Changes in Hydrogen Permeability and Microstructures of Nb-(Ti, Zr)Ni Alloys by Cold Rolling and Annealing

Abstract

Maximum cold rolling reduction rates of as-cast Nb₄₀Ti_30−xZr_xNi₃₀ alloys were measured to evaluate ductility by measuring the change in the thickness. 50% or higher reduction rates were obtained for the alloys containing the Zr content of 12 mol% or less, but lower values were obtained for the alloys substituted with more Zr. Changes of hydrogen permeability (Φ) and microstructures of the Nb₄₀Ti₁₈Zr₁₂Ni₃₀ alloy caused by cold-rolling and subsequent vacuum annealing were investigated. Φ of this alloy was reduced to the half of the as-cast one by the 50% reduction rate, but recovered to 3.23×10⁻⁸ [molH₂m⁻¹ s⁻¹ Pa^−0.5], which is 1.13 times higher than that of as-cast one, by a subsequent annealing for 360 ks at 1273 K. Although the eutectic phase disappeared and was replaced by a small spherical (Nb, Ti, Zr) phase embedded in the (Ti, Zr)Ni matrix after rolling and subsequent annealing, these alloys showed good resistance to the hydrogen embrittlement at 523 K or more.