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O

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Microstructure and Properties of Nano-Sized Ni-Fe Alloy Dispersed Al

O

Composites

Seok Namkung, Jae-Young Jeong, Sung-Tag Oh, Jai-Sung Lee, Hong-Jae Lee* and Young-Keun Jeong*

Dept. of Metallurgy and Materials Science, Hanyang University, Ansan 425-791, Korea

*Nano Materials Lab., Korea Institute of Ceramic Engineering and Technology, 233-5 Gasan-Dong, Seoul 153-023, Korea

(Received 23 April 2002 ; Accepted form 4 June 2002)

Abstract - Processing and properties of Al₂O₃ composites with Ni-Fe content of 10 and 15 wt% were investigated.

Homogeneous powder mixtures of Al₂O₃/Ni-Fe alloy were prepared by the solution-chemistry route using Al₂O₃, Ni(NO₃)₂Á6H2O and Fe(NO₃)₃Á9H2O powders. Microstructural observation of composite powder revealed that Ni-Fe alloy particles with a size of 20 nm were homogeneously dispersed on Al₂O₃ powder surfaces. Hot-pressed composites showed enhanced fracture toughness and magnetic response. The properties are discussed based on the observed microstructural characteristics.

Keywords : Nanocomposite, Chemical processing, Fracture toughness, Magnetic property

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of the calcined powder mixture with 10 wt% Ni-Fe and 15 wt% Ni-Fe in the final composite during heat up to 700^oC at a rate of 10^oC/min.

Fig. 2. XRD profiles for powder mixtures of (a) Al₂O₃/10 wt% Ni-Fe and (b) Al₂O₃/15 wt% Ni-Fe, reduced by hydrogen at 700^oC for 1 h ((::) Al2O₃, (00) γ-Ni-Fe).

Fig. 3. TEM micrograph of hydrogen-reduced powder mixture.

Fig. 4. XRD profiles of (a) Al₂O₃/10 wt% Ni-Fe and (b) Al₂O₃/15 wt% Ni-Fe composites, hot-pressed at 1450^oC and 30 MPa for 1 h ((::) Al2O₃, (00) γ-Ni-Fe, (55) FeAl2O₄).

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Ni-Fe and (c) Al₂O₃/15 wt% Ni-Fe composite.

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98% šç~ ç&&ê¢ ¾æÚº ²ÖÚ¢ B–~&

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Table 1. Fracture toughness for Al₂O₃ and Al₂O/Ni-Fe composites.

MPaÁm^1/2

Monolithic Al₂O₃ 3.32±0.18

Al₂O₃/10 wt% Ni-Fe 3.87±0.23 Al₂O₃/15 wt% Ni-Fe 5.26±0.79

Fig. 6. SEM microstructure of Al₂O₃/15 wt% Ni-Fe com- posite. Crack introduced by indentation.

Fig. 7. Room-temperature magnetization versus applied magnetic-field curve for hot-pressed composites.

Table 2. Magnetic saturation and coercive force for each hot-pressed specimens and pure Fe-Ni.

Saturation Magnetization Coercive Force Al₂O₃/10 wt% Ni-Fe 138 emu/g of alloy 16.82 Oe Al₂O₃/15 wt% Ni-Fe 109 emu/g of alloy 6.94 Oe γ-Ni-Fe alloy 140~180 emu/g of alloy 0.1~200 Oe

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