Microstructural stability of ultrafine grained cold sprayed 6061 aluminum alloy

- UFG cold spray 6061 layer was analyzed by in situ hot-stage TEM.
- Locations and temperatures of different microstructural changes were observed.
- Y direction was found to preserve UFG structures after heating up to 450 °C.
- In Z direction, the UFG's were not resistant to grain coursing.

The microstructural stability of ultrafine grained (UFG) cold spray 6061 aluminum deposits produced by high pressure cold spray were investigated by in situ heating to a fully annealed state via a hot-stage transmission electron microscope (TEM). It was possible to observe the precise locations and temperatures of different microstructural changes, like dislocation movement and other restoration processes. Even after heating up to the annealing temperature for this alloy, the deposited layer in the perpendicular direction was found to preserve the UFG structures, which were the result of different recrystallization mechanisms caused by the high strains present during cold spraying. Extensive solute segregation at the grain boundaries acted as an obstruction for grain boundary migration in this direction, thereby preventing grain growth. However, in the direction parallel to the deposited surface, the UFGs were not resistant to grain coursing like the other direction, since the grain boundaries had much less solute segregation.