Dynamic microstructure evolution in cold sprayed Ni-Ti composite coatings

The severe plastic deformation inherent to cold spray provides a unique opportunity to study dynamic microstructure evolution under extremely high strain rates, not achievable in conventional laboratory experiments. In this study, the correlation between dynamic deformation and microstructure evolution is investigated for a heterogeneous system, using cold spray of blended Ni-Ti powder mixtures. EBSD analyses of the Ni and Ti particles show different degrees of dynamic recrystallization (DRX) especially at particle boundaries, which are attributed to different materials properties and dissimilar materials interaction. A heterogeneous structure of Ni-Ti composite was achieved with Ni particle being embedded in an ultra-fine grain Ti matrix with an average grain size of 500 nm. Results show hierarchical structures including twins with a thickness of about 500 nm, micro-bands and low angle boundaries, which are associated with a grain subdivision mechanism through continuous dynamic recrystallization (CDRX). The results also demonstrate a drastically different response of Ti and Ni to the same loading conditions, hence provide an insight to the role of intrinsic material properties in DRX at extremely high strain rates.

Automated summary

Cold spray allows for studying dynamic microstructure evolution under extremely high strain rates, with Ni-Ti powder mixtures demonstrating different dynamic recrystallization behaviors. The study shows a heterogeneous structure of Ni-Ti composite achieved through continuous dynamic recrystallization, revealing insights into the role of material properties in dynamic recrystallization at extremely high strain rates.