Phase Stability and Mechanical Properties of IrAl Alloys

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  • Phase Stability and Mechanical Properti

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Abstract

Phase stability and mechanical properties of B2 type IrAl intermetallic alloys are investigated. Three types of IrAl alloys are obtained by arc-melting, followed by homogenization at 2023 K for 14.4 ks in vacuum, and are slowly cooled for removing thermal vacancies. Phase stability is studied using optical microscopy, X-ray diffractometry and differential thermal analysis up to 1973 K. Mechanical properties are investigated 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 boundaries. Lattice parameters of both phases are calculated to be 298.8 pm for B2 IrAl and 384 pm for fcc Ir solid solutions. Micro-Vickers hardness is measured to be HV 1050 in average, HV 1100 for B2 phases and HV 1000 through 700 for eutectic structures. Although all alloys show brittleness at room temperature, compressive ductility appears over 1273 K. 0.2% flow stress decreases rapidly with increasing test temperatures: 90 MPa at 1473 K and 30 MPa at 1873 K. It is concluded: (1) IrAl/Ir eutectic structures are induced through solidification, and the eutectic structures remain through the homogenization treatment, and (2) the strength and specific strength of IrAl alloys are higher than those of other intermetallics such as NiAl, Ni3Al and TiAl.

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