Solid-Solution Hardening in the Ni-40at%Co-X Ternary Alloys

Abstract

With ternary Ni-40at%Co-X alloys the solid-solution hardening (ssh) due to solutes X of transition-metal group (TM) elements like Ta and Nb and of B-subgroup (B) ones like Sn and Al was investigated. The results were compared with the previous study on the ssh of pure Ni. The value of ssh, Δσ, for a solute X in the Ni-Co alloy is greater than that for X in pure Ni. This increase in Δσ, however, is not explicable in terms of the changes in size-misfit and shear modulus with alloying Co in Ni solvent because these changes are not so great. Instead, for the ssh normalized by the size-misfit, there found a trend of it being greater in the order of the alloy group (A) of Ni-X making a continuous solid solution, the group (B) of Ni-X having a solid solubility, and the group (C) of Ni-Co-X having a smaller solid solubility than that for the group B. This suggests that the increase in the normalized ssh for the Ni-Co-X alloy might be deeply related with the reduction in solid solubility due to the addition of Co. A probable reason for this has been discussed.