기계적 합금화에 의한 (V, Fe)-N계 비정질 합금의 제조 및 구조변화
Mechanical alloying effect and structural observation of (V, Fe)-N amorphous alloy powders
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본 연구에서는 기계적 합금화(MA)에 의한 고상-기상반응에 있어서 질소원자가 V-Fe계 합금의 비정질화에 미치 는 영향을 조사하였다. 유성형 볼밀을 사용하여 V70Fe30 혼합분말을 질소가스 분위기 중 MA 처리하였다. 그 결과 160시간 MA 처리에 의하여 비정질상이 생성됨을 알 수 있었다. 160시간 동안 MA 처리한 (V70Fe30)0.89N0.11 분말시료의 열분석 결과 약 600oC에 비정질상의 결정화에 의한 발열 peak가 관찰되었다. 또한 bcc 결정에서 비정질상으로의 구조변화 과정을 X선 및 중성자 회절법을 통하여 조사하였으며, 특히 중성자회절에서는 V원자의 중성자에 대한 간섭성 핵산란진폭이 매우 작은 특징을 이용하였다. 그 결과, 이 합금계에서의 비정질화는 모든 결정구조에서 전형적으로 존재하는 8면체 unit가 우선적으 로 붕괴되어 4면체 unit로 변환되어 가는 과정임을 알 수 있었다. 또한 중성자 회절에 의한 구조해석 결과 질소원자는 V원 자로 이루어진 다면체의 중심에 위치하고 있음을 알 수 있었다.
Abstract
In this study, we investigated the effect of a nitrogen atom on the amorphization of V-Fe alloy through solid-gas reaction during mechanical alloying (MA). MA by planetary ball mill of V70Fe30 elemental powders was carried out under the nitrogen gas atmosphere. Amorphization has been observed after 160 hours of ball milling in this case. The DSC spectrum for the mechanically alloyed (V70Fe30)0.89N0.11 powders exhibits a sharp exothermic peak due to crystallization at about 600oC. Structural transformation from the bcc crystalline to amorphous states was also observed through X-ray and neutron diffractions. We take a full advantage of a negligibly small scattering length of the V atom in the neutron diffraction measurement. During amorphization process the octahedral unit, which is typical of a polyhedron formed in any crystal structures, was preferentially destroyed and transformed into the tetrahedral unit. Futhermore, neutron diffraction measurements revealed that a nitrogen atom is selectively situated at a center of the polyhedron formed by V atoms.
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