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The deformation and structural evolution characteristics of cementite in tribolayers significantly impact the friction and wear properties of pearlitic steels. However, the mechanism and size dependency of cementite amorphization remain unclear. Herein, the focused ion beam (FIB) lift-out technique was used to prepare transmission electron microscopy (TEM) samples of tribolayers formed during dry sliding of pearlitic steel. The microstructure of and elemental distributions in the tribolayers were characterized. Furthermore, molecular dynamics (MD) simulations were employed to analyze the behavior of dislocation slip systems in ferrite that extended toward cementite and induced amorphization. The results indicated that cementite amorphization occurred prior to dissolution within the tribolayer. Dislocation slips at the phase interface resulted in C diffusion and cementite amorphization. The transformation of cementite was size dependent. Thin lamellae transformed into amorphous lamellae, while local deformation and shear bands formed in thick lamellae. These research findings could contribute to rational design of cementite and to control of its structural evolution behavior within a tribolayer, thereby enhancing the wear resistance of a material. • Dislocation slip at the phase interface results in diffusion of C and amorphization of cementite in a tribolayer. • The amorphization process is size dependent, with 5 nm being the size that most easily forms amorphous materials. • Thin lamellae transform into amorphous lamellae, while local deformation and shear bands form in relatively thick lamellae. [ABSTRACT FROM AUTHOR]

High density TiC-based cermets were fabricated using a simple melt-infiltration/sintering method, with three different grades of stainless steel binder. Reciprocating wear tests were conducted using a ball-on-flat geometry, with the test material sliding against a WC-Co counter face. The morphology of the worn surface and wear debris were investigated using SEM and EDS chemical analysis. FIB microscopy was applied to study sub-surface damage within the wear tracks, to aid explanation of the operative wear mechanism(s). The wear behaviour is moderately complex, transitioning from two- to three-body abrasive wear, with both steel binder extrusion and TiC fragmentation observed to contribute towards third-body formation. A further transition to adhesive wear is also observed, with tribolayer generation on both tribo pair surfaces. [ABSTRACT FROM AUTHOR]

The search for Mo-Si-B based alloys exhibit excellent high-temperature wear resistance is highly demanding for their structural applications. For this target, the Mo-Si-B-xTi (x = 10, 20 and 30 wt%) alloys were fabricated and their dry sliding tribological properties at 25–1000 °C in air were systemically investigated. It indicates that the tribological properties of the MoSiBTi alloys are greatly determined by the test temperature and Ti content that correlates to oxidization process and oxidation products. Compared with other alloys, the Ti30 alloy shows an excellent wear resistance at 600–1000 °C due to the formation of dense tribo-oxides layer and improved oxidation resistance. Meantime, the friction coefficient at 800 °C is as low as 0.31 because of the formed self-lubricating tribolayer. • Dry sliding tribological properties at 25–1000 °C were systemically investigated. • Tribological behavior is greatly influenced by Ti content and test temperature. • Oxidization process and products determines the lubricating and wear mechanism. • COF of 0.26–0.31 can be obtained at 800 °C because of the excellent self-lubricity. • Ti30 alloy with 30 wt% Ti shows an excellent wear resistance at 600–1000 °C. [ABSTRACT FROM AUTHOR]

Using techniques such as scanning electron microscopy (SEM), micro-Raman spectroscopy and glow discharge optical emission spectroscopy (GDOES), this work aimed to develop a physico-chemical methodology for characterising tribolayers. Reciprocating sliding tests (DLC slides without rolling on a flat surface of AISI 304 stainless) under a special atmosphere (refrigerant R134a) were performed. The use of scanning electron microscopy made characterising the evolution of the tribolayers possible. The Raman spectroscopy results revealed the formation of an oxide tribolayer associated with the incorporation of fluorine from the atmosphere. This result was corroborated by GDOES analysis, which also provided information about the effect of the test time on the tribolayer thickness. [ABSTRACT FROM AUTHOR]

Fretting wear evolution of γ-TiAl alloy was investigated. Evolution of wear scar, tribolayer and wear debris were studied using optical microscope and scanning electron microscope. The results show that the wear debris generated from γ-TiAl alloy can be compacted to form a tribolayer rapidly after 100 fretting cycles. At the starting stage, the rapid formation and rupture of tribolayer alternatively occur due to insufficient thickness of the tribolayer. With the proceeding of fretting, the thickness of tribolayer increases due to increase in the amount of the wear debris, which makes the tribolayer more stable. The evolution of the wear debris and the formation of tribolayer significantly influence the fretting wear behavior of γ-TiAl alloy. The wear rate of γ-TiAl alloy decreases rapidly from 255.6 × 10−3μm3 /(N·μm) after 2000 fretting cycles to 35.5 × 10−3μm3 /(N·μm) after 10,000 fretting cycles when a thick tribolayer is formed. A physical model was proposed to describe the evolution process of the fretting wear of γ-TiAl alloy. • Wear debris of γ-TiAl alloy can be compacted to form a tribolayer rapidly. • Rapid rupture of tribolayer occur due to insufficient thickness. • Increase in thickness makes tribolayer more stable. • Evolution of tribolayer significantly influences fretting wear of γ-TiAl alloy. [ABSTRACT FROM AUTHOR]

Cu-based brake pads for high-speed train were tested in full-scale at braking speeds as high as 380 km/h. The microstructure, composition and properties of the original, worn and lateral surfaces were investigated. The results show that a ~2 μm thick nanostructured tribolayer composed of CuO and Fe 2 O 3 was formed on the worn surface, owing to the plastic deformation, mechanical mixing, oxidation and sintering processes. The tribolayer enables significantly higher friction coefficient and wear resistance than original surface, which can be attributed to oxide-based composition and high hardness. The graphite particles in the worn and lateral surfaces were burned and the copper matrix was oxidized. The tribological property of brake pad highly depends on the composition and microstructure of the tribolayer. Image 1 • Cu-based brake pads for high-speed train were tested in full-scale braking at 380 km/h. • A nanostructured tribolayer composed of CuO and Fe 2 O 3 was formed on the worn surface. • The tribolayer enables high friction coefficient and excellent wear resistance. • Oxidation, delamination and spallation are the dominant wear mechanisms. [ABSTRACT FROM AUTHOR]

Graphene and modified graphene can provide exceptional lubrication when used as additives. Here, we applied several types of graphene on steel tribo-couples to perform friction tests. The results indicate that the solution concentration and processing method regarding the graphene-containing alcohol solution can significantly affect the lubrication performance. Graphene nanoflakes aggregated on the sliding interfaces and underwent structural transformation under high contact pressure after the alcohol completely evaporated. The wear track and wear scar were then effectively protected by the in situ as-formed tribolayer. In contrast, a tribolayer could not form when the tribo-couples slid in a solution environment, as the graphene adsorbed on the contact area could be removed away by the alcohol. • Various types of graphene lubricants are investigated regarding the interfacial friction evolution. • The optimization concentration and processing method with respect to the graphene solution for lubrication are clarified. • The growth mechanisms and structural characteristics of the graphene-induced tribolayers are analyzed at the atomic scale. [ABSTRACT FROM AUTHOR]