Nature provides countless examples of surface structures featuring extraordinary properties such ... more Nature provides countless examples of surface structures featuring extraordinary properties such as directional fluid transport. In order to mimic the morphology and outstanding wetting behaviour of bark bugs, ultrashort laser pulses with durations in the fs- to ps-range were employed for large area surface processing of steel. By scanning the laser beam across the surface of initially polished flat sample surfaces and systematically varying the laser processing parameters (peak fluence, scan velocity, line overlap), different regimes associated with characteristic surface morphologies (laser-induced periodic surface structures (LIPSS), grooves, spikes, etc.) could be identified. Additionally, different laser processing strategies were applied, varying laser wavelength, pulse duration and repetition rates, which allowed to achieve a range of morphologies that resemble different structures found on bark bugs. For identifying the ideal combination of parameters for mimicking such bug-...
Diamond like carbon (DLC) coatings of seven different suppliers were deposited on steel discs (10... more Diamond like carbon (DLC) coatings of seven different suppliers were deposited on steel discs (100Cr6). These coatings were tested under slip-rolling conditions in an Amsler type testing rig with paraffin oil under boundary/ mixed lubrication. The initial, average specific pressure was adjusted to P m = 1,0 GPa, P m = 1,25 GPa and P m = 1,5 GPa. The results show a different behaviour not only from supplier to supplier, but also within the same batch of the same supplier. The topographies of the coatings were investigated on the microscopic scale in order to clarify whether or not any differences in the coating surfaces are responsible for these observations.
Laser texturing is an emerging technology for generating surface functionalities on basis of opti... more Laser texturing is an emerging technology for generating surface functionalities on basis of optical, mechanical, or chemical properties. Taking benefit of laser sources with ultrashort (fs) pulse durations features outstanding precision of machining and negligible rims or burrs surrounding the laser-irradiation zone. Consequently, additional mechanical or chemical post-processing steps are usually not required for fs-laser surface texturing (fs-LST). This work aimed to provide a bridge between research in the field of tribology and laser materials processing. The paper reviews the current state-of-the-art in fs-LST, with a focus on the tribological performance (friction and wear) of specific self-organized surface structures (so-called ripples, grooves, and spikes) on steel and titanium alloys. On the titanium alloy, specific sickle-shaped hybrid micro-nanostructures were also observed and tribologically tested. Care is taken to identify accompanying effects affecting the materials hardness, superficial oxidation, nano-and microscale topographies, and the role of additives contained in lubricants, such as commercial engine oil.
Laser-induced periodic surface structures (LIPSS, ripples) are a universal phenomenon that can be... more Laser-induced periodic surface structures (LIPSS, ripples) are a universal phenomenon that can be observed on almost any material after the irradiation by linearly polarized laser beams, particularly when using ultrashort laser pulses with durations in the picosecond to femtosecond range. During the past few years significantly increasing research activities have been reported in the field of LIPSS, since their generation in a single-step process provides a simple way of nanostructuring and surface functionalization towards the control of optical, mechanical or chemical properties. In this contribution current applications of LIPSS are reviewed, including the colorization of technical surfaces, the control of surface wetting, the tailoring of surface colonization by bacterial biofilms, and the improvement of the tribological performance of nanostructured metal surfaces.
Reibungsminderungspotentiale von uberrollbestandigen Dunnschichten auf Standardsubstraten und von... more Reibungsminderungspotentiale von uberrollbestandigen Dunnschichten auf Standardsubstraten und von beschichteten und unbeschichteten alternativen Stahlen sowie durch Schmierstoffadditive werden in ein Erstbefullungsol bei 120°C und Pressungen bis zu P0mean= 2,5 GPa aufgezeigt.
The aim of this research is to characterize a surface that has experienced low wear on asperities... more The aim of this research is to characterize a surface that has experienced low wear on asperities. The procedure used is similar to an Abbott-Firestone approach and based on functional bearing of projected area, surface area and material volume. Surface features extracted from surface height maps provide more comprehensive information about topography changes due to wear. Thus, they were used to detect low wear volumes on the top of asperities.
