D. I. Nikolaev, T.A. Lychagina, A. V. Pakhnevich, R. N. Vasin, T. I. Ivankina, V. V. Sikolenko, B. Altangerel

The SKAT instrument (spectrometer for quantitative analysis of textures) is designed to measure crystallographic texture that is an ensemble of grain orientations of a polycrystal. Interest in the research of crystallographic texture concerns on the one hand, the fact that it is taken during the production and growth of polycrystals and on the other hand, the fact that it determines the anisotropy of material properties.

Preferential orientations occur in the pressure processing of metals and alloys: when rolling sheets or drawing wires, the crystal lattice of grains is oriented in a regular way along the direction of the plastic flow of the material. The texture that occurs during the recrystallization of metals is often different from the deformation texture. Textures are also developed during extrusion of powders, electrodeposition and sputtering of thin films. Since texture often results from an external impact, it contains information about it. In the case of metals and alloys, this  information is about the nature of material processing; in the case of rocks, the information is about the deformation history of the rock mass from which the test sample has been taken; in biological objects, the texture is developed during the growth of organisms. Recently, there has been interest in studying the crystallographic textures of biological objects: shells of modern and fossil molluscs, corals, fossil woods and brachiopods. (http://www.jinr.ru/posts/uchenye-oiyai-izuchili-kak-izmenilis-rakoviny-iskopaemyh-mollyuskov/). The neutron diffraction technique allows to study the global texture without destroying samples up to 100 cm³ in volume that allows to measure the entire mollusc shells up to 5 cm in size.

Fig.1. Schematic of the SKAT instrument on beamline 7A-1 of the IBR-2 high flux pulsed reactor. The length of the neutron guide system is 104 m that allows for a high resolution. The linear dimensions of the neutron beam at the output of the system are 90×50 cm that allows to measure large samples up to 100 cm3 in volume. Detector-collimator complexes are installed on a single Debye-Scherrer cone around the beam falling at a scattering angle 2θ = 90°. The sample rotates relative to the horizontal axis of the goniometer at 5° intervals

Traditionally, textures have been measured using X-ray diffraction. However, for coarse-grained samples of rocks, structural materials and biological objects with grain sizes of a few millimeters, the use of neutron diffraction is the only way to provide the amount of grains required for texture analysis. This is due to the greater penetrating power of thermal neutrons compared to X-rays.

 A technique for estimating retained austenite in high-strength steels using neutron diffraction has been been developed. Current procedures for quantitative analysis of retained austenite in steels using neutron diffraction ignore the impact of crystallographic texture and rely on a priori parameters rather than direct calibration with appropriate standards. The neutron diffraction spectra have been measured using the SKAT texture instrument in order to exclude the impact of texture on the result. Calibration samples with a given austenite content have been measured. Based on the results of measurements of these samples, calibration straight lines have been constructed and have been used to determine the fraction of retained austenite in samples from a range of different steels. It has been discovered that with an increase in the annealing temperature to 300°C, the fraction of retained austenite decreases that is in good agreement with the dilatometry data. The results of the research are published in the international peer-reviewed journal “Advanced Engineering Materials”.

Fig.2. Cover of the journal “Advanced Engineering Materials”, issue 20, number 4, 2018 with graphs and figures from the article “Directly verifiable neutron diffraction technique to determine retained austenite in steel”

Time-of-flight neutron diffraction has been used to study the crystallographic texture and mineral composition in the shells of the fossil mollusc from the Middle Callovian–Lower Oxfordian deposits (Jurassic system) Gryphaea dilatata [1]. The shells have been collected in three different quarries in the Kursk, Oryol and Moscow regions. It has turned out that the shells completely consist of calcite and the texture type of this mineral depends on the shape of the shell valves and does not depend on the habitat and burial conditions of organisms. This indicates that crystallographic texture is a stable parameter that can be used to understand how organisms that lived millions of years ago were arranged at the crystalline level.

Fig.3. Calcite pole figures of the Gryphaea dilatata shell from the Mikhailovsky quarry near Zheleznogorsk (the Kursk region), Middle Jurassic Callovian deposits a) for left convex valves b) for right flattened valves; calcite pole figures of the Gryphaea dilatata shell from a quarry in the Oryol region, Middle Jurassic Callovian deposits c) for left convex valves d) for right flattened valves

Publications:

1. Nikolayev D., Lychagina T., Zisman A.A., et al., Directly verifiable neutron diffraction technique to determine retained austenite in steel. Advanced Engineering Materials, 20(4), 1700559 (2018). Doi:10.1002/adem.201700559
2. Pakhnevich A., Nikolayev D., Lychagina T., Crystallographic Texture of the Mineral Matter in the Bivalve Shells of Gryphaea dilatata Sowerby, 1816, Biology, 11(9), 1300 (2022). Doi:10.3390/biology11091300
3. Pakhnevich A., Nikolayev D., Lychagina T., et al., Global Crystallographic Texture of Freshwater Bivalve Mollusks of the Unionidae Family from Eastern Europe Studied by Neutron Diffraction. Life, 12(5), 730 (2022). Doi:10.3390/life12050730
4. Пахневич А.В., Николаев Д.И., Лычагина Т.А., Сравнение кристаллографической текстуры раковин современных, ископаемых и субфоссильных двустворчатых моллюсков, Палеонтологический журнал, 6, 3-14 (2021). https://www.elibrary.ru/item.asp?id=46621789