Influence of Microstructure on Microhardness of Fe 81 Si 4 B 13 C 2 Amorphous Alloy after Thermal Treatment
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IRON-BASED amorphous alloys have been the focus of considerable scientific interest in recent times, both from fundamental and practical points of view.[1,2] Commercial soft magnetic nanocrystalline materials were recently successfully obtained by crystallization of amorphous precursors.[3,4] Materials such as this are characterized by a microstructure of nanocrystals embedded into an amorphous matrix, exhibiting superior soft magnetic and mechanical properties to both amorphous and crystalline magnetic alloys.[5,6] The theoretical investigation of nanoscale phase separation in small Fe80B20 and Fe83B17 clusters predicts formation of Fe-pure regions, Fe-rich regions (which contain around 9 pct B), and B-rich regions.[7] While amorphous alloys can be multifunctional and used as corrosion-[8] and wear-resistant coatings, the ability to use them to manufacture bulk components has stimulated new interest in their mechanical properties.[9,10] The effect of boron, carbon, and silicon on the hardness of iron alloys has been well documented.[11–13] Recent investigation of microhardness in boronizing layers of Fe-powder compacts[11] showed that, when iron particles are doped with boron through sintering of DRAGICA M. MINIC´, Professor, and VLADIMIR A. BLAGOJEVIC´, Research Scientist, are with the Faculty of Physical Chemistry, University of Belgrade, Belgrade 11000, Serbia. Contact e-mail: [email protected] DUSˇAN M. MINIC´, Research Scientist, is with the Military Technical Institute, Belgrade 11000, Serbia. ALEKSANDRA GAVRILOVIC´ and LIDIJA RAFAILOVIC´, Graduate Students, are with CEST Kompetenzzentrum fu¨r Elektrochemische Oberfla¨chentechnologie GmbH, Wiener Neustadt 2700, Austria. TOMASˇ ZˇAK, Senior Research Scientist, is with the Institute of Physics of Materials, Academy of Sciences of the Czech Republic, Brno 61662, Czech Republic. Manuscript submitted March 7, 2011. Article published online July 22, 2011 4106—VOLUME 42A, DECEMBER 2011
iron powders at temperatures above 1273 K (1000 °C), the surface structure of the particles exhibits three distinct areas, going from the surface down inside the particle layer: the surface boride zone is followed by a transition zone of diminishing boron content and then, finally, the iron matrix without any boron. A study of the effect of carbon on the hardness of borided iron layers[13] showed that the addition of up to 0.4 mass pct of carbon improves the microhardness in FeB and Fe2B types of phases, by creating a more regular interface of the borided layer and improving its compactness. This study also showed that significant substitution of boron with carbon is impossible in these phases. A recent study of iron-based alloy powders[14] suggests that dense packing of crystalline nanoparticles in an amorphous matrix is responsible for the increase in microhardness, when compared to completely amorphous or crystalline material of the same composition. The amorphous/crystal interface has lower interfacial energy than the crystal/crystal interface, and this structure suppresses propagati
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