Abstract Downsizing (power-to-weight ratio) and higher speeds lead to a rise in Hertzian contact ... more Abstract Downsizing (power-to-weight ratio) and higher speeds lead to a rise in Hertzian contact pressures in combination with an increase in surface or oil temperatures. Under such conditions, commonly used bearing steels, such as 100Cr6, reach their limits, creating a demand for alternative slip-rolling resistant steel alloys. The present work therefore compares the slip-rolling performance of various steel types with Maraging- and PM-type steel alloys such as e.g. CSS-42L™, ASP2012, BIMAX42+, in the Hertzian contact pressure range up to P0max of 4 GPa. Through-hardened 100Cr6H (AISI 52100), case-hardened 20MnCr5 (AISI 5120H) and nitrogen alloyed Cronidur30 (AMS 5898) still compete in terms of slip-rolling and wear resistance and load carrying capacity, whereas Maraging- and PM-type steel alloys offer superior strength and toughness properties.
Nano-cristalline diamond and DLC (ta-C, a-C:H) coatings on 100Cr6 steel and SSiC (Ekasic D) subst... more Nano-cristalline diamond and DLC (ta-C, a-C:H) coatings on 100Cr6 steel and SSiC (Ekasic D) substrates were tested under lubricated slip rolling conditions. The tests were performed in an Amsler-type testing rig with unadditivated paraffin oil or glycol (PAG 46) under boundary/ mixed lubrication. The initial average specific pressure was adjusted between P m = 1,0 GPa, and P m = 2,0 GPa. Discs consisting of diamond coated SSiC, HIP-ZrO 2 or 100Cr6 steel served as counterparts. In all tests presented here, glycol led to lower friction coefficients, but larger damages, with respect to paraffin oil. Under paraffin oil lubrication, DLC-coatings on 100Cr6 substrates tested against 100Cr6 discs showed virtually no sign of damage after n = 1.000.000 cycles. In contrast, diamond coatings on SSiC tested against discs of the same material or 100Cr6 discs failed after about n = 10.000 cycles. Starting point for the failure of the diamond coatings are fractures in the SSiC substrates. Using HIP...
Slip-rolling tests were performed on diamond coatings and diamond like coatings deposited on SSiC... more Slip-rolling tests were performed on diamond coatings and diamond like coatings deposited on SSiC-substrates as well as 100Cr6 steel substrates against various counter bodies under paraffin oil lubrication or under non-lubricated conditions. The average specific pressure was initially set between P m = 1,0 GPa and P m = 1,5 GPa. During these tests the signals of the acoustic emission (AE) were recorded. It turned out that the onset of the failure of a coating was indicated by a temporarily increase in the number of hits (AE-activity). If a continuous, intense AE-activity was recorded, the respective images taken with an optical microscope showed that the DLC coating had lost its wear protective function. Using the intensity of the hit rate in combination with slip-rolling tests carried out on uncoated reference samples under similar conditions, the origin of different AE-signals could be deduced.
The efficiency of high temperature energy generation plant and aero-engines is critically impacte... more The efficiency of high temperature energy generation plant and aero-engines is critically impacted by solid particle erosion, particularly at elevated temperatures. This damage process can reduce the efficiency of turbines by as much as 7 to 10%, and in the case of a large power plant cause an additional emission of 250,000 tonnes of CO2 over the lifetime of the plant [1]. The cause and type of solid particle erosion varies across different industries and locations in plant, for instance the particles could be volcanic ash in aero-engines, fly ash in boilers, exfoliated scale in steam turbines or mineral matter in oil excavation. In all cases the performance of materials can be improved through better surface engineering and coatings, but the development of these is restricted due to lack of generic models, well controlled and instrumented tests and international standards. A framework is required therefore that can be applied to these different situations to characterise the high t...
