Crystallization of Fe-Ni Based Amorphous Alloy

Abstract

The devitrification of the Fe-Ni-B-Si amorphous ribbon was investigated by the differential scanning calorimetry (DSC) with scanning and isothermal methods. The devitrification of rapidly quenched ribbons is a multilevel process. On the basis of DSC investigations it was determined that crystallization occurs in three processes up to 700°C in the Fe40Ni40B16Si4 alloy. In the present work the first and second steps have been discussed. The first crystallization step involves the segregation of the Fe-Ni crystalline solid solution from the amorphous matrix. During the second crystallization phase, in addition to austenite, nickel silicide and two types of iron borides crystallize as well. The ribbons were relaxed at 380°C for 2 hours, following the pre-annealing at different temperatures. Pre-annealing was performed in the DSC within the temperature range elapsing from 395°C to 420°C. The preannealing at temperatures below the first exothermal DSC peak has an effect on the crystallization processes. After the pre-annealing the samples were investigated by DSC. The DSC peak of the first crystallization step shifts to higher temperatures and decrease its enthalpy. The scanning DSC measurements, applied after the isothermal pre-annealing, were performed in order to determine the fraction of the ribbon transformed in the primary crystallization step. The second DSC peak shifts to lower temperatures with a maximum of 4°C. The X-ray diffraction (XRD) analyses reveal that the lattice constant changes with the pre-annealing temperatures. Such observation was also supported by the circumstance that the composition of the Fe-Ni solid solution undergoes certain modifications.