New hard ternary Hf-Ir-B borides formed by reaction hafnium diboride with iridium

A variety of the ternary Hf-Ir-B phases formed via the reaction between iridium and hafnium diboride at elevated temperatures was found. The data on the phase and elemental composition, as well as crystal structure, obtained by powder and single-crystal X-ray diffraction, scanning electron microscopy/energy-dispersive X-ray spectrometer, and time-of-flight neutron diffraction analysis unambiguously confirm that HfIr3Bx solid solution, two known ternary borides (HfIr3B4, Hf2Ir5B2), as well as two novel ternary HfIr2.1B1.3 and HfIr5.7B2.7 phases, are formed at elevated temperatures. This result is fundamentally different from that previously obtained by us for the Hf-Ir-C system in which only one binary intermetallic compound, HfIr3, was produced. The measured Vickers microhardness for all the aforementioned ternary borides (13-19 GPa) allows us to consider them hard. The coefficients of thermal expansion of ternary borides were measured by in situ high-temperature X-ray analysis.