Influence of Mechanical Deformation at Tg on the Magnetic Properties in Fe-Based Bulk Metallic Glassy (FeCoZrMoWB) Alloy

Mechanical deformation effect on the magnetic properties in a bulk metallic glass (BMG) Fe60Co8Zr10Mo5W2B15 alloy at its glass transition temperature (Tg) was studied to investigate the possibility of some influence on the micro, nano-structure and magnetic properties of Fe-based BMG. Three different mechanical strains of 5, 10 and 20% were applied to specimens at Tg (=882 K). From the results by vibrating sample magnetometer (VSM) measurement, magnetic susceptibility (χ) and coercive force (Hc) were low in as-cast material, on the other hand, in the samples after strains of 10% and 20%, both χ and Hc increased very much. Transmission electron microscope (TEM) observation shows that very small crystalline precipitations with grain size of several nm order appeared and it's volume fraction gradually increases in the deformed samples. The morphological change seen in the selected area electron diffraction (SAED) pattern was well agreed with the changing tendency of the X-ray diffraction (XRD) analysis. Barkhausen noise (BHN) pulse voltage which is directly related to the dynamic behavior (i.e. magnetic pinning effect) of magnetic domains' movements increased with increasing the strain and BHN outbreak timing moved to higher magnetization level. These behaviors seem to correspond with the increase in Hc and χ. Therefore, a suitable deformation conditions (i.e. the amount of strain and temperature) at Tg should be chosen to maintain the excellent magnetic characteristics in Fe-BMG.