AbstractA Swiss industrial company developed ultra hard coatings (ta-C DLC) as protection against abrasion and contamination of surfaces. Advantages are hardness of >5000HV, low friction coefficient of 0.1, low process temperature of <100°C, control of coating thickness down to a few nanometers. The company is looking for industrial partners (e.g. medical, watch, electronic field) to market these advantages for new opportunities, e.g. for surface hardening, protection against wear, solid lubrication.
DetailsCoatings are used to improve surface characteristics, for example hardness and wear, or to improve lubrication.
Diamond Like Coatings are composed of carbon, which to a great extent possess the same structures as diamond (sp3-configured carbon, see fig. 2) and therefore are extremely hard.
The tetrahedral amorphous carbon Diamond Like Carbon (ta-C DLC) coatings developed by this Swiss company have out-standing properties compared to both existing DLC and conventional coatings: considerably reduced friction, extreme hardness and wear resistance. It is a solution for both industrial and aesthetical applications.
The premise for the production of the special DLC layers is a patented technology developed by the Swiss company: the deposition of its coatings takes place through a filtered arc Physical Vapour Deposition (PVD) process. During the filtered arc PVD process, pure carbon is vapor-deposited under controllable conditions directly onto the substrate – a special technology that is particularly efficient:
• By forgoing the often applied Chemical Vapour Deposition (CVD) process, the company is able to employ processing temperatures below 100° C. This permits almost any material to be coated, without effect on the material properties
• Furthermore, contrary to most DLC coatings, there is no deposition of hydrogen in the coating, therefore rendering it about twice as hard (about 5300 HV)
• Extremely low friction coefficient of 0.1 and lower against steel
• Growth rate of the coating can be controlled within a few nanometers. This, together with low process temperatures, grants form stability of the coated objects, without rounding off edges (e.g. of tools)
Chemically, the coating consists of 100% carbon, to a great extent in the tetrahedral structure of diamond: This quota of diamond, therefore sp3-configured carbon, lays around 70-90%, which is the reason for its utmost hardness.
The remaining residual quota of graphite improves the gliding properties of the layer (extremely low friction coefficient of 0.1 against steel). Thus the coating is an optimal solution in the domain of carbon layers with almost unlimited application possibilities.
These advantages can open new opportunities to mechanical or electronic applications, e.g. as protection against wear and contamination, surface hardening or solid lubrication etc.
For a few years now, these DLC coatings are marketed successfully within the field of machine tools, electronic components and the watch industry.
For visualization see fig. 1 SEM-Picture of multi-layer, ultra hard DLC coating
Fig 2: The pyramid explains the different forms of appearance of graphite and therefore also its properties in the world of coatings:
• sp2-configured carbon is a black and very soft material.
• Polymer-CH: Through the Chemical Vapour Deposition (CVD) process, hydrogen is incorporated into the carbon layer. However, this reduces the hardness of the layer and entails very low application temperatures.
• sp3-configured carbon is pure diamond – famous for its extreme hardness.
The unique structure endows the coatings with the following properties:
• Extreme hardness of about 5'300 HV and more (twice as hard as other DLC layers)
• Utmost wear resistance (around two times compared to other DLC layers)
• Very low friction coefficient of 0.1 and lower
• Perfect adherence, thanks to a special intermediate layer
• 100% biological compatibility
• Chemical stability and corrosion resistance