Assessment of the effectiveness of transition metal solutes in hardening of Ni solid solutions

The degree of solid solution strengthening associated with various transition metal elements alloyed with nickel was systematically investigated using a variety of instrumented indentation techniques on binary Ni alloy systems. The measured hardness of the alloys was shown to vary as a function of the solute species. For a nominally constant level of alloying, additions of Nb, Ta, Rh and Ir were revealed to be most potent with respect to enhancing the hardness of the solid solution, binary Ni alloys. A modified Labusch relationship was applied to correlate the various transition metal solutes to the hardness of the alloys and quantify the effectiveness of the elements as solid solution strengtheners in Ni. The results of this investigation suggest that the dominant mechanism by which solid solution strengthening occurs is not due to the localized lattice strains in the proximity of the solute, but rather by the nature of the electronic structure interaction and the resultant change in stacking fault energy.