Prof Christoph Beckermann - University of Iowa, USA
Dr. Beckermann received his M.S. and Ph.D. degrees in Mechanical Engineering from Purdue University in 1984 and 1987, respectively. He has since been a faculty member at the University of Iowa (UI), where he currently holds a UI Foundation Distinguished Professorship. His research interests are in the area of solidification and metal casting. Dr. Beckermann has co-authored 135 journal articles that have been cited more than 4,800 times in the literature (h-index: 37). His awards include a 1989 National Science Foundation Presidential Young Investigator Award, the 2009 Sir Humphrey Davy Scientific Merit Award from the American Foundry Society, the 2009 Thomas E. Barlow Award of Honor from the Steel Founders Society of America, and the 2010 Bruce Chalmers Award from The Minerals, Metals and Materials Society (TMS). He is a Fellow of the American Society of Mechanical Engineers (ASME) and a Life Member of TMS.
Additional information at: http://www.engineering.uiowa.edu/~becker/cb.html
Coarsening-driven dendrite fragmentation in directional solidification
H. Neumann-Heyme1 and C. Beckermann2
1 Technical University Dresden, Institute for Fluid Dynamics, D-01062 Dresden, Germany
2 University of Iowa, Dept. Mechanical and Industrial Engineering, Iowa City, IA 52242, USA
Dendrite fragmentation is an important mechanism for generating new grains during solidification of alloys. Sidebranch detachment has been associated with growth transients, which can be caused by convection or variations in the isotherm velocity. These transients affect the sidebranch evolution during both growth and coarsening. Three-dimensional phase-field simulations are performed of the directional solidification of a binary alloy, including the sidearm coarsening stage far behind the primary dendrite tips. The numerical results allow for a detailed examination of the evolution of the dendrite sidebranches under both steady and transient growth conditions. Near the primary tip, the sidebranches grow rapidly inside the diffusive boundary layer. This is followed by relatively slow curvature-driven coarsening and further solidification near equilibrium. Coarsening results in either retraction of a sidearm towards the primary stem or in coalescence of neighbouring sidearms. These processes strongly affect the morphology of the remaining sidearms and the potential for sidearm pinch-off during growth transients. Sidearm pinch-off is controlled by two competing effects. The narrow neck region near the junction with the primary stem is destabilized by its circumferential (positive) curvature, whereas continued solidification due to decreasing temperature has a stabilizing effect. Phase-field simulations of a simplified single dendrite arm system are conducted to systematically study the dynamics of the pinching phenomenon over a broad set of solidification parameters.