Materials Design Approaches and Experiences V: Poster Session
Sponsored by: TMS Structural Materials Division, TMS: High Temperature Alloys Committee, TMS: Integrated Computational Materials Engineering Committee
Program Organizers: Akane Suzuki, GE Aerospace Research; Ji-Cheng Zhao, University of Maryland; Michael Fahrmann, Haynes International; Qiang Feng, University of Science and Technology Beijing; Michael Titus, Purdue University

Tuesday 5:30 PM
February 25, 2020
Room: Sails Pavilion
Location: San Diego Convention Ctr


L-28 (Invited): Integrated Study of First-principles Calculations and Experimental Measurements for Hydrogen Effect on FCC to HCP Martensitic Transformation: Satoshi Iikubo1; Kenji Hirata1; Y. Kuroki1; Shoya Kawano1; Hiroshi Ohtani1; Motomichi Koyama1; Kaneaki Tsuzaki1; 1Kyushu Institute of Technology
    Hydrogen, which can act as an interstitial species in steels, has been recognized to promote phase transformation from FCC to HCP. However, we reported a dramatic effect of interstitial hydrogen that suppresses this hcp phase transformation experimentally. More specifically, the fraction of hcp phase that forms during cooling decreases with increasing diffusible hydrogen content. To understand this new finding, first-principles calculations were employed to investigate the effect of hydrogen on the chemical driving force of the transformation of iron from the FCC to HCP phase. The minimum energy path from FCC to HCP phases shows that FCC becomes stable with increasing hydrogen content. Furthermore, vibrational contribution to the free energy destabilizes HCP phase with hydrogen, throughout the temperature region. These results explain the observed anomalous suppression of the martensitic transformation in the hydrogen-charged steel.