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

Abstract

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 HfIr 3 B x solid solution, two known ternary borides (HfIr 3 B 4 , Hf 2 Ir 5 B 2 ), as well as two novel ternary HfIr 2.1 B 1.3 and HfIr 5.7 B 2.7 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, HfIr 3 , 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.

Evolution of the Microstructure and Phase Composition of the Products Formed in the Reaction between Iridium and W2B

“…Based on this result, the new ternary boride can be considered the hard phase. This value is lower than that reported previously for the ternary Hf–Ir–B boride of similar composition (18.2 ± 1.7 GPa for Hf 2 Ir 5 B 2 ) [ 30 ].…”

“…In the metal-rich portion, the rapidly solidified W–Ir–B alloy (the 60:20:20 atomic ratio) was found to be composed of two crystalline phases (namely, the orthorhombic IrW and tetragonal W 2 B phases); no ternary borides were found [ 3 ]. Nevertheless, taking into account the high diversity of ternary borides for similar systems (Mo–Ir–B [ 22 , 25 , 26 ], Hf–Ir–B [ 27 , 28 , 29 , 30 ], and Zr–Ir–B [ 28 , 31 ]), one can suggest that ternary borides other than the aforementioned one could be formed in the W–Ir–B system. Here, it should be emphasized that the simultaneous presence of very heavy (W, Ir) and very light (B) elements in the composition is the main difficulty in investigating such a system.…”