Abstract This work presents a critical assessment of wear volume determination methods for ball-o... more Abstract This work presents a critical assessment of wear volume determination methods for ball-on-flat linear reciprocating sliding tribological tests. It revealed that the ASTM D7755-11 standard leads to the highest relative errors (up to 106%) and deviations (up to 27%) depending on the regularity of the wear track shape. The present study suggests improvements for the ASTM D7755-11 wear computation, which can reduce errors from 106% to 17% when analysing irregularly shaped wear tracks. In addition, a five-year period review of two relevant tribology journals revealed that the most used methods for wear determination, namely three-dimensional (3D) profilometry (46%) and nonstandard profile-based methods (36%), are overall reported with incomplete procedural information for wear computation. Furthermore, as many as 8% of the papers specify no data regarding the computation method and only 3% explicitly cited and followed the existing standards (ASTM D7755-11 or G133-05). The present study highlights the importance of the correct selection, implementation, and reporting of wear volume computation method and quantifies the potential errors.
Laser material processing is an innovative technology that generates surface functionalities on t... more Laser material processing is an innovative technology that generates surface functionalities on the basis of optical, mechanical, or chemical properties [...]
High-power piezo-electric motors with power densities of 1.4 kW/kg display a potential for substi... more High-power piezo-electric motors with power densities of 1.4 kW/kg display a potential for substituting hydraulic actuators. For this application, two novel tribometers of the same type have been designed using commercially available components for sliding motion at 40 kHz with amplitudes between 2.5 m and 5 m. The tribometers are equipped with means to measure amplitude, frequency, power required to keep the samples in motion and load applied. The effective motion between the two contacting bodies is monitored in each of the tribometers. These data are used to evaluate the coefficient of friction. The wear rate was determined after the tests. The setups were tested using well-known 100Cr6H (AISI 52100) samples before investigating novel, non-commercial substrates such as AlFeCrTi-alloys and tungsten carbide-based coatings as well as Magnéli-type coatings (Ti n−2 Cr 2 O 2n−1 and Ti n O 2n−1). This paper presents the principle of the ultra-high frequency tribometers and first tribological quantities of materials and coatings tested up to and above 10 11 cycles. Very low wear rates in the range 10 −8 mm 3 /Nm down to 10 −10 mm 3 /Nm were determined under dry oscillation in air.
For the production of raw materials, the generation of energy and for their mobility, the industr... more For the production of raw materials, the generation of energy and for their mobility, the industrialized countries strongly depend on the import of fossil resources. Second generation resources, such as Jatropha, grow on arid soils and produce non-edible oils. Thus, their cultivation does not compete with food production for farmland. Oils of such plants are therefore suggested as sustainable, CO2-neutral and regenerative alternatives to fossil fuels and lubricants. The present work establishes one of the first functional profiles of second generation oils with properties relevant for the use as fuel or lubricants in order to validate the potential for substituting fossil resources. It concentrates on the characterization of oil gained from the Jatropha Curcas plant to be used as fuel and lubricant. Properties were determined such as pour point, flash point, lubricity of diesel-like fuel in high frequency reciprocating rig, high-temperature/high-shear viscosity, and viscosities as function of temperature, extreme pressure behavior, oxidation resistance as well as its toxicity and bio-degradability. These properties are compared to those of currently used plant oils and fossil oils. The fatty acid chain length distribution of Jatropha oil was determined and found to be close to that of palm oil. This qualifies Jatropha oil as a substitute, thus releasing the pressure on the prices of food based oils. First tribological characterizations were carried out and are presented here, showing impressive performance of the as pressed filtered pure Jatropha plant oil. In oil dilution tests carried out on piston-ring/cylinder-liner test rigs, the performance of oils processed from plants such as Jatropha are compared to ester-based, polyalkylene glycol based, and hydrocarbon-based oils. Finally, functional properties of Jatropha were compared to further possible second generation bio-oils and aspects of availability and costs are discussed.
