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Aluminum is a very commonly used material at present, and roughly half of the produced aluminum products undergo forming during manufacturing. Galling is a severe form of wear that occurs during sheet metal forming operations and is a common failure mode of materials in sliding contact; however, the causes and mechanisms of galling are poorly understood. In this work, sliding wear experiments were conducted to produce galling wear between a tool steel ball bearing and aluminum alloy Al5083, to study the relationship between the coefficient of friction, the lump growth on the tool and the scratch morphology. Whilst the characteristic friction regimes were observed, the characteristic damage (grooves running parallel to the scratch direction) was not observed. Instead, when galling was developed on the indenter, the scratch surface morphology displayed a series of peaks and grooves perpendicular to the scratch direction. It is likely that the difference in scratch morphology observed once galling was initiated is due to the lower hardness and reduced work hardening behavior of the Al5083 alloy, compared to the high strength steels previously examined in sheet metal forming applications. The evolution of the scratch morphology has been characterized in a novel way by investigating the distribution of the longitudinal cross-section profile height along the scratch length in relation to the three-stage friction regime observed. This showed that, as the galling wear progressed, the longitudinal cross-section profile height distribution shifts towards negative values, with a corresponding shift in the distribution of material transferred to the tool shifting to the positive. This indicates that, as the amount of material adhered to the indenter increased, the depth of the grooves on the scratch surface perpendicular to the sliding direction also increased. [ABSTRACT FROM AUTHOR]

A dicationic liquid (DIL) was synthesized and used as a base lubricant. IL-grafted graphene oxides (MGO) were manufactured as an additive to the DIL lubricant. Then, the MGO/DIL was applied as a lubricant for the surface contact between a stainless steel ball and bearing steel. The tribological performance of MGO/DIL was measured and compared to those from a monocationic liquid (MIL) based lubricant. The MGO/DIL lubricant produced better friction and wear performance at room temperature but poor wear at 100 °C. Through novel instrumentation techniques, it could be found that when DIL is exposed to air at higher temperatures, more oxygen is adsorbed into DIL, which accordingly reacts with underlying bearing steel, resulting in critical surface oxidation and wear. • The DIL [(C 1 im) 2 C 6 ][NTf 2 ] 2 lubricants and IL-grafted GO additive were synthesized • Wear and COF of steel alloy were investigated at room temperature and 100 °C • Compared to MIL, the DIL showed better thermal stability but poor friction and wear • Due to its doubly charged cation, the DIL produced severe wear at high temperature [ABSTRACT FROM AUTHOR]

In this study, the wear resistance of AISI M2 high-speed tool steel produced using direct energy deposition (DED) was investigated in detail. Wear behavior was studied under different wear loads and sliding speeds using ball-on-disk tribology tests with two different counterpart balls (bearing steel and ZrO2). The wear test results revealed that there was almost no wear damage in the M2 alloy when a bearing steel counterpart ball was used. When a ZrO2 ball was used as the counterpart, a measurable, but small, amount of wear weight loss of M2 was observed. It was found that M2 alloy fabricated by DED has excellent wear resistance, greater than fully carburized conventional steel and high wear resistance steel produced by DED. The formation of a lubricious tribo-oxide film on the worn DED M2 surface is likely the reason for its excellent wear performance. The total wear weight losses of only ~1.5 mg was observed for the M2 produced by the DED, both in the as-DEDed and heat treated states against ZrO2 balls, under the wear loading conditions of 50 N wear load, 100 mm/s sliding speed and total sliding distance of 500 m. In comparison to the other wear-resistance materials, the wear weight loss of the M2 produced by the DED was more than 6 times smaller than the fully carburized structural steel and 1.5–4 times smaller than high wear resistance steel produced by the DED. Thus, DED of the M2 alloy offers a great potential for the production of wear-resistance hard-facing of tribological components. [ABSTRACT FROM AUTHOR]

