In-situ alloying on synthesis of nanosized Ni-Fe powder

Diffusion Properties of Internal Interfaces in Bulk Nanocrystalline Materials: Radiotracer Investigation

The radiotracer technique was applied to measure self- (Fe, Ni) and solute- (Ag) grain boundary diffusion in nanocrystalline Fe-40wt.%Ni alloy. The nanocrystalline material was prepared by pressureless sintering of the nanoalloy powders. The nano-sized crystallites were found to be clustered in micrometer-large agglomerates. Two types of internal interfaces with fundamentally different properties exist in the nanomaterial: the grain boundaries between the nanocrystallites and the interfaces between the agglomerates. A complete and consistent model of the diffusion processes in such material is elaborated. Whereas the nanocrystalline boundaries reveal diffusivities, which are similar to those in coarse-grained material, diffusion along interagglomerate interfaces occurs faster by orders of magnitude. This behavior is explained by a nonrelaxed structure of the inter-agglomerate interfaces.

The Optimization of Hydrogen Reduction Process for Mass Production of Fe-8wt%Ni Nanoalloy Powder

The present investigation has attempted to optimize hydrogen reduction process for the mass production of Fe-8wt%Ni nanoalloy powder from Fe2O3-NiO powder. In-situ hygrometry study was performed to monitor the reduction behavior in real time through measurement of water vapor outflowing rate. It was found that the reduction process can be optimized by taking into account the apparent influence of water vapor trap in the reactor on reduction kinetics which strongly depends on gas flow rate, reactor volume and reduction.

Densification Behavior and Microstructural Development of Nano-Agglomerate Powder during Sintering

Densification behavior of nano-agglomerate powder during pressureless sintering of Fe-Ni nanopowder was investigated in terms of diffusion kinetics and microstructural development. To understand the role of agglomerate boundary for sintering process, densification kinetics of Fe-Ni nano-agglomerate powder with different agglomerate size was investigated. It was found that activation energy for densification process was lower in the small-sized agglomerate powder. The increase in the volume fraction of inter-agglomerate boundary acting as high diffusion path might be responsible for the enhanced diffusion process.