Automatic containerless measurements of thermophysical properties of quasicrystal forming melts
High temperature studies of reactive melts can be difficult due to contamination issues associated with process container and measuring apparatus transferring material to the melts. Even minor amounts of contaminants can drastically affect thermophysical properties such as surface tension. To overcome this problem, containerless processing techniques that levitate small samples, preventing contact, can be used. In using levitation techniques, available heterogeneous nucleation sites are reduced allowing molten samples to undercool below their equilibrium melting temperatures. This capability is extremely attractive to quasicrystal research as the quasicrystal structure is similar to icosahedral ordering that forms in undercooled liquids. As the degree of icosahedral ordering changes with undercooling, changes in thermophysical properties should be observed. By measuring thermophysical properties in the undercooled state valuable insight can be gained into what parameters affect icosahedral ordering, ultimately leading to better understanding of quasicrystal formation, and possible process control for manufacturing.
The goal of this research is to measure surface tension, viscosity and density of several titanium, zirconium and nickel (TiZrNi) based quasicrystal forming and related alloys. These measurements are performed using containerless processing combined with optical non-contact measuring methods. In addition to these measurements, the Transient Calorimetric Technique used to measure specific heat in electrostatic levitation based containerless processing is assessed. This research is done as part the NASA-funded microgravity flight project Quasicrystalline Undercooled Alloys for Space Investigation (QUASI). These 1-g measurements will be part of a thermophysical property database which will be used to help plan and compare against, microgravity experiments.*
*This dissertation is a compound document (contains both a paper copy and a CD as part of the dissertation).
0794: Materials science