Effect of Al and Fe Additions on Fatigue Crack Initiation and Growth Behavior of Fatigue Cracks in Cu–Ti alloys

Abstract

Cu–3.2 Ti–1.1 Al–0.1 Fe (wt.％) alloy (Cu–Ti–Al–Fe) exhibits superior fatigue properties compared to Cu–3.2 Ti alloy (Cu–Ti). In this study, the microstructure of the Cu–Ti–Al–Fe alloy was identified, and then investigated the initiation and propagation behavior of fatigue cracks in the alloy. In the solid solution treated Cu–Ti–Al–Fe alloy, granular (Cu,Fe)₃Ti₂ with a size of several tens of nanometers was dispersed overall the alloy. The pinning effect of the (Cu,Fe)₃Ti₂ particles results in a fine matrix grain size of 4 μm. On aging, β’–Cu₄Ti continuously precipitates within the grains, and simultaneously Cu₂TiAl with a size of about 1 μm precipitates on the grain boundaries. Note that the cellular structure at grain boundaries in aged Cu–Ti alloy is not formed. During fatigue tests, nucleation and growth of fatigue cracks suppressed in the aged Cu–Ti–Al–Fe alloy due to no week cellular structure at grain boundaries, and due to the small grain size, resulting in improvement of fatigue properties.