• 한국분말재료학회지
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• 제25권4호
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• pp.302-308
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• 2018

A lean alloy is defined as a low alloy steel that minimizes the content of the alloying elements, while maintaining the characteristics of the sintered alloy. The purpose of this study is to determine the change in microstructure and mechanical properties due to the addition of silicon or tin in Fe-Mo-P, Fe-Mn-P, and Fe-Mo-Mn-P alloys. Silicon- or tin-added F-Mo-P, Fe-Mn-P, and Fe-Mo-Mn-P master alloys were compacted at 700 MPa and subsequently sintered under a $H_2-N_2$ atmosphere at $1120^{\circ}C$. The sintered density of three alloy systems decreases under the same compacting pressure due to dimensional expansion with increasing Si content. As the diffusion rate in the Fe-P-Mo system is higher than that in the Fe-P-Mn system, the decrease in the sintered density is the largest in the Fe-P-Mn system. The sintered density of Sn added alloys does not change with the increasing Sn content due to the effect of non-dimensional changes. However, the effect of Si addition on the transverse rupture strengthening enhancement is stronger than that of Sn addition in these lean alloys.

• 한국세라믹학회지
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• 제37권5호
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• pp.511-515
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• 2000

The effect of Ba2+ ion dissolution with different pH and amount of PAA on microstructural changes of green and sintered bodies and its electrical properties was studied in aqueous nano-size BaTiO3 slurry system. The dissolution of Ba2+ was least at strong base, pH 10.8 and by addition of amount of 0.15 wt% PAA. The green body with the lowest of dissolution of Ba2+ at pH 10.8 and 0.15 wt% PAA had minimum values of average pore size, 40nm and shown high increase of sintered density. The compact sintered at 125$0^{\circ}C$ for 2 hr with highest Ba2+ dissolution had low density and dielectric constant due to abnormal grian growth. However, the sintered body with the lowest Ba2+ dissolution had high sintered density and then shown high dielectric constant.

• 한국세라믹학회지
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• 제40권6호
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• pp.572-576
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• 2003

$UO_2$-20 wt% CeO$_2$ 소결 펠렛의 밀도에 따른 개/폐 기공도, 기공의 크기 및 그 분포 그리고 기공의 형태를 조사하였다. 이론 소결밀도 약 96% 이상에서는 기공도는 개기공이 거의 없는 폐기공으로 나타났다. 반면에 기공크기 분포는 소결밀도에 관계없이 bimodal 형태를 보이나, 소결밀도가 증가할수록 기공 개수만 적게 나타났다. 기공의 형태는 소결밀도가 증가할수록 불규칙한 형태에서 둥근 형태로 바뀌었다.

• 한국분말재료학회지
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• 제24권5호
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• pp.400-405
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• 2017

The addition of a large amount of alloying elements reduces the compactibility and increases the compacting pressure, thereby shortening the life of the compacting die and increasing the process cost of commercial PM steel. In this study, the characteristic changes of Fe-Mo-P, Fe-Mn-P, and Fe-Mo-Mn-P alloys are investigated according to the Si contents to replace the expensive elements, such as Ni. All compacts with different Si contents are fabricated with the same green densities of 7.0 and $7.2g/cm^3$. The transverse rupture strength (TRS) and sintered density are measured using the specimens obtained through the sintering process. The sintered density tends to decrease, whereas the TRS increases as the Si content increases. The TRS of the sintered specimen compacted with $7.2g/cm^3$ is twice as high as that compacted with $7.0g/cm^3$.

• 한국분말재료학회지
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• 제16권4호
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• pp.268-274
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• 2009

For the purpose of obtaining basic information on the development of lead-free materials, a high density composites (a) W-Cu, (b) W-Sn (c)W-Cu-Sn and (d) W-Cu-Ni were fabricated by the P/M method. The particle size of used metal powders were under 325 mesh, inner size of compaction mould was $\phi8$ mm, and compaction pressure was 400 MPa. A High density composite samples were sintered at a temperature between $140^{\circ}C$ and $1050^{\circ}C$ for 1 hour under Ar atmosphere. The microstructure, phase transformation and physical properties of the sintered samples were investigated. As the results, the highest relative density of 95.86% (10.87 g/$cm^3$) was obtained particularly in the sintered W-Cu-Sn ternary system sample sintered at 450 for 1hr. And, Rockwell hardness (HRB) of 70.0 was obtained in this system.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part2
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• pp.738-739
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• 2006

This paper will describe a powder and processing method that facilitates single press-single sintered densities approaching $7.5g/cm^3$. At this sintered density, mechanical properties of the powder metal (P/M) component are significantly improved over current P/M technologies and begin to approach the performance of wrought steels. High performance gears have the added requirement of rolling contact fatigue durability that is dependent upon localized density and thermal processing. Combining high density processing of engineered P/M materials with selective surface densification enables powder metal components to achieve rolling contact fatigue durability and mechanical property performance that satisfy the performance requirements of many high strength automotive transmission gears. Data will be presented that document P/M part performance in comparison to conventional wrought steel grades.

