Dislocation densities and intergranular stresses of plastically deformed austenitic steels

Significance 

Development of advanced composite materials has revolutionized new applications in areas of structural, building and manufacturing industries. In particular, plastically deformed austenitic steel composites have attracted significant attention of researchers owing to their excellent properties. Consequently, a recent study has revealed the existence of strong anisotropy in polycrystalline austenitic steel composites. Therefore, understanding the effects and the behaviors of the embedded grains within the matrix will be of great significance in optimizing the properties of these composite materials for high-performance applications.

Presently, several methods have been developed to study the behavior of embedded grains. Unfortunately, most of these available methods concentrate on the deformation behavior at the surface while ignoring the specimen interior thus leading to inaccurate results. In addition, the difference in deformation at the interior and free surface of the specimen has not been fully explored. Therefore, researchers have been looking for alternatives and have identified monitoring density changes and dislocations arrangements within the embedded grain as a promising solution.

Recently, Ibaraki University researchers: Prof. Yo Tomota, Dr. Ojima, Dr. Harjo, Dr. Gong and Prof. Sato in collaboration with Prof. Ungár from Eötvös University assessed the behavior of austenitic steel composites during heterogenous plastic deformation. They proposed to determine the average dislocation density and the dislocation density in the individual grain family using the contrast factors. This would in turn help in examining the individual grain deformation criteria and their influence in the strain-stress behavior. Their research work is currently published in the research journal, Materials Science and Engineering A.

In brief, the authors did a detailed cross-examination of the density changes and dislocations arrangement in tensile deformation. Next, they employed various approaches including neutron diffraction measurement method and electron back scatter diffraction to determine the plastic deformation behavior of the individual grains taking into consideration the tensile direction of the austenitic steel composite material. Consequently, convolutional multiple whole profile fitting technique was used to analyze the resulting diffraction profiles.

The researchers observed different deformation behavior for differently oriented crystals constituting a polycrystalline stainless-steel composite. This was attributed to the different behavior of the individual grains under either plastic or elastic deformation. In addition, for the elastic-plastic deformation, the results obtained by both electron back scatter diffraction and neutron diffraction methods showed good agreement. This further simplified the deformation behavior thus making it easy to understand as the two methods complemented each other very well. However, convolutional multiple whole profile fitting produced different results for the oriented grain family dislocation densities. For instance, in tensile direction neutron diffraction, the dislocation density in <110> grains-family was reported to be twice that of <211>.

In summary, Prof. Yo Tomota and colleague presented a successful approach for determining the intergranular stresses and dislocation densities in plastically deformed austenitic steel composites. In general, the strong consistency in the obtained results will lay a great foundation studying plastically deformed austenitic steels to develop high-performance composites for numerous applications.

Reference

Tomota, Y., Ojima, M., Harjo, S., Gong, W., Sato, S., & Ungár, T. (2019). Dislocation densities and intergranular stresses of plastically deformed austenitic steels. Materials Science and Engineering: A, 743, 32-39.

Go To Materials Science and Engineering A

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