Micro morphological observation and mechanism analysis of boundary layer evolution in mixed powder lubrication

Abstract

In mixed‐powder‐lubricated interfaces, the lubrication performance is strongly affected by evolution of the boundary layer features. Therefore, the current investigation uses a laser microscopy system to observe the behaviours of boundary layer formed on the brass specimens during the process of graphite‐lubricated 0.45 C steel (HRC56) sliding upon brass alloy (HV160). The evolution process of mixed powder lubrication can be divided into 4 typical stages: running‐in, stable, deterioration, and damage. Multiple micro phenomena are observed in the boundary layers at different stages. These include extent of layer coverage, flaking, local adhesion, lamellar shedding, blisters, pits, and abrasion damage. These phenomena indicate that the boundary layer deteriorates from full coverage to a damaged powdery film, and eventually the serious wear on metal substrate. Moreover, an interface model of mixed powder lubrication is established to explain the changes in boundary layers. The model displays that the typically micro events above are related to the quantitative degree of overlapping of the asperities between opposing surfaces. At first, many particles bear the load collectively and adapt to velocity differences through inner shearing in powder layer. Later, plastic deformation and abrasion between asperities play a major role in surface velocity accommodation, and the metal substrates bear the load more directly.

Using a coupled FEM-DEM method to study the nonlinear phenomena of third-body behavior

“…Scholars have observed different shapes, distributions, microcrystal structures, and mechanical properties of third-body from frictional surfaces 7,8 or external sources. 9,10 The caulking and covering effect of small particles and the elastic deformation of large particles in third-body interface were observed 11 and simulated, 12 thereby showing that the third-body particles have various ways to affect the surface damage, macro-friction force, and morphology of third-body interface. Experiments show that the properties of particles such as size, hardness, and fracture toughness have obvious influence on the tribological behaviors of third-body interface.…”

Using FEM to study the frictional instability induced by third-body particles confined in frictional interface

“…This theory has been widely researched in many fields, such as three-body wear (Stachowiak and Stachowiak, 2001), solid contamination in mechanical pairs (Maru et al, 2007) and granular lubrication (Renouf et al, 2011). Previous simulation works show various dynamic properties of frictional surfaces induced by the thirdbody particles between them but always under the assumption that the third-body particles can form a continual flow which separates the two surfaces (Wang et al, 2015;Wang et al, 2018;Wang et al, 2014).…”