Oerlikon Balzers DLC coating extends life, performance of sliding ceramic, metallic and polymer components

Oerlikon Balzers (Balzers, Liechtenstein), a company that produces specialized diamond-like carbon (DLC) coatings for components globally, recommends its advanced tetrahedral amorphorous carbon (ta-C) coating, Balinit Milubia, to reduce the coefficient of friction (COF) of ceramic, metallic and polymer components in water environments that are under high loads or subject to extreme friction, wear and contact with other parts, while increasing wear resistance.

Components used in water, lubricated or submersed environments, face considerable tribological challenges that can ultimately affect performance and reduce the life of the larger system — particularly those that come in contact or slide against other parts. This process includes pump parts, mechanical seals and high-pressure valves often manufactured using ceramic substrates designed to survive wet, corrosive environments. These substrates, however, are also easily damaged due to high friction of sliding/mated parts due to a consistently high COF when uncoated. 

Industrial DLC coatings, like Balinit Milubia, are reportedly able to increase the surface hardness of even hard, ceramic substrates, ensuring a low value of COF. For example, Oerlikon Balzers has demonstrated that the ta-C coating can reduce COF to level that consistently approach 0.1-0.2, even in wet or dry running conditions. Moreover, the coating can be applied through experienced toll processors at a very low cost per part, increasing the performance and life of critical parts. Ultimately, DLC coatings are able to prevent parts from pitting, galling, seizing and failing in the field.

According to the company, coatings within the DLC family can be highly engineered based on factors such as hydrogen content (hydrogenated or hydrogen-free), the selection of additional metallic and non-metallic doping elements, the presence of sub-layers and the choice of deposition and bonding methods. Together, these factors can be precisely controlled to create a broad range of thinly applied (typically 1-5 μm) DLC coatings with a hardness of 8-80 GPa.

Oerlikon Balzer ta-C coatings offer a typical hardness of 40-60 GPa, ideal for components that are exposed to extreme operating forces over the long term, such as shafts and seals, where friction can cause components to overheat or fail. The ta-C coating is typically applied in a thickness of only 0.5-2μm using physical vapor deposition (PVD) by arc evaporation. This produces ta-C, which has substantially higher abrasive wear resistance than a-C:H alternatives.

Because the coating can be applied at a temperature below 150°F (65°C) distinctive even within the DLC family, it can be applied to thermally sensitive substrates such as polymers and elastomers that before now have been difficult to coat. “Among all DLC coatings, Balinit Milubia provides the lowest friction coefficient possible compared to other materials and uncoated metals, ceramics, polymers and elastomers in water environments,” according to Dr. Oliver Jarry of Oerlikon Balzers.

Concerning alumina (Al₂O₃) and silicon carbide (SiC) ceramic components, i.e., pump, valve and faucet components, a ta-C coating has reduced COF and associated thermal rise, outperformed typical PVD coatings such as chromium nitride (CrN).

For polymers substrates, which are relatively soft and quickly wear or are damaged in high-contact, high-friction applications, a ta-C DLC coating is can provide a coating hardness of up to 50 GPa to increase component durability and lifespan. As polymers are characterized by a low thermal stability — meaning they can melt or deform at the temperatures most PVD coatings require — a ta-C coating coating can also be applied at a temperature below 150°F (65°C) which is low enough to avoid thermal deformation of most polymers. This coating also attenuates or evacuates electrostatic discharge (ESD) on polymer substrates — a common challenge for traditional coatings, which are difficult to apply over an insulating substrate — and modifies its surface energy. The same process can be used to increase or decrease the wettability of polymers as required.

Elastomer substrates, which also generate high friction, leading to energy and efficiency losses (e.g., sealing rings in motorbike fork tubes), have also performed well with ta-C. Conducted tribology tests have demonstrated that the COF remained near 0.1, despite altering the speed and load of the sliding/contacting parts. In contrast, the uncoated NBR elastomer exhibited COF values 10x higher, approaching 1.0.