AbstractReverse-torsion fatigue tests on Cu–10Ni alloys containing small quantities of iron in 1 atm gaseous hydrogen, oxygen, and humid air environments, showed that the fatigue life was significantly influenced by the test environment. Multiple crack initiation, crack branching, and changes in fracture mode were observed in the aggressive environments when compared with tests conducted in dry helium. The results are rationalized by a softening mechanism promoted by either hydrogen-assisted overaging or oxidation of the iron particles leading to subsequent decohesion of interfaces in the deformation zones ahead of the crack front.MST/585