Role of temperature in tribolayers in fretting wear ofγ-TiAl alloy

The formation of tribolayers may play significant influences on fretting wear.At elevated temperature,the adhesion among wear debris and the increased diffusion rate facilitate the formation of tribolayers.However,the intensification of oxidation at elevated temperature and the low diffusion rate in oxides may play an adverse role.The present study aims to investigate the role of temperature in tribolayers in fretting wear using aγ-TiAl alloy.Scanning electron microscope,energy dispersive spectrometer,Raman spectrometer,transmission electron microscope and nanoindentation were utilized to investigate the wear debris,tribolayers,and wear scars.The fretting tests showed that,compared with that at room temperature(RT)and 350℃,significant reduction in wear rate and decrease in the fluctuation of friction coefficient occurred at 550 and 750℃.It was further revealed that when temperature raised from room temperature(RT)to 750℃,the oxidation of the wear debris increased slightly and the diffusion coefficients increased prominently,which facilities the formation of well tribo-sintered tribolayers.The well tribo-sintered tribolayers presented homogenous structure,nanocrystalline grains with excellent mechanical properties,and resulted in the improvement in the fretting wear resistance of theγ-TiAl alloy at 550 and 750℃.

Tribological Behavior of Ni-based Self-lubricating Composites with the Addition of Ti3SiC2 and Ag2W2O7

The tribological properties of Nickel-based composites containing Ti3SiC2 and Ag2W2O7 fabricated by spark plasma sintering against Si3N4 balls were investigated using a ball-on-disk tribometer from room temperature to 600℃. The tribolayers formed on the friction surface and their effects on the tribological properties of composites at different temperatures were discussed based on the worn surface characterization. The results show that Ag2W2O7 is decomposed into metallic silver and CrWO4 during the high-temperature fabrication process. The composite with the addition of 20 wt% Ti3SiC2 and 5 wt% Ag2W2O7 exhibits a friction coefficient of 0.33-0.49 and a wear rate of 7.07x 10~5-9.89x 10~5 mm3/(Nm) over a wide temperature range from room temperature to 600℃. The excellent tribological properties at a wide temperature range are attributed to the formation of a glaze layer at low temperature and a tribooxide layer at high temperature, which can provide a low shearing strength for the synergistic effects of Ag and tribooxides.

Tribologically induced nanostructural evolution of carbon materials: A new perspective

Carbon-based solid lubricants are excellent options to reduce friction and wear,especially with the carbon capability to adopt different allotropes forms.On the macroscale,these materials are sheared on the contact along with debris and contaminants to form tribolayers that govern the tribosystem performance.Using a recently developed advanced Raman analysis on the tribolayers,it was possible to quantify the contactinduced defects in the crystalline structure of a wide range of allotropes of carbon-based solid lubricants,from graphite and carbide-derived carbon particles to multi-layer graphene and carbon nanotubes.In addition,these materials were tested under various dry sliding conditions,with different geometries,topographies,and solid-lubricant application strategies.Regardless of the initial tribosystem conditions and allotrope level of atomic ordering,there is a remarkable trend of increasing the point and line defects density until a specific saturation limit in the same order of magnitude for all the materials tested.

Galvanically induced potentials to enable minimal tribochemical wear of stainless steel lubricated with sodium chloride and ionic liquid aqueous solution

The effect of galvanically induced potentials on the friction and wear behavior of a 1 RK91 stainless steel regarding to tribocorrosion was investigated using an oscillating ball-on-disk tribometer equipped with an electrochemical cell. The aim of this investigation is to develop a water-based lubricant. Therefore 1 molar sodium chloride(NaCl) and 1% 1-ethyl-3-methylimidazolium chloride [C_2 mim][Cl] water solutions were used. Tribological performance at two galvanically induced potentials was compared with the non-polarized state: cathodic potential-coupling with pure aluminum- and anodic potential-coupling with pure copper. Frictional and electrochemical response was recorded during the tests. In addition, wear morphology and chemical composition of the steel were analyzed using scanning electron microscopy(SEM) and X-ray photoelectron spectroscopy(XPS), respectively. The galvanically induced cathodic polarization of the stainless steel surface results in electrochemical corrosion protection and the formation of a tribolayer. Cations from the electrolyte(sodium Na^+ and 1-ethyl- 3-methylimidazolium [C_2 mim]^+) interact and adhere on the surface. These chemical interactions lead to considerably reduced wear using 1 NaC l(86%) and 1% 1-ethyl-3-methylimidazolium chloride [C_2 mim][Cl](74%) compared to the nonpolarized system. In addition, mechanical and corrosive part of wear was identified using this electrochemical technique. Therefore this method describes a promising method to develop water-based lubricants for technical applications.

Fretting wear behaviour of machined layer of nickel-based superalloy produced by creep-feed profile grinding

Fretting wear has an adverse impact on the fatigue life of turbine blade roots.The current work is to comparatively investigate the fretting wear behaviour of the nickel-based superalloy surfaces produced by polishing and creep-feed profile grinding,respectively,in terms of surface/subsurface fretting damage,the friction coefficient,wear volume and wear rate.Experimental results show that the granulated tribolayer aggravates the workpiece wear,while the flat compacted tribolayer enhances the wear resistance ability of workpiece,irrespective of whether the workpiece is processed by polishing or grinding.However,the wear behaviors of tribolayers are different.For the polished surface,when the normal load exceeds 100 N,the main defects are crack,rupture,delamination and peeling of workpiece materials;the wear mechanism changes from severe oxidative wear to fatigue wear and abrasive wear when the loads increase from 50 to 180 N.As for the ground surface,the main wear mechanism is abrasive wear.Particularly,the ground surface possesses better wear-resistant ability than the polished surface because the former has the lower values in coefficient friction(0.23),wear volume(0.06×10^(6)μm^(3))and wear rate(0.25×10^(-16)Pa^(-1)).Finally,an illustration is given to characterize the evolution of wear debris on such nickel-based superalloy on the ground surface.

Influence of lubrication,tool steel composition,and topography on the high temperature tribological behaviour of aluminium

The use of high strength aluminium alloys,such as 6 XXX and 7 XXX series,is continuously increasing for automotive applications in view of their good strength-to-weight ratio.Their formability at room temperature is limited and they are thus often formed at high temperatures to enable production of complex geometries.Critical challenges during hot forming of aluminium are the occurrence of severe adhesion and material transfer onto the forming tools.This negatively affects the tool life and the quality of the produced parts.In general,the main mechanisms involved in the occurrence of material transfer of aluminium alloys at high temperature are still not clearly understood.Therefore,this study is focussed on understanding of the friction and wear behaviour during interaction of Al6016 alloy and three different tool steels in as-received and polished state.The tribotests were carried out under dry and lubricated conditions,with two distinct lubricants,using a reciprocating friction and wear tester.The worn surfaces were analysed using scanning electron microscopy(SEM)and energy dispersive X-ray spectroscopy(EDS).The results showed a high dependence of friction and wear behaviour on the tool steel roughness as well as on the stability of the lubricant films.Tribolayers were found to develop in the contact zone and their capacity to improve the tribological behaviour is seen to be drastically impacted by the surface roughness of the tool steel.When the tribolayers failed,severe adhesion took place and led to high and unstable friction as well as material transfer to the tool steel.