Nanocrystalline ZrN particles embedded in Zr-Fe-Cu-Al-Ni amorphous matrix.
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Nanocrystalline ZrN particles embedded in Zr-Fe-Cu-Al-Ni amorphous matrix. Marisa A. Bab1,2, Laura C. Damonte1, Luis Mendoza-Zélis1, Stefano Deledda3 and Jurgen Eckert3 1 Departamento de Física, Universidad Nacional de La Plata, La Plata, Argentina 2 CIC – Comisión de Investigaciones Científicas de la provincia de Buenos Aires, Argentina 3 IFW Dresden, Institute of Metallic Materials, P.O. Box 270016, D-01171 Dresden, Germany. ABSTRACT Melt-spun Zr64Al7Cu17Ni10Fe2 amorphous ribbons were milled under nitrogen atmosphere for different times. The resulting nitrided powders were studied by x-ray diffraction, Mössbauer spectroscopy and differential scanning calorimetry. The formation of nanosized crystalline particles, with cubic δ-ZrN structure, dispersed in the amorphous matrix was observed along with a change in the composition of the amorphous phase. Prolonged milling leads to the additional precipitation of late transition metals (Fe,Ni,Cu). The nitride particles affect the crystallization behavior and modify the thermal stability of the amorphous alloy.
INTRODUCTION Composites based on bulk amorphous alloys are receiving considerable attention due to their improved mechanical properties, such as hardness, ductility and yield stress, with respect to single-phase amorphous alloys. These improvements are obtained by hindering propagation of shear bands and favouring the formation of multiple shear bands. Recently, the Zr-Al-Cu-Ni system has been intensively investigated as amorphous matrix in order to form composites containing a variety of particles such as W[1], TiN, AlN[2], CaO, ZrC[3], SiC[4], MgO and CeO[5]. Amorphous Zr based multicomponent alloys, like Zr65Al7.5Cu17.5Ni10, show a wide supercooled liquid region and crystallize with the simultaneous formation of tetragonal CuZr2 and hexagonal Zr6NiAl2 [6]. However, their crystallization behavior strongly depends on chemical composition. In particular, amorphous (Zr65Al7.5Cu17.5Ni10)1-xFex alloys are known to crystallize, primarily, to a metastable Ti2Ni-type structure [7]. This fact has been used to obtain hybrid nanostructures after partial crystallization of the starting amorphous alloy. Alternatively, H incorporation to these amorphous alloys induces the preferential formation of crystalline Zrhydrides, reducing the number of Zr atoms in the amorphous matrix, which is at the same time enriched in Al, Cu and Ni. This deteriorates the thermal stability and results in the formation of crystalline phases with a smaller Zr content [8]. On the other hand, ball milling of Zr alloys or compounds in N2 atmosphere has proved to be an effective way to produce increasing fractions of δ-ZrN particles dispersed in the remaining matrix [9,10]. This processing method would offer the possibilty of studying the effect of the ceramic volume fraction on the mechanical properties and the crystallization behavior of the resulting composite. In this work, we present results on the formation of nanocrystalline δ-ZrN particles dispersed in a Zr-Al-Cu-Ni-Fe amorphous matrix
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