Diamond-like carbon (DLC) coatings are perceived as part of a strategy for low frictional tribosy... more Diamond-like carbon (DLC) coatings are perceived as part of a strategy for low frictional tribosystems. Especially the automotive industry anticipates a benefit in applying such coatings in association with the lightweight construction of mechanical parts, for instance in gear and engine components. Therefore, in previous investigations amorphous carbon (a-C) and tetragonal amorphous carbon (ta-C) coatings were inspected. For up to ten million cycles at Hertzian contact pressures P 0max of 2.9 GPa it was shown that these coatings are slip-rolling resistant not only at room temperature in the presence of unaddivated paraffin oil, but also up to 120 • C oil temperature. The steel substrates in this investigation were made of the hardened and tempered steels 100Cr6H and Cronidur 30. The aim of the current work is manifold. The Hertzian contact pressures should be increased up to P 0max of 4.2 GPa by using new steel metallurgies as substrates for thin film coatings. These steel metallurgies are also assessed, if they can compete as uncoated couples. Two high toughness spring steels and an ultra-high toughness aerospace steel were tested in a twin disc tribometer of the Amsler type as well as in an Optimol 2Disk test rig under mixed/boundary conditions in a factory fill SAE 0W-30 engine oil. Different factors such as influences of the lubrication, surface chemistry and wear behaviour were investigated.
In this contribution, chemical, structural, and mechanical alterations in various types of femtos... more In this contribution, chemical, structural, and mechanical alterations in various types of femtosecond laser-generated surface structures, i.e., laser-induced periodic surface structures (LIPSS, ripples), Grooves, and Spikes on titanium alloy, are characterized by various surface analytical techniques, including X-ray diffraction and glow-discharge optical emission spectroscopy. The formation of oxide layers of the different laser-based structures inherently influences the friction and wear performance as demonstrated in oil-lubricated reciprocating sliding tribological tests (RSTTs) along with subsequent elemental mapping by energy-dispersive X-ray analysis. It is revealed that the fs-laser scan processing (790 nm, 30 fs, 1 kHz) of near-wavelength-sized LIPSS leads to the formation of a graded oxide layer extending a few hundreds of nanometers into depth, consisting mainly of amorphous oxides. Other superficial fs-laser-generated structures such as periodic Grooves and irregular Sp...
Commercial grade-1 titanium samples (Ti, 99.6%) were treated using three alternative methods, (i)... more Commercial grade-1 titanium samples (Ti, 99.6%) were treated using three alternative methods, (i) femtosecond laser processing, (ii) thermal heat treatment, and (iii) electrochemical anodization, respectively, resulting in the formation of differently conditioned superficial titanium oxide layers. The laser processing (i) was carried out by a Ti:sapphire laser (pulse duration 30 fs, central wavelength 790 nm, pulse repetition rate 1 kHz) in a regime of generating laser-induced periodic surface structures (LIPSS). The experimental conditions (laser fluence, spatial spot overlap) were optimized in a sample-scanning setup for the processing of several square-millimeters large surface areas covered homogeneously by these nanostructures. The differently oxidized titanium surfaces were characterized by optical microscopy, micro Raman spectroscopy, variable angle spectroscopic ellipsometry, and instrumented indentation testing. The tribological performance was characterized in the regime of mixed friction by reciprocating sliding tests against a sphere of hardened steel in fully formulated engine oil as lubricant. The specific tribological performance of the differently treated surfaces is discussed with respect to possible physical and chemical mechanisms.
ABSTRACT This paper shows how Angle-Resolved Scattering can reveal wear on engineered surfaces. T... more ABSTRACT This paper shows how Angle-Resolved Scattering can reveal wear on engineered surfaces. The samples studied, three discs made of steel 100Cr6H used in gear wheels in the automotive industry, were assessed after they had undergone ball-on-disc tests. Scattering maps recorded for spatial frequencies from 0.1 µm−1 to 2.7 µm−1 show a contrast inversion around 0.36 µm−1 revealing the wear trace. Besides measurements of rms roughness, where mean values are 20 nm and 24 nm depending on the locations considered, stationarity and isotropy, we demonstrate the ability of the technique to reveal localized wear on this type of surface in a rapid, robust and convenient way. We show that the tool trace is influenced by the load magnitude rather than by the number of oscillation cycles and highlight the key role played by surface roughness in how the sample responds to wear tests.
