Abstract
The effects of deviation from stoichiometry and boron addition on the mechanical properties of A15 type Nb3Ir intermetallic compounds were studied. All the alloys, with and without boron, were prepared by arc-melting, followed by homogenization at 2073 K for 86.4 ks in an argon atmosphere. The amounts of boron addition were 0.05 mass% and 0.15 mass%. Mechanical properties were investigated by micro-Vickers hardness measurements at room temperature and compression tests up to 1773 K. It was found that the lattice parameter of Nb3Ir decreases, while the micro-Vickers hardness increases monotonically with increasing Ir concentration, and that there is no singularity at stoichiometry in the Ir concentration dependence of micro-Vickers hardness and lattice parameter at room temperature. The 0.2% flow stress was not observed due to premature failure in all the Nb3Ir alloys with or without boron in the temperature range of room temperature to 1473 K. At 1773 K, the 0.2% flow stress was observed which increases with increasing Ir concentration, and it was higher in the boron-free alloys. Unfortunately, there was no favorable effect of boron addition on ductility improvement in Nb3Ir alloys, because boron is almost insoluble in Nb3Ir intermetallic compound, and the addition of boron leads to the formation of boride mainly at the grain boundaries. The 0.2% flow stress of the A15-type intermetallic compounds dropped rapidly above 0.6Tm, and the temperature is higher than that for other intermetallic compounds such as NiAl, Ni3Al and TiAl.
