Microhardness and Thermal Expansion of Some Binary and Ternary Boride Phases in the Ca–Ir–B System

— We have studied the thermal expansion of CaIr 4 B 4 , IrB 1.1 , and CaB 6 . The results demonstrate that the crystal lattices of these phases expand linearly with temperature and that their thermal expansion coefficients lie in the range (5–10) × 10 –6 K –1 . We have determined the average microhardness of the CaIr 4 B 4 , IrB 1.1 , and CaB 6 phases. The average microhardness of the CaIr 4 B 4 phase is ~15 GPa, which is a factor of 3 lower than that of the CaB 6 phase.