• Journal of Powder Materials
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• v.7 no.1
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• pp.42-49
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• 2000

Densificationbehavior of conventional austenitic stainless steel powder compacts was studied by comparing the relative density of sintered compact(Ds)with that of green compacts(Dg)prepared with various catbon contents and P/M process. Dg of 304and 316 powders by warm compaction under pressure of 686 MPa at heating temperature of powder(553K) and dies (573K) were 80% and 81%, repectively, whichwere 2 and 3% higher than those of conventional green compacts at the same pressure. Ds of 304 compacts sintered at 1373K in H2 gas has the same value of 84% max. regardless of compacting temperature, and Ds of 316 compacts at the same sintering conditions were 80% by conventional compaction and 83% by warm compaction. Oxygen contents of 304 and 316 sintered compacts were increased 1.43∼2.94% and 0.010∼0.921% higher than those of raw powders and warm green compacts, respectively. In other case, Ds of 316 compacts sintered at 1573K in vacuum had the same value of 86%max. And Ds of 316 compacts at the same sintering conditions were 83% and 86% by conventional and warm compaction, respectively. Oxygen contents of 304 sintered compacts were 0.321% and 0.360%, and in case of 316, they were 0.419% and 0.182% by the respective compating condition. With carbon additions in the range 0.1∼0.6% Ds increased to the extent of 86∼89% in 304 sintered compacts, and to 82∼84% and 85∼87% in 316 according to different two compacting peocesses compared to those of sintered compacts without carbon addition.

• Journal of Powder Materials
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• v.11 no.5
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• pp.383-390
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• 2004

In order to investigate behavior of abnormal expansion of the iron-copper compacts, we compared the dilatometric curves of the compacts which mixed the copper powder to the iron powder with those of compacts which mixed the copper powder to the iron-copper alloy powder. The dilatometric curves were obtained below the sintering conditions, which heated up to 115$0^{\circ}C$ by a heating rate of 1$0^{\circ}C$/min, held for 60min at 115$0^{\circ}C$ and cooled down at a rate of 2$0^{\circ}C$/min to room temperature. The dilatometric curves of the compacts showed the different expansion behavior at temperatures above the copper melting point in spite of same chemical composition. All of the compacts of former case showed large expansion, but all of the compacts in latter case showed large contraction. The microstructures of sintered compacts also showed the different progress in alloying of the copper into the iron powder. Namely we could observe the segregation at alloy part of copper into iron powder in case of the sintered compacts, which mixed the copper powder to the iron powder, but could not observe the segregation in compacts which mixed the copper powder to the iron-copper alloy powder. But the penetration of liquid copper into the interstices between solid particles was occurred at both cases. Therefore, the showing of the different dimensional changes in the compacts in spite of same chemical composition is due to more the alloying of copper into iron powder than the penetration of liquid copper into the interstices between solid particles.

• Journal of the Korean institute of surface engineering
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• v.34 no.6
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• pp.568-574
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• 2001

Mixed powders of Fe + 0.7% C, Fe + 0.7% C + 1.6% Cu, and Fe + 0.7% C + 0.3% MnS were pressed in a mold so that the green-compact densities were 6.3, 6.5, 6.7, and 6.9 g/㎤, respectively. Then, the compacts were sintered at $1125^{\circ}C$ for 30 minutes and subsequently steam treated at $600^{\circ}C$ for 60 minutes. From the results, it was found that the overall properties of the steam-treated compacts, such as the weight gain of the sintered compacts, the diffusion of oxides into the sintered compacts, the surface hardness, and the formation of surface oxide layer, were primarily influenced by the density of the compacts and the oxides that were formed on the surface of the compacts by the steam treatment.

• Journal of Powder Materials
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• v.4 no.3
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• pp.188-195
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• 1997

In most of sintered metal powder compacts, the sintered density distribution is controlled to be as high and uniform as possible to ensure the required mechanical properties. In general, the density distribution in the compacts is not uniform and not easy to measure. In the present study, a method for measuring the density distribution was developed, based on the indentation force equation by which the hardness and the relative density were related. The indentation force equation, expressed as a function of strength constant, workhardening coefficient and relative density, was obtained by finite element analysis of rigid-ball indentation on sintered powder metal compacts. The present method was verified by comparing the predicted density distribution in the sintered Fe-0.5%C-2%Cu compacts with that obtained by experiments, in which the density distribution was directly measured by machining the compacts from the outer surface progressively.

