Availableonlineatwww.sciencedirect.com 魔 。 ScienceDirect WEAR ELSEVIER Wear263(2007)872-877 www.elseviercomlocate/wea Evaluation of scuffing behavior of single-crystal zirconia ceramic materials C. Lorenzo-Martin, O.O. Ajayi, D. Singh, J.L. Routbort Argonne National Laboratory Energy Systems Division, 9700S. Cass Avenue, Argonne, IL 60439, United States Received 16 August 2006; received in revised form 13 December 2006: accepted 18 December 2006 Available online 23 May 2007 Abstract Scuffing, described as sudden catastrophic failure of lubricated sliding surfaces, is usually characterized by a sudden rapid increase in friction, temperature, and noise, and is an important failure mode on sliding surfaces. In metallic materials, scuffing results in severe plastic deformatio of surfaces in contact. This study evaluated the scuffing behavior of two variants of zirconia(ZrO2) ceramic. Using a block-on-ring contact configuration and unformulated polyalphaolefin(PAO)lubricant, step-load-increase scuffing tests were conducted with single crystals of cubic ZrO2-9.5% Y2O3 and tetragonal ZrO2-3% Y2O3 Phenomenological"scuffing", characterized by a sudden rise in friction coefficient and noise, vas observed in the cubic material. For this material, "scuffing"occurred by sudden fracture at the end of test. The tetragonal material underwent no sudden failure(scuffing). This lack of scuffing is attributed to the sequential operation of three plastic deformation mechanisms: ferroelastic domain switching, tetragonal-to-monoclinic phase transformation, and dislocation slip as the frictional stress and energy dissipation pathway Published by Elsevier B.V. Keywords: Scuffing: Zirconia; Plastic deformation; Phase transformation; Ferroelastic; Fracture 1. Introduction sible for scuffing and the development of theories to predict scuffing behavior, mostly in metallic materials. In spite of these Scuffing is a tribological failure event described as a sudden efforts, scuffing remains one of the least understood phenom- catastrophic failure of lubricated sliding surfaces. It is character- ena in the field of tribology. Because of the complexities of this ized by a sudden rise in friction, contact temperature, vibration, phenomenon, the majority of studies have focused on scuffing and noise, resulting in surface roughening through severe plas- prevention strategies, based mostly on phenomenological obser- tic flow and loss of surface integrity [1]. Because of its sudden vations [2]. Indeed, many variables influence the occurrence of nd catastrophic nature, scuffing poses a major reliability prob- scuffing: the materials in contact; the method of preparation of lem for tribological components. Many machine components the sliding surfaces; the composition and nature of the lubri- involved in sliding contact such as gears, seals, and bearings are cant; and the contact operating conditions(temperature, sliding all susceptible to scuffing failure at some point in their oper- ed, and load) ating life. Moreover, there is an ever-increasing technological Scuffing resistance depends on the material properties an demand for higher power density and higher relative sliding the surface finish. In general, heterogeneous materials and speeds in tribological systems and components, thereby rais- superfinished surfaces are more scuffing resistant [2-4]. Also, ing their susceptibility to scuffing failure. For these reasons, the chemistry and rheological properties of the lubricant affect the study of scuffing and its prevention have attracted a strong the occurrence of scuffing. Lubricants containing extreme pres interest in the field of tribology for many decades. Significant sure(EP)additives usually produce a protective surface reaction efforts have been devoted to the study of mechanisms respon- layer(the so-called boundary films), which delay or may even prevent the onset of scuffing [5]. In terms of operating contact 4 Work supported by the Department of Energy, under Contract DE-AC02. conditions, higher temperatures, sliding speeds, and loads often 06CH11357 ranslate to a higher propensity for scuffing failure [6] Corresponding author. Tel. +1 630 252 9021: fax: +1 630 2524798. In view of the increasing demands on tribological com- E- mail address. ajayi@anl. gov (O.O. Ajayi ponents, the phenomenologically based strategies for scuffing 0043-1648/S-see front matter. Published by