Deformation mechanisms and ductility of mechanically alloyed NiAl

Abstract

An NiAl-based alloy has been produced by mechanical alloying and hot extrusion, resulting in material which is fully dense, with a homogeneous distribution of oxide particles and with a fine grain size of less than 1 μm. Mechanical properties of the mechanically alloyed (MA) NiAl were studied by compression testing from room temperature to 1300 K. At room temperature, the alloy exhibited high yield strength (1380 MPa) and considerable compressive ductility (greater than 11.5%). Transmission electron microscopy of the compressed specimens was carried out. In order to determine the Burgers vectors of slip dislocations a rigorous procedure was followed. The 〈100〉 slip was found to be predominant but strong evidence of 〈110〉 slip was also gathered. The occurrence of the slip vectors satisfies the general requirement for plasticity and contributes to the notable compressive ductility. Cast and hot extruded NiAl has been also investigated for comparison with the MA material. At room temperature, it exhibited a poor ductility (2.3%), low yield strength (400 MPa) and only 〈100〉 slip dislocations were observed. The 〈100〉 slip provides three independent slip systems, an insufficient number for general plasticity. The different behavior of cast and MA NiAl is believed to be a result of distinct textures, 〈111〉 and 〈110〉 respectively, exhibited by these differently processed materials.