Solid solution hardening in ternary Ni-Y(Y:Co,Pd,Fe)-Nb alloys.

Abstract

Solid solution hardening in Ni-Co, Ni-Pd and Ni-Fe binary matrix alloys is investigated mainly by the addition of Nb and the results are compared with that in nickel. It is shown that the rate of solid solution hardening per 1at% of Nb is larger in the following order; Ni-Co, Ni-Fe>Ni>Ni-Pd. Since there is no appreciable difference in the size misfit parameter of Nb in these alloy systems, such difference cannot be interpreted solely by the elastic interaction theory. To be noted is the fact that the limit of solid solubility of Nb would be reduced in Ni-Co and Ni-Fe alloys but be increased in Ni-Pd alloy both as compared to that in Ni. Then the limit of solid solubility is shown to be well correlated with the magnitude of the interaction parameter between the solute and the solvent. If it is large negative, there should be a strong tendency for the solution to have a short range order and if it is large positive the solute atoms should tend to form clusters. In relation to the limit of solid solubility, it is suggested that in Ni-Co and Ni-Fe alloys dislocations would no more be interacting with discrete single solutes distributed randomly but with some kind of solute aggregates to cause the extra hardening as compared to Ni.