Elsevier B.V. doi:10.1016wea2006.12054Wear 263 (2007) 872–877 Evaluation of scuffing behavior of single-crystal zirconia ceramic materials C. Lorenzo-Martin, O.O. Ajayi ∗, D. Singh, J.L. Routbort Argonne National Laboratory, Energy Systems Division, 9700 S. Cass Avenue, Argonne, IL 60439, United States Received 16 August 2006; received in revised form 13 December 2006; accepted 18 December 2006 Available online 23 May 2007 Abstract Scuffing, described as sudden catastrophic failure of lubricated sliding surfaces, is usually characterized by a sudden rapid increase in friction, temperature, and noise, and is an important failure mode on sliding surfaces. In metallic materials, scuffing results in severe plastic deformation of surfaces in contact. This study evaluated the scuffing behavior of two variants of zirconia (ZrO2) ceramic. Using a block-on-ring contact configuration and unformulated polyalphaolefin (PAO) lubricant, step-load-increase scuffing tests were conducted with single crystals of cubic ZrO2–9.5% Y2O3 and tetragonal ZrO2–3% Y2O3. Phenomenological “scuffing”, characterized by a sudden rise in friction coefficient and noise, was observed in the cubic material. For this material, “scuffing” occurred by sudden fracture at the end of test. The tetragonal material underwent no sudden failure (scuffing). This lack of scuffing is attributed to the sequential operation of three plastic deformation mechanisms: ferroelastic domain switching, tetragonal-to-monoclinic phase transformation, and dislocation slip as the frictional stress and energy dissipation pathway. Published by Elsevier B.V. Keywords: Scuffing; Zirconia; Plastic deformation; Phase transformation; Ferroelastic; Fracture 1. Introduction Scuffing is a tribological failure event described as a sudden catastrophic failure of lubricated sliding surfaces. It is character￾ized by a sudden rise in friction, contact temperature, vibration, and noise, resulting in surface roughening through severe plas￾tic flow and loss of surface integrity [1]. Because of its sudden and catastrophic nature, scuffing poses a major reliability prob￾lem for tribological components. Many machine components involved in sliding contact such as gears, seals, and bearings are all susceptible to scuffing failure at some point in their oper￾ating life. Moreover, there is an ever-increasing technological demand for higher power density and higher relative sliding speeds in tribological systems and components, thereby rais￾ing their susceptibility to scuffing failure. For these reasons, the study of scuffing and its prevention have attracted a strong interest in the field of tribology for many decades. Significant efforts have been devoted to the study of mechanisms respon- Work supported by the Department of Energy, under Contract DE-AC02- 06CH11357. ∗ Corresponding author. Tel.: +1 630 252 9021; fax: +1 630 252 4798. E-mail address: ajayi@anl.gov (O.O. Ajayi). sible for scuffing and the development of theories to predict scuffing behavior, mostly in metallic materials. In spite of these efforts, scuffing remains one of the least understood phenom￾ena in the field of tribology. Because of the complexities of this phenomenon, the majority of studies have focused on scuffing prevention strategies, based mostly on phenomenological obser￾vations [2]. Indeed, many variables influence the occurrence of scuffing: the materials in contact; the method of preparation of the sliding surfaces; the composition and nature of the lubri￾cant; and the contact operating conditions (temperature, sliding speed, and load). Scuffing resistance depends on the material properties and the surface finish. In general, heterogeneous materials and superfinished surfaces are more scuffing resistant [2–4]. Also, the chemistry and rheological properties of the lubricant affect the occurrence of scuffing. Lubricants containing extreme pres￾sure (EP) additives usually produce a protective surface reaction layer (the so-called boundary films), which delay or may even prevent the onset of scuffing [5]. In terms of operating contact conditions, higher temperatures, sliding speeds, and loads often translate to a higher propensity for scuffing failure [6]. In view of the increasing demands on tribological com￾ponents, the phenomenologically based strategies for scuffing 0043-1648/$ – see front matter. Published by Elsevier B.V. doi:10.1016/j.wear.2006.12.054