Xingzhong Zhao

Effects of lubricants on friction and wear of Ti(CN)1045 steel sliding pairs

Abstract The friction and wear properties of Ti(CN) 1045 steel rubbing pairs were investigated under dry and lubricated conditions by using a pin-on-disk tribometer. The selected speed range was 0.8 to 3.2 m/s and the load range was 58.8 to 235.2 N. Distilled water and a mineral oil (no additives) were used for lubrication, respectively. The wear of Ti(CN) ceramic under dry conditions was caused mainly by adhesion between the rubbing surfaces and the microfracture of Ti(CN). With the load and speed increasing, the adhesion and diffusion between rubbing surfaces increased and resulted in wear increasement of Ti(CN). Because of the brittleness of ceramics, the microfracture wear of Ti(CN) increased rapidly when the load was raised to some high values. The lubricating and cooling effects of the lubricants could improve the frict on and wear. Compared with water, oil was much better in improving the tribological properties. The analysis results obtained from XPS and AES examinations showed that ferrous oxide was produced on the wear scars, which could reduce the adhesion between the rubbing surfaces to some extent. The lubricating effects of the oil under boundary lubrication conditions were attributed to the formation of carbon films on the rubbing surfaces.

Effects of lubricant rheology and additive chemistry in the wear of Si3N4 sliding on steel

Abstract The friction and wear characteristics of silicon nitride/steel sliding couples were examined with a pin-on-disk tribometer under geometry, speed and loads that simulate those encountered in the high-speed machining of steel. The tests were performed in dry sliding and under lubrication with pure paraffin and with paraffin containing 2% chlorinated paraffin or sulfurized olefin. In all conditions, the steel is transferred to the silicon nitride surface and the latter wears by fatigue-induced fracture during the removal of the transferred steel. In dry sliding, it was found that the wear of silicon nitride increases with the amount of frictional power dissipated. At high loads, however, high wear is caused by macroscopic fracture of the silicon. In the tribological conditions, chosen here to simulate those of high-speed cutting, lubricated sliding occurs in the mixed lubrication mode. Accordingly, pure paraffin causes a decrease in friction and wear that is more pronounced as the sliding speed increases or the load decreases. The EP additives used in this test reduce the friction coefficient further by boundary lubrication and decrease the wear rate of Si 3 N 4 by another order of magnitude. Scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) were used for the analyses of the worn surfaces. Tribochemical reactions with the additives occurred on the steel surfaces only. Iron sulfides and chlorides were formed on the steel disk and chlorates and sulfates were found on the steel covering the ceramic disk. These differences are explained by the differing temperatures of pin and disk.

Tribological properties of TiC-based ceramic/high speed steel pairs at high temperatures

Abstract The tribological properties of three TiC-based ceramics — HM1, HM2 and HM3 — against high speed steel were investigated by using a pin-on-disk tribometer at 25 °C and 600 °C. The results of the tests indicated that the friction coefficient and wear rate of HM2 were the lowest among the three ceramics. Its friction coefficient was 0.19, and its wear rate was 1.14 × 10 −14 m 3 /N.m. The examinations of wear scars for ceramics by means of scanning electron microscope (SEM), X-ray diffractometer (XRD) and electron probe analyser indicated that the composition and structure of oxide films formed on the sliding tracks of the ceramics exhibit an important effect on the high temperature self-lubricating behaviour. This investigation also proved that Mo can improve the tribological properties of ceramics, while WC shows a negative effect on them. The different wear mechanisms of HM1 and HM2 were also discussed in this study.

Wear simulation of Si3N4 cutting tool material on a pin-on-disc tester

Abstract Si 3 N 4 -based ceramic cutting tools are used nowadays for machining cast iron, nickel-based alloys, etc. Austenitic stainless steel AISI 321 is one of the most difficult to cut materials. In order to investigate the wear behaviour of Si 3 N 4 ceramic when cutting the stainless steel, wear tests are carried out on a pin-on-disc tribometer, which can simulate a realistic cutting process. The selected load range is from 58.8 N to 235.2 N, the speed range is from 0.8 m/s to 3.2 m/s. The test results show that the wear of Si 3 N 4 ceramic increases with both load and speed and the wear of the ceramic is mainly caused by adhesion between the rubbing surfaces. Scanning electron microscope (SEM), electron probe microanalyser (EPMA) and energy dispersive X-ray analyser (EDXS) were used for examinations of the worn surfaces. The wear mechanisms of Si 3 N 4 ceramic sliding against the stainless steel were discussed in detail.

Tribological characteristics of Si3N4 ceramic sliding on stainless steel

Abstract Austenitic stainless steel AISI 321 is one of the most difficult to cut materials. In order to investigate the wear behavior of Si3N4 ceramic when cutting stainless steel, wear tests were carried out using a pin-on-disk tribometer which could simulate a real cutting process. Test results show that the wear of Si3N4 ceramic is caused mainly by adhesion between the rubbing surfaces; the wear increases with load and speed. When oil is used for lubrication, the friction coefficient of the sliding pairs and the wear rate of the ceramic are reduced. Scanning electron microscopy, electron probe microanalysis, and energy-dispersive X-ray analysis were used for examination of the worn surfaces. The wear mechanisms of Si3N4 ceramic sliding against stainless steel are discussed in detail.

Effects of antiwear additives on the friction and wear of Si3N4/steel sliding contacts

Abstract Si 3 N 4 -based ceramics have been used for machining cast iron at very high speeds. However, they have been found to be unsuitable for machining steel because of the severe wear of the ceramic cutting tools, which is thought to be mainly caused by the chemical dissolution of the ceramic in the chip at the high temperatures reached at the cutting edge. In this paper, a simulation test was carried out on a pin-on-disk tribometer in order to investigate the effects of two antiwear additives on the friction and wear of Si 3 N 4 /1045 steel sliding contacts. Sliding speeds 1.6 m s −1 and 3.2 m s −1 were used, respectively, the selected test load was 117.6 N. The test results show that lubricants containing antiwear additives used in this lest could greatly reduce the friction coefficient and wear rate of Si 3 N 4 ceramics. Scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction spectroscopy were used for the analyses of the worn surfaces. Tribochemical reactions about the additives occurred on the frictional surfaces, the tribochemical films formed on the rubbing surfaces improved the boundary lubrication conditions of the sliding contacts, the interdiffusion and adhesion between the rubbing surfaces were prevented or were greatly reduced.

Wear behavior of Al2O3-TiCN composite ceramic sliding on stainless steel

It is well known that austenitic stainless steel AISI302 is relatively difficult to cut. In order to investigate the wear behavior of Al2O3-TiCN composite ceramic when machining austenitic stainless steels, a blockon-ring tribometer was used to simulate a real machining process. The test results showed that the wear of both the ceramic and the stainless steel increased rapidly with increasing load and speed. The boundary lubrication actions of water and oil used in this test could not reduce the wear of the rubbing materials. Scanning electron microscopy and energy-dispersive x-ray spectroscopy analyses identified material transferred between the ceramic and the stainless steel surfaces in rubbing process. On the one hand, stainless steel transferred on the ceramic surface because of adhesion; on the other, some ceramic fragments caused by microfracture of the ceramic were found to be embedded in the worn stainless steel surface. The wear of Al2O3-TiCN ceramic sliding against stainless steel was caused primarily by adhesion between the rubbing surfaces and the microfracture of the ceramic.