Influence of Microstructure on Microhardness of Fe81Si4B13C2 Amorphous Alloy after Thermal Treatment

Abstract

The influence of microstructure, and its changes, on microhardness of the amorphous Fe 81 Si 4 B 13 C 2 alloy after thermal treatment at different temperatures from 298 K to 973 K (25°C to 700°C) was studied. The as-prepared alloy ribbon containing a small amount of crystalline phases, as well as domains of short-range crystalline ordering embedded in the amorphous matrix, exhibits unexpectedly high microhardness, mostly due to its composition. After thermal treatment above 723 K (450°C), the alloy samples begin to crystallize, creating a nanocomposite structure involving nanocrystals embedded in an amorphous matrix, leading to an increase in microhardness. Further growth of the nanocrystals, as the heating temperature was increased to 973 K (700°C), caused the change from nanocomposite structure into a more granulated and porous structure, with a dominant type of interface changing from amorphous/ crystal to crystal/crystal, leading to a decrease in microhardness.

Thermal Stability and Phase Transformations of Multicomponent Iron-Based Amorphous Alloys

“…The changes of their relative intensities and areas point out the changes in microstructural parameters of the formed phases provoked by thermal treatment at different temperatures. The appearance and disappearance of some sharp peaks in the XRD patterns with a rise in temperature of thermal treatment indicate the processes of recrystallization and formation of one phase at the expense of another [15,18,20,26,30]. The analysis of the obtained XRD patterns yielded the information about microstructure of the studied samples and the phase composition diagrams (Figure 3, Table 2).…”

“…Iron-based amorphous alloys studied herein were prepared in the form of the 30-35 μm thin ribbons by melt-quenching technique [15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30]. The nominal composition of the as-prepared alloy samples can be represented as follows in atomic %: Fe 81 Si 4 X-ray diffraction (XRD) measurements were performed in Bragg-Brentano geometry, using a Co K α radiation source, at room temperature.…”

“…In order to obtain detailed information on microstructure of the as-prepared alloys and the nature of individual crystallization steps, the XRD and Mössbauer spectroscopy methods were applied [15,20,25,28,30]. The XRD results revealed that the microstructure of the as-prepared alloys is characterized by short-range atomic ordering showing characteristic broad diffraction halo maxima.…”

“…Due to the presence of bcc-Fe-like atomic configuration in the ordered domains of the as-prepared alloys, the α-Fe(Si) phase is the first crystalline phase formed in amorphous matrix during thermal treatment of the alloys [15,18,20,26,30].…”

“…In the as-prepared form, the examined alloys exhibit relatively high microhardness values, over 900 HV [20,26,30] (Figure 6a). Thermally induced formation of nanocrystalline structure results in an increase in the microhardness value, which reaches maximum at around 500-600°C and then declines (Figure 6a).…”