• 한국해양공학회지
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• 제13권4호통권35호
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• pp.37-44
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• 1999

Hardness characteristics and microstructures of $Nb/MoSi_2$ laminate composites were evaluated from the variation of fabricating conditions such as preparation temperature, applied pressure and pressure holding time. $Nb/MoSi_2$ laminate composites composed of $MoSi_2$ powder and Nb sheets were fabricated by the hot press. From experimental results, it was found that the lamination from Nb sheet and $MoSi_2$ powder was an excellent strategy to improve hardness characteristics of monolithic $MoSi_2$. However, interfacial reaction products like(Nb, Mo)$SiO_2\;and\;Nb2Si_3$ formed at the interface of $Nb/MoSi_2$ and increased with fabricating temperature.

• 대한기계학회논문집A
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• 제27권7호
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• pp.1132-1137
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• 2003

This study dealt with the suppression of interfacial reaction between Nb and MoSi$_2$ for the fabrication of high toughness Nb/MoSi$_2$ laminate composites, based on the results of a thermodynamical estimation. Especially, the effect of ZrO$_2$ particle on the interfacial reaction of Nb/MoSi$_2$ bonding materials has been examined. Nb/MoSi$_2$ bonding materials have been successfully fabricated by alternatively stacking matrix mixtures and Nb sheets and hot pressing in the graphite mould. The addition of ZrO$_2$ particle to MoSi$_2$ matrix is obviously effective for promoting both the interfacial reaction suppression and the sintered density of Nb/MoSi$_2$ bonding materials, since it is caused by the formation of ZrSiO$_4$ in the MoSi$_2$-ZrO$_2$ matrix mixture. The interfacial shear strength of Nb/MoSi$_2$ bonding materials also decreases with the reduction of interfacial reaction layer associated with the content of ZrO$_2$ particle and the fabrication temperature.

• 대한기계학회논문집A
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• 제26권6호
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• pp.1047-1052
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• 2002

The impact value, the interfacial shear strength, the tensile strength and the fracture strain of Nb/MoSi$_2$laminate composites, which were associated with the interfacial reaction layer, have been investigated. Three types of Nb/MoSi$_2$ laminate composites alternating sintered MoSi$_2$ layers and Nb foils were fabricated as the parameter of hot press temperature. The thickness of interfacial reaction layer of Nb/MoSi$_2$ laminate composites increased with increasing the fabrication temperature. The growth of interfacial reaction layer increased the interfacial shear strength and led to the decrease of impact value in Nb/MoSi$_2$ laminate composites. It was also found that in order to maximize the fracture energy of Nb/MoSi$_2$ laminate composites, interfacial shear strength and the thickness of interfacial reaction layer must be secured appropriately.

• Journal of Mechanical Science and Technology
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• 제14권8호
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• pp.830-835
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• 2000

The thermodynamical estimation of the interfacial reaction and the impact properties of $Nb/MoSi_2$ laminate composites containing SiC, $NbSi_2$ or $ZrO_2$ particles are investigated. Laminate composites, which comprise alternating layers of $MoSi_2$ with the particle and Nb foil, were fabricated by the hot press process. It is clearly found out that the interfacial reaction of $Nb/MoSi_2$ can be controlled by the addition of $ZrO_2$ particle to the $MoSi_2$ phase. The addition of $ZrO_2$ particle increases both the impact value and the sintered density of Nb/McSij, The suppression of the interfacial reaction is caused by the formation of $ZrSiO_2$ in $MoSi_2-ZrO_2$ matrix mixture.

• 한국재료학회지
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• 제24권4호
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• pp.180-185
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• 2014

The current concern about these materials ($MoSi_2$ and $NbSi_2$) focuses on their low fracture toughness below the ductile-brittle transition temperature. To improve the mechanical properties of these materials, the fabrication of nanostructured and composite materials has been found to be effective. Nanomaterials frequently possess high strength, high hardness, excellent ductility and toughness, and more attention is being paid to their potential application. In this study, nanopowders of Mo, Nb, and Si were fabricated by high-energy ball milling. A dense nanostructured $MoSi_2-NbSi_2$ composite was simultaneously synthesized and sintered within two minutes by high-frequency induction heating method using mechanically activated powders of Mo, Nb, and Si. The high-density $MoSi_2-NbSi_2$ composite was produced under simultaneous application of 80MPa pressure and an induced current. The sintering behavior, mechanical properties, and microstructure of the composite were investigated. The average hardness and fracture toughness values obtained were $1180kg/mm^2$ and $3MPa{\cdot}m^{1/2}$, respectively. These fracture toughness and hardness values of the nanostructured $MoSi_2-NbSi_2$ composite are higher than those of monolithic $MoSi_2$ or $NbSi_2$.

• 한국해양공학회지
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• 제25권4호
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• pp.66-71
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• 2011

The flexural strength of $MoSi_2$ based composites reinforced with Nb sheets has been investigated, based on the detailed examination of their microstructure and fractured surface. Both sintered density and porosity of Nb/$MoSi_2$ composites were also examined. Nb/$MoSi_2$ composites were fabricated by different conditions such as temperature, applied pressure and its holding time, using a hot-press device. The volume fraction of Nb sheet in this composite system was fixed as 10%. The characterization of Nb/$MoSi_2$ composites were investigated by means of optical microscopy, scanning electron microscope and three point bending test. Nb/$MoSi_2$ composites represented a dense morphology at the interfacial region, accompanying the creation of two types of reaction layer by the chemical reaction of Nb and $MoSi_2$. Nb/$MoSi_2$ composites possessed an excellent density at the fabricating temperature of $1350^{\circ}C$, corresponded to about 95% of theoretical density. The flexural strength of Nb/$MoSi_2$ romposites were greatly affected by the pressure holding time at the same fabricating temperature, owing to the large suppression of porosity in the microstructure. Especially, Nb/$MoSi_2$ composites represented a good flexural strength of about 310 MPa at the fabricating condition of $1350^{\circ}C$, 30MPa and 60min, accompanying the pseudo-ductile fracture behavior by the deformation of Nb sheet and the interfacial delamination.

