Proceedings of the 5th International Conference on Metals & Hydrogen P021

Proceedings of the 5th International Conference on Metals & Hydrogen P021

Simulation of hydrogen thermal desorption spectra for iron with strain-Induced vacancy-type defects included

K. Ebihara (*) * (1)1 , Y. Sugiyama (2)2 , R. Matsumoto (3)3 , K. Takai (4)4 , T. Suzudo (1)1

  • (1) 1

    Center for Computational Science & e-Systems, Japan Atomic Energy Agency, JAPAN

  • (2) 2

    Graduate School of Science and Technology, Sophia University, JAPAN

  • (3) 3

    Nagamori Institute of Actuators, Kyoto University of Advanced Science, JAPAN

  • (4) 4

    Department of Engineering and Applied Science, Faculty of Science and Technology, Sophia University, JAPAN

  • (*) *

    (corresponding author)
    ebihara.kenichi@jaea.go.jp

Abstract

Hydrogen embrittlement is known as a cause of delayed fracture in high strength steels and cracks at the heat-affected zone in weld metals. Since the fracture and cracks suddenly happen without obvious symptoms, it is critical to elucidate its mechanism for predicting and preventing hydrogen embrittlement. Recently, the excess formation of vacancy-type defects in iron and steel specimens charged with hydrogen atoms during the deformation is shown by thermal desorption spectrometry and the measurement of positron annihilation lifetime. It is also reported that excess vacancy-type defects themselves cause the reduction of elongation in the specimens. Thus these results are considered to support the hydrogen enhanced strain-induced vacancy model that is one of the candidate mechanisms explaining hydrogen embrittlement [1]. Because the quantitative discussion on the amount of and the size of the vacancy-type defects has not been done sufficiently yet, we examined the formed vacancy-type defects by numerically simulating the thermal desorption spectra of an iron specimen that contains strain-induced vacancy-type defects.

First, we experimentally obtained hydrogen desorption spectra of a thin iron specimen with 0.3mm in thickness using the thermal desorption spectrometry apparatus, which can measure hydrogen desorption from temperatures as low as -200oC. The obtained spectra had a distinctive peak corresponding to vacancy-type defects at the high-temperature side of a large peak mainly related to dislocations. Next, we calculated the spectra using a model that was constructed by combining the model representing diffusion, annihilation, aggregation, and dissociation of vacancies and vacancy clusters [2] to the McNabb-Foster model [3]. In the model, the binding energy between hydrogen atoms and vacancies and vacancy clusters was evaluated by molecular statics simulation using an EAM potential. We will discuss the possibility of reproducing the experimental spectra by the model and the effect of the size of vacancy-type defects on the spectra. This presentation is based on the paper [4].

Acknowledgment: This was supported partially by JSPS KAKENHI Grant Number 19K05069.

Keywords

  • Hydrogen embrittlement
  • Numerical simulation
  • HESIV model
  • Vacancy and vacancy cluster

Introduction


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