On the mechanism of porosity formation during welding of titanium alloys

Jianglin L. Huang, Nils Warnken, Jean-Christophe Gebelin, Martin Strangwood, Roger C. Reed

Research output: Contribution to journalArticle

54 Citations (Scopus)

Abstract

The mechanism of porosity formation during the fusion welding of titanium and its alloys is studied. Porosity formed during the electron beam welding of titanium is characterized using high-resolution X-ray tomography, residual gas analysis and metallographic sectioning; the results confirm that porosity formation is associated with evolution of gas, especially hydrogen. A model for hydrogen diffusion-controlled bubble growth is proposed, to aid in the interpretation of these findings. To investigate further the effect of hydrogen on porosity formation, hydrogen charging is used to achieve different hydrogen levels prior to welding. The results confirm that porosity can be suppressed even at every high hydrogen levels, when welding is carried out with optimized welding parameters and perfect joint alignment; on the other hand, porosity is exacerbated when a small beam offset is employed. This is because any beam offset alters the size of the liquid zone at the melting front, where the joint edges first become melted. It is proposed that the thickness of the liquid film at the melting front is crucial for bubble nucleation and bubble survival in the weld pool; bubbles can escape through the keyhole by breaking through this liquid film, when it is too thin. This challenges the common assumption of bubble escape by flotation to the weld pool surface. Thus the nucleation rate in the liquid zone at the melting front determines the likelihood of porosity occurring. This suggests that the beam offset is likely to be one factor influencing porosity formation in these circumstances. The paper provides fundamental insights into the mechanism of porosity formation during the welding of titanium alloys and guidance to aid in its elimination.
LanguageEnglish
Pages3215-3225
Number of pages11
JournalActa Materialia
Volume60
Issue number6-7
DOIs
Publication statusPublished - 30 Apr 2012
Externally publishedYes

Fingerprint

Titanium alloys
Welding
Porosity
Hydrogen
Melting
Liquid films
Titanium
Welds
Nucleation
Electron beam welding
Gas fuel analysis
Liquids
Flotation
Tomography
Fusion reactions
Gases
X rays

Keywords

  • titanium alloys
  • welding
  • porosity Formation
  • modelling

Cite this

Huang, Jianglin L. ; Warnken, Nils ; Gebelin, Jean-Christophe ; Strangwood, Martin ; Reed, Roger C. / On the mechanism of porosity formation during welding of titanium alloys. In: Acta Materialia. 2012 ; Vol. 60, No. 6-7. pp. 3215-3225.
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Huang, JL, Warnken, N, Gebelin, J-C, Strangwood, M & Reed, RC 2012, 'On the mechanism of porosity formation during welding of titanium alloys' Acta Materialia, vol. 60, no. 6-7, pp. 3215-3225. https://doi.org/10.1016/j.actamat.2012.02.035

On the mechanism of porosity formation during welding of titanium alloys. / Huang, Jianglin L.; Warnken, Nils; Gebelin, Jean-Christophe ; Strangwood, Martin; Reed, Roger C.

In: Acta Materialia, Vol. 60, No. 6-7, 30.04.2012, p. 3215-3225.

Research output: Contribution to journalArticle

TY - JOUR

T1 - On the mechanism of porosity formation during welding of titanium alloys

AU - Huang, Jianglin L.

AU - Warnken, Nils

AU - Gebelin, Jean-Christophe

AU - Strangwood, Martin

AU - Reed, Roger C.

PY - 2012/4/30

Y1 - 2012/4/30

N2 - The mechanism of porosity formation during the fusion welding of titanium and its alloys is studied. Porosity formed during the electron beam welding of titanium is characterized using high-resolution X-ray tomography, residual gas analysis and metallographic sectioning; the results confirm that porosity formation is associated with evolution of gas, especially hydrogen. A model for hydrogen diffusion-controlled bubble growth is proposed, to aid in the interpretation of these findings. To investigate further the effect of hydrogen on porosity formation, hydrogen charging is used to achieve different hydrogen levels prior to welding. The results confirm that porosity can be suppressed even at every high hydrogen levels, when welding is carried out with optimized welding parameters and perfect joint alignment; on the other hand, porosity is exacerbated when a small beam offset is employed. This is because any beam offset alters the size of the liquid zone at the melting front, where the joint edges first become melted. It is proposed that the thickness of the liquid film at the melting front is crucial for bubble nucleation and bubble survival in the weld pool; bubbles can escape through the keyhole by breaking through this liquid film, when it is too thin. This challenges the common assumption of bubble escape by flotation to the weld pool surface. Thus the nucleation rate in the liquid zone at the melting front determines the likelihood of porosity occurring. This suggests that the beam offset is likely to be one factor influencing porosity formation in these circumstances. The paper provides fundamental insights into the mechanism of porosity formation during the welding of titanium alloys and guidance to aid in its elimination.

AB - The mechanism of porosity formation during the fusion welding of titanium and its alloys is studied. Porosity formed during the electron beam welding of titanium is characterized using high-resolution X-ray tomography, residual gas analysis and metallographic sectioning; the results confirm that porosity formation is associated with evolution of gas, especially hydrogen. A model for hydrogen diffusion-controlled bubble growth is proposed, to aid in the interpretation of these findings. To investigate further the effect of hydrogen on porosity formation, hydrogen charging is used to achieve different hydrogen levels prior to welding. The results confirm that porosity can be suppressed even at every high hydrogen levels, when welding is carried out with optimized welding parameters and perfect joint alignment; on the other hand, porosity is exacerbated when a small beam offset is employed. This is because any beam offset alters the size of the liquid zone at the melting front, where the joint edges first become melted. It is proposed that the thickness of the liquid film at the melting front is crucial for bubble nucleation and bubble survival in the weld pool; bubbles can escape through the keyhole by breaking through this liquid film, when it is too thin. This challenges the common assumption of bubble escape by flotation to the weld pool surface. Thus the nucleation rate in the liquid zone at the melting front determines the likelihood of porosity occurring. This suggests that the beam offset is likely to be one factor influencing porosity formation in these circumstances. The paper provides fundamental insights into the mechanism of porosity formation during the welding of titanium alloys and guidance to aid in its elimination.

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KW - welding

KW - porosity Formation

KW - modelling

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DO - 10.1016/j.actamat.2012.02.035

M3 - Article

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JO - Acta Materialia

T2 - Acta Materialia

JF - Acta Materialia

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