Papers by Author: Chul Jin Kim

Abstract: Metal sulfide (MeS) is well known and widely used an additive for enhancing machinability, but the problems is extremely sensitive to reaction with moisture and thermal decomposition during sintering. In this study, micron or nano size compound powders of FeS were produced by mechano-chemical process. The machinability was also evaluated at the metal sulfide added sintered steel. Compared with the MnS additive, addition of the FeS powders to the iron resulted the formation of the sintering materials containing a spherical shape of pore, partly remained FeS rich-phase in iron matrix. Relative machinability behavior of sintering materials was investigated by the lathe manufacturing. Mechanical properties of sintering material with 1.2%FeS powders were improved rather than its using MnS powders.

Abstract: TiC cermet is widely used for working dies with a high hardness and tool materials. In this research, we attempted to produce submicron sized TiC powders from the ball milled TiH2 and carbon black mixture by thermal treatment. The titanium hydride and carbon composite powders were milled under argon atmosphere for 7 hours at various ball to powder ratios. At the initial stage, an increase in particle size was observed, and graphite phase disappered. The TiC phase of 300nm mean particle size was obtained by milling for 5 hours. As a result, its morphologies were excessively agglomerated. At the heat treating temperature of 500°C, TiH2 phase transformed to Ti completely and the complete TiC of lattice parameter 0.431 nm was formed when the temperature reached 1000°C. Metal matrix composites(MMCs) based on the Fe-TiC system can be synthesized by spark plasma sintering. Specimen formed sintering Fe-TiC powders display a microstructure of uniformly dispersed TiC grain in a continuous metal matrix.

Abstract: TiC particulate reinforced Fe matrix composite compacts with controlled interfacial reaction was processed by spark plasma sintering after mechanical alloying. Milled powders were fabricated for 1-5 hours by spex shaker mill with the ball to powder ratio of 25:2. Metal matrix composites (MMCs) based on the Fe-40%TiC system can be synthesized by spark plasma sintering of the D’AE powders with TiH2-graphite powders under vacuum in the temperature range 1273-1473K for 5-20 min. TiC phase was formed by self combustion reaction with temperature increase. The specimen that was formed by sintering Fe-TiC powders displayed a microstructure of uniformly dispersed TiC grain in a continuous metal matrix. The densifications of the TiC-Fe materials were increased as the heat-treatment holding time increasing. In the same time, relative density and hardness of TiC-Fe sintering materials was increased.