Dislocation mobility in ⟨100⟩-oriented NiAl single crystals containing iron and hafnium additions

The dislocation mobility produced by deformation at room temperature has been studied in ⟨100⟩-oriented single crystals of NiAl and of those containing hafnium and iron additions. Comparison of the dislocation microstructures produced by compression with those observed after hardness indentation of thin foils and during in-situ tensile tests in the transmission electron microscope have shown that only ⟨100⟩ dislocations are sufficiently mobile in the three alloys. The iron-containing alloy shows a sufficient density of ⟨111⟩ dislocation segments activated during compression while the binary and the hafnium-containing alloys only deform by ⟨100⟩ dislocations because of kinking. The latter glide preferentially on {110} planes while they are more mobile on {010} planes in the iron-containing material. These differences have been interpreted as being due to a change in kink density or structure produced by the presence of the iron atoms that cause a lower kink mobility on {110} planes in that alloy.