• Title/Summary/Keyword: Metal Powders

Search Result 577, Processing Time 0.026 seconds

Cracking Susceptibility of Laser Cladding Process with Co-Based Metal Matrix Composite Powders (레이저 클래딩 공정 조건이 코발트 합금-텅스텐 카바이드 혼합 코팅층의 균열 발생에 미치는 영향)

  • Lee, Changmin;Park, Hyungkwon;Lee, Changhee
    • Journal of Welding and Joining
    • /
    • v.32 no.6
    • /
    • pp.41-46
    • /
    • 2014
  • In this study, cracking susceptibility of laser cladding was investigated according to the processing parameters such as laser power, scan speed and feeding rate with blended powders of stellite#6 and technolase40s (WC+NiCr). The solidification microstructure of clad was composed of Co-based dendrite structures with ${\gamma}+Cr7C3$ eutectic phases at the dendritic boundaries. The crack propagation showed transgranular fracture along dendritic boundaries due to brittle chrome carbide at the eutectic phases. From results of fractography experiments, the fracture surface was typical cleavage brittle fracture in the clad and substrate. The number of clad cracks, caused by a tensile stress after the solidification, increased with increase of laser power, scan speed and feeding rate. Increase of the laser power caused large pores by facilitating WC decarburizing reaction. And the pores affected increase of crack susceptibility. High scan speed caused increment of clad cracks due to thermal stress and WC particle fractures. Also, increase of the feeding rate accompanied an amount of WC particles causing crack initiation and decarburizing reaction.

Heterogeneous nucleations in the polyol process for the preparation of fine cobalt particles (미립 코발트분말 합성을 위한 polyol공정에서 비균질계 핵생성 반응)

  • 김동진;정헌생;우상덕;이재장;안종관
    • Journal of the Korean Crystal Growth and Crystal Technology
    • /
    • v.12 no.2
    • /
    • pp.73-79
    • /
    • 2002
  • The polyol process which applies to cobalt, nickel. copper and precious metals is a interesting and unexpected example of such a method for preparing uniform metal powders. The reaction proceeds via dissolution, and the polyol acts simultaneously as a solvent, a reducing agent, and to some extent a protective agent. Submicrometer uniform cobalt particles can be obtained by seeding the reactive medium ($AgNO_3$) to achieve a complete substitution of homogeneous by heterogeneous nucleation. By varying the number of nuclei it is possible to control to some extent the average particle size in the submicrometer (0.5$\mu$m) range.

Fabrication of Injection Molded Fe-50%Ni Sintered Bodies (사출성형된 Fe-50%Ni 소결체의 제조)

  • Kim Ki-Hyun;Yoon Hyeong-Chul;Choi Chul-Jin;Lee Byong-Taek
    • Journal of Powder Materials
    • /
    • v.11 no.6 s.47
    • /
    • pp.472-476
    • /
    • 2004
  • The Fe-Ni compact bodies were fabricated using Fe-Ni mixed powders with 50 nm in diameter by injection molding process. The relationship between microstructure and material properties was characterized with respect to the volume ratio of powder/binder and sintering temperature with SEM and TEM. In the compact body having the volume percent ratio of 45(Fe-Ni) : 55(binder), which was sintered at $900^{\circ}C$ the values of relative density and hardness were low about 97.7% and 277.1 Hv, respectively. Using the composition of 50(Fe Ni) : 50(binder) and sintered at $900^{\circ}C$, the values of relative density and hardness were 98.5%, 294.4 Hv, respec-tively. The grain size of sintered bodies strongly depended on the sintering temperature. In both samples sintered at $600^{\circ}C$ and $900^{\circ}C$, the average grain sizes were about 150 nm and 500 nm in diameter, respectively.

