Shu Li

Preparation of NiMoO2S2 nanoparticle and investigation of its tribological behavior as additive in lubricating oils

Nickel oxythiomolybdate (NiMoO2S2) nanoparticles with an average size of 13 nm were synthesized in the microemulsion system of sodium dodecyl-sulphate (SDS)/isopentanol/cyclohexanene/water. The tribological performances of the prepared NiMoO2S2 nanoparticles as a lubricating additive were evaluated in four-ball wear tester and a pin-on-disc tester at elevated temperature. The results showed that NiMoO2S2 nanoparticles as additive exhibit very good EP behavior and possess good anti-frictional performance with a smooth transition from fluid film lubrication at low temperature to solid film lubrication at elevated temperature, which could fit the needs of lubrication at large temperature range

Wear Behavior of Thermally Sprayed Coatings under Different Loading Conditions

Wear behavior of three kinds of thermally sprayed coatings with similar hardness have been investigated under steady-state and dynamic loading tests. The steady-state loading tests were conducted on a reciprocating sliding device and the dynamic loading tests were conducted with a single-pendulum scratching device. Experimental results show that the wear mechanisms of the coatings under steady-state sliding friction testing are microcutting and microploughing, whereas the material losses under the dynamic impact scratch testing are mainly due to split cutting and fracture. Tribo-oxidization in the sliding process was found to have an influence on the wear behaviors of the thermally sprayed coatings. The results also indicated that wear resistance of thermally sprayed coatings can be correlated to hardness, plasticity, toughness, and cohesion. As far as the coatings of similar hardness were concerned, the wear resistance under steady-state loading was mainly due to the cohesion of the laminar structure of the coatings and the wear resistance under dynamic loading was mainly due to the toughness and deformation compatibility of the coatings.

The corrosive wear behavior of Cr-Mn-N series casting stainless steel

Abstract The corrosive wear behavior of Cr–Mn–N stainless steel with additions of Cu and Mo in solutions of H2SO4, HNO3, HAC has been investigated. Its corrosive wear resistance is much better than that of 304 stainless steel. A new method, which can be used to indicate the wear resistance of materials by relationship of consumed energy and scratch volume in single pendulum grooving, has been utilized. This method is simpler, quicker and allows measurement of energy dissipated in a scratching event with much limited scatter. Moreover, the tester can simulate a single event of an abrasive elements scratching with impact across a surface and magnify the event into convenient dimensions for structure or wear mechanism. The reason why the Cr–Mn–N stainless steel has a better corrosive wear resistance than 304 stainless steel is that the former is more likely to engender deformation strengthening than the later except for their similar corrosive resistance. This material can be used as product of pump and valve in wear condition in chemical industry.

Study on the High-Speed Rubbing Wear Behavior Between Ti6Al4V Blade and Nickel–Graphite Abradable Seal Coating

The wear behavior of Ti6Al4V blade rubbed against nickel-graphite (Ni-G) abradable seal coating was studied with a high-speed rub test rig. According to the test results acquired at different incursion per passes and linear speeds, blade wear increased with the increment of linear speed at a fixed incursion per pass. With incursion per pass increasing, blade wear increased when linear speed was fixed at 30 m/s, while decreased at 90 and 150 m/s. Referring to the macromorphology observation, scanning electron microscopy (SEM) and dispersive X-ray spectroscopy analyses of the wear scars, rubbing at 30 m/s, microcutting and microploughing with coating adhesion was the main blade wear mechanism while spalling accompanied by densification was the main coating wear mechanism. Rubbing at 90 and 150 m/s, plastic deformation was the main blade wear mechanism while transfer mixed layer that resulted from blade transferred was identified as the main coating wear mechanism. Quantitative analysis of coating densification and microhardness detection of the transfer mixed layer indicated that high coating densification made great contribution to low blade wear at 30 m/s and aggravated blade wear at high linear speed was due to the high frictional heat and the resultant high-hardness transfer mixed layer. It could therefore be concluded that high linear speed guarantees enough frictional heat output while low incursion per pass is responsible for the accumulation of frictional heat.

Material Transfer Behavior between a Blade and Two Types of Coating during High-Speed Rubbing

ABSTRACT The material transfer behaviors of Al-hBN and NiAl-hBN coatings rubbed by a Ti6Al4 V blade at different linear speeds and single pass depths were studied using a high-speed rubbing tester. The blade height variation analysis, morphologies, energy-dispersive spectroscopy, and X-ray diffraction studies of the blade and the coating wear scars indicated that the coating material transferred to the blade during rubbing with the Al-hBN coating. For the NiAl-hBN coating, the blade material transferred to the coating. The temperature differences at the interface, varying melting points of the coatings, and blade plastic flow softening under high temperatures were regarded as factors for different material transfer behaviors.

Ti6Al4V Blade Wear Behavior During High-Speed Rubbing with NiAl-hBN Abradable Seal Coating

The high-speed rubbing wear behavior between a Ti6Al4V blade and a NiAl-hBN seal coating was studied with a high-speed rub test rig. Blade wear behavior, which had not received enough attentions, was the key concern of this study. The rub tests conducted at different linear speeds and single-pass depths indicated that although wear distance was constant and rub forces decreased at high linear speed, blade wear increased with the increment of linear speed when single-pass depth was invariable. According to scanning electron microscopy, x-ray diffraction, electron probe microanalysis and microhardness analyses of the wear scars, different blade and coating wear mechanisms were observed when rubbed at different linear speeds. Remarkably, when rubbing was done at high linear speed, there was severe blade oxidation with the generation of oxidation layer full of cracks and high-hardness transfer layer in the coating wear scar, and these were identified as reasons of aggravated blade wear.

Comparative Study on the Tribological Performances of Barium Perrhenate, Molybdenum Disulfide, and Calcium Carbonate as Lubricant Additives in a Wide Temperature Range

ABSTRACT Barium perrhenate [Ba(ReO4)2], a compound used as an oil additive, was synthesized via the aqua-solution method. Its tribological properties were examined using the four-ball test and ball-on-disc tribotester in a wide temperature range and compared with those of oil that contained the additive molybdenum disulfide (MoS2) and calcium carbonate (CaCO3) compound. X-ray diffraction analysis, scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and differential thermal analysis/thermogravimetry were performed to determine the possible mechanism of the antifriction behavior of the lubricants. Results of the four-ball test showed that all of the additives can improve the extreme pressure property of the base oil and decrease the wear scar diameters of low-carbon steel balls. The results of the ball-on-disc test suggested that the MoS2 additive exhibited better lubrication property than the Ba(ReO4)2 and CaCO3 additives at below 450°C. The CaCO3 additive displayed moderate performance in friction reducing in the high-temperature period. The Ba(ReO4)2 additive exhibited preferable comprehensive antifriction performance in a wide temperature range because of its intrinsic shear-susceptible property and crystalline change with varied temperatures, which could form a protective layer with some native oxides of the disc sample and thus effectively prevented direct contact between rubbing parts. The detailed friction-reducing mechanism of the three additives is also discussed.