Surface treatments

VAPOUR DEPOSITION

1. General description

Vapour deposition is divided into two main categories: chemical vapor deposition (CVD, Chemical Vapor Deposition) and physical vapor deposition (PVD, Physical Vapor Deposition). The two technologies are similar and are themselves divided into sub-categories. The principle consists of placing the part to be treated (substrate) in a vacuum reaction chamber. The substrate is heated (between 700 °C and 1000 °C for CVD, between 200 °C and 450 °C for PVD). One or more elements (precursors) are then introduced in gaseous form into the reaction chamber. The precursors can be of different natures: Silicon, Carbon, Tungsten, Gold, etc.

In the case of CVD treatments, a chemical reaction occurs between the substrate and the precursors, which merge together, ensuring excellent coating adhesion. As for PVD treatments, the precursor layers are physically deposited onto the substrate’s surface through condensation. While CVD offers better durability, the high temperatures it requires limit its use.

Depending on the precursors chosen, Vapour deposition can protect the substrate against corrosion, harden its surface, or modify its friction coefficient or electrical conductivity. The range of applicable colours is far wider than that offered by other Surface treatments and continues to expand. The fields of application in watchmaking are vast, and Vapour deposition treatments are used for the External parts (case, dial, hands), the Movement and tooling. Depending on the precursors and the method used, the process can be given various names. Thus, the term DLC (Diamond-Like Carbon) is used to designate a PVD treatment whose main precursor is amorphous carbon, valued for its Hardness.

2. Interview with Lucien Steinmann (Positive Coating)

3. History

It was in 1954 that the CVD process was patented. Its goal at the time was to produce a Diamond synthesised through growth. It would not be until two years later that this technology produced the first synthetic diamond. Synthetic diamonds are still produced today using this process, at a rate of billions of carats each year. While this production will probably never replace natural diamonds for jewellery use, synthetic diamonds find multiple industrial and technological applications. In watchmaking, diamond synthesis mainly concerns tooling (cutting tools, Diamond polishing). CVD and PVD will therefore continue to develop and, depending on the precursors used, will find almost unlimited fields of application. From frying pans to surgical instruments, vapour-phase deposits are everywhere. It was from 1995 onwards that horologists (watchmakers) adopted these technologies, first for external parts (case, dial, hands) components (cases), then for all the components of a watch (dials, movements, hands, etc.). The physical, mechanical and aesthetic properties of such treatments, along with the almost infinite range of colours they allow, are a major attraction, and it is likely that these new technologies will, in the near future, completely replace traditional electroplating treatments (galvanic treatments) (Gilding, plating, Rhodium plating).

4. Advantages and disadvantages

Advantages

Protection against oxidation and corrosion

Allow the surface Hardness of the substrate to be modified

Allow the coefficient of friction to be modified

(Almost) unlimited range of colours and precursors

Do not require an electrically conductive substrate

No toxic emissions

Disadvantage

Cutting-edge technology involving costly know-how and infrastructure

Substrate must withstand high temperatures

Do not allow stripping (reconditioning)

High energy consumption