Nature provides countless examples of surface structures featuring extraordinary properties such ... more Nature provides countless examples of surface structures featuring extraordinary properties such as directional fluid transport. In order to mimic the morphology and outstanding wetting behaviour of bark bugs, ultrashort laser pulses with durations in the fs- to ps-range were employed for large area surface processing of steel. By scanning the laser beam across the surface of initially polished flat sample surfaces and systematically varying the laser processing parameters (peak fluence, scan velocity, line overlap), different regimes associated with characteristic surface morphologies (laser-induced periodic surface structures (LIPSS), grooves, spikes, etc.) could be identified. Additionally, different laser processing strategies were applied, varying laser wavelength, pulse duration and repetition rates, which allowed to achieve a range of morphologies that resemble different structures found on bark bugs. For identifying the ideal combination of parameters for mimicking such bug-...
Diamond like carbon (DLC) coatings of seven different suppliers were deposited on steel discs (10... more Diamond like carbon (DLC) coatings of seven different suppliers were deposited on steel discs (100Cr6). These coatings were tested under slip-rolling conditions in an Amsler type testing rig with paraffin oil under boundary/ mixed lubrication. The initial, average specific pressure was adjusted to P m = 1,0 GPa, P m = 1,25 GPa and P m = 1,5 GPa. The results show a different behaviour not only from supplier to supplier, but also within the same batch of the same supplier. The topographies of the coatings were investigated on the microscopic scale in order to clarify whether or not any differences in the coating surfaces are responsible for these observations.
Laser texturing is an emerging technology for generating surface functionalities on basis of opti... more Laser texturing is an emerging technology for generating surface functionalities on basis of optical, mechanical, or chemical properties. Taking benefit of laser sources with ultrashort (fs) pulse durations features outstanding precision of machining and negligible rims or burrs surrounding the laser-irradiation zone. Consequently, additional mechanical or chemical post-processing steps are usually not required for fs-laser surface texturing (fs-LST). This work aimed to provide a bridge between research in the field of tribology and laser materials processing. The paper reviews the current state-of-the-art in fs-LST, with a focus on the tribological performance (friction and wear) of specific self-organized surface structures (so-called ripples, grooves, and spikes) on steel and titanium alloys. On the titanium alloy, specific sickle-shaped hybrid micro-nanostructures were also observed and tribologically tested. Care is taken to identify accompanying effects affecting the materials hardness, superficial oxidation, nano-and microscale topographies, and the role of additives contained in lubricants, such as commercial engine oil.
Laser-induced periodic surface structures (LIPSS, ripples) are a universal phenomenon that can be... more Laser-induced periodic surface structures (LIPSS, ripples) are a universal phenomenon that can be observed on almost any material after the irradiation by linearly polarized laser beams, particularly when using ultrashort laser pulses with durations in the picosecond to femtosecond range. During the past few years significantly increasing research activities have been reported in the field of LIPSS, since their generation in a single-step process provides a simple way of nanostructuring and surface functionalization towards the control of optical, mechanical or chemical properties. In this contribution current applications of LIPSS are reviewed, including the colorization of technical surfaces, the control of surface wetting, the tailoring of surface colonization by bacterial biofilms, and the improvement of the tribological performance of nanostructured metal surfaces.
Reibungsminderungspotentiale von uberrollbestandigen Dunnschichten auf Standardsubstraten und von... more Reibungsminderungspotentiale von uberrollbestandigen Dunnschichten auf Standardsubstraten und von beschichteten und unbeschichteten alternativen Stahlen sowie durch Schmierstoffadditive werden in ein Erstbefullungsol bei 120°C und Pressungen bis zu P0mean= 2,5 GPa aufgezeigt.
