Cemented ternary borides

As discussed before, hard metal-like composites can be prepared by pressureless sintering of ternary borides with Fe, Ni, or Co melts. Materials with x-phase (M21M2 Bg, where = Fe, Ni, or Co, and M = Zr, Hf, Nb, Ta, or W with M as the matrix phase) have not been developed for technical use but Ni-based alloys with x are in applications as wear- and corrosion-resistant coatings on steels [355]. The x phase is also used for the improvement of the creep resistance of Ni-based superalloys. 

The other kind of ternary phases, cp and to, have and M2M B2 stoichio- 

The process starts with a pressed powder mixture of one or more binary borides of M -type metals and the metals required for the constituent of the ternary phase and for the binder phase. This method enables the fabrication of tailored M -M -solid solutions in the ternary boride as well as allows the introduction of high-performance Fe- or Ni-based alloys with exceptional properties. The metal powders are usually atomized alloys but may also consist of powder blends of the particular elements of interest. In Fig. 113 [360] the reaction process is schematically summarized showing the M alloy denoted as metal . In principle, the first step is the boronization of the powder particles by boron diffusion 

1000-1100 2 Mo + 2 Fb2B — Mo2FeB2 -1- 3 Fe Solid state reaction, enhanced growth of sinter necks, formation of spherical particles and clusters 

1150 Mo2FeB2 4- Cr — Mo2(Fe, Cr)B2 Solid-state reaction, later also in liquid state high-density clusters with rounded surfaces, initial growth of faceted grains by surface and volume diffusion 

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