Accelerated thermal degradation of DLC-coatings via growth defects

作者：Braak R^*; May U; Onuseit L; Repphun G; Guenther M; Schmid C; Durst K

来源：Surface and Coatings Technology, 2018, 349: 272-278.

DOI：10.1016/j.surfcoat.2018.05.063

• DLC
• Thermal degradation
• Growth defects
• Adhesion
• Thermo-chemical stability
• Cavitation

Diamond-like carbons (DLC) are frequently used as wear protection coatings for tribologically loaded steel parts in the automotive industry. Diverse interlayer concepts are applied to increase the coatings adhesion which is otherwise poor on blank steel. Our focus lies on the influence of the adhesion layer design on the thermo-chemical stability of a H-containing DLC-coating and the significant role of growth defects.
At the interfaces between individual layers or in more elaborated transition zones, several stability issues might arise under certain conditions: E.g. a thermally driven, intrinsic aging can lower the adhesion strength. With sufficiently low adhesion, stress corrosion cracking along the interface can occur, leading to delamination progression at subcritical loads.
In the present paper two Cr-carbide based interlayer systems are investigated as adhesion support. Annealing experiments are performed in an N-2-furnace at 350 degrees C with some amount of residual air. Analysis of the interface regions of the adhesion layer system was performed by indentation based, disruptive (adhesion) tests and via the more extensive cavitation erosion test, particularly subsequent to the annealing. Ion milling cuts are performed to evaluate the interfaces even further.
Thermal aging was not observed, but instead a thermo-chemical attack at the interface via growth defects. Cavities are formed along the interface leading to locally confined delaminated areas in just one coating system, whereas in the second one, this failure mode is inhibited.

• 出版日期2018-9-15