On the effect of the crystalline structure on the form of fatigue curves: The case of iron–nickel alloys

Abstract

The possible effect of the crystalline structure on the form of fatigue curves was examined. Different pure iron–nickel alloys melted in vacuo and carefully prepared in identical way with different crystalline structures were submitted to rotating bending fatigue. The alloys tested were: (A) face-centred cubic: pure Ni, Ni 85 Fe 15, Ni 75 Fe 25, Fe 50 Ni 50, and (B) body-centred cubic: Fe 90 Ni 10, Fe 96·5, Ni 3 Ti 0·5%, pure Fe (0·2% Ti). It is shown that all the alloys examined have fatigue limit, the only difference being that fatigue curves of the b.c.c. alloys more frequently show a knee and reach the fatigue limit in the region of about 10⁶ cycles, while the face-centred alloys generally reach the limit around 10⁷, 10⁸ cycles. It is suggested that the difference is, for a large part, related to the different form of the strain-hardening curve of the fatigued material, related in turn to the type of structure.