Microstructural comparison of Zr_73.5Nb₉Cu₇Ni₁Al_9.5 nanostructure-dendrite composites produced by different casting techniques

다국어 초록 (Multilingual Abstract)

<P><B>Abstract</B></P><P>Zr<SUB>73.5</SUB>Nb<SUB>9</SUB>Cu<SUB>7</SUB>Ni<SUB>1</SUB>Al<SUB>9.5</SUB> (numbers indicate at.%) nanostructure-dendrite composites were fabricated using three different casting techniques: suction casting, centrifugal casting and arc-melting. The microstructure of the suction casting sample consists of micrometer-scale dendrites in a nanostructured matrix. However, some areas in the matrix contain nano-scale crystals together with an amorphous phase revealing an inhomogeneity of the specimen. On the contrary, the microstructures of the centrifugally-cast and the arc-melted samples are overall homogeneous, consisting of micrometer-scale dendrites that are homogeneously distributed in a nanostructured matrix. The dendrites correspond to a body centered cubic (bcc) β-Zr phase, whereas the nanostructured matrix consists of body centered tetragonal (bct) Zr<SUB>2</SUB>Cu-type and hexagonal close-packed (hcp) MgZn<SUB>2</SUB>-type phases. The comparison of the microstructures of these two alloys reveals that the formation of nano-scale twins and a disordered ω-phase in the β-Zr dendrites only happens in the centrifugally-cast sample. The differences in the phases and the microstructures between the differently prepared samples significantly influence the corresponding mechanical properties of the specimens.</P>