Investigation into the thermal behaviour of the B2-NiAl intermetallic alloy produced by compaction and sintering of the elemental Ni and Al powders

A cubic B2-NiAl alloy was synthesized by mixing of elemental Ni and Al powders followed by cold compacting and sintering of some samples at 750 degrees C and other samples at 1300 degrees C. The alloys sintered at 1300 degrees C exhibited a brittle B2-NiAl structure easily crushable into powder, while the 750 degrees C sintered alloys were not nearly as brittle. Electron Backscatter Diffraction (EBSD) results show that the B2-NiAI alloy sintered at 750 degrees C for a longer time (120 h) has larger grain size associated with the < 111 > -oriented grains encountering high mobility boundaries than the alloy sintered at 750 degrees C for a shorter time (48 h). Samples morphologies were analyzed using the Scanning Electron Microscope (SEM). Structural development of the alloy was studied via the x-ray diffraction (XRD) technique. The B2-NiAl intermetallic developed a thin scale of stable Al2O3 alloy due to oxidation in air at 750 degrees C for 120 h. As a result, further oxidation on the samples surface was restricted, except the traces of Al2O3 formed via intergranular oxidation transformed into a metastable monoclinic oxynitride phase due to nitrogen (N) contamination.