Gaseous Tribochemical Products of Hydrogenated DLC Film and Stainless Steel Pair in Air Detected by Mass Spectrometry

Abstract

A technique for detecting gaseous products in an air atmosphere was achieved based on a quadrupole mass spectrometer and a space-minimized sliding unit settled in a vacuum chamber for the purpose of controlling the flow of sample gas and increasing the concentration of products. The test results showed that when a hydrogenated DLC film was rubbed in a dry air environment, carbons were oxidized to form CO 2 . However, in a humid air atmosphere, water molecules competitively reacted with carbons to form hydrocarbons, so the oxidization of carbons by oxygen was inhibited. The different tribochemistry is thought to play an important role in the tribological behaviors of DLC films.

Tribochemistry of Carbon Films in Oxygen and Humid Environments: Oxidative Wear and Galvanic Corrosion

“…In dry oxygen and dry air, much deeper wear tracks (60−90 nm) were created on H-DLC (Figure 5). Based on the previous findings about the easy oxidation of the H-DLC surface and the wear susceptibility of the oxidized surface layer, 5,7,8 the increase in H-DLC wear in O 2 and air environments can be attributed to the combined actions of continuous surface oxidation by oxygen and repeated removal of the oxidation product by interfacial shear during sliding. The wear of H-DLC substrate in dry O 2 and dry air was accompanied by the SS counter-surface wear.…”

“…In the presence of oxygen, continuous formation of oxide layers and their removal by the counter surface result in significant H-DLC wear. 44 This is evident by the significantly higher wear rate in dry oxygen (P O2 = 760 Torr) compared to dry air (P O2 = 152 Torr), indicating that the amount of oxygen in the environment plays a critical role. Removal of the oxidized layers from the DLC surface produces wear debris that can have abrasive effect on the counter surface resulting in mutual wear of both surfaces.…”

“…5−8 Several studies reported that amorphous carbon oxidation is dependent on its microstructure and the oxidizing environment as well. 7,8 In tribological contacts, the shearing action by countersurfaces adds another layer of intricacy to the interfacial oxidation behaviors. 9 The presence of water vapor inside the sliding contact area further complicates the oxidation process since it can change chemical and mechanical properties of the sliding surfaces during the course of sliding.…”

“…5,19 An in situ gas analysis study in vacuum conditions showed that the tribo-chemical reaction products produced during sliding were different for water and oxygen adsorption cases. 8 Polycrystalline and hydrogen-free amorphous carbon films (a-C) show water vapor effects opposite to the H-DLC case; water vapor reduces friction of a-C significantly compared to dry environments. 20,21 This was attributed to the ability of water to dissociate at carbon surfaces, forming a passivated layer at the sliding interface.…”

Role of Water and Oxygen Molecules in the Lubricity of Carbon Nitride Coatings under a Nitrogen Atmosphere

“…Generally, it has been noted that wear of CN X and DLC coatings increases with increasing oxygen levels because of the reactions that occur between the coating and the oxygen molecules [13,14]. Xu et al reported that the tribochemical reactions of DLC coatings in dry air led to oxidation of carbon, resulting in the formation of CO 2 [25]. The structure of worn CN X changes from that of the deposited CN X because of desorption of nitrogen atoms inside the coating [10].…”