Influence of Boron Addition on High Temperature Mechanical Properties of Nb<SUB>3</SUB>Ir Intermetallic Compounds

Abstract

The effects of deviation from stoichiometry and boron addition on the mechanical properties of A15 type Nb 3 Ir intermetallic compounds were studied. All the alloys, with and without boron, were prepared by arc-melting, followed by homogenization at 2073 K for 86.4ks 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 ol Nb 3 Ir 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 Nb 3 Ir 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 Nb 3 Ir alloys, because boron is almost insoluble in Nb 3 Ir 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 0.6T m , and the temperature is higher than that for other intermetallic compounds such as NiAl, Ni 3 Al and TiAl.