PHASE-STABILITY AND MECHANICAL-PROPERTIES OF IRAL ALLOYS

Phase stability and mechanical properties of B2 type IrAl intermetalli c alloys are investigated. Three types of IrAl alloys are obtained by arc-melting, followed by homogenization at 2023 K for 14.4 ks in vacuu m, and are slowly cooled for removing thermal vacancies. Phase stabili ty is studied using optical microscopy, X-ray diffractometry and diffe rential thermal analysis up to 1973 K. Mechanical properties are inves tigated by micro-Vickers hardness measurements at room temperature and compression tests up to 1873 K. All alloys after heat treatment have eutectic structures composed of B2-IrAl and fcc Ir solid solution: B2 IrAl is the primary phase and Ir solid solutions exist at grain bounda ries. Lattice parameters of both phases are calculated to be 298.8 pm for B2 IrAl and 384 pm for fee Ir solid solutions. Micro-Vickers hardn ess is measured to be H-V 1050 in average, H-V 1100 for B2 phases and H-V 1000 through 700 for eutectic structures. Although all alloys show brittleness at room temperature, compressive ductility appears over 1 273 K. 0.2% flow stress decreases rapidly with increasing test tempera tures: 90 MPa at 1473 K and 30 MPa at 1873 K. It is concluded: (1) IrA l/Ir eutectic structures are induced through solidification, and the e utectic structures remain through the homogenization treatment, and (2 ) the strength and specific strength of IrAl alloys are higher than th ose of other intermetallics such as NiA1, Ni3Al and TiAl.