Synthesis of Zr-Ti Alloy Powder by Magnesium Reduction (마그네슘환원에 의한 지르코늄-티타늄 합금분말 합성)

  • Lee, Dong-Won;Park, Geun-Tae;Lim, Tae-Soo;Lee, Hye-Moon;Yu, Ji-Hun
    • Journal of Powder Materials
    • /
    • v.18 no.4
    • /
    • pp.359-364
    • /
    • 2011
  • Zr-Ti alloy powders were successfully synthesized by magnesium thermal reduction of metal chlorides. The evaporated and mixed gasses of $ZrCl_4+TiCl_4$ were injected to liquid magnesium and the chloride components were reduced by magnesium leading to the formation of $MgCl_2$. The released Zr and Ti atoms were then condensed to particle forms inside the mixture of liquid magnesium and magnesium chloride, which could be dissolved fully in post process by 1~5% HCl solution at room temperature. By the fraction-control of individually injected $ZrCl_4$ and $TiCl_4$ gasses, the final compositions of produced alloy powders were changed in the ranges of Zr-0 wt.%~20 wt.%Ti and their purity and particle size were about 99.4% and the level of several micrometers, respectively.

Effect of Blending Aids the Magnetic Properties of Anisotropic NdFeB Magnet Prepared by CAPA Process (통전가압법으로 제조한 이방성 NdFeB 영구자석의 자기특성에 미치는 첨가제의 영향)

  • Kim, H.T.;Cho, S.H.;Kim, Y.B.;Kim, H.S.
    • Journal of the Korean Magnetics Society
    • /
    • v.12 no.3
    • /
    • pp.88-93
    • /
    • 2002
  • Rapidly solidified NdFeB powders were mixed with fine powders of pure metal elements before CA-press employed to obtain a fully dense isotropic precursor. Subsequently, the precursor was deformed by CA-deformation to obtain an anisotropic magnet. The CA-deformed anisotropic NdFeB magnets with 0.3 wt.% Zn or Sn exhibited the coercivities about 80% higher (11.4. and 11.2 kOe, respectively) than that (6.4 kOe) of the additive-free magnet.

$MgB_2$ Sheets using Mixture of Mg and B Powders by Powder Roll Compaction (Mg과 B 혼합분말을 이용하여 분말압연 공정으로 제조된 $MgB_2$ 초전도 판재연구)

  • Chung, K.C.;Chang, S.H.;Sinha, B.B.;Kim, J.H.;Dou, S.X.
    • Progress in Superconductivity
    • /
    • v.13 no.3
    • /
    • pp.184-188
    • /
    • 2012
  • $MgB_2$ superconducting sheets have been fabricated by powder rolling method using mixture of Mg and B powders. Sheet-type $MgB_2$ bulk samples of ~10 mm width and 50-100 mm long were squeezed out after compacted by two rotating rolls of 130 mm diameter with gap distance of 0.5 mm and speed of ~40 cm/min (~1 rpm). The nominal composition of Mg, which is ductile metal, was added up to 30% to facilitate forming the $MgB_2$ sheets. The annealed samples at $900^{\circ}C$ and 3 hrs showed superconducting transition temperature of ~32 K and critical current densities at zero fields were ${\sim}10^5A/cm^2$ at 5 K and ${\sim}5{\times}10^4A/cm^2$ at 20 K.

Improvement of $CO_2$Decomposition by Impregnating Noble Metals to Nano-size (Ni, Zn)-ferrites (귀금속 첨가에 의한 나노 (Ni, Zn)-페라이트의 $CO_2$분해 향상)

  • Kim, Jeong-Sik;An, Jeong-Ryul;Gang, Gye-Myeong
    • Korean Journal of Materials Research
    • /
    • v.11 no.10
    • /
    • pp.846-850
    • /
    • 2001
  • In the present study, nano-size powders of ternary ferrites, $Ni_{0.5}Zn_{0.5}Fe_2O_4$, as the potential catalysts of $CO_2$decomposition, were prepared by the wet processing of hydrothermal synthesis and coprecipitation method, and the catalyzing effects of impregnation of the noble metals, Pt and Pd, onto $Ni_{0.5}Zn_{0.5}Fe_2O_4$for the $CO_2$decomposition were investigated. XRD results of the synthesized ferrites showed a typical spinel structure of ferrite and the particle size was very small as about 6~10 nm. BET surface area of the ternary ferrites was not affected by the impregnation of Pt and Pd. The reactivity of the $CO_2$decomposition to carbon was improved by the impregnation of the noble metals of Pd and Pt. The effect of Pd-impregnation on the $CO_2$decomposition rate was higher than Pt-impregnation.

