초청논문 : 원자력 산업에서의 분말야금

박원구 ( W . K . Park ) 대한금속재료학회 ( 구 대한금속학회 ) 1992 분말야금 Vol.4 No.-

미소 비커스 압입균열에 의한 초경합금의 파괴 인성치 측정

이억섭(O. S. Lee),손인수(I. S. Son),홍성경(S. K. Hong),박원구(W. K. Park),황선근(S. K. Hwang) Korean Society for Precision Engineering 1995 한국정밀공학회지 Vol.12 No.2

TiB2/TiAl 계 금속간화합물기 복합재료의 in-situ 합성에 관한 연구

박원구,황선근,이태원,이지환 대한금속재료학회(대한금속학회) 1996 대한금속·재료학회지 Vol.34 No.7

This study was focused to examine fabrication process of TiB₂ particle reinforced TiAl based intermetallic composites by reactive synthesis. The mixed powders were canned, hot-pressed under vacuum and then hot-extruded at 420℃ under extrusion ratio of 15:1. Subsequently. reactive synthesis was carried out at 700℃ under vacuum Thermal analysis has been perfomed to investigate the ignition temperature and combustion temperature for Ti-Al system and Ti-Al-B system. The combustion temperature of Ti-Al-B powder mixture was found to be higher than that of Ti-Al powder mixture. The Ti-Al-B powder mixture was reacted exothermically to form the material consisting of TiAl and TiB₂. The tensile strength of the TiB₂/TiAl composites was proved to be higher than that of the matrix. Swelling phenomenon, resulting from formation of a large amount of pores was observed at all reactive synthesis conditions.

TiAl 계 금속간화합물의 반응합성온도에 미치는 압출과 승온속도의 영향

박원구,황선근,김석준,이태원,이지환 대한금속재료학회(대한금속학회) 1995 대한금속·재료학회지 Vol.33 No.10

This paper was focused to investigate the effect of extrusion and heating rate on the reactive synthesis and the microstructure of products formed by reactive synthesis. The mixing of elemental powders was carried out by V-blender. The mixed powders were canned, sealed under vacuum, and were hot extruded at 450℃ under extrusion ratio 20 : 1. For powder extruded and cold compacted specimens, thermal analysis have been performed. In the effect of extrusion, the ignition temperature(T₁) of extruded specimens was found to be lower than that of cold compacted specimens. This may be due to breakdown of aluminium oxide films and elongation of mixed powders by hot plastic-deformation. In the effect of heating rate, both ignition temperature(T₁) and combustion temperature(T_c) was found to be increased with increasing heating rate. In particular, the ignition temperature of extruded specimens was below the melting temperature of aluminium under the heating rate of 40℃/min. Also, phase of reaction products depended upon combustion temperature. Microstructure of reaction products consists of unreacted titanium, TiAl and Ti₃Al. However, unreacted titanium was not observed after heat treatment.

WC-0.8SiC-10Ni 초경합금의 제조 및 기계적 성질의 연구

박원구,이억섭,황선근,김영도 대한금속재료학회(대한금속학회) 1996 대한금속·재료학회지 Vol.34 No.8

Effects of the amounts of SiC coating on the properties of WC-SiC-Ni cemented carbide were investigated. A highly condensed sintered material with a theoretical density higher than 98% was obtained for SiC with 0.8w/o when W powders coated with SiO2 were carburized at 1450℃ and SiC coated WC was sintered with Ni. The particle size of W C powders in this sintered material was about 0.9 ㎛ and very uniform. The Vickers hardness was measured to be as high as 1760 ㎏/㎟. Transeverse Rupture Strength (TRS) to be 338 ㎏/㎟. These good properties of the cemented carbide were able to be obtained by forming a condensed SiC layer for SiC of 0.8w/o which enhanced the interface reaction of the carbide with Ni and thus by inhibiting WC particle growth, making the particle size uniform, and making the sintered material condensed.

UO2 소결체의 열적 고밀화에 관한 연구

박원구,이종남,이규암 대한금속재료학회(대한금속학회) 1977 대한금속·재료학회지 Vol.15 No.5

UO₂ 소결체의 열적 고밀화에 미치는 영향을 규명하기 위하여 재소결과정에 있어서의 기공의 크기와 그 분포 상태의 변화를 조사하였다. 휘발성 첨가제인 polyethylene glycol 1 weight percentage을 40μ-125μ의 범위로 분류하여 UO₂분말에 건식 혼합하여 제조한 92-96%의 이론밀도(theoretical density)를 지닌 UO₂ 소결체를 1600℃에서 10시간 동안 혼합가스(98.5N₂-1.5N₂) 분위기 내에서 재소결 결과, 2㎛ 이하의 미세기공 조직을 지닌 소결체의 경우 밀도 변화율(Δρ/ρ)은 12.3×10^(-3)인 반면, 40㎛의 조대한 기공이 존재하는 소결체의 경우 밀도 변화율이 가장 낮은 값인 Δρ/ρ=6.0×10^(-3)을 보였다. 본 실험결과 2㎛ 이하의 미세기공 조직은 열적 고밀화 현상이 크고 평균 40㎛이상의 조대한 기공조직은 안정하다는 것이 나타났다. The thermal densification of the sintered UO₂ pellets has been investigated by resintering of them in the terms of variations of pore size and pore size distribution. The pore size and its distribution of presintered pellets were controlled by the addition of 1 weight percentage polyethylene glycol sized in the range of 40-125㎛ as a volatile pore former. The density of the pellets were in the range of 92 to 96% of theoretical density. A review of resintering experiments at 1600℃ for 10 hours in the 98.5 v/o N₂-1.5 v/o H₂ mixed gas indicated that the pellet containing large pores with diameter of 40㎛ had the lowest fractional density change of 6.0×10^(-3), while that of 12.34×10^(-3) had been revealed in the pellet containing finer pores than 2㎛. The observations led to the conclusion that high thermal stability was achieved by forming large pores of around 40㎛ in the pellets and high densification was induced by small pores approximately less than 2㎛.

