Geon-Yong Lee

Consolidation of Hierarchy-Structured Nanopowder Agglomerates and Its Application to Net-Shaping Nanopowder Materials

This paper provides an overview on our recent investigations on the consolidation of hierarchy-structured nanopowder agglomerates and related applications to net-shaping nanopowder materials. Understanding the nanopowder agglomerate sintering (NAS) process is essential to processing of net-shaped nanopowder materials and components with small and complex shape. The key concept of the NAS process is to enhance material transport through controlling the powder interface volume of nanopowder agglomerates. Based upon this concept, we have suggested a new idea of full density processing for fabricating micro-powder injection molded part using metal nanopowder agglomerates produced by hydrogen reduction of metal oxide powders. Studies on the full density sintering of die compacted- and powder injection molded iron base nano-agglomerate powders are introduced and discussed in terms of densification process and microstructure.

Consolidation of Iron Nanopowder by Nanopowder-Agglomerate Sintering at Elevated Temperature

【The key concept of nanopowder agglomerate sintering (NAS) is to enhance material transport by controlling the powder interface volume of nanopowder agglomerates. Using this concept, we developed a new approach to full density processing for the fabrication of pure iron nanomaterial using Fe nanopowder agglomerates from oxide powders. Full density processing of pure iron nanopowders was introduced in which the powder interface volume is manipulated in order to control the densification process and its corresponding microstructures. The full density sintering behavior of Fe nanopowders optimally size-controlled by wet-milling treatment was discussed in terms of densification process and microstructures.】

Microstructural Feature of Full-densified W-Cu Nanocomposites Containing Low Cu Content

The microstructure evolution during sintering of the W-5 wt.%Cu nanocomposite powders was investigated for the purpose of developing a high density W-Cu alloy. The W-5 wt.%Cu nanopowder compact, fully-densified during sintering at 1623 K, revealed a homogeneous microstructure that consists of high contiguity structures of W-W grains and an interconnected Cu phase located along the edges of the W grains. The Vickers hardness of the sintered W-5 wt.%Cu specimen was Hv much higher than that ( Hv) of the conventional heavy alloy. This result is mostly due to the higher contiguity microstructure of the W grains compared to the conventional W heavy alloy.

Effect of Process Temperature on the Sm2Fe17 Alloying Process During a Reduction-Diffusion Process Using Fe Nanopowder

This study investigated the effect of process temperature on the alloying process during synthesis of Sm2Fe17 powder from ball-milled samarium oxide (Sm2O3) powders and a solid reducing agent of calcium hydrides (CaH2) using iron nanopowder (n-Fe powder) by a reduction-diffusion (R-D) process. The n-Fe-Sm2O3CaH2 mixed powders were subjected to heat treatment at 850~1100°C in Ar-H2 for 5 h. It was found that the iron nanopowders in the mixed powders are sintered below 850°C during the R-D process and the SmH2 is synthesized by a reduced Sm that combines with H2 around 850°C. The results showed that SmH2 is able to separate Sm and H2 respectively depending on an increase in process temperature, and the formed Sm2Fe17 phase on the surface of the sintered Fe nanopowder agglomerated at temperatures of 950~1100°C in this study. The formation of the Sm2Fe17 layer is mainly due to the diffusion reaction of Sm atoms into the sintered Fe nanopowder, which agglomerates above 950°C. We concluded that nanoscale Sm2Fe17 powder can be synthesized by controlling the diffusion depth using well-dispersed Fe nanopowders. (Received July 5, 2010)