Wetting and spreading, or capillary phenomena, for liquid metals typically involve reactions between the liquid and the solid on which the liquid wets. Such reactions are often exploited to develop strong mechanical bonds between two metals or a metal and a ceramic during technological processes including soldering and brazing. Typically observed reactions are substrate dissolution into the liquid or nucleation of a third phase at the solid/liquid interface. In the latter case, good wetting may be achieved on the newly grown phase, even if the liquid poorly wets the unreacted solid. Examples systems will be reviewed demonstrating that, while the bulk phase diagram may provide some information as to what reactivity can emerge for a given system, this is not always so.
The success of high temperature joining processes like brazing, soldering, and welding depends upon reactive capillary flow. Understanding fundamental phenomena in high temperature reactive wetting bears potential for impact on technology and theory; nonetheless, mechanisms driving the advancement of the contact line between liquid/solid/vapor remain elusive to experiment due to high temperature processing conditions and a difficulty to probe a sufficiently small length and time scale. Molecular dynamics (MD) simulations are a useful counterpart to experiment in describing fundamental wetting mechanisms. This talk will review MD simulations of high temperature wetting for metals in a braze geometry. Infiltration of molten eu into a solid Ni pore is simulated and, in agreement with expectations from the bulk binary phase diagram, the solid Ni dissolves into the liquid Cu during infiltration. Simulations reveal a i'egime where the dissolution reaction is aggressive enough to alter the kinetics of infiltration from what is expected via the well known Washburn equation for describing infiltration kinetics. MD simulations are coupled with Monte Carlo calculations to draw quantitative connections between the free energy of the dissolution reaction and the kinetics of pore infiltration. The talk will conclude with suggestions on how atomistic scale computations can be used to develop improved continuum constitutive relations for describing reactive capillary flow.
Edmund Webb III received his doctorate in Ceramic and Materials Science and Engineering from Rutgers, The State University of New Jersey where he used atomic scale models to study the surfaces of oxide glasses. He then assumed a post-doctoral research position at Exxon Research and Engineering, studying hydrocarbon upgrade processes for automotive lubricant production. Following this, Prof. Webb joined the ranks of Sandia National Laboratories, where he worked for 12 years before coming to Lehigh University in 20 10. As a national laboratOlY research scientist, Prof. Webb applied numerical simulations on high performance computing resources to a range of materials and mechanics problems, including capillary driven fluid flow, friction mitigation, stress evolution in thin films, nanoscale thermal transport, and liquid droplet impacts.
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