Hydrogen-induced cracking and hydrogen embrittlement of Ni2MnGa FSMAs

Abstract

Hydrogen-induced cracking and hydrogen embrittlement of Ni50Mn30Ga20 ferromagnetic shape memory alloys (FSMAs) were studied through indentation and tension experiments supplemented with in situ observation. The results showed that for Ni50Mn30Ga20 FSMAs, hydrogen-induced cracking could occur with the residual stress caused by indentation during dynamic hydrogen charging. Hydrogen-induced cracking was initiated and propagated during dynamic hydrogen charging in the pre-cracked specimens under constant deflection. The fracture toughness KIC decreased from 1.9 MPa m1/2 for the uncharged specimens to 0.4 MPa m1/2 for the samples charged with hydrogen. The possible mechanism of hydrogen-induced cracking and hydrogen embrittlement for Ni50Mn30Ga20 FSMAs is due to diffusible hydrogen decreasing the efficient surface energy.