Wear Protection through diadur®/DLC Coating

A diadur®/DLC coating (Diamond-Like Carbon) is used for performing lasting modifications of the surface properties of components and tools. In this process, 2-3µm thin layers are evaporated on the surface at temperatures of less than 150°C by using an environmentally friendly PACVD procedure (Plasma Activated Chemical Vapor Deposition).

A diadur®/DLC carbon coating creates completely new usage properties of the surface without changing the base material. Special features of a diadur®/DLC coating are an extremely high microhardness and excellent sliding friction properties.

Benefit from our strengths:

• Longer life cycles due to optimal wear protection for tools and machine components
• Reduction of lubricant use and less power loss
• Without using releasing agents in forming processes
• Development of new application areas in medical and food technology

Due to the extraordinary material properties of diadur®/DLC these layers are used in all relevant industries. Particularly in systems exposed to tribological stress diadur®/DLC coatings have many advantages. In places where component surfaces move against each other creating friction and wear a surface coating is recommendable.

• As diamond-like carbon layer on silicium carbide sliding rings diadur®/DLC enhances the performance to an extent that has not been achieved so far. Whether in stirring unit or compressor sealings – the precision surfaces are optimally protected.
• In case of aluminium forming processes diadur®/DLC prevents cold welding of the die surface. The use of releasing agents is not necessary. The endurance of the forming dies is improved.
• In motor sports, chassis and engine components are equipped with diadur®/DLC for ensuring a smooth race. Thus, performance losses are minimized and premature wear is prevented.

Diamond-like coatings from the gas phase
The components are inserted in a vacuum chamber. Then they are evacuated and purged with process gas. After achieving the process pressure, the gas phase is transformed to a plasma by applying electrical voltage between two electrodes. The subsequent coating process can be divided into two steps.

1) In the plasma-physical etching process argon is used as process gas. During gas discharge Ar+ ions are produced which are accelerated in component surface direction at a high speed. The pulse transmission of the Ar+ ions allows for the removal of impurities near to the surface.

2) After cleaning the coating process is performed. Carburet hydrogen is introduced into the plasma zone and then ionized and fragmented. Products of C_xH_y compounds condense on the component where they crosslink to a diamond-like plasma polymer layer.

diadur®/DLC layers
Different modifications of carbon are known – diadur®/DLC is one of them. Besides diamond known as the hardest material and graphite appreciated as excellent lubricant diadur®/DLC is a third carbon modification offering both the high hardness of diamond and the excellent sliding friction properties of graphite.

Crystalline structure

• Each C atom has four neighbouring C atoms
• Tetrahedron-shaped arrangement (atom distance: 0.154nm)
• High bonding forces in all space directions
• Extremely high mechanical stability

Graphite structure 

• Each C atom has three neighbouring C atoms (atom distance: 0.142nm)
• Planar arrangement in a hexagonal ring structure
• Larger distance between the sliding planes (atom distance: 0.333nm)
• The sliding planes can be easily shifted against each other

Amorphous structure – diadur®/DLC 

• Irregular arrangement of the C atom (black) and the H atom (yellow)
• Strongly cross-linked structure: hydrogen percentage between 15-25at% (hard coating)
• Weakly cross-linked structure: hydrogen percentage between 30-50at% (soft coating)

Due to its low hydrogen content diadur®/DLC layers are considered extremely hard carbon coatings.



The special feature of diadur®/DLC coatings is the combination of a high microhardness and an extremely low sliding COF (Coefficient Of Friction).

Microhardnesses by comparison		COF by comparison
Diamond	100.0 GPa	100Cr6 Hard metal	µ = 0.78 µ = 0.4
diadur®/DLC	25.0 - 30.0 GPa	diadur®/DLC	µ = 0.12
100Cr6 Steel	8.0 -  8.5 GPa 4.0 – 4.5 GPa	counter body: 100Cr6

 

	Coating thickness
	diadur®/DLC	diadur®/CS
Coating thickness 1 / µm	1 – 4	1 - 10
Microhardness2 HIT / GPa	25 - 30	15 -19
COF3 vs. 100Cr6	0.12	0.10
Wear coefficient4 vs. diamond suspension / m³/Nm*10-15	0.6	18
Adhesion class5 n. VDI 3198	1	1
Operation temperature / °C	350	400
Coating temperature / °C	< 150	< 150
Color	Black	anthracite

Test method
1 Stylus method
2 Nano-indentor
3 Pin on disc
4 Calo prep.
5 Rockwell

Measurement and testing technology: 
In addition to a modern system control that constantly controls, monitors and documents the coating process quality controls of the produced coatings are performed in our test laboratory on a regular basis.

In the pro-beam test laboratory the guaranteed thin film properties are continuously controlled. In this process the relevant measuring methods such as coating thickness, adhesion and wear determination as well as measuring the microhardness of the coatings.

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