Beta decomposition of (Hf/sub x/Zr/sub 1-x/)80Nb20 ternary alloys

The processes of beta decomposition have been examined in ternary alloys of the form (Hf/sub x/Zr/sub 1-x/)80Nb20 to determine the influence of Hf additions to a basic Zr80Nb20 composition. In the chill cast condition, Hf additions have been found to decrease the temperature coefficient of electrical resistivity from a value of -0.0015%/K for the binary Zr80Nb20 alloy to a value of -0.011%/K for a (Hf50Zr50)80Nb20 ternary alloy. This change is explained in terms of the bcc lattice instability typical of Ti, Zr, and Hf alloys. The Hf additions enhance the kinetics of omega-phase precipitation during aging at 648 K. The aging of a (Hf05Zr95)80Nb20 alloy for 12 h results in the precipitation of a high volume fraction of cuboidal shaped omega-phase particles. A phase separation which results in the formation of solute lean discs (β/sub l/) occurs together with the precipitation of the omega-phase. These discs formed both randomly within the matrix and heterogeneously along dislocations and at grain boundaries