Formation of Nanosize Crystalline Structures during Rapid Cooling of Melt and Crystallization of Amorphous Ribbon of Iron-Based Alloy with Complex Alloying

Both structure and mechanical characteristics of melt-spun glassy ribbons with a thickness of 20 mu m and bulk plates of 2 and 3 mm thick with nanocrystalline structure fabricated by the ejection copper mould casting method of Fe61.7Cr13.4Mo1.9Nb1.9Mn0.5Cu0.5Al1Si1C1.9B16.2 alloy as well as the transition of the amorphous phase into crystalline state are examined by x-ray diffraction analysis, differential scanning calorimetry and microhardness measurements. Crystallization of the glassy phase occurred via two stage by sequential formation of alpha-Fe solid solution and Me2B nanocrystals, respectively. The analysis of glass forming ability and crystallization of amorphous phase show that formation of two-phase (alpha-Fe + Me2B) nanocrystalline structure with grain sizes in the range of 16-43 nm in bulk samples is a result of both the enhanced nucleation rate of alpha-Fe solid-solution crystals caused by the Cu clustering as well as the retardation of the growth processes due to formation of Nb-rich shells around the alpha-Fe nanocrystals and the necessity of essential atomic rearrangements for growth of the boride crystals. The strength characteristics of both the as-cast amorphous ribbons and the nanocrystalline plates estimated from their hardness (10.3 and 10.9-11.2 GPa, respectively) correspond to the highest ultimate strength reported for the crystalline Fe-based alloys (3.3 GPa) while the maximum value of hardness for the alloy investigated (17.7 GPa) is reached in the fully-crystallized ribbon with a nanocrystalline structure.