Defect structures created during abnormal grain growth in pulsed-laser deposited nickel

The thermal stability of nanograined pulsed-laser deposited nickel was studied by annealing free-standing thin films in situ in a transmission electron microscope. The observed grain growth was sporadic and catastrophic, as expected for abnormal grain growth. The large grains contained a variety of defects that included twins, dislocation lines, small dislocation loops and stacking-fault tetrahedra. This microstructure was developed at annealing temperatures as low as 498 K and was stable at the annealing temperature. The proposed source of the defects and especially the stacking-fault tetrahedra is the grain boundaries, which have excess free volume. This defect source provides insight to the structure of the deposited grain boundaries, which has important consequences for the macroscopic mechanical properties of nanograined pulsed-laser deposited nickel.