Effect of Humidity on Friction and Wear—A Critical Review

Abstract

The friction and wear behavior of materials are not intrinsic properties, but extrinsic properties; in other words, they can drastically vary depending on test and environmental conditions. In ambient air, humidity is one such extrinsic parameter. This paper reviews the effects of humidity on macro- and nano-scale friction and wear of various types of materials. The materials included in this review are graphite and graphene, diamond-like carbon (DLC) films, ultrananocrystalline diamond (UNCD), transition metal dichalcogenides (TMDs), hexagonal boron nitride (h-BN), boric acid, silicon, silicon oxide, silicates, advanced ceramics, and metals. Details of underlying mechanisms governing friction and wear behaviors vary depending on materials and humidity; nonetheless, a comparison of various material cases revealed an overarching trend. Tribochemical reactions between the tribo-materials and the adsorbed water molecules play significant roles; such reactions can occur at defect sites in the case of two-dimensionally layered materials and carbon-based materials, or even on low energy surfaces in the case of metals and oxide materials. It is extremely important to consider the effects of adsorbed water layer thickness and structure for a full understanding of tribological properties of materials in ambient air.

Characterization of the Effect of Moisture on Tribology of Titanium Rubbed Against Different Pin Materials

“…cycles. Chen et al [7] reported that the friction coefficient and wear decreased for steel and brass as humidity was increased [2]. In our study also, the friction decreased for both aluminum/titanium and steel/titanium interactions at very high humidity levels.…”

“…For diamond-like carbon, ultra-low friction can be obtained at dry conditions. However, the effect is lost even at low humidity [7]. Since most applications involving pure metal-metal contact use solid or liquid lubricants to reduce interfacial friction, [8][9][10], the tribological study of pure metal-metal interaction is studied less extensively [7].…”

“…However, the effect is lost even at low humidity [7]. Since most applications involving pure metal-metal contact use solid or liquid lubricants to reduce interfacial friction, [8][9][10], the tribological study of pure metal-metal interaction is studied less extensively [7]. Some research has been conducted to understand the effect of humidity on the friction of steel and aluminum [10][11][12].…”

Investigation of the Tribofilm Formation of HiPIMS Sputtered MoSx Thin Films in Different Environments by Raman Scattering

“…The high friction in a humid environment is caused by the surrounding water molecules which are, for instance, responsible for limiting the crystallite alignment and shearing [3]. Since the investigated film is randomly oriented and the (100) crystallite edges are postulated to be favorite areas for water adsorption, the friction increases [19].…”

The Influence of Preparation Conditions on the Structural Properties and Hardness of Diamond-Like Carbon Films, Prepared by Plasma Source Ion Implantation

“…Comparisons of friction coefficient values have to be made with caution, since environmental and test conditions, especially humidity [43], temperature [44], sliding velocity [45], load [46] and material of the counter face [47,48], influence the absolute value of the friction coefficient [49]. Concentrating on literature values from near-identical experiments, values of 0.1 or somewhat below are commonly found for a-C:H films prepared by PSII [50], whereas values of 0.05 are usually only achieved when dopants are added [51].…”