Beta decomposition of (HF_xZr_{1_x})₈₀Nb₂₀ ternary alloys

Abstract

The processes of beta decomposition have been examined in ternary alloys of the form (Hf_xZr_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 pct/K for the binary Zr8oNb2o alloy to a value of-0.011 pct/K for a (Hf_xZr_1-x)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 ω-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 co-phase particles. A phase separation which results in the formation of solute lean discs (β₁) occurs together with the precipitation of the ω-phase. These discs formed both randomly within the matrix and heterogeneously along dislocations and at grain boundaries.