Relationship between hydrogen permeation and microstructure in Nb-TiCo two-phase alloys

The relationship between the microstructure and hydrogen permeability of as-cast Nb-TiCo alloys was investigated and is discussed on the basis of the mixing rule. The chemical compositions of these Nb-TiCo alloys may be expressed as (Nb4Ti47Co49)(1) (x)(Nb90Ti8Co2)(x). The alloys for which x = 0 and 1 exhibit essentially single TiCo and (Nb, Ti) phases, respectively. The microstructure of the alloy for which x = 0.3 is fully eutectic, and is composed of (Nb, Ti) and TiCo phases in the as-cast state. In the range of 0.3 < x < 1, the Nb-TiCo alloys present a primary (Nb, Ti) phase surrounded by a TiCo + (Nb, Ti) eutectic structure, and their hydrogen permeability values do not obey the mixing rule. In the region of 0 < x < 0.3, the alloys have a primary TiCo phase, and the hydrogen permeability values of these alloys are slightly higher than the values estimated using the mixing rule. (C) 2015 Elsevier B.V. All rights reserved.