Hydrogen transport during the welding of titanium alloy Ti-6Al-4V is analysed. A coupled thermody... more Hydrogen transport during the welding of titanium alloy Ti-6Al-4V is analysed. A coupled thermodynamic/kinetic treatment is proposed in which the driving force for hydrogen migration is its chemical potential gradient, which is in turn calculated using the Thermo-Calc software package. The model is applied to the case of the electron beam welding of Ti-6Al-4V, for which a simple process model is presented for the temperature evolution expected. There is a thermodynamic driving force for accumulation of hydrogen in the weld pool. However, agreement with the limited amount of experimental data in the literature for the hydrogen field caused by welding indicates that account needs to be taken of the hydrogen degassing from the weld pool.
The mechanism of porosity formation during the fusion welding of titanium and its alloys is studi... more 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.
The transport of hydrogen during fusion welding of the titanium alloy Ti-6Al4V is analyzed. A cou... more The transport of hydrogen during fusion welding of the titanium alloy Ti-6Al4V is analyzed. A coupled thermodynamic/kinetic treatment is proposed for the mass transport within and around the weld pool. The modeling indicates that hydrogen accumulates in the weld pool as a consequence of the thermodynamic driving forces that arise; a region of hydrogen depletion exists in cooler, surrounding regions in the heat-affected zone and beyond. Coupling with a hydrogen diffusion-controlled bubble growth model is used to simulate bubble growth in the melt and, thus, to make predictions of the hydrogen concentration barrier needed for pore formation. The effects of surface tension of liquid metal and the radius of preexisting microbubble size on the barrier are discussed. The work provides insights into the mechanism of porosity formation in titanium alloys.
This thesis is concerned with the porosity formation mechanism during electron beam welding of ti... more This thesis is concerned with the porosity formation mechanism during electron beam welding of titanium-based alloys. During the welding of titanium alloys for aerospace engine applications, porosity is occasionally found in the solidified welds. Hence the key factors ...
... Multi-Relaxation-Time Lattice Boltzmann Method Jianglin Huang∗, Liliang Chen, and Jianxin Zho... more ... Multi-Relaxation-Time Lattice Boltzmann Method Jianglin Huang∗, Liliang Chen, and Jianxin Zhou State Key Laboratory of Material Processing and Die and Mould Technology, Huazhong University of Science and Technology, Wuhan 430074, China ...
Hydrogen transport during the welding of titanium alloy Ti-6Al-4V is analysed. A coupled thermody... more Hydrogen transport during the welding of titanium alloy Ti-6Al-4V is analysed. A coupled thermodynamic/kinetic treatment is proposed in which the driving force for hydrogen migration is its chemical potential gradient, which is in turn calculated using the Thermo-Calc software package. The model is applied to the case of the electron beam welding of Ti-6Al-4V, for which a simple process model is presented for the temperature evolution expected. There is a thermodynamic driving force for accumulation of hydrogen in the weld pool. However, agreement with the limited amount of experimental data in the literature for the hydrogen field caused by welding indicates that account needs to be taken of the hydrogen degassing from the weld pool.
The mechanism of porosity formation during the fusion welding of titanium and its alloys is studi... more 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.
The transport of hydrogen during fusion welding of the titanium alloy Ti-6Al4V is analyzed. A cou... more The transport of hydrogen during fusion welding of the titanium alloy Ti-6Al4V is analyzed. A coupled thermodynamic/kinetic treatment is proposed for the mass transport within and around the weld pool. The modeling indicates that hydrogen accumulates in the weld pool as a consequence of the thermodynamic driving forces that arise; a region of hydrogen depletion exists in cooler, surrounding regions in the heat-affected zone and beyond. Coupling with a hydrogen diffusion-controlled bubble growth model is used to simulate bubble growth in the melt and, thus, to make predictions of the hydrogen concentration barrier needed for pore formation. The effects of surface tension of liquid metal and the radius of preexisting microbubble size on the barrier are discussed. The work provides insights into the mechanism of porosity formation in titanium alloys.
This thesis is concerned with the porosity formation mechanism during electron beam welding of ti... more This thesis is concerned with the porosity formation mechanism during electron beam welding of titanium-based alloys. During the welding of titanium alloys for aerospace engine applications, porosity is occasionally found in the solidified welds. Hence the key factors ...
... Multi-Relaxation-Time Lattice Boltzmann Method Jianglin Huang∗, Liliang Chen, and Jianxin Zho... more ... Multi-Relaxation-Time Lattice Boltzmann Method Jianglin Huang∗, Liliang Chen, and Jianxin Zhou State Key Laboratory of Material Processing and Die and Mould Technology, Huazhong University of Science and Technology, Wuhan 430074, China ...
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