engleski

The Effect of Thermal Relaxation on the Short-range Order in Melt-quenched Zr-Co and Zr-Ni Alloys

The Zr803d20 (3d= Co, Ni) metallic glasses and the partially crystalline Zr76Ni24 metallic glass were prepared by melt spinning. The effect of thermal relaxation on the short-range order in melt-quenched the Zr803d20 (3d= Co, Ni) metallic glasses and the partially crystalline Zr76Ni24 metallic glass during heat treatment at different heating rates has been investigated by means of the differential scanning calorimeter, DSC, and the X-ray powder diffraction measurements in temperature interval from 300 K to 823 K. According to the X-ray diffraction results, for the partially crystalline Zr76Ni24 metallic glass, melt-quenched alloy consists of a fraction of metastable Zr3Ni crystalline phase and an amorphous phase. The estimated volume of the fraction of the metastable Zr3Ni crystalline phase was 9.6 %. The crystalline peaks of the metastable Zr3Ni crystalline phase were fitted to the orthorhombic structure type. The grain size of the Zr3Ni crystal was estimated using the Sherrer formula to be from 15 nm to 30 nm. Crystallization studies showed that the existence of the metastable orthorhombic Zr3Ni crystalline phase does not change the thermal stability of the amorphous phase against further crystallization and remains unchanged during the annealing samples up to 823 K. On the basis of the DSC and the obtained X-ray experimental data it was possible to list the phases which occur in the heat treatment of the Zr803d20 (3d= Co, Ni) metallic glasses and the partially crystalline Zr76Ni24 metallic glass up to 823 K. The first stage of crystallization of the Zr803d20 (3d= Co, Ni) metallic glasses consists of the evolution of a-Zr nanocrystalline phase which coexist with a 3d-enriched amorphous matrix, whereas for the partially crystalline Zr76Ni24 metallic glass shows the evolution of  -Zr and Zr2Ni nanocrystalline phases. The second stage of crystallization of the Zr80Co20 metallic glass shows the transformation of w-Zr phase to a stable a-Zr nanocrystalline phase and the formation of Zr3Co nanocrystalline phase, whereas the Zr80Ni20 metallic glass crystallizes into a stable a-Zr and Zr2Ni nanocrystalline phases. The second stage of crystallization of the partially crystalline Zr76Ni24 metallic glass shows the transformation of w-Zr phase to a stable a-Zr nanocrystalline phase. The average grain of these nanocrystalline phases were from 10 nm to 30 nm.

Metallic Glasses; Thermal Stability; Crystallization; Nanocrystal

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