• International Journal of Ocean Engineering and Technology Speciallssue:Selected Papers
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• 제3권1호
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• pp.35-39
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• 2000

The present study dealt with the relationships among the interfacial shear strength, the thickness of interfacial reaction layer and the impact value of $Nb/MoSi_2$ laminate composites. In addition, the tensile test was conducted to evaluate the fracture strain of $Nb/MoSi_2$ laminate composites. To change the thickness of the reaction layer, $Nb/MoSi_2$ laminate composites alternating sintered MoSi2 layers and Nb foils were fabricated as the parameter of hot press temperature. It has been found that the growth of the reaction layer increases the interfacial shear strength and decreases the impact value by localizing a plastic deformation of Nb foil. There also exist appropriate shear strength and the thickness of the reaction layer, which are capable of maximizing the fracture energy of $Nb/MoSi_2$.

• 한국해양공학회지
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• 제16권6호
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• pp.60-64
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• 2002

This paper describes the machining characteristics of the MoSi$_2$--based composites through the process of electric discharge drilling with various tubular electrodes. In addition to hardness characteristics, microstructures of Nb/MoSi$_2$laminate composites were evaluated from the variation of fabricating conditions, such as preparation temperature, applied pressure, and pressure holding time. MoSi$_2$-based composites have been developed in new materials for jet engines of supersonic-speed airplanes and gas turbines for high-temperature generators. These high performance engines may require new hard materials with high strength and high temperature-resistance. Also, with the exception of grinding, traditional machining methods are not applicable to these new materials. Electric discharge machining (EDM) is a thermal process that utilizes a spark discharge to melt a conductive material. The tool electrode is almost -unloaded, because there is n direct contact between the tool electrode and the work piece. By combining a non-conducting ceramic with more conducting ceramic, it was possible to raise the electrical conductivity. From experimental results, it was found that the lamination from Nb sheet and MoSi$_2$ powder was an excellent strategy to improve hardness characteristics of monolithic MoSi$_2$. However, interfacial reaction products, like (Nb, Mo)SiO$_2$and Nb$_2$Si$_3$formed at the interface of Nb/MoSi$_2$, and increased with fabricating temperature. MoSi$_2$composites, with which a hole drilling was not possible through the conventional machining process, enhanced the capacity of ED-drilling by adding MbSi$_2$, relative to that of SiC or ZrO$_2$reinforcements.

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2002년도 춘계학술대회 논문집
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• pp.29-34
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• 2002

[ $Nb/MoSi_2-ZrO_2$ ] laminate composites have been successfully fabricated by alternately stacking $MoSi_2-ZrO_2$ powder layer and Nb sheet, followed by hot pressing in a graphite mould. The fabricating parameters were selected as hot press temperatures. The instrumented Charpy impact test was carried out at the room temperature in order to investigate the relationship between impact properties and fabricating temperatures. The interfacial shear strength between $MoSi_2-ZrO_2$ and Nb, which is associated with the fabricating temperature and the growth of interfacial reaction layer, is also discussed. The plastic deformation of Nb sheet and the interfacial delamination were macroscopically observed. The $Nb/MoSi_2-ZrO_2$ laminate composites had the maximum impact value when fabricated at 1623K, accompanying the increase of fracture displacement and crack propagation energy. The interfacial shear strength of $Nb/MoSi_2-ZrO_2$ laminate composites increased with the growth of interfacial reaction layer, which resulted from the increase of fabricating temperature. there is an appropriate interfacial shear strength for the enhancement of impact value of $Nb/MoSi_2-ZrO_2$ laminate composites. A large increase of interfacial shear strength restrains the plastic deformation of Nb sheet.

• 한국자기학회지
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• 제10권6호
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• pp.269-273
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• 2000

Fe-l7Cr-2M(M=Si, Nb, Mo)합금분말을 Electrode Rotating Atomizer로 제조한 후 성형하여 소결한 시편의 첨가원소, 성형 압력 및 소결온도 에 따른 교류자기특성의 변화를 체계적으로 조사하였다 제조된 Fe-l7Cr-2M(M=Si, Nb, Mo) 합금분말의 형상은 구형이며, 포화자화값은 Mo와 Nb을 첨가한 Fe-l7Cr-2Mo과 Fe-l7Cr-Nb의 경우 약 155 emu/g로 Si을 첨가한 경우보다 크다. 성형압력 12 ton/$cm^2$, 소결온도 1200 $^{\circ}C$에서 제조된 Fe-l7Cr-2M(M=Si, Nb, Mo)합금분말 소결체의 진폭비 투자율은 주파수, f=1 kHz에서 3~5 Oe의 인가자장 범위에서 가장 크다. 전력손실은 인가자장 H$_{a}$ =5 Oe, 주파수 f=1 kHz에서 Fe-l7Cr-2Nb 경우 40 mW/cc로 Si이나 Mo를 첨가한 경우 보다 약 1/2값을 나타낸다.