Ceramic coatings by assisted PVD or CVD or plasma spraying

In general, a deposit on the surface of a part is used to give it a particular functionality that it would not otherwise have. Ceramic deposits are used to provide: greater hardness, electrical and thermal insulating properties, improved wear resistance, superior chemical resistance, particularly to corrosion, impermeability to liquids or gases, a decorative effect... Naturally, the choice of deposit and deposition method depends on a number of parameters: thickness, substrate material and its properties, particularly its coefficient of expansion, and the geometry of the area to be covered. The function to be fulfilled by the deposit is also important in the choice (for example, a thick deposit is far preferable to a thin one for wear protection). The same applies to the component's conditions of use, in particular the operating atmosphere and temperature... all this, of course, taking into account the cost of deposition in relation to the gain provided by the deposit. Under certain conditions, it is also possible to seal thick ceramic deposits, which often have open porosities, i.e. channels running through the entire thickness of the deposit.

While ceramics have existed since the Palaeolithic (≍ 29,000 BC), technical ceramics developed in the 20th century. Ceramic deposits only appeared in the second half of the twentieth century, although metal deposition techniques were first developed in the late nineteenth century using PVD (Physical Vapor Deposition) and CVD (Chemical Vapor Deposition). Flame spraying was introduced in the early 20th century, followed by plasma deposition in the 1950s. PVD and CVD evaporation and thermal spraying techniques were really industrialized in the 1960s-1970s.

The ceramic deposits discussed in the following are either thick deposits (from 50 μm to a few mm) deposited by thermal spraying (plasma or flame), or thin deposits (a few tenths to a few tens of μm) obtained :

• Chemical Vapor Deposition (CVD), possibly plasma-assisted (Plasma Enhanced CVD), also known as Plasma Assisted CVD (PACVD). Deposits of several mm have been achieved with these methods, but are routinely limited to 50 μm;

• Physical Vapor Deposition (PVD), Electron Beam PVD (EB-PVD), Laser Pulsed Laser Deposition (PLD). Physical deposits are generally limited to 5 μm.

Whatever their application in the aerospace, automotive, metallurgy, mechanical engineering, chemical, electronics and optics sectors, the most commonly deposited ceramic materials are oxides, nitrides, carbonitrides and borides.

The main properties of the ceramics most commonly used in thin deposits will be presented, followed by thick deposits, and the deposition...