Self-adaptive and self-healing nanocomposite tribocoatings
|PhD ceremony:||H. (Huatang) Cao, MSc|
|When:||March 25, 2019|
|Supervisors:||prof. dr. Y. (Yutao) Pei, prof. dr. J.T.M. (Jeff) de Hosson|
|Where:||Academy building RUG|
|Faculty:||Science and Engineering|
In this thesis the design and exploration of environmental self-adaptive and damage self-healing tribocoating with both an ultralow coefficient of friction and a low wear are studied. Our objective is aimed at producing WS2 in which the porous structure with micocracks are healed and the tribo-system becomes self-repairing and even self-curing. In general the coatings has a coefficient of friction down to 0.02 in dry air (5% RH) and around 0.15 in moisture (55% RH), together with an ultralow wear rate of 10−7 mm3 m−1N−1. The nonreactive WS2/a-C coating is superior to the WS2/a-C:H one for the future development of self-adaptation in varied humidity conditions. HR TEM observations reveal an instant WS2 platelets rearranged parallel to the sliding direction. This corresponds to a short tribological running-period and thus self-adaptive “frictionless” response. Besides, by sliding contact, segmented TMD nanoplatelets are reorientated and bridged to form a closed continuous tribofilm that could consequently repair damages in an adaptive way. In fact, the notched damages are acting as microreservoirs restoring debris which become transformed at a later stage into tribofilm consisting of well aligned WS2 lubricants.. The study sheds new light on the release of the requirement of producing flawless coatings for tribo-applications.