The flow stress of NiAl single crystals below room temperature

The thermally activated dislocation motion in B2-NiAl single crystals of high-purity and stoichiometric composition was studied in a so-called ‘soft’ orientation. The crystals were successively deformed with constant plastic shear-strain rate at different temperatures below room temperature. Tensile tests were combined with stress–relaxation experiments. Between 320 and 230 K, the critical resolved shear stress (CRSS) increases very weakly with decreasing temperature. The CRSS increases rapidly with decreasing temperature between 230 and 76 K. Similarly, the strain-rate sensitivity increases with decreasing temperature <230 K, but reaches a maximum at ≈100 K and decreases again below this temperature. The results are analysed in terms of a solid solution hardening theory.