Study On The Microscopic Damage Mechanism Of Plasma Sprayed Coatings

Plasma spraying is a revolutionary technology that satisfies the requirements demanded by a range of fields, including anti-corrosion,-wear, and-high temperature etc. However, the formation of micro defects produced in the plasma sprayed coatings are influenced by the particle size and spraying processing parameters etc. They can cause the coating fracture or peel off from the substrate, which will further impact on the structure integrity. Therefore, study on the microscopic damage mechanism is very important for the plasma sprayed coating.Wollastonite and316L stainless steel coatings are used as the typical ceramic and metal coatings, separately, in the present work. Fracture of coatings is observed in-situ using a Scanning Electron Microscope (SEM) during the Tapered Double Cantilever Beam (TDCB) specimens open. Subsequently, the microscopic principle for coating damage is uncovered. The study on the fracture toughness of coatings show the damage of coatings relates with the coating microstructure and the cracking propagation. The stress distribution of coatings are simulated through finite element analysis based on the relation of single large pore and2-dimensional pore,2-dimensional ideal coating model and image-based microstructure of coatings.It is found that the initial and propagation of cracks in coatings present a non-continuous tendency. The original pores in coatings guide the cracking, in the mean while, the main stress direction also has an influence on the direction of cracking. More un-connected small cracks present on the front of the crack tip in ceramic coatings than those in the metal coating. Obvious plastic deformation can be found from the edge of cracking in the metal coating. Fracture toughness of coatings relate with the size and distribution of the original pores in coatings. The fracture toughness of wollastonite coatings increases firstly with the increase in the substrate surface temperature. And then a decrement tendency can be found with the further increasing substrate surface temperature. The decrease of spraying particle size causes the fracture toughness of coatings increase. The stress of coating is mainly influenced by the length of non-bonded interface, and then affected by the distance between the non-bonded interfaces and the thickness of lamella in coatings.