Stages in the tribologically-induced oxidation of high-purity copper

Liu, Zhilong; Patzig, Christian; Selle, Susanne; Höche, Thomas; Gumbsch, Peter; Greiner, Christian

doi:10.1016/j.scriptamat.2018.05.008

Cited by 43 publications

(66 citation statements)

References 55 publications

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“…Details of the sample preparation and other experimental procedures can be found in ref [72]. Details of the sample preparation and other experimental procedures can be found in ref [72].…”

Section: Chemical Aspectsmentioning

confidence: 99%

“…[72] This suggests that a stoichiometric cuprous oxide (Cu 2 O) could not be formed due to an insufficient amount of oxygen available for these tribochemical reactions. It yielded an oxygen concentration of 7.2% inside the cluster and 2.1% right outside and in the bulk of the material.…”

Section: Chemical Aspectsmentioning

confidence: 99%

“…It yielded an oxygen concentration of 7.2% inside the cluster and 2.1% right outside and in the bulk of the material. [72] Under the extreme shear imposed by tribological loading, chemical as well as mechanical driving forces apparently act together leading to the formation of these semicircular clusters combining nanocrystalline and amorphous material alike. It is therefore reasonable to assume that the clusters consist of a mixture of Cu 2 O and Cu.…”

Section: Chemical Aspectsmentioning

confidence: 99%

“…Since we could not find any evidence for such clusters for up to ten sliding cycles, we propose the following sequence for the oxidation of copper under tribological loading: As reported for the native oxidation of copper, [74] the process starts with the formation of amorphous cuprous oxide (Cu 2 O) in the form of stochastically distributed and small islands located at the sample surface. [72] Copyright 2018, Elsevier. [75] In the literature and for nontribologically induced oxidation, the growth of individual copper oxide islands has repeatedly been reported.…”

Section: Chemical Aspectsmentioning

confidence: 99%

“…[75] In the literature and for nontribologically induced oxidation, the growth of individual copper oxide islands has repeatedly been reported. [72] Copyright 2018, Elsevier. Initially the clusters are made up of understoichiometric amorphous Cu 2 O.…”

Section: Chemical Aspectsmentioning

confidence: 99%

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Solids Under Extreme Shear: Friction‐Mediated Subsurface Structural Transformations

2019

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reducing energy consumption is a seemingly unlikely candidate: tribology. Tribology is the study of interacting surfaces in relative motion, including friction, wear and lubrication. In the transportation sector, a third of the energy consumed is lost by overcoming friction. [2] As far back as 1977, it was estimated that 11% of the energy used by the transportation, the industrial and the utilities sectors could be saved by new developments in tribology. [3] Although the term "tribology" was only coined in the 1960s, [4] tribological technologies date back to antiquity. Starting a fire by rubbing two pieces of wood together was only possible due to frictional heating. Transportation of the massive stone building blocks of the pyramids required lubricated contacts. [5] Since ancient times, scientific interest in friction and wear has come in cycles, with luminaries like Leonardo da Vinci contributing to the field. [6] In the 1960s tribology rose again to the forefront of government-funded research. Due to limitations in the instrumentation available at the time, the broad interest in tribology then gradually waned. The invention of the atomic force microscope in 1986 [7] and its application to friction in 1987 [8] may be viewed as the origin of a recent renaissance in tribology. [9,10] State of the Art in Materials TribologyGiven tribology's long history and tremendous societal impact, it is somewhat surprising how little mechanistic understanding is available in this field. It has long been recognized, for example, that the complex nature of tribological processes makes it extremely challenging to link nanoscale phenomena to the macroscopic world of gears and engines. [9] On the meso and macro length scales, the elementary mechanisms governing friction and wear, especially for metallic materials, therefore remain elusive. A thorough understanding of the microstructure-properties relation, the key concept of materials science, has not yet been established. Part of the reason is that the microstructure of the material under the contact is highly dynamic [11,12] and its evolution can usually not be observed in situ. This current lack of knowledge makes a strategic tailoring of a material's frictional properties, e.g., during the manufacturing process, very difficult to impossible. Many Tribological contacts consume a significant amount of the world's primary energy due to friction and wear in different products from nanoelectromechanical systems to bearings, gears, and engines. The energy is largely dissipated in the material underneath the two surfaces sliding against each other. This subsurface material is thereby exposed to extreme amounts of shear deformation and often forms layered subsurface microstructures with reduced grain size. Herein, the elementary mechanisms for the formation of subsurface microstructures are elucidated by systematic model experiments and discrete dislocation dynamics simulations in dry frictional contacts. The simulations show how pre-existing dislocations transform into prismatic dis...

