Crystal growth velocity in deeply undercooled melts of glass forming Zr-based alloys

• Applicants: Professor Dr. Dieter M. Herlach (†); Professorin Dr. Britta Nestler
• Subject Area: Thermodynamics and Kinetics as well as Properties of Phases and Microstructure of Materials ; Mechanical Properties of Metallic Materials and their Microstructural Origins
• Term: from 2013 to 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 238485687

• Final Report Year: 2019

Final Report Abstract

Though a maximum in the solidification velocity versus undercooling curve is theorized long ago and experimentally observed for many non-metallic systems, a direct observation in the case of metals remained elusive for a very long time. However, the sophisticated electrostatic levitation technique makes it possible to attain large supercoolings required to enter the diffusion controlled regime of atomic attachment during solidification in the case of glassforming intermetallics. Thus, the Ni-Zr system, an ideal candidate for such experiments, is employed to study the competition between the driving force for crystallization and the diffusion limited attachment kinetics resulting in the observed maximum in the velocity-undercooling curve. These experiments are performed by the project partners at German Aerospace Center (DLR), Cologne. Further, in case of cooperative solidification of alloys, the growth dynamics has always been studied in the low Peclet numbers regime and in unidirectional setting of Bridgman type cells. Remedying this, the composition and undercooling dependence of cooperative growth morphologies and kinetics is investigated through levitation experiments at DLR. Due to the high costs involved in performing and maintaining the associated controlled environments of the ESL experiments, it is desirable to develop cost effective means of gaining insights into the developing microstructures in the form of computer simulations. Thus, trust-worthy numerical models have to be developed, optimized and validated against the experimental observations. In this direction, comprehensive and robust phase-field models are developed and implemented on high performance computers utilizing advanced parallelization schemes by the project partners at Karlsruhe Institute of Technology (KIT), Karlsruhe. The experimental and numerical results are interpreted within the context of the existing theories of cooperative and dendritic growth. The differences and deviations observed are attributed to various approximations and simplifications implemented in the theories and appropriate improvements and generalizations are formulated. The findings also revealed many interesting future directions of research.

Publications

• Dendrite growth in Cu50 Zr50 glass-forming melts, thermodynamics versus kinetics, EPL 105 (2014) 36001
  H. Wang, D.M. Herlach, R.P. Liu
  
• Dendrite growth velocity in the undercooled melt of glass forming Ni50 Zr50 compound, Philosophical Magazine Letters 97 (2017) 249-256
  R. Kobold, W.W. Kuang, H. Wang, W. Hornfeck, M. Kolbe, D.M. Herlach
  
• Analyzing the cooperative growth of intermetallic phases with a curved solidification front, Acta Materialia 159 (2018) 135-149
  Sumanth Nani Enugala, Britta Nestler, Kumar Ankit
  
• Quasicrystal nucleation and Z module twin growth in an intermetallic glass-forming system, Nature Communications 9 (2018) 4054
  W. Hornfeck, R. Kobold, M. Kolbe, M. Conrad, D.M. Herlach
  
• Extension of Jackson-Hunt analysis for curved solid-liquid interfaces, Journal of Crystal Growth 512 (2019) 230-240
  Sumanth Nani Enugala, Britta Nestler
  
• Theoretical and numerical investigation of rod growth of an Ni-Zr eutectic alloy, Journal of Materials Science (2019) 54: 12605
  Sumanth Nani Enugala, Michael Kellner, Raphael Kobold, Johannes Hötzer, Matthias Kolbe, Britta Nestler, Dieter Herlach