• Korean Journal of Materials Research
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• v.11 no.5
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• pp.378-384
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• 2001

In this study, nanostructured Fe-Ce powder with grain size of 10nm was produced by MA (mechanical alloying) process and was consolidated by PECS (pulse electric current sintering) process for the fabrication of bulk nanostructured Fe-Co softmagnetic alloy. PECS process was performed at 700, 800, 900 and $^1000{\circ}C$ with holding time ranging from 0 to 15min. The effectiveness of PECS Process to Produce nanostructured bulk specimens was estimated. The optimal PECS process condition for nanostructured Fe-Co powders was found through observing the change of relative density and microstructure with sintering temperature and holding time. The magnetic properties of the sintered specimens were evaluated through the measurement of coercivity and saturation magnetization.

• Journal of the Korean Ceramic Society
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• v.44 no.7
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• pp.343-348
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• 2007

Alumina/silver nanocomposites were fabricated using a soaking method through a sol-gel route to construct an intra-type nanostructure. The pulse electric-current sintering (PECS) technique was used to sinter the nanocomposites. Several specimens were annealed after sintering. The microstructure, mechanical properties, critical frontal process zone (FPZ) size, and thermo-mechanical properties of the nanocomposites were estimated. The relative densities of the specimens sintered at 1350 and $1450^{\circ}C$ were 95% and 99%, respectively. The maximum value of the three-point bending strength was found to be 780 MPa for the $2{\times}2{\times}10 mm$ specimen sintered at $1350^{\circ}C$. The fracture toughness of the specimen sintered at $1350^{\circ}C$ was measured to be $3.60 MPa{\cdot}m^{1/2}$ using the single-edge V-notched beam (SEVNB) technique. The fracture mode of the nanocomposites was transgranular, in contrast to the intergranular mode of monolithic alumina. The fracture morphology suggested that dislocations were generated around the silver nanoparticles dispersed within the alumina matrix. The specimens sintered at $1350^{\circ}C$ were annealed at $800^{\circ}C$ for 5 min, following which the maximum fracture strength became 810 MPa and the fracture toughness improved to $4.21 MPam^{1/2}$. The critical FPZ size was the largest for the specimen annealed at $800^{\circ}C$ for 5 min. Thermal conductivity of the alumina/silver nanocomposites sintered at $1350^{\circ}C$ was 38 W/mK at room temperature, which was higher than the value obtained with the law of mixture.

• Journal of Powder Materials
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• v.6 no.4
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• pp.301-306
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• 1999

Mechanical properties of oxide based materials could be improved by nanocomposite processing. To investigate optimum route for fabrication of nanocomposite enabling mass production, high energy ball milling and Pulse Electric Current Sintering (PECS) were adopted. By high energy ball milling, the $Al_2O_3$-based composite powder with dispersed Cu grains below 20 nm in diameter was successfully synthesized. The PECS method as a new process for powder densification has merits of improved sinterability and short sintering time at lower temperature than conventional sintering process. The relative densities of the $Al_2O_3$-5vol%Cu composites sintered at $1250^{\circ}C$ and $1300^{\circ}C$ with holding temperature of $900^{\circ}C$ were 95.4% and 95.7% respectively. Microstructures revealed that the composite consisted of the homogeneous and very fine grains of $Al_2O_3$ and Cu with diameters less than 40 nm and 20 nm respectively The composite exhibited enhanced toughness compared with monolithic $Al_2O_3$. The influence of the Cu content upon fracture toughness was discussed in terms of microstructural characteristics.

• Journal of Powder Materials
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• v.7 no.3
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• pp.149-153
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• 2000

In this study, the fabrication of $Al_2O_3$/5vol.%Cu nanocomposite and its mechanical property were discussed. The nanocomposite powders were produced by high energy ball milling of $Al_2O_3$ and Cu elemental powders. The ball-milled powders were sintered with Pulse Electric Current Sintering (PECS) facility. The relative densities of specimens sintered at $1200^{\circ}C$ and $1250^{\circ}C$ after soaking process at $900^{\circ}C$ were 96% and over 97%, respectively. The sintered microstructures were composed of $Al_2O_3$ matrix and the nano-sized Cu particles distributed on grain boundaries of $Al_2O_3$ matrix. The nanocomposite exhibited the enhanced fracture toughness compared with general monolithic $Al_2O_3$. The toughness increase was explained by the crack deflection and bridging by dispersed Cu particles.

• Korean Journal of Materials Research
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• v.12 no.8
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• pp.656-660
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• 2002

It was investigated that $Al_2$$O_3$/Cu nanocomposite powder could be optimally prepared by dispersion and reduction of Cu oxide, and suitably consolidated by employing pulse electric current sintering (PECS) process. $\alpha$-$Al_2$$O_3$ and CuO powders were used as elemental powders. In order to obtain $Al_2$O$_3$ embedded by finely and homogeneously dispersed CuO particles, the elemental powders were high energy ball milled at the rotating speed of 900 rpm, with the milling time varying up to 10 h. The milled powders were heat treated at $350^{\circ}C$ in H$_2$ atmosphere for 30 min to reduce CuO into Cu. The reduced powders were subsequently sintered by employing PECS process. The composites sintered at $1250^{\circ}C$ for 5 min showed the relative density of above 98%. The fracture toughness of the $Al_2$$O_3$/Cu nanocomposite was as high as 4.9MPa.$m^{1}$2//, being 1.3 times the value of pure $Al_2$$O_3$ sintered under the same condition.

• The Korean Journal of Ceramics
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• v.5 no.4
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• pp.395-399
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• 1999

MgO/metal nanocomposite powder mixtures were prepared by solution chemical processes to obtain suitable structure for ceramic/metal nanocomposites. Nickel or cobalt nitrate, as a source of metal dispersion, was dissolved into alcohol and mixed with magnesia powder. After calcined in air, these powders were reduced by hydrogen. Densified nanocomposites were successively obtained by Pulse Electric Current Sintering (PECS) process. The dispersed metal partical size depended on temperature and time in calcination and reduction processes. The phase analyses in the synthesized powders as a functioni of temperature were tracked using a dynamic high temperature X-ray diffractioni (HTXRD) system. Phase and crystallite size analyses were done using X-ray diffractioni and TEM. The MgO/metal nanocomposites were successfully fabricated, and ferromagnetic responses with enhanced coercive force were also investigated for these composites.

• Korean Journal of Materials Research
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• v.10 no.9
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• pp.642-647
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• 2000

Nanocrystalline NiAl alloy containing 36at.%Al was synthesized by mechanical alloying (MA). Synthesized powder was sintered by a pulse electric current sintering (PECS) facility. Effecting parameters on the phase transformation were discussed in terms of cooling rate and time spent on heat treatment. The behavior of phase transformation for sintered parts was examined by differential scanning calorimetry (DSC) and X-ray diffraction (XRD) method. Microstructure was observed by scanning electron microscopy (SEM). Martensitic lattice parameter and volume fraction was calculated by direct comparison method in X-ray diffraction analysis.