Effect of Ni addition on glass forming ability and thermal stability of Nd-Fe-Al-Ni bulk metallic glasses

(Nd60Fe30Al10)100-xNix(where x = 0, 3, 5, 8 and 10 at%) alloy cylinders with a diameter of 3 mm and a length of 55 mm were prepared by copper mold casting. The effect of Ni addition on glass forming ability (GFA) and thermal stability of Nd-based alloy was investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). It was found that a bulk metallic glass (BMG) composite with a small amount of primary crystallites in the amorphous matrix is formed without Ni addition, and the proportion of crystallites decreases with an increase in the amount of Ni. The (Nd60Fe30Al10)92Ni8alloy exhibits the best GFA even though there is no apparent glass transition and supercooled liquid region. It is interesting to note that the main melting temperature of the (Nd60Fe30Al10)92Ni8alloy is lower than its crystallization temperature, resulting in the value of the nominal reduced crystallization temperature Tr(=Tx/Tm) being larger than 1.0. The separation of amorphous phases with different thermal stabilities is believed to be one of the reasons for the anomalous phenomenon. The high GFA of the alloy may be explained in terms of valence concentration and structural stability of the amorphous phase.