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Pore Formation

 

 Gas pores formed between equiaxed dendrites in Al-Ge alloy.
zum BildGas pores formed between equiaxed dendrites in Al-Ge alloy.

Pores are major defects in castings that degrade their mechanical and thermal properties and might lead to cast rejection and rework. Micro-porosity, i.e. gas and shrinkage porosity is particularly difficult to study due to its small size especially in the nucleation stage. Most of the knowledge about pore morphology has been gained from a post-mortem analysis of the fully solidified materials, which often makes the distinction between the different effects difficult to achieve. In this junior research group, we plan to use in-situ X-ray radiography and tomography to understand the entire path of pore formation from its nucleation, through agglomeration and coalescence until the end of solidification. We aim to understand the conditions under which pores form and grow, which can help in casting design process and relocation of porosity-prone areas to less sensitive parts.

Gas pore formation, growth, and removal depends on a number of parameters, whose relative contribution to the process is difficult to assess. Microgravity experiments allow elimination of gravity-dependent variables and phenomena, providing strictly diffusion-controlled conditions. Thus, the relative importance of the gravity-independent parameters can be assessed and unique benchmark data for model validation provided. Furthermore, comparison between on-ground and microgravity experiments allows assessments of which parameters emerge as dominant ones.

Our research focuses on:

 Distance traveled by pores of various size during the microgravity time typical for parabolic flights and sounding rockets.
zum Bild Distance traveled by pores of various size during the microgravity time typical for parabolic flights and sounding rockets.

 

  • investigation of the degassing efficiency during remelting
  • studies of gas and shrinkage pore formation and architecture in Al alloys
  • mapping Niyama criterion for shrinkage pore formation in Al-Cu alloys

 

 

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