Unraveling the complexity of Fe-based bulk metallic glasses: Insights into dynamic mechanical relaxation in atomic-scale

• Published in: Journal of alloys and compounds 2024-10, Vol.1002, p.175410, Article 175410
• Main Authors: Rezaei-Shahreza, Parisa, Hasani, Saeed, Seifoddini, Amir, Nabiałek, Marcin, Czaja, Pawel
• Format: Article
• Language: English
• Subjects: Bulk metallic glasses (BMGs); Mechanical relaxation process; physical aging, Atomic mobility; Structural heterogeneity
• ISSN: 0925-8388
• DOI: 10.1016/j.jallcom.2024.175410

This research conducts a thorough investigation into the structural and mechanical evolution of Fe74B20Nb2Hf2Si2 bulk metallic glass (BMG) subjected to thermal aging. Utilizing X-ray diffraction (XRD) and selected area electron diffraction (SAED), the study verifies the amorphous structure of the as-cast BMG, highlighting evidence of short-range ordering (SRO). Thermal aging conducted between 342 and 570 K induces substantial changes, notably the formation of Fe23B6 and α-Fe phases and reduced defect concentrations. During dynamic mechanical analysis, a significant shift was observed, which is characterized by a decrease in the intensity of β-relaxation and an increase in β-activation energy from 333.3±2.1 kJ/mol (for the sample aged at 342 K) to 384.6±5.6 kJ/mol (for the sample aged at 570 K). Nanoindentation evaluations reveal an increase in hardness from 11.85±0.22 GPa (for the as-cast BMG) to 14.65±0.41 GPa (for the sample aged at 570 K), accompanied by an increase in Young’s modulus from 211.61±3.00–244.24±2.00 GPa. These changes imply tighter atomic packing and diminished free volume due to aging, suggesting an advanced stage of structural relaxation. Additionally, the material demonstrates a decrease in plastic strain from 0.0052 in its as-cast state to 0.0026 at 342 K, progressing to brittle behavior with further aging. This study shows the pivotal role of precise aging temperature control in optimizing BMGs for diverse applications, illustrating the intricate interplay between thermodynamics and kinetics in material science. [Display omitted] •Increasing aging temperatures decreases heterogeneities and defect concentrations in the Fe74B20Nb2Hf2Si2 BMG.•Higher aging temperatures foster the emergence of Fe23B6 and α-Fe phases, enhancing the alloy's mechanical performance.•Aging leads to a decrease in β-relaxation intensity, attributed to greater atomic mobility and reorganization.•Nanoindentation results demonstrate augmented resilience and structural uniformity in samples aged at elevated temperature.•Elevated aging temperatures prompt a transition from ductile to brittle behavior in compression testing.