Journal of Powder Materials

Cold Sintering and Its Applications: J Korean Powder Metall Inst. 2000;7(3):117-122.

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A Study on the Sintering of Simulated DUPIC Fuel: J Korean Powder Metall Inst. 2000;7(3):123-130.

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Abstract PDF: The simulated DUPIC fuel provides a convenient way to investigate fuel properties and behaviours such as thermal conductivity, thermal expansion, fission gas release, leaching and so on. Several pellets simulating the composition and microstructure of the DUPIC fuel were fabricated from resintering powder through the OREOX process of the simulated spent fuel pellets, which were prepared from the mixture of stable forms of constituent nuclides. This study describes the powder treatment, OREOX, compaction and sintering to fabricate simulated DUPIC fuel using the simulated spent fuel. The homogeneity of additives in the powder was observed after attrition milling. The microstructure of the simulated spent fuel was in agreement with the previous studies. The densities and the grain size of simulated DUPIC fuel was pellets are higher than those of simulated spent fuel pellets. Small metallic precipitates and oxide precipitates were observed on matrix grain boundaries.

Three Point Bending Fatigue Property with Heat Treatment Condition in a Powder Metallurgical High Speed Steel JYPS-23: J Korean Powder Metall Inst. 2000;7(3):131-136.

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Abstract PDF: The effect of tempering temperature on the three point bending fatigue behavior of a P/M high speed steel JYPS-23 (1.28% C, 4.20% Cr, 6.40% W, 5.00% Mo, 3.10% V, bal. Fe) was investigated. The number of cycles to failure of the specimen austenitized at 1175°C drastically increased with increasing tempering temperature. As tempering temperature increased from 500 to 620°C, the volume fraction and average size of carbides (MC or M6C) did not significantly changed, while hardness decreased drastically. The reduced hardness is due to the softening of matrix, which increased the resistance of the fatigue crack propagation. For a practical application, powder compacting test were also conducted with the P/M high speed steel punches tempered at 500, 580, and 620°C. The number of compacting cycles to failure of the punches also increased with increasing tempering temperature.

Modelling the Densification Behaviour of Powders Considering Diffusion and Power-Law Creep Mechanisms during Hot Isostatic Pressing: J Korean Powder Metall Inst. 2000;7(3):137-142.

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Abstract PDF: In order to analyze the densification behaviour of stainless steel powder compacts during hot isostatic pressing (HIP) at elevated temperatures, a power-law creep constitutive model based on the plastic deformation theory for porous materials was applied to the densification. Various densification mechanisms including interparticle boundary diffusion, grain boundary diffusion and lattice diffusion mechanisms were incorporated in the constitutive model, as well. The power-law creep model in conjunction with various diffusion models was applied to the HIP process of 316L stainless steel powder compacts under 50 and 100 MPa at 1125°C. The results of the calculations were verified using literature data. It could be found that the contribution of the diffusional mechanisms is not significant under the current process conditions.

Toughness and Damping Properties of Nanostructured Ni-Al Alloys Produced by Mechanical Alloying Methods: J Korean Powder Metall Inst. 2000;7(3):143-148.

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Abstract PDF: NiAl alloy powders were prepared by mechanical alloying method and bulk specimens were produced using hot isostatic pressing techniques. This study focused on the transformation behavior and properties of Ni-Al mechanically alloyed powders and bulk alloys. Transformation behavior was investigated by differential scanning calorimeter (DSC), XRD and TEM. Particle size distribution and microstructures of mechanically alloyed powders were studied by particle size analyzer and scanning electron microscope (SEM). After 10 hours milling, XRB peak broadening appeared at the alloyed powders with compositions of Ni-36at%Al to 40at%Al. The NiAl and Ni_3Al intermetallic compounds were formed after water quenching of solution treated powders and bulk samples at 1200°C, but the martensite phase was observed after liquid nitrogen quenching of solution treated powders. However, the formation of Ni_3Al intermetallic compounds were not restricted by fast quenching into liquid nitrogen. It is considered to be caused by fast diffusion of atoms for the formation of stable beta(NiAl) phase and Ni_3Al due to nano sized grains during quenching. Amounts of martensite phase increased as the composition of aluminium component decreased in the Ni-Al alloy, which resulted in the increasing damping properties.

Fracture Toughness of Al_2O_3/5vol.%Cu Nanocomposites Fabricated by PECS: J Korean Powder Metall Inst. 2000;7(3):149-153.

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Abstract PDF: 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°C and 1250°C after soaking process at 900°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.

The Evaluation of Thermal Properties for W-Cu Composite Sintered from Mechanically Alloyed Powders: J Korean Powder Metall Inst. 2000;7(3):154-160.

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Abstract PDF: In order to enhance sinterability of W-Cu composites used for heat sink materials, mechanical alloying process where both homogeneous mixing of component powders and fine dispersion of minor phase can be easily attained was employed. Nanostructured W-Cu powders prepared by mechanical alloying showed W grain size ranged of 20-50 nm and were able to be efficiently sintered owing to the fine particle size as well as uniform distribution of Cu phase. The thermal properties such as electrical resistivity, coefficient of thermal expansion and thermal conductivity were evaluated as functions of temperature and Cu content. It was found that the coefficient of thermal expansion could be controlled by changing Cu content. The measured electrical resistivities and thermal diffusivities were also varied with Cu content. The thermal conductivities calculated from the values of resistivities and diffusivities showed similar tendency as a function of temperatures. However, this is in contradiction with thermal conductivities of pure W and Cu which decrease with increasing temperature.

Spark-Plasma Sintering of Mechanically-alloyed NiAl Powder and Ball-milled (Ni+Al) Powder Mixture: J Korean Powder Metall Inst. 2000;7(3):161-167.

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Abstract PDF: Mechanically-alloyed NiAl powder and ball-milled (Ni+Al) powder mixture were sintered by spark-plasma sintering(SPS) process. Mechanical alloying was performed in a horizontal attritor for 20 h with rotation speed of 600 rpm. (Ni+Al) powder mixtures were prepared by ball milling for 1 and 10 h with 120 rpm. Both powders were sintered at 1150°C for 5 min under 10-3 torr vacuum with 50 MPa die pressure in a SPS facility. Sintered densities of 97% and 99% were obtained from mechanically-alloyed NiAl powder and (Ni+Al) powder mixture, respectively. The sintered compact of (Ni+Al) powder mixture showed large grain size by a very rapid grain growth, while the grain size of mechanically-alloyed NiAl powder compact after sintering was extremely fine(80 nm). The difference in densification behavior of both powders were discussed.

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