Research Interests
1. Effect of an External Electric Field on Grain Boundary Evolution in the Course of Nano-Ceramic Sintering.
Nanoceramics have an important place in modern technology and industry. Despite their widespread use, technological approaches for preserving the
nanostructure throughout the processing stages, particularly sintering at high temperatures, are still not firmly in place. Although principles for sintering of
nanoparticles are the same as those for coarse particles, a number of issues and challenges that are specific to nano-sintering remain to be addressed. In recent
years the application of an electric field/current has been under development as a promising new route for obtaining of nanostructured materials. However, the
presence of an electric field/current during sintering has raised some new fundamental questions.
How are the basic defect chemistry and the thermochemistry (interfacial energies) affected by the electric field? What is the sintering mechanism of nano-
powders under the electric field?
In our studies on sintering of nano MgAl2O4 by the spark plasma sintering technology (i.e., sintering in the presence of an electric field), we have found
that this technology helps to preserve the grains at the nano scale (<D> ~80 nm) in almost fully dense ceramics, moreover, the electric filed induces structural
changes at the atomic scale (i.e., disordered to more order transformation). The later were also confirmed by our new calorimetric method.
The overall objective of this research is to reveal the impact of a DC electrical field on the defect chemistry and thermochemistry of grain boundaries in
ionic oxide ceramics during sintering. We hypothesize that the interaction between the electric field and the intrinsic and imposed structural defects will affect the
sintering mechanism. The significance of our studies stems from its potential to identify the effects of an electric field on the interfacial energy, on the chemistry
and physical and mechanical properties of the ceramics, and finally on their resulting microstructures. The results are meant to establish the role of the electric
field during sintering, and thereby to provide novel means for maintaining the structure and properties of nano-ceramics.
1. Metal/ceramic composites, processing, microstructure and properties
The basic concept of combining metal and ceramic on an intimate scale is incorporation of the desirable qualities of either species and suppression of the
undesirable properties. The cermets that we are studying can be divided in two classes: light metal-ceramic composites (B4C-Al, B4C-Si, TiB2-Al, TiC-Al ) and
relatively heavy metal-ceramic composites (B4C-Fe, TiC-Ni, TiC-TiB2-Ni, TiC-Steels). These composites have a very high hardness and improved fracture
toughness compared with the ceramic materials and are very attractive materials for armor applications. Considerable progress was made towards production of
acceptable metal-ceramic composites based on the boron carbide infiltrated with silicon. These composites display some unique characteristic as armor materials.
The results concerning the B4C - Si composites were published in 8 papers and were presented at more than 7 international conferences. In the last 2 years the
further development of the metal-ceramic composites was achieved by applying the concept of Functionally Graded Material (FGM). The FGM concept
provides additional degrees of freedom for designers of material systems and illustrates the modern tendency to custom-design materials for specific applications.
According to this concept, several original approaches for production of composites with a gradual change of the metal-to-ceramic ratio were suggested and
applied for the Al2O3-Ni and Al2O3- Ti systems. The research is in progress.
2. Advanced Casting Technologies
One of the most important and common industrial route for fabrication of metallic parts with a final shape or semi-products for forming (rolling, extrusion,
cold drawing, etc') is a casting process. The metal composition, thermal treatments and microstructure have a profound impact on their mechanical properties,
environmental behavior and weldability. In order to achieve optimal combination of the properties enormous amount of experiments is required if only a "cook
and look" approach is applied. This approach is very expensive and time consuming and isn't suitable for modern R&D programs, that have to combine
computational materials science and well-design experimental investigation. The up-to-date methods of the computational materials science allow simulating the
effect of various technological parameters on the microstructure and mechanical properties of castings as well as to make the experimental work more focused
and efficient.
In this subject we intend to set up a state of the art laboratory which will serve as a center experimental study and modeling of advanced casting
technologies. In this center we We plan to investigate many aspects of casting process, such as melting parameters, chemical and phase composition of metals,
their purity, interaction between liquid metals and crucibles, shrinkage porosity, metal feeding, effects of external electric and magnetic fields, rate of cooling,
nature of the solidification front, etc'. Finally, the relations between process parameters, chemical composition, microstructure and mechanical properties will be
determined.
For example we already study the effect of pulse magneto oscillation treatment on the solidification structure of aluminum. The influence of the
electromagnetic pulse (EMP) treatments (electric current pulsing - ECP, pulse magnetic field - PMF or - PMO) on the solidified structure of alloys or pure
metals has been well demonstrated. The main result of EMP treatment on the solidified microstructure is the transformation from coarse columnar grains to fine
globular microstructure. It may be explained by the appearance of a large amount of nucleation sites in the melt bulk which suppress the dendrites growth from
the mold walls. For the explanation of this phenomenon several models were proposed: the thermodynamic model (i.e. based on the bulk melt free-energy
change in the course of nuclei formation under current density flow) and the crystal rain model, here the magnetic pressure promotes crystal spreading and
creates numerous sites for nucleation. All the proposed models explain some of the processes characteristics, however a whole description of the obtained
experimental data is still lacking. In the current research, we aim to develop a model which will clarify, hopefully this phenomenon.
