• 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 $NbSi_2$.

• 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.

• 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.

• 한국분말재료학회지
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• 제15권4호
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• pp.279-284
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• 2008

Dense nanostructured $NbSi_2$ was synthesized by high-frequency induction-heated combustion synthesis (HFIHCS) method within 1 minute in one step from mechanically activated Nb and Si powders. Highly dense $NbSi_2$ with relative density of up to 99% was simultaneously synthesized and consolidated under the combined effects of an induced current and mechanical pressure of 60 MPa. The average grain size and mechanical properties (hardness and fracture toughness) of the compound were investigated.

• 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.

• 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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• 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.

• 대한금속재료학회지
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• 제49권2호
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• pp.121-127
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• 2011

The mechanical properties of the various heat treatment conditions on Ti-15Mo-3Nb-3Al-0.2Si alloy plates were examined. XRD patterns from the surface of Ti-15Mo-3Nb-3Al-0.2Si were analyzed as a solution-treated Ti alloy has the single-phase ${\beta}$ structure whereas the aged Ti alloys have the ${\beta}$ matrix embedded with ${\alpha}$ needles. High strength (~1500 MPa) with decent ductility (7%) was obtained by the Ti alloy double aged at $300^{\circ}C$ and $520^{\circ}C$ for 8 hours each. The double-aged alloy exhibits the finer structure than the single-aged alloy at $300^{\circ}C$ for 8 hours because of the higher nucleation rate of ${\alpha}$ needles at an initial low aging temperature ($320^{\circ}C$). TEM observation revealed that the fine nanostructure with ${\alpha}$ needles in the ${\beta}$ matrix ensured the excellent mechanical properties in the double aged Ti-15Mo-3Nb-3Al-0.2Si alloy. In the solution treated alloy, the yield drop, stress-serrations and the ductility minimum typically associated with dynamic strain aging can be attributed to the dynamic interaction between dislocations and oxygen atoms. The yield drop and the stress serration were not observed in aged samples because the geometrically introduced dislocations due to phase precipitates suppressed the dynamic strain aging.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2005년도 추계학술강연 및 발표대회강연 및 발표논문 초록집
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• pp.68-69
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• 2005

• 한국분말재료학회지
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• 제13권6호
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• pp.408-414
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• 2006

[ $MoSi_2$ ] alloys with Al, B or Nb were prepared by an advanced consolidation process that combined mechanical alloying with pulse discharge sintering (complex forming) to improve the mechanical properties. Their microstructure and mechanical properties were investigated. The $MoSi_2$ alloys fabricated by complex forming method showed very fine microstructure when compared with the sample sintered from commercial $MoSi_2$ powders. Alloys made from powders milled in Ar gas had fewer silica or alumina phases as compared to their counterparts sintered from powders milled in air. In densification of the sintered body, addition of B was more effective than Al or Nb. Both Victors hardness and tensile test indicated that the alloy fabricated by the complex forming method showed better properties than the sample sintered from commercial $MoSi_2$ powders. The Al added alloy sintered from the powders milled in air had the superior mechanical properties due to the suppression of $SiO_2$ and formation of fine $Al_2O_3$ particles.