  • PDF

Effect of Magnesium Oxide on the Nitridation of Silicon Compact. (규소의 질화반응에 있어 산화마그네시움의 효과)

  • 박금철;최상원
    • Journal of the Korean Ceramic Society
    • /
    • v.20 no.4
    • /
    • pp.305-314
    • /
    • 1983
  • In order to enhance the rate of th nitridation and to give the high density of reaction-bonded silicon nitride MgO powder as nitriding aid were added to silicon powders and the mixture was pressed isostatically into compacts which were nitrided in the furnace of 1, 35$0^{\circ}C$ where 95% $N_2$-5% $H_2$ gases were flowing. As the other nitriding aid $Mg(NO_3)_2 6H_2O$ was selected, A slip made of magnesium nitrate solution and fine silicon particles was spray-dried and then decomposed at 30$0^{\circ}C$. Magnesium oxide-coated silicon powders were formed into compacts prior to the nitridation on the same condition as the former. Magnesium nitrate (MgO, produced from the decomposition of magnesium nitrate) was more effective for the formation of the $\beta$-phase in the initial stage of the nitridation probably due to the easy formation of $MgO-SiO_2$-metal oxide eutectic melt. It has been confirmed that forsterite was formed as a result of the reaction between MgO and $SiO_2$ film of silicon surface. It was considered that MgO produced from magnesium nitrate may be finer more reactive and more uniformly distributed on the surface of silicon particles than original MgO. The higher the forming pressure was the more the $\beta$-phase was formed.

  • PDF

Application of an electroless copper coating in alkaline bath to preparation of the metal hydride electrode (금속 수소화물 전극제조에 있어서 알카리 무전해 구리 도금법의 응용)

  • CHOI, Jeon;PARK, Choong-Nyeon
    • Transactions of the Korean hydrogen and new energy society
    • /
    • v.3 no.2
    • /
    • pp.9-15
    • /
    • 1992
  • Electroless copper plating method using an alkaline bath have been employed in copper coating of the (LM)Ni4.5Co0.1MnO.2A10.2 hydrogen storage alloy powders for electrode preparation. The plating were conducted without any pretreatment of alloy powders. For the preparation of the electrodes, about 0.12g of the copper coated alloy powder (copper to alloy ratio 1/3 by weight) was compacted with pressure of 6 tons/cm2 at room temperature. The disk-type compacts had a diameter of 10mm and thickness of about 0.24mm. The electrode characteristics were examined through SEM observations and electrochemical measurements in a half cell. The electrochemical measurement showed that the maximum discharge capacity of the electrodes prepared by using alkaline bath were 245mAh per gram of coated alloy (327mAh per gram of alloy) and appeared a considerable degradation with increasing number of cycles. The decrease of the discharge capacity after 100 cycles was about 30% It can be suggested that, with a slight of improvement, this electroless copper plating method could be applied to the preparation of the rare earth-nickel based alloy electrode.

  • PDF

Selective Laser Sintering of Co-Cr Alloy Powders and Sintered Products Properties

  • Dong-Wan Lee;Minh-Thuyet Nguyen;Jin-Chun Kim
    • Journal of Powder Materials
    • /
    • v.30 no.1
    • /
    • pp.7-12
    • /
    • 2023
  • Metal-additive manufacturing techniques, such as selective laser sintering (SLS), are increasingly utilized for new biomaterials, such as cobalt-chrome (Co-Cr). In this study, Co-Cr gas-atomized powders are used as charge materials for the SLS process. The aim is to understand the consolidation of Co-Cr alloy powder and characterization of samples sintered using SLS under various conditions. The results clearly suggest that besides the matrix phase, the second phase, which is attributed to pores and oxidation particles, is observed in the sintered specimens. The as-built samples exhibit completely different microstructural features compared with the casting or wrought products reported in the literature. The microstructure reveals melt pools, which represent the characteristics of the scanning direction, in particular, or of the SLS conditions, in general. It also exposes extremely fine grain sizes inside the melt pools, resulting in an enhancement in the hardness of the as-built products. Thus, the hardness values of the samples prepared by SLS under all parameter conditions used in this study are evidently higher than those of the casting products.