• 한국분말재료학회지
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• 제1권1호
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• pp.27-34
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• 1994

Commercial pure iron powder and iron powder of coated 0.45% phosphorus were mixed with graphite powder in dry mixer to control carbon content from 0 wt% to 0.8 wt%. Mixed powder was pressed in the mould under the pressure of 510 MPa. Compacts were sintered at 118$0^{\circ}C$ for 40 min. in cracked ammonia gaseous atmosphere. Some of these sintered specimens were quenched in oil, and tempered in Ar gas. All of these specimens were investigated for microstructure, density and hardness in relation to coated phosphorus and carbon content. The results obtained were as follows: (1) The microstructure of the sintered speciments revealed that the amount of pearlite was increased with increasing C content but decreased by P-addition. (2) The P-addition affected the microstructure of pores in which the pore shape became round and its mean size was decreased by P-addition. (3) After tempering of sintered specimens the structure of pearlite was changed from fine structure to coarse one in P added specimen. (4) Hardness was higher in P added specimens.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part2
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• pp.799-800
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• 2006

Wrought Si-steels are generally used for electromagnetic valves, which are needed good response. To date, Hitachi Powdered Metals Co., Ltd. have produced Fe-Si base sintered magnetic material, EU-52, which shows a magnetic flux density of more than 1.25T at 2000A/m and a maximum permeability of more than 3500. However these magnetic properties are lower than that of wrought Si-steels. Because EU-52 has a low density of $7.2Mg/m^3$. For improving the magnetic properties, it is necessary to increase the density of sintered cores. To increase density, a new mixing method of coating fine Si powders on atomized iron powders was developed, for avoiding the Kirkendall effect. As the result, developed P/M Fe-Si magnetic cores shows higher density of $7.38Mg/m^3$, higher magnetic flux density of 1.48T at 2000A/m and higher maximum permeability of 6800.

• 한국세라믹학회지
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• 제26권3호
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• pp.305-314
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• 1989

Effect of pH variation in starting solution for the making of hydroxyapatite powder was studied in relation to the sinterability of the powder and their mechanical properties of the sintered hydroxyapatite ceramics. The sinterability of hydroxyapatite powder prepared at different pH was found to be improved with increase in pH value of the starting solutions. Thus the powders prepared from the higher pH solutions including 10.5, 11.0 and 11.5 could be well densified almost upto theoretical density by firing for 1 hr at 1,00$0^{\circ}C$. But the powder based on pH 10 exhibited less sinterability even being fired at much higher temperature of 1,10$0^{\circ}C$, it gave only 90-95% of theoretical density. On the other hand the powder prepared on the lowest pH value 9.5 could not be well densified and it could obtain only 78% of theoretical density even by firing at 1,30$0^{\circ}C$ for 1hr. It was found that prismatic crystals of whitlockite were always included in the sintered bodies based on the lower pH values as a minority crystalline phase together with the major crystalline phase of hydroxyapatite and its inclusion might impair the sinterability of powder. However in the case of the higher pH, the powder contained only hydroxyapatite as a crystalline phase on sintering without any minorities. The sphere shape of crystals might help effectively the densification of the bodies. The best mechanical properties could be obtained from the body of pH 11 sintered at 1,10$0^{\circ}C$, which gave 99.5% of theoretical density, 662Kg/$\textrm{mm}^2$ of vickers hardness and 1,352Kg/$\textrm{cm}^2$ of diameteral compression strength.

• 한국분말재료학회지
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• 제27권1호
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• pp.31-36
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• 2020

Phosphorus is an element that plays many important roles in powder metallurgy as an alloy element. The purpose of this study is to investigate the influence of phosphorus addition on the microstructures and mechanical properties of sintered low-alloy steel. The sintered low-alloy steels Fe-0.6%C-3.89%Ni-1.95%Cu-1.40%Mo-xP (x=0, 0.05, 0.10, 0.15, 0.20%) were manufactured by compacting at 700 MPa, sintering in H₂-N₂ at 1260 ℃, rapid cooling, and low-temperature tempering in Ar at 160 ℃. The microstructure, pore, density, hardness, and transverse rupture strength (TRS) of the sintered low-alloy steels were evaluated. The hardness increased as the phosphorus content increased, whereas the density and TRS showed maximum values when the content of P was 0.05%. Based on microstructure observation, the phase of the microstructure changed from bainite to martensite as the content of phosphorus is increased. Hence, the most appropriate addition of phosphorus in this study was 0.05%.