PSI - Issue 23

Yoshikazu Nakai et al. / Procedia Structural Integrity 23 (2019) 83–88 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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planes. In the EBSD analysis, detwinning occurred in this process. Then the value of β is not changed by detwinning while it is changed by plastic deformation occurred in the basal slip planes. These finding indicates that twinning and detwinning in magnesium alloy can be observed by DCT measurement.

5. Conclusions

In the present study, the twinning and the detwinning in tension and compression loading in a magnesium alloy was observed by the DCT using ultra-bright synchrotron radiation X-ray, and the electron backscatter diffraction (EBSD) analysis. The following results were obtained. (1) The shape of each grain in a polycrystalline magnesium alloy was successfully reconstructed, and misorientation of each crystallographic plane was successfully measured by DCT. (2) With increasing applied compression stress, the value of the misorientation in the basal slip plane was decreased, while it is usually increased with plastic strain for materials without twinning. (3) The value of misorientation increased with unloading process, indicating that the twinning was occurred under the compressive applied stress. (4) The EBSD analysis of specimen surface also shows that the twinning was occurred under the compressive applied stress, and the following applied tension stress brought detwinning. The synchrotron radiation experiments have been conducted at SPring-8 with the approval of the Japan Synchrotron Radiation Research Institute under proposal numbers of 2014A1782, 2015A1682, 2016B1627, 2017A1603, 2017A1604 and 2018B1593. The authors are grateful to Dr. K. Kajiwara and Dr. Y. Nakamura for their technical supports. Support of this work through a Grant-in-Aid for Scientific Research (C) from Japan Society for the Promotion of Science under proposal number 18K03837 (Head investigator: Professor Yoshikazu Nakai, Kobe University) is gratefully acknowledged. Gordon, R., Bender, R., Herman, G. T., 1970, Algebraic reconstruction techniques (ART) for three-dimensional electron microscopy and X-ray photography, Journal of Theoretical Biology, 29, 471-481. Tanaka K. Nakai Y. Maekawa O., 1982. Microscopic Study on Fatigue Crack Initiation and Early Propagation in Smooth Specimen of Low Carbon Steel. Journal of the Society of Materials Science, Japan, 31, 376-82. Nakai, Y., Fukuhara, S., Ohnishi, K., 1997. Observation of Fatigue Damage in Structural Steel by Scanning Atomic-force Microscopy. International Journal of Fatigue,19, S223-S36. Nakai, Y., Kusukawa, T., Hayashi, N., 2002. Scanning Atomic-force Microscopy on Initiation and Growth Behavior of Fatigue Slip- bands in α brass, in “ Fatigue and Fracture Mechanics : 32nd Volume ” , ASTM STP 1406, In: Chona, R. (Ed.). American Society for Testing and Materials, West Conshohoken, PA, 122-35. Ludwig, W., Schmidt, S., Lauridsen, E.M., Poulsen, H.F., 2008. X-ray Diffraction Contrast Tomography: A Novel Technique for Three dimensional Grain Mapping of Polycrystals. I. Direct Beam Case, Journal of Applied Crystallography, 41, 302-309. Wu, L., Jain, A., Brown, D.W., Stoica, G.M., Agnew, S.R., Clausen, B., Fielden, D.E., Liaw, P.K., 2008. Twinning – detwinning Behavior During the Strain-controlled Low-cycle Fatigue Testing of a Wrought Magnesium Alloy, ZK60A, Acta Materialia 56, 688-695. Shiozawa, D., Nakai, Y., Miura, R., Masada, N., Matsuda, S., Nakao R., 2016. 4D Evaluation of Grain Shape and Fatigue Damage of Individual Grains in Polycrystalline Alloys by Diffraction Contrast Tomography Using Ultrabright Synchrotron Radiation, International Journal of Fatigue, 82, 247-255. Nakai, Y., Shiozawa, D., Nakao, R., Asakawa, N., Kikuchi, S., 2017. Misorientation Measurement of Individual Grains in Fatigue of Polycrystalline Alloys by Diffraction Contrast Tomography Using Ultrabright Synchrotron Radiation, Materials Science Forum, 879, 355 1360. Nakai, Y., Saka, M., Yoshida, H., Asayama, K., Kikuchi, S., 2019. Fatigue Crack Initiation Site and Propagation Paths in High-cycle Fatigue of Magnesium Alloy AZ31. International Journal of Fatigue, 123, 248-254. References Acknowledgements