III. Polycrystalline and Amorphous Materials


 

                Thermal and Mechanical Behavior of Polycrystalline and Amorphous Materials

Many technologically useful materials are polycrystalline or amorphous in nature. They are used as primary raw materials in energy, semiconductor, solar, manufacturing and photovoltaic industries. 

Polycrystalline materials have a microstructure composed of single crystals and grain boundaries (GB). The thermal and mechanical behavior of polycrystalline materials depends strongly on their microstructure, where the texture (sizes and orientations) of single crystals and the total area of GBs play a critical role. One example is the well-known Hall–Petch relationship, which shows that the strength of the polycrystals increases as the average size of the single crystal is reduced. Moreover, the microstructures depend on the processing techniques (for example, rate of cooling or extent of deformation) and lead to different macroscopic behavior. I am interested in understanding the fundamental physics at each length scale and using them to explain the macroscopic properties of polycrystalline materials. 

Amorphous or glassy materials, on the other hand, have no definite structure, but possess different strength and elastic properties. For example, it is well known that bulk metallic glasses may have higher strength and higher elastic limits compared to their crystalline forms. Therefore, a rich set of behavior can be obtained by systematic control between glassy and crystalline states. 

The questions I like to address in this area are: 

  • How does the texture of single crystals affect the polycrystalline stress-strain behavior?
  • How does grain boundary mechanics (for example, mobility) play a role in the polycrystalline behavior? 
  • When does a material become polycrsytalline or glassy? How do we avoid crystallization?
  • How can we control the texture of single crystals during solidification or cooling process?
  • How do we control GB migration? 
  • How do we use the principles that govern the formation of polycrystalline and glassy materials to create novel materials with desired properties such as elastic moduli, strength, thermal conductivity, etc.?

I am also interested in developing theories and computational methods for obtaining the effective elastic and thermal properties of composite materials under static and quasi-static loading. To this end, I am interested in developing continuum-to-continuum theories (or homogenization methods) that are able to connect two continuum scales. 

© Kranthi K. Mandadapu