Grain size and loading conditions influence on fatigue crack propagation in a Cu-Zn-Al shape memory alloy

•The influence of grain size on the fatigue crack propagation in a copper based shape memory alloy.•A chemical approach to reduce the grain size.•The influence of reversed/cyclic plastic zone on the fatigue crack propagation.•A not usual behaviour of da/dN-Δk curves at R = 0.1 which present five different stages.•Crack surface propagation micromechanisms for different R and different grain size. Due to their capability to recover the initial shape, Shape Memory Alloys (SMAs) are widely used in many applications. Different grades are commercially available and they can be classified considering either their chemical compositions (e.g., Cu based, Ni based, Fe based) or according to their mechanical behaviour. The most used SMAs are the Ni based alloys thanks to their performances both in terms of mechanical resistance and in terms of fatigue resistance, but their costs are quite high. Cu based alloys are good competitors of the Ni based alloys. The recent optimization of their chemical composition improved both the corrosion resistance in aggressive environments and their mechanical performances. In this work, the influence of the grain size on fatigue crack propagation in two Cu-Zn-Al SMAs has been investigated focusing on the damage micromechanisms.