In a successful joint collaboration between Chalmers and Linde, Camille Pauzon has conducted experimental work using high-sensitive gas analysis techniques for additive manufacturing. She recently defended her PhD thesis – a work that resulted in ten scientific papers and four patent applications. Camille explains here how the work was done.
What is the elevator pitch of your research?
"I focus my research on the laser powder bed fusion (LPBF) process which is an additive manufacturing-3D printing process. technique, that is using laser energy to melt micron-size metallic powders, allows us to produce complex components, which are not manufacturable by any other means."
Why study the laser powder bed fusion process?
"LPBF process uses an inert gas, typically Argon, to remove process by-products and limit the oxidation of the hot material that can have a detrimental effect on final impurity and defect concentration in the component. The process has been used rather extensively in the last decades, and the relationship between process-microstructure-properties was widely investigated but mostly focusing on the laser-related parameters."
"Therefore, in my thesis “Tailored process gases for laser powder bed fusion”, we focused on the effect of the inert gas and the purity of the process atmosphere on the interaction of the laser with the material and resulting properties of the component. Focus was placed on the most used alloys which are 316L stainless steel, Alloy 718 and Ti-6Al-4V. We pursued the investigations by studying the effect of the residual oxygen levels from conventionally applied 0,1% down to 0.001%. Effect of alternative protective gases including nitrogen and helium were studied as well."
"We showed that reducing the residual oxygen during the process limits the powder degradation inpurity levels in the components, and hence improving process robustness and material reusability. New process gases containing helium allowed to reduce spatter generation (which are oxidized by-products interacting with the laser) and are promising for the process stability and productivity."
Beside your PhD thesis you have published ten papers and four patent applications. What is the key behind the impressive results?
"The patent applications are a result of the fruitful academic-industrial collaboration between Linde, supporting the PhD thesis work, and Chalmers. I am very lucky to have had the chance to stay for 18 months at the Linde Global Development Centre for Additive Manufacturing, where both the process is developed, and gas are produced. I also had the opportunity to be close to the gas and metallurgist experts, using a wide range of gas analytics, and having access to a variety of gases. The context in which we conducted our studies really allowed us freedom in the design of our experiments. I think this, combined with people working together from different background, really permitted to develop the new ideas. The patent applications mostly address new gas related solutions for the laser powder bed fusion process, namely, the use of specific gas purities or gas composition for intended material properties or process productivity."
What would you say is most significant in your thesis seen from a production perspective?
"I would say the most significant output of my thesis is the clear indication of the importance of the process atmospheres during AM processing, that was largely disregarded until recently. I also hope that our research findings can be of help for many process users’ profiles – from the persons who are curious to know more about what the standard atmosphere process conditions entails for their material, to the users interested to really consider the gas as a process parameter. On a more specific note, our results highlight that control of the process atmosphere purity allows to limit powder degradation and control component properties when exposed to the AM environment, particularly for metals such as Ti-6Al-4V or Ni-based alloys."
"I believe that further development in this area will allow to significantly improve material utilization in AM and hence further improve robustness and sustainability of metal AM technologies."
"Finally, the use of Helium and Argon-Helium mixtures appeared to be really interesting to reduce the generation of spatters during the process. This is greatly promising to limit powder degradation and enhance recyclability, one of the main concerns of the AM community. On a general note, I hope the thesis will raise awareness to the fact that the laser powder bed fusion atmosphere matters as a process variable and can allow to develop a more robust process."
What happens now, after your dissertation?
"I will be continuing my research work at Chalmers for a few more months. I will pursue on topics related to the process atmosphere but also widen my horizons to other subjects more broadly connected to the process-microstructure-properties relationship. Meanwhile, I plan to strengthen my competences in terms of process monitoring and material characterization."
What are your best tips to students who wants to become a PhD student?
"If you are curious and want to better understand a topic and contribute to its advancement, you should go for it. It is a very enriching experience, in which you meet a lot of people sharing the same curiosity and with different points of view. You will learn about science and technology, people and yourself. Before taking the big leap, don’t hesitate to meet and discuss with PhD students and PhDs of their situations and experiences."