Grazyna Stachowiak

The effects of particle characteristics on three-body abrasive wear

The effects of abrasive particle characteristics, especially shape and hardness, on three-body abrasive wear of metallic samples have been investigated. The experimental tests were carried out on a modified pin-on-disc tribometer using dry abrasive particles and on a ball-on-plate tribometer using slurry. Spike parameter quadratic fit (SPQ) was used in the characterization of particles angularity. Better correlation between wear rates and particle angularity was found in ball-on-plate tests. The noted exception was quartz that generated less wear in all the tests than could be expected from its high SPQ value. Additional characteristics such as particle toughness, orientation in the contact, and embedment in the worn surfaces affected the wear results. Damage due to rolling (indentation) wear prevailed on the plate samples from ball-on-plate tests, whereas both sliding and rolling wear was found on the cylindrical samples from modified pin-on-disc tests. The morphology of worn surfaces correlated well with the shapes of abrasive particles. Rounded particles generated round craters and smooth grooves while angular particles produced sharp indents and narrow cutting grooves.

Metallic film transfer during metal-ceramic unlubricated sliding

Abstract The friction and wear characteristics of metallic materials in sliding contact with oxide ceramics were examined, using a pin-on-plate configuration and reciprocating motion. Friction was monitored continuously and wear rate was evaluated by microscopic measurements of worn pin scars. Operating wear mechanisms were determined using an optical and scanning electron microscope with an energy-dispersive X-ray attachment. It was shown that the metallic film transfer onto ceramic surfaces depended on the physical properties of the metallic materials and their affinity towards a particular ceramic material. It was concluded that metallic films on the ceramic surfaces acted as a form of protection against wear, leaving most of the original ceramic surfaces undamaged.

Unlubricated friction and wear behaviour of toughened zirconia ceramics

Abstract The purpose of this investigation was to determine the nature of the behaviour of several ceramic and metal combination pairs in unlubricated sliding wear at room temperature. Friction and wear behaviour of Mg-PSZ and Y-TZP ceramics sliding against each other and in contact with metallic materials were studied and the results are presented. The experiments were performed on a high frequency wear test rig with pin-on-plate geometry and reciprocating motion. Both friction and wear results are described as a function of sliding pair combination and test conditions. A scanning electron microscope with energy-dispersive X-ray attachment and profilometry measurements were used for analysis and determination of the wear mechanisms. It has been found that the wear mechanism for metal-ceramic sliding pairs is governed by metallic film transfer on to the ceramic surface. For ceramic-ceramic sliding pairs plastic deformation and delamination processes dominate. The high coefficient of friction values obtained put in question the feasibility of unlubricated applications of ceramics and some form of lubricant seems to be necessary.

Unlubricated wear and friction of toughened zirconia ceramics at elevated temperatures

Abstract The urlubricated friction and wear of toughened zirconia ceramics in contact with themselves and with metallic counterparts were investigated in air at temperatures up to 400 °C. A pin-on-plate tribometer with reciprocating sliding motion was used to carry out the experiments. It was found that the temperature significantly influenced friction and wear characteristics of the tested pairs. The coefficients of friction in the range of 0.3–0.7 were found with the tendency to increase at elevated temperatures. Generally, severe pin wear was recorded with the higher wear rates at higher temperatures for metallic pins, and mostly lower wear for ceramic pins. Promising results were obtained for cast iron-ceramic pairs at room temperature and partially stabilized zirconia-partially stabilized zirconia pairs at 400 °C, where the wear rates were in the range of 10 −6 mm 3 m −1 . The wear scars and wear debris were examined by scanning electron microscopy with an energy-dispersive X-ray attachment.

Wear and Friction Characteristics of Ion-implanted Zirconia Ceramics

Abstract Yttria-tetragonal zirconia polycrystals (Y-TZP) and magnesia-partially stabilized zirconia (Mg-PSZ) ceramics were implanted with ions of C or a combination of Ti+C using a metal vapour vacuum arc (MEVVA) ion implanter. Wear and frictional characteristics of ion-implanted Y-TZP and Mg-PSZ ceramic plates against unimplanted TZP and PSZ pins were investigated using a pin-on-plate reciprocating rig under two levels of load of 1.2 and 2.0 N and an average velocity of 0.1 m s −1 . The effects of ion implantation on friction coefficients and wear rates have been explored by comparing the results with those of unimplanted self-mated zirconia ceramics. It was found that the friction coefficients of the Ti+C and C ion-implanted ceramics were lower than those of the unimplanted ceramics tested under the same conditions but the duration of low friction was short. The wear resistance of the C-implanted zirconia ceramics was significantly higher during the first 400–600 m of sliding (4×10 4 –6×10 4 cycles) than that of the unmodified ceramics, especially at a lower load of 1.2 N. Ti+C ion implantation reduced the wear of TZP only slightly and did not affect the wear of PSZ ceramics due to a quite rapid removal of the implanted layer. The C-implanted layer persisted on the ceramic surfaces over a much longer sliding distance.

