engleski

The appearance of phases in melt-quenched Zr76Ni24 alloy

Rapid solidification by melt spinning is widely spread method in producing metallic glasses. By varying the quenching rate during melt spinning it is also possible to produce partially crystalline and nanocrystalline alloys. Recently, the alloys that consist of a nanocrystalline phase embedded in the amorphous matrix have attracted a lot of attention because of their potential applications. Also, Zr-based metallic glasses are good candidates for hydrogen storage application. In this work we will give some preliminary results about quench-in structures in Zr76Ni24 alloy depending on quenching rate during melt spinning and the influence of hydrogen storage on the structure. As quenched ribbons (about 0.05 mm thick) prepared by rapid melt solidification on a single-roll spinning copper wheel in an argon atmosphere and heated with the heating rates of 10 K/min and 60 K/min up to temperatures between 563 K and 823 K were investigated by XRD using a PHILIPS PW 1820 diffractometer with Cu Ka radiation. It was found that two sides of the quenched ribbons (in contact with the wheel-the dark side of the ribbon or DSR ; in contact with the inert atmosphere-shiny side of the ribbon or SSR) showed different structures. The diffraction pattern of the DSR shows a broad maximum centred at 2a = 36.1o of dw = 4.2o corresponding to an amorphous phase. A diffraction peak was found to be superimposed on the amorphous pattern and it was found to belong to the (002) peak of a-Zr (hexagonal close packed structure). On the other hand, the XRD pattern of the SSR showed to consist of a set of sharp lines. We were able to fit the peaks to the orthorhombic metastable Zr3Ni phase. The derived lattice constants are as follows: a= (1.098 +- 0.002) nm, b= (0.880 +- 0.001) nm and c= (0.333 +- 0.002) nm. We found that the SSR crystalline layer was relatively thin. After the SSR was abraded for about 0.005 mm and examined with XRD only a broad maximum was present on diffraction pattern, which means that the thickness of the crystalline layer was about 0.005 mm of thickness. We conclude that the existence of the Zr3Ni crystalline phase on the SSR is a consequence of lower quench rate achieved in rapid solidification on this side of ribbon. Some preliminary results about the influence of the absorbed hydrogen up to 4.4 wt. % H on the structure of the ribbons will be also presented.

Metallic Glasses; Thermal Stability; Crystallization; Nanocrystal

nije evidentirano