Ultra-hot test rig for Space-Age ceramics
7 Jan 2013 by Evoluted New Media
Researchers at Berkeley Lab have developed the first testing facility that enables CT-scanning of ceramic composites under controlled loads at ultrahigh temperatures in real time.
Berkeley Lab’s Advanced Light Source (ALS) is a leading source of X-ray and ultraviolet light beams. Here, researchers have created a mechanical testing rig for performing X-ray computed microtomography to reveal the growth of microcrack damage under loads at temperatures of up to 1750 °C.
“The combination of our in situ ultrahigh temperature tensile test rig and the X-rays at ALS Beamline 8.3.2 allows us to obtain measurements of the mechanical properties of advanced ceramic materials at temperatures that are literally unprecedented,” said Robert Ritchie, a Berkley Lab materials scientist who led the work. The work is described in Nature Materials.
Clay ceramics have been used as construction materials for thousands of years due to their renowned ability to resist damage from water, chemicals, oxidation and –most importantly – heat. However, traditional ceramics suffer from brittleness – a serious deficit. These days, the materials are reinforced with ceramic fibres to form composites that can be structured along the lines of natural materials such as bone and shells.
Unfortunately, while ceramic composites are hardier than their clay ancestors, tiny cracks can form and grow within their complex microstructures.
“Like bone and shells, ceramic composites achieve robustness through complexity, with their hierarchical hybrid microstructures impeding the growth of local damage and preventing the large fatal cracks that are characteristic of brittle materials. However, complexity in composition brings complexity in safe use. For ceramic composites in ultrahigh temperature applications, especially where corrosive species in the environment must be kept out of the material, relatively small cracks, on the order of a single micron can be unacceptable,” explained Ritchie.
The ALS Beamline 8.3.2 is powered by a 6 Tesla superconducting bend magnet and is designed for X-ray computed microtomography which provides non-destructive 3D imaging of solid objects at a resolution of approximately one micron. Combined with the team’s unique tensile testing rig, Richie and colleagues can maintain in situ ultrahigh temperature environments in either inert or oxidising atmospheres while obtaining real-time 3D images of sample microstructures.
“The capacity for validating virtual testing models through direct, real-time, non-invasive experimental observations should greatly advance our understanding and help promote the technological innovation of ceramic composites,” added Richie.
