Eun-Kwang Park

Quantitative Study on the Refinement Behaviors of TiC Powders Produced by Mechanical Milling Under Different Impact Energy

This study investigated refinement behaviors of TiC powders produced under different impact energy conditions using a mechanical milling process. The initial coarse TiC powders with an average diameter of 9.3 were milled for 5, 20, 60 and 120 mins through the conventional low energy mechanical milling (LEMM, 22G) and specially designed high energy mechanical milling (HEMM, 65G). TiC powders with angular shape became spherical one and their sizes decreased as the milling time increased, irrespective of milling energy. Based upon the FE-SEM and BET results of milled powders, it was found initial coarse TiC powders readily became much finer near 100 nm within 60 min under HEMM, while their sizes were over 200 nm under LEMM, despite the long milling time of up to 120 min. Particularly, ultra-fine TiC powders with an average diameter of 77 nm were fabricated within 60 min in the presence of toluene under HEMM.

Rapid and direct synthesis of complex perovskite oxides through a highly energetic planetary milling

The search for a new and facile synthetic route that is simple, economical and environmentally safe is one of the most challenging issues related to the synthesis of functional complex oxides. Herein, we report the expeditious synthesis of single-phase perovskite oxides by a high-rate mechanochemical reaction, which is generally difficult through conventional milling methods. With the help of a highly energetic planetary ball mill, lead-free piezoelectric perovskite oxides of (Bi, Na)TiO3, (K, Na)NbO3 and their modified complex compositions were directly synthesized with low contamination. The reaction time necessary to fully convert the micron-sized reactant powder mixture into a single-phase perovskite structure was markedly short at only 30–40 min regardless of the chemical composition. The cumulative kinetic energy required to overtake the activation period necessary for predominant formation of perovskite products was ca. 387 kJ/g for (Bi, Na)TiO3 and ca. 580 kJ/g for (K, Na)NbO3. The mechanochemically derived powders, when sintered, showed piezoelectric performance capabilities comparable to those of powders obtained by conventional solid-state reaction processes. The observed mechanochemical synthetic route may lead to the realization of a rapid, one-step preparation method by which to create other promising functional oxides without time-consuming homogenization and high-temperature calcination powder procedures.

An Investigation of the Stability of Y 2 O 3 and Sintering Behavior of Fe-Based ODS Particles Prepared by High Energy Ball Milling

Abstract Fe-based oxide dispersion strengthened (ODS) powders were produced by high energy ball milling, fol-lowed by spark plasma sintering (SPS) for consolidation. The mixed powders of 84Fe-14Cr-2Y 2 O 3 (wt%) weremechanically milled for 10 and 90 mins, and then consolidated at different temperatures (900~1100 o C). Mechani-cally-Alloyed (MAed) particles were examined by means of cross-sectional images using scanning electron micros-copy (SEM). Both mechanical alloying and sintering behavior was investigated by X-ray diffraction (XRD) and highresolution transmission electron microscopy (HR-TEM). To confirm the thermal behavior of Y 2 O 3 , a replica methodwas applied after the SPS process. From the SEM observation, MAed powders milled for 10 min showed a lamellastructure consisting of rich regions of Fe and Cr, while both regions were fully alloyed after 90 min. The results ofsintering behavior clearly indicate that as the SPS temperature increased, micro-sized defects decreased and the den-sity of consolidated ODS alloys increased. TEM images revealed that precipitates smaller than 50 nm consisted ofYCrO

Milling Behaviors of Al-B 4 C Composite Powders Fabricated by Mechanical Milling Process

In the present work, Al- composite powders were fabricated using a mechanical milling process and its milling behaviors and mechanical properties as functions of sizes ( , 500 nm and 50 nm) and concentrations (1, 3 and 10 wt.%) were investigated. For achieving it, composite powders and their compacts were fabricated using a planetary ball mill machine and magnetic pulse compaction technology. Al- composite powders represent the most uniform dispersion at a milling speed of 200 rpm and a milling time of 240 minutes. Also, the smaller particles were presented, the more excellent compositing characteristics are exhibited. In particular, in the case of the 50 nm added compact, it showed the highest values of compaction density and hardness compared with the conditions of and 500 nm additions, leading to the enhancement its mechanical properties.

Dispersion Behaviors of Y 2 O 3 Particles Into Aisi 316L Stainless Steel by Using Laser Cladding Technology

The present work investigated the dispersion behavior of Y2O3 particles into AISI 316L SS manufactured using laser cladding technology. The starting particles were produced by high energy ball milling in 10 min for pre- alloying, which has a trapping effect and homogeneous dispersion of Y2O3 particles, followed by laser cladding using CO2 laser source. The phase and crystal structures of the cladded alloys were examined by XRD, and the cross section was characterized using SEM. The detailed microstructure was also studied through FE-TEM. The results clearly indi- cated that as the amount of Y2O3 increased, micro-sized defects consisted of coarse Y2O3 were increased. It was also revealed that homogeneously distributed spherical precipitates were amorphous silicon oxides containing yttrium. This study represents much to a new technology for the manufacture and maintenance of ODS alloys.