Photo of heated steel sample in the analysis chamber at the HERMES beamline, Soleil,
If you watched a wildlife documentary and then visited your local zoo, you may have been disappointed. Animals in captivity don’t behave the same as those in the wild. In the same way, when we study materials in the lab, they often don’t behave the same as they do in real life. This is important, I don’t care how the steel that reinforces my apartment behaves in the lab, I care how strong it is in my wall.
Lisa Rullik who recently defended her Ph.D. thesis at the Division of Synchrotron Radiation in Lund, has been addressing this exact issue, with support from the Swedish metal industry and SSF. She was interested in different metal alloys which are important in industry for the different properties they possess. Many previous studies of metal alloys had taken measurements under ultra-high vacuum which is not at all representative for most alloy applications in the real world. Furthermore, most studies on metal alloys had focussed on specially produced crystals which are easier to handle and measure but not representative of the structure of metal alloys in use.
While these studies have been valuable, they don’t give us a complete picture. They are the caged tigers of the material science world and Lisa wanted to change that. To do this she took a twofold approach, firstly she used X-ray techniques that could probe into the metals at ambient temperatures. Then, using her contacts in the metal industry, she took real samples of the metal to study instead of single crystal models.
Lisa started by using techniques such as X-ray reflectivityand X-ray photoelectron spectroscopy measure the thickness of aluminium alloys when compared to electrochemical impedance spectroscopy. She found that the X-ray techniques more accurately measured the thickness of the aluminium layer which is important for regulating industrial processes such as fabricating coatings and how they can be protected from corrosion. She then set out to investigate the widely used industrial technique, brazing. This is where two metals are joined together by flowing a molten filler metal in between as used for the production of heat exchangers for cars. Using X-ray photoelectron emission microscopy and X-ray photoelectron spectroscopy, Lisa found that the chemical state of different elements in the alloy were changing upon heating and cooling. She also found that if you study this process at ambient pressure or high pressure significantly affects the results which highlights the need to examine samples in realistic environments.
Lisa’s work has helped us to understand the brazing process and sets an example to industry for what can be done using X-rays at a synchrotron. Hopefully this will lead to better processes in the future leading to better and safer end products as well as more efficient ways to produce things with metal.
LINK TO THESIS AND PAPERS
In press, just submitted the proof, should be available online soon
Rullik L, Evertsson J, Johansson N et al.
Surface oxide development on aluminum alloy 6063 during heat treatment.
Surf Interface Anal. 2019;1-11.
This work was financially supported by the Swedish Foundation for Strategic Research (SSF project RMA11-0090, aluminum oxides for processing and products [ALUX]).
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