SECAT Newsletter, Vol. 5, Issue 1

National Aeronautics and Space Administration (NASA) has selected to fund a four-year research project entitled “Brazing of Aluminum Alloys in Space”. The project is in response to the NASA Research Announcement “Research Opportunities in Materials Science – MaterialsLab, Open Science Campaigns for Experiments on the International Space Station”.

The Principal Investigator of the project is Dusan P. Sekulic, Secat J.G. Morris Aluminum Professor at the College of Engineering, Department on Mechanical Engineering and the Institute of Sustainable Manufacturing at the University of Kentucky, Lexington, KY. The project is aimed at scientific research, both theoretical and experimental, of the brazing process to be executed in a microgravity environment. A significant emphasis of the research objectives is aluminum brazing technology development.

The proposal includes a collaborative participation of the School of Mechanical and Material Engineering, Washington State University, Pullman, WA, as a subcontractor. The overall project, directed by Dr. Sekulic as a Principal Investigator, is structured as an international research endeavor involving, in addition to NASA, the European Space Agency (ESA/BELPOS) and Russian Space Agency (ROSCOSMOS). The NASA funding is US $600,000 for the period between November 2016 and November 2020. The ESA will fund European collaborative partner, KU Leuven, Department of Materials Science, with up to Euro 490,000 and ROSCOSMOS will fund the Russian collaborating institution, Udmurt State University with up to Rubles 3,000,000. The total funding is expected to be around 1.2 Million US Dollars, half of it already appropriated by NASA for the US based research.

The motivation for the proposed research work is rooted within a pragmatic technological advancement needed to resolve critical issues involving current and future endeavors in space exploration, as mandated by NASA’s mission and associated activities. Among these, a resolution and/or mitigation of two outstanding problems are of both short-term and long-term importance. The outer hulls of space vehicles and structures may suffer damage caused by micro-meteorites or orbital debris impact. Thousands of submicron craters form over time but may not cause catastrophic consequences, but occasionally an impact leads to a serious penetration, as indicated by one of the project’s motivation arguments. A brazing method suited for implementation in outer space and/or at the International space station (ISS), intended to mitigate that impact, requires a variety of aluminum research studies. Moreover, the need for facilitating construction in space will be necessary in future space missions. Structural elements, transported to Earth’s orbit and beyond to the Moon and/or Mars must subsequently be joined under extraterrestrial conditions. Joining aluminum by brazing would be one of the most seriously considered options.

This research program involves controlled atmosphere and vacuum brazing of aluminum to be performed in the Brazing Laboratory of Dr. Sekulic at the University of Kentucky. The phase change cycle of aluminum alloys studied in real time and in situ will include studies of the kinetics of surface tension drivel liquid metal flows, capillary phenomena, melting and solidification of the clad/filler of aluminum alloys in the presence or absence of flux. The terrestrial tests will be complemented with tests on the ISS under microgravity conditions. The experimental work performed under terrestrial and space conditions will be coordinated by the University of Kentucky team. This work will be complemented by the work at UK Leuven, Belgium, by Dr. Jan Fransaer, and Dr. Mikhail Krivilev at the Udmurt State University, Russia. The computational and theoretical modeling program will be conducted by the Co-PI, Sinisa Dj. Mesarovic at the Washington State University Dr. David Seveno, KU Leuven, and Dr. M. Krivilev in Russia. The capillary flow of liquid aluminum alloys is a complex phenomenon and follows equally complex solid state and fluid phase transformations, leading ultimately to solidification and along the way an evolution of microstructure of the joining domain. For example, in the capillary flow phase, the moving boundary and topological discontinuities (breakup and coalescence of domains) have been very difficult computational problems. These problems will be resolved by using phase field modeling.

In addition to an extensive study of the brazing process, and in particular spreading and wetting capillary phenomena, the studies of aluminum alloy filler metal design will be considered. An Al-Si-(KFAl) alloy electrodeposition will be utilized, assisted by Si nanoparticles. Subsequently 3000- and 2000-series Al substrate will be coated with so-developed clad.

All experimental and theoretical/numerical works, under both terrestrial and microgravity conditions, will significantly broaden understanding of joining phenomena involving metals (aluminum in particular) and will advance the technology of aluminum brazing.