• Understanding of dendrite evolution has been dramatically increased by microgravity experiments, principally in undercooled pure materials.
• Understand the dynamics that lead to uniform and reproducible three-dimensional pattern formation in materials, particularly alloys
• Obtain benchmark data required for establishing the detailed dynamics of interface pattern selection during the solidification of alloys.
• A fundamental understanding of interface dynamics is central to tailor microstructures to optimize materials properties.

Dynamic Selection of Three-Dimensional Interface Patterns in Directional Solidification Quad Chart

• Defects in directionally solidified dendritic alloys result in production losses.
  Misalignment of dendrite arms and macrosegregation are produced by
  uncontrolled convection.
• NASA’s interest is in enhancing the mathematical modeling of solidification with
  global objectives.
• A specific objective is the simulation of solidification in castings of changing
  cross section.
  

Microstructure Formation in Castings of Technical Alloys under Diffusive and Magnetically-Controlled Convective Conditions (MICAST) Quad Chart

• In crystal growth there is a need to understand the relation between processes in the fluid phase, both liquid and vapor, such as buoyancy driven convection, the incorporation of impurities, and defects in the resulting crystal.
• Relation between fluid phase processes and the generation of defects in a grown crystal is an outstanding problem in materials growth.
• Studies in microgravity will be compared with modeling and will be used to optimize ground-based experiments.

Crystal Growth of Ternary Compound Semiconductors (GTS) Quad Chart

• Determine the influence of liquid and solid short-range order on the nucleation barrier
• Determination the composition dependence of nucleation rate and evaluate a new coupled flux model for nucleation
• Correlate the nucleation kinetics with the local structure of the liquids
• Correlate the local structure with containerless measurements of thermophysical properties
• Determine changes in the growth rate of the solid as a function of the complexity of the solid phase

Quasi-Crystalline Undercooled Alloys for Space Investigation (QUASI) Quad Chart

• Partially detached crystals can be grown on Earth
• Test the theory that solidification free of wall contact reduces defect density
• Evaluate competing theories for the production of critical materials by testing different growth configurations and using the space environment
  
  
  

Reduction of Defects in Germanium Silicon (RDGS) Quad Chart

• Complex stainless steels can form a metastable dendritic ferrite phase, prior to the formation of the stable austenite phase
• Determine governing factors behind kinetics of transformation in these commercially relevant structural materials
• Determine the effects of fluid flow in nucleation of the second phase, within the meta-stable phase in the mushy zone
• Correlate the local structure with containerless measurements of thermophysical properties

The Role of Convection and Growth Competition in Phase Selection in Microgravity Quad Chart