Structure and mechanical properties of NiAl and Ni3Al-based alloys

The investigation of Ni-Al-Fe-Ti-B alloys was carried out to determine the influence of iron and small titanium and boron additions on the phase compo sition, microstructure and mechanical characteristic, particularly with res pect to high-temperature deformation conditions. These alloys, containing A l 35.8 at% and Fe 3.6-8.6-17.6 at% were prepared from high-purity component s and Al master alloy containing Ti2B particles. The influence of alloying additions of chromium and iron on the mechanical properties of directionall y solidified Ni-Al-Cr-Fe alloy was investigated. Additions of both Cr 8 at% and Fe 2 at% result in higher strength than exhibited by unalloyed Ni, Al. However, the ductility is reduced by the formation of the beta' phase. The typical, lamellar structure of Ni-20Al-8Cr-2Fe alloy undergoes coagulation during a high-temperature deformation process. The sequence of structural changes of NiAl and Ni, Al-based alloys has been correlated with mechanical characteristics of high-temperature deformation process, determined in uni -axial compression tests. Two ranges of work hardening have been identified on the stress-strain curves of these alloys. It has been found that the fi rst range of the deformation of Ni-Al-Fe-Ti-B alloys corresponds to the int ergranular slip system operating within individual grains, while the second one is connected with transgranular slip. In the directionally solidified Ni-20Al-8Cr-2Fe alloy similar work hardening curves were observed in relati on to the microstructural evolution from the lamellae shape, through ellipt ical shape into circular shape. (C) 2000 Elsevier Science Ltd. All rights r eserved.