Detailed surface roughness characterization of engineering surfaces undergoing tribological testing leading to scuffing

Abstract

Controlled tribological scuffing experiments were conducted on typical engineering surfaces (Al390-T6 discs and 52100 steel pins) under starved lubrication conditions (a mixture of R410A refrigerant combined with a polyolester (POE) lubricant) to simulate the contact conditions in an automotive air conditioning compressor. The time-to-scuff was established and was repeatable using a test protocol with increasing load increments. Test were then conducted for periods of 25, 50, and 75% of the time-to-scuff to investigate the progression of surface change preparatory to scuffing. Detailed studies of the surface topography were conducted using line and areal (usually referred as one dimensional (1D) and two dimensional (2D), respectively) analyses. Simple amplitude roughness parameters as well as more detailed spatial, hybrid, and functional parameters were calculated and used to track detailed roughness changes as the Al390-T6 samples undergo progressive wear until scuffing occurs. One-dimensional amplitude descriptors, such as the root-mean-square value, were not reliable in tracking surface topographic changes. However, 2D functional parameters, such as the surface bearing index and the fluid retention index, clearly showed progressive changes as the surfaces wear and reach scuffing.