Prof. Naresh N. Thadhani

My current research activities include:
Reaction synthesis and processing of structural materials. Non-equilibrium powder processing techniques involving a wide range of chemical reaction rates (10+3 to 10-6) are used for the synthesis of structural materials. Mechanical alloying by ball milling of powders, uses diffusion (accelerated by presence of defects) controlled reactions occurring in time scales of hours, to form crystalline and noncrystalline alloys and dispersion strengthened materials. Self sustaining solid-state combustion reactions can be thermally initiated in a green compact of a powder mixture, such that the reaction propagates in the form of a wave travelling at the rate of cm/s and leading to materials synthesis. Such solid state chemical reactions in powder mixtures can also be initiated by shock compression, leading to materials synthesis in time durations of a microsecond.

The unique characteristics of these processes are advantageously utilized to synthesize and fabricate structural materials e.g., intermetallic alloys, ceramics, and composites, in bulk form. The nonequilibrium nature of these processes also allows synthesis of novel and/or metastable phases and microstructures, not possible by conventional processing technologies. The focus of our work is to understand the process mechanisms, and develop microstructure and mechanical property correlations for the synthesized materials.

High-pressure and high-strain-rate deformation of materials:
Dynamic high-pressure shockcompression and high-strain-rate deformation of materials, generated by high velocity impact, produces a unique combination of physical, chemical, mechanical, and structural effects. In solids, the deformation effects can lead to asymptotic increases in the flow stress of the material, as well as dynamic fracture dominated by stress wave interactions. Structural phase transitions resulting in synthesis of high-pressure phases, e.g., martensitic transformations in shape memory NiTi alloys and in graphite (forming diamond), can also occur in shock compressed solids.

In the case of high-strain-rate deformation of powders, unique defect states and dense-packing characteristics can be produced, which can alter the solid-state mass transport characteristicsand enhance their chemical reactivity. Thus, not only can difficult to sinter powders by dynamically consolidated, but chemical reactions can be initiated in mixtures of powders resulting in synthesis of novel and/or metastable materials. Additionally, highly activated powders with radically modified microstructures can also be produced, for example in ceramics, to improve powder sinterability or catalytic activity, or to even introduce flux pinning centers in ceramic oxide superconductors for obtaining higher critical current densities. A high velocity impact facility has been developed at Georgia Tech, to perform fundamental studies on high-strain-rate deformation of solids and powder materials. The emphasis of the research is to correlate the mechanics and microstructural aspects to predict and establish the material behavior with respect to mechanical property changes, dynamic fracture, and solid-state phase transitions and chemical reactions.

Academic Experience:
Failure Analysis, metal forming
Consultant to Battelle on U.S. Army Research Office Programs
DOE Panel Reviewer on Programs Involving Decontamination and Recycling of Nuclear Metallic Wastes
Engineering Research Initiative Award National Science Foundation (NSF), 1987
Science Support Award ALCOA Foundation, 1990
NSF Panel Reviewer on programs for the Mechanics and Materials Processing Division of the Engineering Directorate
Reviewer of proposals for NSF, ARO and DOE