Treelike PS-PVD coating: Hierarchical branching by shading and sintering

A structure zone model (SZM) with columnar structures for conventional physical vapor deposition (PVD) has been assigned to plasma spray-physical vapor deposition (PS-PVD) coatings. However, many different comprehensive properties between PS-PVD and conventional PVD coatings reveal the essential different microstructures. In this work, an impact-diffusion model was established based on the impact and diffusion behavior of depositing units. The microstructure formation of PS-PVD coatings was simulated. Results clearly display that the PS-PVD coating shows a novel treelike structure with hierarchical branches rather than a well-known columnar structure. The hierarchical branching is determined by the shadowing effect. Besides, temperature-promoting diffusion of vapor units can generate the in-situ sintering of the coatings. In-situ sintering happens during the deposition process and can govern the branching behavior. A novel treelike SZM is established as an enlargement of the conventional one, marked by successive transformations in branching and densifying. The treelike SZM is experimentally proved by the electron microscopy images and mechanical properties of typical PS-PVD YSZ coatings.