Structural evolution of amorphous and nanocrystalline TiAl films under helium implantation

Abstract

The structure evolution and mechanism of the material during helium ion implantation are directly related to their performance and service life, towards the nuclear application. Despite the growing interest in amorphous and nanocrystalline films for a range of nuclear applications, many specifics about how their structure evolves during helium implantation are unclear. Here, the amorphous and nanocrystalline TiAl films produced by magnetron sputtering were in situ observed in a helium ion microscope to further understand the mechanism of microstructural evolution under severe ion implantation of two distinct structured nanomaterials. The result shows that a blister suddenly appeared on the surface of the nanocrystalline TiAl film, caused by a laterally ordered distribution of bubbles along the 〈111〉 crystal direction when the implantation dose reached 3.5 × 1017 ions cm−2. Instead, significant swelling of the whole implantation region of amorphous TiAl film was observed. At the final dose (9 × 1017 ions cm−2), the swelling thickness of the amorphous film was 200 nm and no exfoliation and cracking occurred. Due to long-range disorder, the degradation processes of amorphous TiAl film significantly differ from those of nanocrystalline TiAl film. This research has the potential to classify applications of materials in the nuclear field while providing a new viewpoint on the material structure design.