Microstructure and hydrogen permeability in Nb–TiFe alloys

• Hydrogen permeation in Nb–TiFe alloys is investigated.
• The TiFe + (Nb, Ti) eutectic structure is obtained in the Nb16Ti53Fe31 alloy in the as-cast state.
• Hydrogen permeable alloys consist of the primary TiFe phase and the eutectic structure.
• Hydrogen permeation performance is increased with Nb content.

The relationship between the microstructure and hydrogen permeability of Nb–TiFe alloys is investigated. The fully eutectic alloy, which consisted of the bcc-(Nb, Ti) and B2-TiFe phases, is found in the Nb16Ti53Fe31 composition. The alloys formed between the Fe50Ti50 and Nb16Ti53Fe31 compositions, expressed as (Ti50Fe50)1−x(Nb16Ti53Fe31)x, consist of the eutectic structure, including the primary TiFe phase for x < 1 or the primary (Nb, Ti) phase for x > 1. The volume fraction of the primary phase is decreased (0 < x < 1) and increased (x > 1) with increasing x. The alloys with 0.4 < x < 0.8 are hydrogen permeable at 673 K. The Nb12Ti52Fe36 alloy with 60 vol% of the primary FeTi phase exhibits a high hydrogen permeability of 2.9 × 10−8 molH2/m/s/Pa0.5 at 673 K without hydrogen embrittlement. The formation of hydrogen permeable Nb–TiFe alloys is possible at higher Ti content and lower Nb content than those of the Nb–TiNi and Nb–TiCo alloys.