Fundamental Investigation on the Tribological Failure Mechanisms of Compressor Surfaces, Scuffing: Detailed Roughness Analysis of Al390-T6

摘要

Scuffing that occurs at tribological contacts in mechanical components, brings about topographical,chemical, and mechanical changes mainly at the sub-micron surface. In this project, extensive studies involving theuse of various engineering and scientific tools were performed to better understand the exact mechanisms behindthis phenomenon. A High Pressure Tribometer (HPT) was used to simulate shoe-on-disk tribological contacts undervarious conditions as encountered in compressor surfaces. Specifically, Al390-T6 disk/52100 steel pin tribo-pairsare representative of typical contacting surfaces used in swash plate-type air-conditioning compressors. Once thetime to scuff a sample under the test protocol was determined, subsequent HPT tests were stopped at 0.25 x ScuffingTime, 0.50 x Scuffing Time, and 0.75 x Scuffing Time intervals. The progressive change in disk topography leadingup to scuffing was first observed in the 1-D roughness study [1], but more extensively captured by the 2-DBirmingham-14 roughness characterization that is also described in this report [2]. When the chemical analyseswere conducted on the uppermost surfaces for depths of 120 nm, significant changes in some of the major chemicalelement concentration were revealed at scuffing. The major chemical compositional changes include a depletion ofsilicon, which was used to strengthen the aluminum alloy, and a drastic increase of oxygen component, signalingheavy oxidation at scuffing [1]. The mechanical properties of the disks undergoing tribological evolution were alsoinvestigated through various experimental hardness measurements, ranging from macro- to micro-, and to nanoscales[3]. Based on the experimental hardness results, it was found that the hardness of the material becomeshigher at the micro- and sub-micro scales than the bulk, regardless of the amount of wear towards scuffing. It wasalso observed that there was a gradual weakening of the uppermost 60 nm. In this report, we describe in detail thesurface roughness changes that occur to the Al390-T6 samples as they undergo progressively longer tribologicaltesting, eventually leading to scuffing.[1] Patel, J.J., Polycarpou, A.A., and Conry, T.F., 2002, ???Investigation of the Scuffing Mechanism Under StarvedLubrication Conditions Using Macro, Meso, Micro, and Nano Analytical Techniques,??? ACRC TR-191,University of Illinois.[2] Suh, A.Y., Polycarpou, A.A., Conry, T.F., 2003, ???Detailed Surface Roughness Characterization ofEngineering Surfaces Undergoing Tribological Testing Leading to Scuffing,??? Wear, in press.[3] Pergande, S.R., Polycarpou, A.A., and Conry, T.F., 2002, ???Use of Nano-Indentation and Nano-ScratchTechniques to Investigation Near Surface Material Properties Associated with Scuffing of EngineeringSurface,??? ACRC TR-193, University of Illinois.