Solidification is an important process in many industrial processes including but not limited the following:
Solidification of alloys involves nucleation and growth of one or more phases in multiple stages depending on the physical and thermodynamic parameters of the system chosen as well as the kinetic constraint imposed by the processing conditions. The final microstructure that determines the performance of the material is thus a complex function of material properties and processing conditions. A predictive capability to design the material and the product requires a deep insight into the physical processes that take place during solidification.
The driving force for nucleation and growth is determined by undercooling which dictates the growth rate of the solidifying phases, their structure and morphology. In most of the materials processes listed above, the temperature of the solidification front and thus, the undercooling is determined by the processing conditions and is not easy to determine experimentally. Undercooling experiments are an attractive and powerful tool to study solidification since the degree of undercooling can be quantified and be chosen as a control parameter too. An undercooled liquid is in a metastable state and provides access to metastable phases and non-equilibrium solidification making design of new materials and microstructures possible.
Undercooling of alloys is achieved by eliminating external, heterogeneous nucleation sites. Melt flux processes achieve it by choosing a non-reactive glassy flux to surround the material under study while container-less processing techniques achieve it by simulating microgravity conditions eliminating the container and thus, the external heterogeneous nucleation sites. A number of container-less processing techniques exist including the following:
Undercooling as a control parameter makes possible the following studies that are of immense scientific value and of relevance to industrial applications: