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Densification Behavior and Magnetic Properties of Fe-2%Ni Sintered Compact Fabricated by Metal Injection Molding

사출성형법에 의해 제작된 Fe-2%Ni연자성 소결체의 소결 및 자기적 특성

  • Lim, Tae-Hwan (Department of Advenced Materials Engineering, Sunmoon University)
  • 임태환 (선문대학교 신소재공학과)
  • Received : 2018.08.23
  • Accepted : 2019.01.04
  • Published : 2019.01.31

Abstract

3 kinds of fine powder, Fe-2%Ni alloy powder(N Ltd.) and Fe+2%Ni mixed powder(B Ltd. and S Ltd.), were fabricated into sintered compacts of bending strength specimens and ring type specimens by metal injection molding, debinding and controlling sintering conditions (reduction and sintering atmospheres, sintering temperature, sintering time and cooling rates). Density and magnetic properties of the sintered compacts were evaluated with the following conclusions. (1) When each compact was hold at 1123K for 3.6ks in H2 and sintered at 1623K for 14.4ks in Ar, the density of N, B and S Ltd.'s sintered compacts were measured as 96, 99 and 99%, and oxygen/carbon contents were measured as 0.0041%O/0.0006%C, 0.0027%O/0.0022%C, and 0.160%O/0.0026%C, respectively. (2) Magnetic characteristics of B Ltd. compact in Ar with the best results showed $B_{25}=14.3KG$, $B_r=7.75KG$, and $H_c=2.1Oe$, but not enough as those made by melting process. (3) Magnetic properties of B Ltd. compact which were sintered at 1673K for 14.4ks in Ar gas, and cooled at $0.83Ks^{-1}$ to 1123K and then cooled at $0.083Ks^{-1}$ down to room temperature were measured as $B_{25}=14.8KG$, $B_r=8.3KG$, and $H_c=1.3Oe$, almost similar to those made by melting process. Objected soft magnetic materials properties were obtained through sintering process by controlling sintering conditions (reduction condition, sintering atmosphere, sintering temperature and sintering time) and cooling rates.

미립의 3종류 Fe-2%Ni합금 분말(N사), Fe+2%Ni혼합 분말(B사 및 S사)을 항절력 시험편 및 링(ring)형상의 시험편으로 사출 성형, 탈지, 소결 조건(환원 및 소결 분위기, 소결 온도, 소결시간, 냉각속도)을 변화시켜 소결체를 제작하였다. 얻어진 소결체에 대하여는 소결체의 밀도 및 자기적 특성을 평가하여 다음과 같은 결론을 얻었다. (1) 탈지한 각 성형체를 수소 중에서 $1123K{\times}3.6ks$유지하고, Ar중에서 $1623K{\times}14.4ks$로 소결할 경우 N(사), B(사), S(사)소결체의 밀도는 각각 96, 99, 99%로 나타났고, 소결체의 산소 탄소량은 각각 0.0041%O, 0.0006%C, 0.0027%O, 0.0022%C, 0.160%O, 0.0026%C의 값을 나타내었다. (2) 위에의 결과로부터 보면 B(사)의 소결체가 가장 우수한 결과를 나타내므로 B(사)의 Ar중 소결체에 대하여 자기적 특성을 조사한 결과, $B_{25}=14.3KG$, $B_r=7.75KG$, $H_c=2.1Oe$로 용해해서 만든 제품의 값에는 미치지 못했다. (3) B(사)의 성형체를 Ar가스 중에서 $1673K{\times}14.4ks$로 소결 후 1123K까지는 $0.83Ks^{-1}$로 냉각하고 1123K부터 실온까지는 $0.083Ks^{-1}$로 냉각한 소결체의 자기적 특성은 $B_{25}=14.8KG$, $B_r=8.3KG$, $H_c=1.3Oe$로 용해해서 만든 제품의 값과 거의 동일한 값을 얻었다. 이상, 소결 조건 제어(환원조건, 소결분위기, 소결온도, 소결시간) 및 냉각속도 제어를 통한 소결 공정으로 목적하는 연자성 재료특성을 얻었다.

Keywords

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Fig. 1. Effects of sintering(reduction) temperature on the oxygen and carbon content of vacuum-sintered compacts.

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Fig. 2. Effects of sintering(reduction) temperature on the oxygen and carbon content of sintered compacts in H2 gas.

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Fig. 3. Effects of sintering temperature on the relative density of sintered compact(Ds) in H2 gas.

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Fig. 4. Effects of sintering temperature, sintering time on the relative density of sintered compacts in H2 gas.

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Fig. 5. Effects of sintering time on the oxygen and carbon content of sintered compacts in H2 gas. white marker: oxygen, black marker: carbon.

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Fig. 6. Effects of sintering temperature, sintering time on the relative density of sintered compacts in Ar after H2 gas reduction.

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Fig. 7. Effects of sintering temperature on oxygen and carbon content of sintered compacts in Ar after H2 gas reduction. white marker: oxygen, black marker: carbon.

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Fig. 8. Typical microstructures of Fe+2%Ni(B Ltd) mixed compact hold at 1123K for 3.6ks in H2 gas and sintered at 1623K for 14.4ks in Ar gas.

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Fig. 9. Typical microstructures of B Ltd Sintered Compacts controlled by furnace cooling and cooling rate. (a) Ar, Ts=1673K, ts=14.4ks ⇨ R.T, furnace cooling. (b) Ar, Ts=1673K, ts=14.4ks ⇨ Tc=1123K ⇨ R.T. Tc=1123K ⇨ R.T, cooling rate control(0.083Ks-1).

Table 1. Magnetic properties of B Ltd sintered compact according to cooling conditions

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