VAPOUR PHASE DEPOSITIONS

Vapour phase deposition is divided into two main categories: Chemical Vapour Deposition (CVD) and Physical Vapour Deposition (PVD). Both technologies are similar and are further subdivided into subcategories. The principle involves placing the piece to be treated (substrate) in a vacuum reaction chamber. The substrate is heated (between 700°C and 1000°C for CVD, and between 200°C and 450°C for PVD). One or more elements (precursors) are then introduced in a gaseous state into the reaction chamber. The precursors can be of different types: silicon, carbon, tungsten, gold, etc.

In the case of CVD treatments, a chemical reaction occurs between the substrate and the precursors, which chemically fuse, ensuring excellent adhesion of the treatment. For PVD treatments, the precursor layers are physically deposited on the surface of the substrate by condensation. While CVD provides better adhesion, the high temperatures it requires limit its use.

Depending on the chosen precursors, vapour phase deposition can protect the substrate from corrosion, harden its surface, modify its coefficient of friction, or change its electrical conductivity.

The range of applicable colours is much broader than those offered by other surface treatments and continues to expand. The applications in watchmaking are extensive, with vapour phase deposition treatments used for the casing, movement, and tooling. The process can have various names depending on the precursors and the chosen method. For instance, DLC (Diamond-Like Carbon) is used for a PVD treatment where the main precursor is amorphous carbon, valued for its hardness.

The CVD process was patented in 1954, with the aim of producing synthetic diamonds by growth. Two years later, the first synthetic diamond was made using this technology. Today, synthetic diamonds are still produced using this process, amounting to billions of carats each year. While they will probably never replace natural diamonds for jewellery use, synthetic diamonds have numerous industrial and technological applications. In watchmaking, diamond synthesis primarily concerns tooling (cutting tools, diamond-tipped tools).

CVD and PVD technologies have since continued to develop, finding virtually unlimited areas of application depending on the precursors used. From frying pans to surgical instruments, vapour phase deposition has become ubiquitous.

Starting from 1995, watchmakers began adopting these technologies for exterior components (cases) and subsequently for all watch components (dials, movements, hands, etc.). The physical, mechanical, and aesthetic properties of such treatments, and the virtually infinite range of colours they propose, are of major attraction. It is likely that these new technologies will soon completely replace traditional galvanic treatments (gilding, plating, rhodium plating).

Advantages:

Protection against corrosion
Ability to modify the surface hardness of the substrate
Ability to modify the coefficient of friction
Almost unlimited palette of colours and precursors
Do not require an electrically conductive substrate

Disadvantages:

Advanced technology that requires expensive expertise and infrastructure
Substrate must withstand high temperatures
Do not allow for scouring (reconditioning)