Insights into the influence of Ni4Ti3 precipitates and martensite transformation on the glide of a[100] dislocation in austenitic NiTi alloys: an atomistic simulation study

Dislocation-dominated plastic deformation in austenitic NiTi alloys is highly detrimental and it could be suppressed by precipitation of Ni4Ti3. Additionally, at a certain temperature range, not only Ni4Ti3 precipitate but also the B19′ martensite produced from stress-induced martensitic transformation may prevent dislocation glide in austenitic NiTi alloys. In order to shed further light on this issue, four atomic configurations were constructed using an edge dislocation (a[100]) and two Ni4Ti3 precipitate variants (precipitate-V1 and precipitate-V2) to investigate dislocation glide in austenite containing Ni4Ti3 precipitate under shear at temperatures of 500 K or 700 K. As a result, all configurations at 500 K undergo the shear-induced martensitic transformation, producing B19′ martensite that impedes dislocation glide. And at 700 K, dislocation was pinned by precipitate or distortion zones caused by the superposition of strain field of precipitate and dislocation, without martensitic transformation. Furthermore, it was proven that precipitate-V1 impedes dislocation glide more strongly than precipitate-V2 at both temperatures of 500K and 700 K. It was attributed to the different in spatial relative location between the precipitate and dislocation and explained by the Orowan dislocation-precipitate bypass stress. Finally, three strategies for achieving high shear fatigue resistance in NiTi shape memory alloys were proposed based on these findings.