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“…Details of the sample preparation and other experimental procedures can be found in ref [72]. Details of the sample preparation and other experimental procedures can be found in ref [72].…”

Section: Chemical Aspectsmentioning

confidence: 99%

Section: Chemical Aspectsmentioning

confidence: 99%

Section: Chemical Aspectsmentioning

confidence: 99%

Section: Chemical Aspectsmentioning

confidence: 99%

Section: Chemical Aspectsmentioning

confidence: 99%

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Solids Under Extreme Shear: Friction‐Mediated Subsurface Structural Transformations

2019

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Three Regimes in the Tribo‐Oxidation of High Purity Copper at Temperatures of up to 150 °C

et al. 2022

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Surface oxidation of high‐purity copper is accelerated under tribological loading. Tribo‐oxide formation at room temperature is associated with diffusion processes along defects, such as dislocations or grain boundaries. Herein, the additional influence of temperature on the tribo‐oxidation of copper is investigated. Dry, reciprocating sliding tests are performed with a variation of the sample temperature between 21 and 150 °C. Microstructural changes are monitored and analyzed with state‐of‐the‐art electron microscopy techniques. Oxide layer formation through thermal oxidation is observed for 150 °C, but not for lower temperatures. As the temperature increases from room temperature up to 100 °C, a significantly stronger tribo‐oxidation into deeper material layers and an increase in the amount of formed pores and oxides is detected. Up to 75 °C, diffusional processes of oxygen along grain boundaries and dislocation pipes are identified. Starting at 100 °C, CuO is detected. Hence, tribological loading significantly alters the CuO formation in comparison with static oxidation. Along with the CuO formation at temperatures ≥90 °C, the oxide layer thickness decreases while the friction coefficient increases. The observations broaden the understanding of the elementary mechanisms of tribo‐oxidation in copper. Eventually, this will allow to systematically customize surfaces showing tribo‐oxidation for specific tribological applications.

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How Tribo‐Oxidation Alters the Tribological Properties of Copper and Its Oxides

Lehmann

Schwaiger

Rinke

et al. 2020

Adv Materials Inter

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Tribochemical reactions in many applications determine the performance and lifetime of individual parts or entire engineering systems. The underlying processes are however not yet fully understood. Here, the tribological properties of copper and its oxides are investigated under mild tribological loading and for dry sliding. The oxides represent the late stages of a copper–sapphire tribo‐contact, once the whole copper surface is covered with an oxide. For this purpose, high‐purity copper, thermally‐oxidized and sintered Cu2O and CuO samples are tribologically loaded and eventually formed wear particles analyzed. The tribological behavior of the oxides is found to be beneficial for a reduction of the coefficient of friction (COF), mainly due to an increase in hardness. The results reveal tribochemical reactions when copper oxides are present, irrespective of whether they form during sliding or are existent from the beginning. Most strikingly, a reduction of copper oxide to metallic copper is observed in X‐ray photoelectron spectroscopy measurements. A more accurate understanding of tribo‐oxidation will allow for manufacturing well‐defined surfaces with enhanced tribological properties. This paves the way for extending the lifetime of contacts evincing tribo‐oxidation.

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Stages in the tribologically-induced oxidation of high-purity copper

Cited by 43 publications

References 55 publications

Solids Under Extreme Shear: Friction‐Mediated Subsurface Structural Transformations

Solids Under Extreme Shear: Friction‐Mediated Subsurface Structural Transformations

Three Regimes in the Tribo‐Oxidation of High Purity Copper at Temperatures of up to 150 °C

How Tribo‐Oxidation Alters the Tribological Properties of Copper and Its Oxides

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