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First Full 3-D View Of Cracks Growing In Steel

Date:
July 22, 2008
Source:
European Synchrotron Radiation Facility
Summary:
Researchers have revealed how a growing crack interacts with the 3-D structure of stainless steel. By using a new technique, they could determine the internal 3-D structure of the sample without destroying it. Afterwards, they initiated a crack and studied how it grew between the grains. The results could be useful to make more performing materials for, for example, safer power plants.

Cracks forming in the inside of a stainless steel wire are coloured red.
Credit: Andrew King

A team of researchers from the University of Manchester, the National Institute of Applied Sciences (INSA) in Lyon (France) and the ESRF has revealed how a growing crack interacts with the 3D crystal structure of stainless steel. By using a new grain mapping technique it was possible to determine the internal 3D structure of the material without destroying the sample.

Afterwards, a crack was initiated in the stainless steel, and the scientists were able to study how the crack grew between the grains. This is the first time that such an experiment has used the 3D grain mapping technique, and the first results have just been published in the journal Science.

Cracks can appear in stainless steel components when stress or strain is combined with a corrosive environment that attacks sensitive grain boundaries. These cracks represent a critical failure mechanism. In power generation plants, certain grain boundaries can become sensitive during heat treatments or during fast neutron irradiation in nuclear power stations.

Most metals used for engineering are made up of many small crystals or grains. The scientists used a new technique called diffraction contrast tomography, developed at the ESRF, to obtain a 3D map of all grains in a section of a stainless steel wire measuring 0.4 mm in diameter. This map contained the shapes, positions, and orientations of 362 different grains. The next stage of the experiment involved putting the wire into a suitable corrosive liquid, and applying a load to cause microcracks to grow between grains. During the crack growth, 3D tomographic scans (of 30 minutes each) were made at intervals of between two hours and a few minutes to follow the progress of the crack. This is the first in-situ experiment of this kind to use non-destructive 3D grain mapping techniques.

“The cracks grew along the boundaries between the grains which we had mapped in 3D, and we could visualize both the growing crack and certain special boundaries that resist cracking”, explains Andrew King, corresponding author of the paper in Science. “Some of these resistant boundaries were not the ones that we expected".

The special, crack-resistant boundaries may be of key importance to the metallurgy industry. Materials containing more of these boundaries are also more resistant to this type of cracking. Being able to study crack growth in-situ will allow scientists to understand what types of grain structures will give the best performing materials, leading, for example, to more efficient and safer power plants, and more generally to more lightweight alloys in other sectors of metallurgy and engineering.


Story Source:

The above story is based on materials provided by European Synchrotron Radiation Facility. Note: Materials may be edited for content and length.


Journal Reference:

  1. King, A. et al. . Science, 18 July 2008

Cite This Page:

European Synchrotron Radiation Facility. "First Full 3-D View Of Cracks Growing In Steel." ScienceDaily. ScienceDaily, 22 July 2008. <www.sciencedaily.com/releases/2008/07/080717140421.htm>.
European Synchrotron Radiation Facility. (2008, July 22). First Full 3-D View Of Cracks Growing In Steel. ScienceDaily. Retrieved July 28, 2014 from www.sciencedaily.com/releases/2008/07/080717140421.htm
European Synchrotron Radiation Facility. "First Full 3-D View Of Cracks Growing In Steel." ScienceDaily. www.sciencedaily.com/releases/2008/07/080717140421.htm (accessed July 28, 2014).

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