Collaborative Research: ISS: Segregation of Inhomogeneous Alloy Melt Driven by Capillary Flow in Microgravity

Collaborative research: ISS: Segregation of inhomogeneous alloy melt driven by capillary flow in microgravity Project summary We propose to investigate the concurrent melting and capillary flow of a molten alloy in microgravity. The proposed study is fundamental. It aims to explain and quantify hitherto unexplained experimental observations and thus provide understanding of the dynamics of concurrent diffusion-controlled (partial) melting and capillary/gravitational flow of the melt. But it also has a significant broader impact. In previous study, we have observed a segregation of the near eutectic molten binary alloy, such that it solidifies into two very different microstructures. The extent of segregation varies, apparently depending on the temperature regime as well as on the geometry of the capillary flow. We propose: (i) a series of experiments at ISS, with simultaneous ground-based experiments. Since the melting/flow solidification process cannot be observed directly, we propose (ii) a detailed mesoscale modelling program of the process (phase field computations). The objectives of the project are: (i) to understand the detailed physical mechanisms of segregation during capillary flow under both microgravity and terrestrial conditions (effects of gravity, peak temperature, and interaction of diffusion-controlled melting and flow of the melt), and, (ii) Develop the process design methodology which will ensure reliable joining metals in space resulting in homogeneous solid bonds. Intellectual Merit. We propose integrated rational and empirical investigation of the concurrent diffusion-controlled melting and capillary/gravitational flow of a molten metal under micro- gravity at ISS and terrestrial conditions. To the best knowledge of the authors, the phenomena under investigation have not been considered in the past. These will include empirical studies of capillary flow of the multiphase molten alloy over wetting and non-wetting substrates and corresponding phase field computational modeling. A new theory and a predictive model, based on phase field formulation of the capillary flow under conditions of voids formation will be verified. The microstructure differences of the re-solidified melts obtained in microgravity and under terrestrial conditions will be identified. Broader impact. The resulting understanding of wetting of liquid metal alloy composite and the predictive models will enable advances in brazing and soldering joining technologies, relevant for both terrestrial and microgravity environments. In addition to brazing at moderate temperatures, the results will be relevant for capillary phenomena involving low temperature soldering as well as processes related to bonding of ceramics and metals at high temperatures. In addition to the terrestrial technology development, understanding of molten flow driven by surface tension with/without gravity will enable brazing in space as a tool for repair following collisions with micro meteoroids and space debris, as well as for permanent bonding required for construction in space. Further, the findings of this project will lead to better understanding of capillary phenomena involved with multilayer metal deposition in advanced technologies such as the additive manufacturing via selective laser melting. Educational impacts include addition of new modules to the existing graduate courses at WSU and UK, research experience for undergraduates, and outreach to high school students.