Control of fretting friction and wear of roping wire by laser surface alloying and physical vapour deposition coatings

Abstract Surface alloying and thin coatings were applied to roping wire as a means of suppressing fretting wear and friction. Wires were treated by physical vapour deposition (PVD), electroplating and laser surface alloying (LSA). The wear and friction levels of treated wires under dry fretting were measured using a high frequency wear test rig. Chromium and zirconium were chosen as coating materials based on previous evidence for fretting resistance, corrosion resistance and possible strengthening of steel wire. A solid lubricant, molybdenum disulphide, was also deposited by PVD. It was found that LSA provided a more durable friction reduction than PVD coatings. The friction of molybdenum disulphide coating was dependent on coating thickness: a thin coating failed rapidly after an initially low friction, while thicker films afforded a gradual rise in friction from a similar low initial friction coefficient. LSA enabled friction to be raised as well as lowered and laser treatment without alloying had little effect on friction. When high levels of zirconium were used in LSA, a large reduction in wear resulted and laser hardening alone also caused a decrease in wear.

Environmental effects on wear and friction of toughened zirconia ceramics

Abstract The friction and wear of toughened zirconia ceramics in self-mated sliding contacts in various liquid environments were investigated and compared with those observed in air. Tests were performed in distilled water, pure ethyl alcohol and synthetic silicone oil. A pin-on-plate tribometer with reciprocating sliding motion was used to carry out the experiments. It was found that the friction and wear characteristics of the tested pairs were significantly influenced by environment. The lubricated coefficients of friction in the range of 0.1–0.4 were found and wear was generally low. All three environments reduced wear of zirconia ceramics from about 10−14 m3 N−1 m−1 in dry sliding down to about 10−16 m3 N−1 m−1 at the tested temperature and load-speed conditions. The wear scars were examined by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) and the effects of the environment on wear morphology are presented in this paper.

Ferrography and fractal analysis of contamination particles in unused lubricating oils

Abstract Contamination particles suspended in lubricating oils have been characterized by fractal geometry. The contaminant particles present in clean lubricating oils were captured by ferrography and examined by scanning electron microscopy (SEM). Their image was later analysed by a developed computer image analysis system. The system was designed to characterize the morphology of the found particles by their fractal dimensions. Boundary fractal dimensions of the texture and structure were used as the primary parameters. It was found that these parameters can be used for the characterization of particle morphology. The suitability of this technique for the effective characterization of the particles has been evaluated by correlating boundary fractal dimensions of the particles with results obtained from standard microscopy examination. It has been concluded that the method offers the possibility of classifying the particles whose boundary shapes vary significantly. The method, when perfected, could be used as a routine screening technique for the unused oils. Fractal parameters of the contaminants found in oils could be incorporated in a criterion for a specific application of the lubricant.

Fretting wear and friction behaviour of engineering ceramics

Friction and wear characteristics of partially stabilized zirconia (PSZ) fretted against itself and against high carbon steel were investigated. The results for the transformation toughened PSZ ceramics are compared with the behaviour of more brittle alumina ceramic under the same test conditions. Fretting tests in air were carried out on a high frequency wear test rig at room temperature using a cross-cylinder configuration. It was found that both the oxide ceramics were more resistant to fretting wear than the steel. Surface cracking was observed on the alumina wear scars while microfracture and delamination dominated on the PSZ wear scars. When metallic samples were fretted against ceramics, metallic film transfer to the ceramic surfaces occurred.

Suppression of fretting wear between roping wires by coatings and laser-alloyed layers of molybdenum

Abstract Samples of steel roping wires were coated with thin layers of molybdenum by physical vapour deposition and then subjected to a fretting wear test. A further set of molybdenum-coated roping wire samples were processed by laser surface alloying prior to wear testing. Molybdenum-coated wires showed lower wear but not lower friction than uncoated wires in the fretting wear test. A thick coating of molybdenum was found to reduce fretting wear without the need for laser treatment. Fretting wear between molybdenum-coated wires was characterized by the formation of molybdenum oxides on the worn surfaces which suppressed adhesion between the fretting wires. Lifetime of the molybdenum coating during fretting wear tests was determined by coating fracture and spalling.