UO2 의 저온소결에 있어서 산소의 영향

박원구,김한수,이준노 대한금속재료학회(대한금속학회) 1981 대한금속·재료학회지 Vol.19 No.10

Taking notice of the accelerating effect of oxygen on sintering of UO₂, this study was undertaken to investigate effects on sintering characteristics of slightly oxidizing atmospheres with use of CO₂/CO mixed gas and other sintering conditions. When the sintering atmosphere for UO₂powder is made slightly oxidizing by adjusting the CO₂/CO ratio of the mixed gas, the sintering temperature can be lowered as much as 600℃ or more in comparison with sintering under the conventional reducing atmosphere. Sintered pellets having the O/U ratio of 2.01 can be readily obtained by reducing at 1100℃ for one hour pellets sintered under a slightly oxidizing atmosphere. Sintered pellets having the density of 96% of the theoretical density can be readily obtained by sintering for a short period under a slightly oxidizing atmosphere followed by a reducing treatment.

주철에 있어서의 흑연구상화 기구에 관한 연구 (3)

박원구,이재선,최형섭 대한금속재료학회(대한금속학회) 1965 대한금속·재료학회지 Vol.3 No.1

The melting of Fe·C, Fe·C·Zr and Fe·C·Ca alloys in graphite crucible placed in vacuum was carried out at 1540℃, and then cooled down with the rate of 35℃/sec or more. To eliminate from the problems as many composition variables as possible, the samples used in these experiments consisted simply of pure iron and reactor grade graphite with pure nodulizing element. The results show that under these relatively simple and limited conditions, nodular graphite is produced by the addition of strong deoxidizing agent such as Zr or Ca in the critical concentration. This suggests that the spheroidization of graphite in the cast iron may partially be attributed to the deoxidation of the iron which may induce the supercooling of the melt. The experimental results also indicate that the spheroidizing tendency of graphite in cast iron was increased by rapid cooling and thereby higher degree of supercooling or supersaturation of the carbon in the melt or both. These factors, however, were aidding the improvement of the spheroidization of graphite but not decisive in the formation of nodular graphite. The most favourable factor seemed to be the increase of the interfacial energy between the liquid iron and graphite surface due to the adsorbtion of nodulizing element on the graphite surface.

베릴륨 박막 용가재에 의한 Zircaloy 튜브 brazing 효과

박원구,정성훈 대한금속재료학회(대한금속학회) 1981 대한금속·재료학회지 Vol.19 No.12

In joining spacers and pads on the cladding tube of the Candu type nuclear fuel pin, brazing is employed with a filler metal of Be. It is well known that the mechanical properties of the joint depends significantly on the thickness of the filler metal as well as on the brazing time and temperature. In the present study, it was attempted to find the optimum thickness of the filler metal which could give a good joint between thin Zr-4 tube and the spacer. Furthermore, the corrosion rate of the brazed area was examined in conjunction with the microstructures of the brazed zone. Brazing was carried out by induction heating for 20 seconds at 1000℃-1040℃ which is just above the eutectic point of α-Zr-ZrBe₂, the best result was obtained with the thickness of the filler metal in the range of 8-10 ㎛, where the joint strength was 20㎏/㎟. The basket weave structure was observed in the heat affected zone in brazing. The corrosion rate of this area was lower than that of the annealed structure.

우라늄기 알루미늄 합금에서 변태 및 조직변화에 미치는 냉각 속도의 영향

박원구,정성훈,홍종휘 대한금속재료학회(대한금속학회) 1976 대한금속·재료학회지 Vol.14 No.5

순수 우라늄 및 순수 우라늄에 알루미늄을 각각 650ppm, 1500ppm 첨가하였을 때 냉각 속도에 따른 변태온도의 변화, 현미경 조직, 미소경도를 조사하였다. 알루미늄 첨가는 우라늄의 γ→β, β→α 변태온도를 낮추었다. 변태온도가 낮아지는 정도는 냉각속도가 커짐에 따라 또 알루미늄 양이 증가함에 따라 커졌다. 냉각속도가 커짐에 따라 입자 크기는 감소했고 합금의 경우 큰 냉각속도에서는 넓은 침상조직을 나타냈다. 합금에서는 입내와 입계에서 UAI₂의 석출물을 볼 수 있었다. 석출물의 크기는 냉각속도가 커짐에 따라 감소했다. 냉각속도가 클수록 알루미늄의 첨가량이 많을수록 경도는 증가했다. 경도의 증가는 석출물의 크기와 martensite 변태로 인한 lattice hardening에 기인된 것으로 생각된다. The effect of cooling rate on transformation temperature, microstructures and microhardness of pure uranium and U-(650, 1500 ppm) Al alloy s was investigated. It was found that the transformation temperatures of both gamma-to-beta and beta-to-alpha decreased with the increase of the aluminum contents. The degree of the lowering of the transformation temperature was increased as the aluminum contents and cooling rate were increased. Grain size was decreased with increasing the cooling rate. An feathery or accicular structures were obtained when aluminum added alloys were severely cooled from gamma range. The precipitates of UAI₂ appeared with in grains or on the grain boundaries of alloys. The size of the precipitates decreased with the increase of the cooling rate. Microhardness measurement showed that hardness increases as the alumiunm contents and coding rate were increased. The increase of the hardness is supposed to be resulted from the size of precipitation arid lattice hardening due to the martensite transformation.