SIMULATION OF HYDROGEN THERMAL DESORPTION CHARACTERISTICS IN METALS

CONTAINING LARGE VOIDS

IWSMT132016.10. 30 11. 4

H. Yamashita1*, K. Sato2, S. Komazaki2

1Advanced Fast Reactor Cycle System Research and Development Center, Japan Atomic Energy Agency

2Research Field in Engineering, Science and Engineering Area, Research and Education Assembly, Kagoshima University

H

H

Fe Fe

FeFe

FeFe

FeV

H

H

H

Fe

Fe Fe FeFeFeFe Fe

Fe

Fe FeFe FeFe FeFe

Fe FeFeFeFe

Fe Fe FeFeFeFe Fe

Fe Fe FeFeFeFe

Fe Fe FeFeFeFe

HH

HH H

H

HH

H

HH

H

H

H

H HH

H HH

It is well known that a large number of hydrogen and helium atoms are formed in the structural materials of the spallation neutron sources. The formed gas causes damage to materials.

The hydrogen trapped by defects such as vacancies, small vacancy clusters, dislocations, grain boundaries, precipitates, voids/bubbles, etc., can be released from each trap site by heating the material.

The temperature range of desorption varies according to the kind of trap site, because the binding energy between hydrogen and each trap site is different.

v Vacancy4050kJ/molv Vacancycluster70kJ/mol

v DislocationDislocationcore60kJ/molElasticstress4050kJ/mol

v G.B.5060kJ/molv CarbidesFe3C,TiC

80100kJ/mol

Hydrogen

evolutio

nrate

Temperature

Measured hydrogen evolution curve

TrappingsiteA TrappingsiteB TrappingsiteC TrappingsiteD

Hydrogen in Steels

H

H

H

Fe Fe

FeFe

FeFe

FeV

H

H

H

Fe

Fe Fe FeFeFeFe Fe

Fe

Fe FeFe FeFe FeFe

Fe FeFeFeFe

Fe Fe FeFeFeFe Fe

Fe Fe FeFeFeFe

Fe Fe FeFeFeFe

HH

HH H

H

HH

H

HH

H

H

H

H HH

H HH

It is well known that a large number of hydrogen and helium atoms are formed in the structural materials of the spallation neutron sources. The formed gas causes damage to materials.

The hydrogen trapped by defects such as vacancies, small vacancy clusters, dislocations, grain boundaries, precipitates, voids/bubbles, etc., can be released from each trap site by heating the material.

The temperature range of desorption varies according to the kind of trap site, because the binding energy between hydrogen and each trap site is different.

v Vacancy4050kJ/molv Vacancycluster70kJ/mol

v DislocationDislocationcore60kJ/molElasticstress4050kJ/mol

v G.B.5060kJ/molv CarbidesFe3C,TiC

80100kJ/mol

Hydrogen

evolutio

nrate

Temperature

Measured hydrogen evolution curve

TrappingsiteA TrappingsiteB TrappingsiteC TrappingsiteD

Hydrogen in Steels

H

In the present study, the most stable structure of hydrogen in avoid and vacancy cluster of the pure iron has been investigatedby first principle calculations. In addition, the simulationtechnique for studying the effect of irradiation-induced defectson hydrogen desorption curves has been developed.

The most stable structure of hydrogen in a void and vacancy cluster

First principle calculations condition

ProgramcordViennaAbInitioSimulationPackage(VASP)

CrystalstructureBCCunitcell238Vacuumlayer11.348Aboutfourtimesoflattice

constantofBCCCrystalsurface100 crystalplanes

MagnetismFeFerromagnetics

SamplingofkpointMonkhorst-Pack642

Cutofenergy348eV

RelaxationcalculationAtomicpositionShapeofunitcellVolume

ConvergenceconditionForceappliedto atomislessthan0.005eV/

The hydrogen was introduced into adsorption site such as 4F,2F of the ironcrystal surface (the void surface).

First principle calculations condition

4F+2F4FFeH

Numberof4F site/04 +

/36 + 12 = 6

Numberof2F site/310 + 17 = 12

4F(2)-a

4F(2)-b 4F(2)-cFeH

First principle calculations condition

4F(2)-aAdsorption site

Number of H atomsStructure

In this model, the structure may be different even if the adsorption hydrogen is the samenumber. So, when calculation result was written, kind of the structure was written.

Determination method of stable structure of hydrogen

4F(5)

4F(6)

>or