Institute of Materials and Machine Mechanics
Topic
Investigation of Weld Pool Dynamics and Metallurgical Mechanisms of Capacitor Discharge Stud Welding on Aerospace Aluminium Alloys Under Vacuum Conditions
PhD. program
Engineering Technologies and Materials
Year of admission
2026
Name of the supervisor
Ing. Marek Gebura, PhD.
Contact:
Receiving school
Faculty of Special Technology, Alexander Dubček University of Trenčín
Annotation
This PhD thesis focuses on developing a comprehensive physical and metallurgical understanding of Capacitor Discharge Stud (CCDS) welding performed under vacuum conditions (10-3 Pa) on key aerospace aluminium alloys used in space systems—specifically 2195, 2219, 6062, 7050, and 7075. These materials in the form of thin sheets will be used in their heat treatment conditions typical for their space application. Their surface will be covered by a space-grade paint, anodized layer, multi-layer insulation (MLI) blanket, but also the raw surface conditions will be examined. The research will investigate both similar-material joining, using alloy-matched aluminium studs, as well as dissimilar-material configurations employing A2-50 steel studs, which have already demonstrated capability to penetrate coatings and MLI while forming joints and are therefore highly relevant for in-orbit applications (existing Institute’s ESA contract). The thesis will retain the flexibility to explore and evaluate additional stud materials or coatings, where scientifically justified, to achieve superior joint integrity, metallurgical compatibility, and operational reliability in space.
A central focus is the altered plasma and arc physics that arise in vacuum, where the absence of atmospheric gas modifies the diffusive arc regime, suppresses the dynamic jet term, and fundamentally changes the arc pressure profile acting at the stud–workpiece interface. While the electromagnetic pinch force remains present, the lack of gas density leads to different plasma expansion characteristics, which in turn influence weld pool stability, depression, turbulence, and molten metal expulsion compared to atmospheric CCDS welding.
From the metallurgical side, the absence of air yields a more controlled and predictable chemical environment, yet intermetallic compound (IMC) formation in both similar and dissimilar material pairs remains a critical factor. The thesis will study IMC formation kinetics and morphology across aluminium systems with different alloying elements—Li-containing alloys (2195), Cu-rich alloys (2219), Mg–Si alloys (6062), and Zn-rich high-strength alloys (7050, 7075). Special attention will be given to the Al–Fe system arising from steel studs, where IMC formation in vacuum may be altered but not eliminated. The work will also analyse how vacuum conditions influence porosity, segregation, grain refinement, and the thermal history of the rapidly solidifying weld.
In addition, the presence of surface coatings and MLI introduces another layer of complexity to the physical and metallurgical understanding of the CCDS process in vacuum. On the physical side, coatings influence the local electric field distribution as the arc is forced to initiate and burn through the penetrated region, altering arc attachment behaviour and plasma stability. On the metallurgical side, fragments and decomposition products from the coatings or MLI can enter the plasma, become ionized, and subsequently interact with the molten pool. These foreign species may modify the melt chemistry, influence IMC formation pathways, affect solidification behaviour, and ultimately contribute to changes in weld composition and microstructure.
By integrating plasma-physical modelling, melt pool dynamics, and advanced microstructural and mechanical characterisation, the thesis aims to establish the first mechanistic explanation of CCDS welding behaviour under vacuum for these alloy systems. The resulting models and experimental findings will form the scientific foundation required to deploy CCDS welding reliably in in-orbit manufacturing, lunar construction, and orbital debris capture, where joining operations must function in low-pressure environments fundamentally different from terrestrial conditions.
The experimental work will be conducted at the Institute, which is equipped with a modernized vacuum chamber and a CCDS welding end-effector prototype capable of producing dozens of samples per week. The PhD candidate will have direct access to state-of-the-art characterisation techniques, including SEM with EDS, EBSD, TEM, and XRD, available either on-site or within the Slovak Academy of Sciences. Process and physical modelling will be performed using freely available scientific software such as Octave, FreeFEM, OpenFOAM, MOOSE or equivalent open-source tools, ensuring reproducibility and methodological transparency. The thesis will be embedded within the ongoing ROBSIM project funded through the Slovak Recovery and Resilience Plan, and the research activities will be aligned with planned applications for additional ESA contracts and APVV call.
A central focus is the altered plasma and arc physics that arise in vacuum, where the absence of atmospheric gas modifies the diffusive arc regime, suppresses the dynamic jet term, and fundamentally changes the arc pressure profile acting at the stud–workpiece interface. While the electromagnetic pinch force remains present, the lack of gas density leads to different plasma expansion characteristics, which in turn influence weld pool stability, depression, turbulence, and molten metal expulsion compared to atmospheric CCDS welding.
From the metallurgical side, the absence of air yields a more controlled and predictable chemical environment, yet intermetallic compound (IMC) formation in both similar and dissimilar material pairs remains a critical factor. The thesis will study IMC formation kinetics and morphology across aluminium systems with different alloying elements—Li-containing alloys (2195), Cu-rich alloys (2219), Mg–Si alloys (6062), and Zn-rich high-strength alloys (7050, 7075). Special attention will be given to the Al–Fe system arising from steel studs, where IMC formation in vacuum may be altered but not eliminated. The work will also analyse how vacuum conditions influence porosity, segregation, grain refinement, and the thermal history of the rapidly solidifying weld.
In addition, the presence of surface coatings and MLI introduces another layer of complexity to the physical and metallurgical understanding of the CCDS process in vacuum. On the physical side, coatings influence the local electric field distribution as the arc is forced to initiate and burn through the penetrated region, altering arc attachment behaviour and plasma stability. On the metallurgical side, fragments and decomposition products from the coatings or MLI can enter the plasma, become ionized, and subsequently interact with the molten pool. These foreign species may modify the melt chemistry, influence IMC formation pathways, affect solidification behaviour, and ultimately contribute to changes in weld composition and microstructure.
By integrating plasma-physical modelling, melt pool dynamics, and advanced microstructural and mechanical characterisation, the thesis aims to establish the first mechanistic explanation of CCDS welding behaviour under vacuum for these alloy systems. The resulting models and experimental findings will form the scientific foundation required to deploy CCDS welding reliably in in-orbit manufacturing, lunar construction, and orbital debris capture, where joining operations must function in low-pressure environments fundamentally different from terrestrial conditions.
The experimental work will be conducted at the Institute, which is equipped with a modernized vacuum chamber and a CCDS welding end-effector prototype capable of producing dozens of samples per week. The PhD candidate will have direct access to state-of-the-art characterisation techniques, including SEM with EDS, EBSD, TEM, and XRD, available either on-site or within the Slovak Academy of Sciences. Process and physical modelling will be performed using freely available scientific software such as Octave, FreeFEM, OpenFOAM, MOOSE or equivalent open-source tools, ensuring reproducibility and methodological transparency. The thesis will be embedded within the ongoing ROBSIM project funded through the Slovak Recovery and Resilience Plan, and the research activities will be aligned with planned applications for additional ESA contracts and APVV call.