◆ Environmentally-assisted fracture problem

 The mechanical properties of metallic materials are influenced by the surrounding environment. Particularly, ductility and toughness are significantly reduced when hydrogen is absorbed, which is know as hydrogen embrittlement (HE). From a microscopic viewpoint, grain boundaries (GBs) tends to be a typical fracture site when HE is promoted. The susceptibility of GBs to HE then needs to be studied in detail.
We successfully evaluated for the first time the HE property of a discrete GB by utilizing our micromechanical testing method (see micro-materials fracture problem). By comparing samples taken from different GBs, it was found that HE susceptibility depends both on orientation difference and GB type.

For more detail, see:
Y. Takahashi, H. Kondo, R. Asano, S. Arai, K. Higuchi, Y. Yamamoto, S. Muto, N. Tanaka, Direct evaluation of grain boundary hydrogen embrittlement: a micro-mechanical approach, Materials Science & Engineering A, Vol. 661, 2016, pp. 211–216 (http://dx.doi.org/10.1016/j.msea.2016.03.035).

Related studies:

Y. Takahashi, I. Ashida, S. Arai, K. Higuchi, Y. Yamamoto, S. Muto, Interfacial fracture strength evaluation of Cu/SiN micro-components: applicability of the linear fracture mechanics criterion under a hydrogen environment, International Journal of Fracture, Vol. 210, 2018, pp. 223–231 (https://doi.org/10.1007/s10704-018-0269-8)

Y. Takahashi, K. Yamaguchi, M. Tanaka, K. Higashida, H. Noguchi, On the micro-mechanism of hydrogen-assisted cracking in a single-crystalline iron-silicon alloy thin sheet, Scripta Materialia, Vol. 64, 2011, pp. 537–540 (https://doi.org/10.1016/j.scriptamat.2010.11.035)

Y. Takahashi, M. Tanaka, K. Higashida, K. Yamaguchi, H. Noguchi, An intrinsic effect of hydrogen on cyclic slip deformation around a {110} fatigue crack in Fe-3.2 wt.% Si alloy, Acta Materialia, Vol. 58, 2010, pp. 1972–1981 (https://doi.org/10.1016/j.actamat.2009.11.040)