Concentrated polymer brushes (CPBs) synthesized by advanced surface-initiated controlled radical polymerization have received increasing attention in the tribological field because CPBs in good solvents exhibit superlow friction phenomena under macroscopic severe sliding conditions. To realize tribological applications of CPBs, an understanding of the wear mechanisms of CPBs is required to develop a method to enhance their durability. In this study, an operando tribo-Raman spectroscopic experiment, which is an effective approach for revealing the wear mechanisms of tribo-materials, was conducted on the frictional interface between a polymethyl methacrylate (PMMA)-CPB and a bearing steel ball immersed in an ionic liquid (IL), which is a good solvent for PMMA-CPBs. From the operando tribo-Raman results, the concentrations and molecular structures of the PMMA-CPBs and IL at the frictional interface were found to be constantly changing with the sliding cycles during operation. Moreover, their time-dependent changes strongly affected the wear process and superlow friction phenomena of the PMMA-CPB lubricated with the IL. Consequently, our results suggest that controlling the degree of swelling of CPBs at frictional interface is an effective approach for realizing a durable-superlow frictional tribo-system of CPBs. • Tribological phenomena of CPB–steel tribo-systems in ionic liquids were investigated. • The Tribo-Raman method was conducted to reveal the tribological phenomena. • The conformation of CPB chains and ILs were changed during friction test. • The concentration of CPB chains and ILs decreased during friction test. • Their conformation is a key factor for achieving superlubricity of the system. [ABSTRACT FROM AUTHOR]

Abstract: The tribological behavior of a Ni3Al alloy prepared by hot-pressed sintering was investigated at dry friction and sea water condition against AISI 52100 steel ball in ambient environment and at varying loads. The tribological results suggested that the Ni3Al alloy has the better wear resistance properties compared to Ti–6Al–4V alloy at dry friction and sea water conditions, and the Ni3Al alloy possesses the excellent wear resistance properties under sea water environment. Sea water plays a significant role in the improvement of tribological properties of the Ni3Al alloy, which has lubricating, cooling, and corrosive effects on the friction pairs. [Copyright &y& Elsevier]

Formulae are derived from first principles which predict the wear depth of a ball and a flat surface through time as they slide against each other, in relation to any phenomenological law for wear volume, and taking into account the effect of component geometry. The equations can be fit using experimental wear volume data from ball-on-flat tribometers. The formulae remove previous limiting approximations made in the literature and extend to the prediction of the wear depth of both contacting surfaces. The wear model accords with a previous model that is validated by pin-on-disc testing of a steel/steel contact. The current paper uses the formulae derived to predict the wear depth of a diamond-like carbon (DLC) coating and a steel ball as they slide against each other in deionised water. An Archard equation is used to predict the wear volume of each surface; however, a DLC coating is known to form a transfer layer which reduces the rate of wear, and since this scenario does not obey Archard's law directly, a time-dependent-specific wear rate is used to fit a semi-empirical model to experimental results. The final model predicts the wear depth of the ball and flat accurately. [ABSTRACT FROM AUTHOR]

Abstract: Surface texture design of a tribo-pair affects its tribological behaviors and temperature distribution, subsequently its performance behaviors and servicing life. Numerical simulation and experiment to study the influence of rectangular texture, on UHMWPE acetabular cup reciprocally slid with steel ball was performed. Results demonstrated the occurrence of periodical and regular fluctuation of the surface temperatures in the cup and ball in accordance with the swing of the ball arm. Higher temperature and amplitude of fluctuation were observed in the ball for cup/steel-ball pairs. Predicted temperature for steel ball sliding in UHMWPE cup with rectangular texture is close and comparable with experimental data under steady state. Prediction reveals that: (i) increase in load and frequency increases the wear depths; (ii) wear of rectangular texture for the condition of short sliding time seems agreeable with experimental data; (iii) thermal effect changes the service performance of UHMWPE after a significant long period of operation that may be explained by the viscoelastic behavior of polymer; and (iv) thermal effect is likely to accelerate the degradation of polymer. [Copyright &y& Elsevier]

The dry-sliding wear mechanism of Si3N4-based composites against AISI-52100 steel ball was studied using a ball-on-disc mode in a reciprocation motion. The addition of TiN particles can increase the fracture toughness of Si3N4-based composites. The fracture toughness of Si3N4-based composites played an important role for wear behavior. The Si3N4-based composites exhibits a small friction and wear coefficient compared to monolithic Si3N4. Atomic force microscopy (AFM) studies displayed fine wear grooves along the sliding traces. The subsurface deformation shows that the microcrack propagation extends along the TiN/Si3N4 grain interface. The wear mechanisms were determined with scanning electron microscopy, transmission electron microscopy, X-ray diffraction and atomic force microscopy. [Copyright &y& Elsevier]