Scuffing of Aluminum/Steel Contacts Under Dry Sliding Conditions

摘要

Some typical applications where scuffing may occur are gear teeth, piston rings andcylinder pairs, cams and followers, splines, sleeve bearings, and parts of swash and wobble platecompressors. Unlike other tribology-related failures, scuffing occurs very fast, without anywarning, and usually leads to the complete destruction of the sliding pair. Practical experiencewith steel has helped to outline safe ranges of operation for some components. Very little,however, is known about aluminum, which is the second most commonly used engineering metal.The aim of this study is to obtain a better understanding scuffing and seizure of aluminum/steelcontacts.The research includes an experimental study of scuffing of aluminum/steel contacts underdry sliding conditions, a study of the physics of the scuffing process, evaluation of varioushypotheses for scuffmg, and modeling of scuffing.The experiments are conducted in a custom-designed tribometer, which provides accuratecontrol of the environmental conditions. Special instrumentation, experimental procedures andsoftware are developed as a part of the experimental program. These provide a reliablereproduction and identification of scuffing under laboratory conditions. The scuffingcharacteristics of five materials are obtained in air and refrigerant (R134a) environments. Theeffects of load, sliding velocity, mechanical strength, environmental temperature, specimengeometry, time, loading history, and type of environment are evaluated.The mechanisms leading to scuffing are studied by examination of surfaces, subsurfacesand wear debris of specimens in the process of scuffing. Quantitative measurements of subsurfaceplastic strain are also obtained.The theoretical part of the study includes the development of a finite element model for thecontact of runned-in rough surfaces and several other models for subsurface stresses,temperatures, and strains. These models provide information about the local conditions in thesubsurfaceBased on the experimental observations and the scuffing models a new hypothesis forscuffing is proposed. According to this hypothesis, scuffing involves initiation of cracks due tosubsurface plastic deformation, propagation of these cracks leading to the removal of the existingprotective surface layers, and finally cold welding due to adhesion between bare metal surfaces.