Effect of hydrogen and magnetic field on the mechanical behavior of magnetostrictive iron–gallium alloy single crystal

Abstract

Magnetostrictive Fe–Ga and other iron alloys are candidates for use in sensing, actuation and large-scale energy harvesting applications. Exposure to aqueous electrochemical environments is anticipated in some of these applications which could potentially introduce hydrogen into the alloy and cause severe ductility reduction due to the hydrogen embrittlement effect. In this work, the effect of hydrogen and magnetic field on the fracture behaviors of [100] oriented Fe–17.5at% Ga alloy single crystals are examined. Three-point bend test was used to measure the fracture stress. Hydrogen embrittlement was characterized by a change in fracture surface from a ductile fracture mode to a brittle cleavage type fracture. The cleavage fracture occurred along the (001) plane. Critical stress for the initiation of fracture was measured under different conditions and an upper bound for cleavage stress in these alloys is obtained. Applied magnetic field was seen to affect the fracture stress and strain of hydrogen charged sample. Acoustic emission signals collected during the test appear to be consistent with the fracture behavior.