Influence of boron addition on high temperature mechanical properties of Nb3Ir intermetallic compounds

The effects of deviation from stoichiometry and boron addition on the mecha nical properties of A15 type Nb3Ir intermetallic compounds were studied. Al l the alloys, with and without boron, were prepared by are-melting, followe d by homogenization at 2073 K for 86.4 ks in an argon atmosphere. The amoun ts of boron addition were 0.05 mass% and 0.15 mass%. Mechanical properties were investigated by micro-Vickers hardness measurements at room temperatur e and compression tests up to 1773 K. It was found that the lattice paramet er of Nb3Ir decreases, while the micro-Vickers hardness increases monotonic ally 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% now stress was not obse rved 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 % how stress was observed which increases with increasing Ir concentration, and it was higher in the boron-free alloys. Unfortunately, there was no fa vorable 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 boun daries. The 0.2% flow stress of the A15-type intermetallic compounds droppe d rapidly above 0.6T(m), and the temperature is higher than that for other intermetallic compounds such as NiAl, Ni3Al and TiAl.