Mechanical spectroscopy studies of partially amorphous Nd60Fe30Al10 alloys

The hard magnetic properties of melt spun Nd60Fe30Al10 alloys are attributed to a major matrix nominally amorphous for X-ray diffraction, composed by two metastable nanosized (similar to5nm) phases with different intrinsic magnetic properties. This composite system is investigated for the first time by mechanical spectroscopy techniques in the temperature range between 50 K and 450 K (1 kHz) where large annealing effects and two damping phenomena are detected. The as-cast microstructure irreversibly changes during annealing above 330 K, leading to a large modulus recovery accompanied by a reduction in the internal friction level. A relatively large relaxation effect is observed about 290 K, evidenced by a narrow internal friction peak with the corresponding step in the elastic modulus; this peak remains stable under thermal cycling between 200 K and 300 K but is affected by aging at 330 K and practically vanishes after heating to 450 K. Another internal friction peak is observed at about 250 K which has associated an anomalous modulus effect; in this temperature range, the internal friction and the elastic modulus exhibit heating/cooling hysteresis, which strongly depends on the extreme temperatures of the thermal cycle, a behavior frequently associated to first-order phase transformations. (C) 2004 Elsevier B.V. All rights reserved.