading treatment, single-crystal titanium dioxide exhibited a substantial increase in deformability, achieving 10 per cent strain at room temperature,” Zhang said. “Aluminium oxide also showed plastic deformability, six per cent to 7.5 per cent strain, using the preloading technique.”

The research team now plans to collaborate with industry on large-scale demonstrations of this approach in various ceramics systems.