Amorphization of the intermetallic compounds Co2Zr and Fe2Zr under mechanical grinding

The crystalline intermetallic compounds Co₂Zr and Fe₂Zr were produced in the stoichiometric composition and milled in a planetary ball mill for different milling periods. The samples were investigated in respect to the question if a crystal-to-glass transition occurs due to the milling process. Three different experimental methods were used for this study: X-ray diffraction, Mößbauer spectroscopy, and measurements of the specific heat capacityc_p. The intermetallic compound Fe₂Zr is very suitable for this study since it is ferromagnetic at room temperature. Thus it shows characteristic features in the Mößbauer spectrum and in the measurement of the specific heat capacityc_p. The investigation shows that the intermetallic compounds Co₂Zr and Fe₂Zr undergo a crystal-to-glass transition under mechanical grinding but the X-ray diffraction patterns show that the transformation is not complete. Even after long milling periods always an amount of a crystalline phase is present in the milled samples. In comparison the mechanically ground samples show the same properties as mechanically alloyed powder mixtures of the two elements of the same chemical composition. A probable explanation for the development of an amorphous phase by mechanical grinding of the crystalline compounds Co₂Zr and Fe₂Zr is the accumulation of internal strain in the crystalline grains. Another possible explanation, the addition of iron impurities to the crystalline compounds due to the wear debris of the milling equipment, seems to be improbable since the intermetallic phases Co₂Zr and Fe₂Zr show extended existance ranges in the equilibrium phase diagrams and hence are stable in respect to a variation in the composition.