• Journal of Powder Materials
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• v.9 no.4
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• pp.203-210
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• 2002

A new PIM in-process joining technique has been developed for more complicated and functional PIM components by application of the exuded wax from the green compacts during solvent debinding step. At first, various stainless steels and iron compacts with rectangular shape were combined, and the joining behaviors and properties were investigated by shear and tensile test, and microscopic observation. Subsequently, perfect joined three pieces of thin and hollow compacts were obtained for the combination of same and different stainless steels, and it was difficult to join the iron and stainless steel compacts in hydrogen atmosphere because of the different starting temperature of shrinkage. However, pretty good joined iron and stainless steel compacts were obtained by consideration of particle size and vacuum atmosphere. Finally, for the combination of ferro-silicon and austenitic stainless steel compacts, high functionality (magnetic (1.60Tes1a) & non-magnetic) and perfect joint were obtained.

• Transactions of the Korean hydrogen and new energy society
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• v.10 no.2
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• pp.81-89
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• 1999

Various characteristics - mechanical propertis, thermal cyclic hydriding characteristics and resistance to degradation by $H_2O$, CO in hydrogen - of hydrogen storage alloy powder compacts using PTFE and silicon sealant as a polymer binder were studied. Diametral tensile strength of 10wt% PTFE and 5wt% silicon sealant added compacts showed relatively high value of $4kg/cm^2$ and $10kg/cm^2$, respectively. Compacts show a good resistance to degradation by $H_2O$ in hydrogen. But hydrogen absorption rate and capacity of compacts were decreased by CO in hydrogen with the number of cycles. Cu coated and PTFE bonded compacts showed very small decrease of capacity and a good strength even after 1000 cycles of thermal hydriding and dehydriding.

• Journal of Powder Materials
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• v.7 no.4
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• pp.218-227
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• 2000

It is well known that the Cu-Cr alloys are very difficult to be made by conventional sintering methods. This difficulty originates both from limited solubility of Cr in the Cu matrix and from limited sintering temperature due to high vapor pressures of Cr and Cu components at the high temperature. Densification of Cu-50%Cr Powder compacts by conventional Powder metallurgy Process has been studied. Three kinds of sintering methods were tested in order to obtain high-density sintered compacts. Completely densified Cu-Cr compacts could be obtained neither by solid state sintering method nor by liquid phase sintering method. Both low degree of shrinkage and evolution of large pores in the Cu matrix during the solid state sintering are attributed to the anchoring effect of large Cr particles, which inhibits homogeneous densification of Cu matrix and induces pore generation in the Cu matrix. In addition, the effect of undiffusible gas coming from the reduction of Cu-oxide and Cr-oxide was observed during liquid phase sintering. A two-step sintering method, solid state sintering followed by liquid phase sintering, was proved to have beneficial effect on the fabrication of high-dendsity Cu-Cr sintered compacts. The sintered compacts have properties similar to those of commercial products.

• Journal of the Korean Ceramic Society
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• v.25 no.4
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• pp.380-384
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• 1988

This investigation includes nitridation phenomena of silicon powder compacts in air. Nitridation reaction condition has been provided with using silicon nitride bed and active carbon additive. Reaction products are Oxynitride, $\alpha$-Si3N4, and $\beta$-Si3N4, Oxynitride(Si2N2O) phase in formed at outer surface layer ofsilicon powder compacts. $\alpha$-Si3N4, and $\beta$-Si3N4 are formed at inner region of powder compacts. Microstructural observation indicates that nitridation mechanism in this work is the same as conventional nitridation mechanism nitrogen gas.

• Journal of the Korean Ceramic Society
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• v.30 no.4
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• pp.251-258
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• 1993

A constitutive model is proposed to analyze creep densification and grain growth of ceramic powder compacts. The creep strain rates for powder compacts are obtained from constitutive equations proposed by Rahaman et al. and Helle et al. The grain-growth rate is obtained by assuming time, grain size, and strain rate as its internal state variables. the proposed constitutive model is compared with experimental data for alumina compacts obtained by Venkatachari and Raj for sinter forging and by Son et al. for hot pressing.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1998.03a
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• pp.168-174
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• 1998

In the present study, a method for measuring the relative density by the hardness measurement was proposed for sintered metal powder compacts. It is based on the indentation force equation, by which the relative density is related with the hardness, that was obtained by the finite element analysis of rigid-ball indentation on sintered metal powder compacts. For verifying the method, it was applied to prediction of density distributions in sintered and sintered-and-forged Fe-0.5%C-2%Cu powder compacts.