Abstract
In the present study, the microstructure development and mechanical properties of the cast boron-rich Fe–B–C alloys cooled at 10 and 103 K/s were investigated as functions of alloying elements additions. These alloys were prepared in the following compositional ranges: B (10–14 wt.%), C (0.1–1.2 wt.%), M (5 wt.%), where M – Cu, Ni or Mn, balance Fe. Structural properties were characterized by quantitative metallography, X-Ray diffraction, scanning electron microscopy, and energy dispersive spectroscopy. Mechanical properties of the structural constituents, such as microhardness and fracture toughness, were measured by a Vickers indenter. Copper becomes negligibly incorporated into the phases Fe(B,C) and Fe2(B,C) of the Fe–B–C alloys, but solubility limit forces the remaining solute into the residual liquid. As a result, the globular Cu inclusions are seen in the structure. As compared with copper, nickel has higher solubility in the constituent phases, with preferential solubility observed in the Fe2(B,C) crystals, where Ni occupies Fe positions. Having limited solubility, nickel also forms secondary Ni4B3 phase at the Fe2(B,C) boundaries. Manganese was found to dissolve completely in the Fe–B–C alloys forming substitutional solid solutions preferentially with Fe(B,C) dendrites. By entering into the iron borides structure, Mn and Ni improve their ductility but lower microhardness. The peculiarities in the structure formation and properties of the doped boron-rich Fe–B–C alloys were explained with electronic structure of the alloying elements considered.
Highlights
Boron-rich Fe–B–C alloys containing more than 10 wt. % B are among the few alloys to have been studied in terms of several of their physical properties, such as hardness, elevated temperature strength, and thermal stability [1,2,3]
The master Fe–B–C alloys exhibit peritectic structure: primary dendrites of Fe(В,С) monoboride are observed in the background of peritectically formed Fe2В hemiboride alloyed with carbon [27]
The Fe2(В,С) and Fe(В,С) phases have no noticeable solubility for copper (Fig. 1) which is confirmed by lattice parameters measurements (Table 1)
Summary
Boron-rich Fe–B–C alloys containing more than 10 wt. % B are among the few alloys to have been studied in terms of several of their physical properties, such as hardness, elevated temperature strength, and thermal stability [1,2,3]. Previous studies have shown that Fe–B–C alloys have excellent wear, oxidation, and corrosion resistance [4,5] These alloys are available and have the favorable cost. To apply the boron-rich Fe–B–C alloys as fillers of composites fabricated by infiltration, the contact interaction processes between the filler and the molten Cu–Ni–Mn binder should be studied [12, 13]. These processes may be accompanied by diffusion of binder constituent components, Cu, Ni or Mn, into solid Fe–B–C filler. The performance characteristics may drastically deteriorate in case of negative influence of the diffusing elements on the structure and properties of structural constituents of the Fe–B–C alloys [14, 15]
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