The aim of this research is to characterize a surface that has experienced low wear on asperities... more The aim of this research is to characterize a surface that has experienced low wear on asperities. The procedure used is similar to an Abbott-Firestone approach and based on functional bearing of projected area, surface area and material volume. Surface features extracted from surface height maps provide more comprehensive information about topography changes due to wear. Thus, they were used to detect low wear volumes on the top of asperities.
Abstract Downsizing (power-to-weight ratio) and higher speeds lead to a rise in Hertzian contact ... more Abstract Downsizing (power-to-weight ratio) and higher speeds lead to a rise in Hertzian contact pressures in combination with an increase in surface or oil temperatures. Under such conditions, commonly used bearing steels, such as 100Cr6, reach their limits, creating a demand for alternative slip-rolling resistant steel alloys. The present work therefore compares the slip-rolling performance of various steel types with Maraging- and PM-type steel alloys such as e.g. CSS-42L™, ASP2012, BIMAX42+, in the Hertzian contact pressure range up to P0max of 4 GPa. Through-hardened 100Cr6H (AISI 52100), case-hardened 20MnCr5 (AISI 5120H) and nitrogen alloyed Cronidur30 (AMS 5898) still compete in terms of slip-rolling and wear resistance and load carrying capacity, whereas Maraging- and PM-type steel alloys offer superior strength and toughness properties.
Nano-cristalline diamond and DLC (ta-C, a-C:H) coatings on 100Cr6 steel and SSiC (Ekasic D) subst... more Nano-cristalline diamond and DLC (ta-C, a-C:H) coatings on 100Cr6 steel and SSiC (Ekasic D) substrates were tested under lubricated slip rolling conditions. The tests were performed in an Amsler-type testing rig with unadditivated paraffin oil or glycol (PAG 46) under boundary/ mixed lubrication. The initial average specific pressure was adjusted between P m = 1,0 GPa, and P m = 2,0 GPa. Discs consisting of diamond coated SSiC, HIP-ZrO 2 or 100Cr6 steel served as counterparts. In all tests presented here, glycol led to lower friction coefficients, but larger damages, with respect to paraffin oil. Under paraffin oil lubrication, DLC-coatings on 100Cr6 substrates tested against 100Cr6 discs showed virtually no sign of damage after n = 1.000.000 cycles. In contrast, diamond coatings on SSiC tested against discs of the same material or 100Cr6 discs failed after about n = 10.000 cycles. Starting point for the failure of the diamond coatings are fractures in the SSiC substrates. Using HIP...
Slip-rolling tests were performed on diamond coatings and diamond like coatings deposited on SSiC... more Slip-rolling tests were performed on diamond coatings and diamond like coatings deposited on SSiC-substrates as well as 100Cr6 steel substrates against various counter bodies under paraffin oil lubrication or under non-lubricated conditions. The average specific pressure was initially set between P m = 1,0 GPa and P m = 1,5 GPa. During these tests the signals of the acoustic emission (AE) were recorded. It turned out that the onset of the failure of a coating was indicated by a temporarily increase in the number of hits (AE-activity). If a continuous, intense AE-activity was recorded, the respective images taken with an optical microscope showed that the DLC coating had lost its wear protective function. Using the intensity of the hit rate in combination with slip-rolling tests carried out on uncoated reference samples under similar conditions, the origin of different AE-signals could be deduced.
The efficiency of high temperature energy generation plant and aero-engines is critically impacte... more The efficiency of high temperature energy generation plant and aero-engines is critically impacted by solid particle erosion, particularly at elevated temperatures. This damage process can reduce the efficiency of turbines by as much as 7 to 10%, and in the case of a large power plant cause an additional emission of 250,000 tonnes of CO2 over the lifetime of the plant [1]. The cause and type of solid particle erosion varies across different industries and locations in plant, for instance the particles could be volcanic ash in aero-engines, fly ash in boilers, exfoliated scale in steam turbines or mineral matter in oil excavation. In all cases the performance of materials can be improved through better surface engineering and coatings, but the development of these is restricted due to lack of generic models, well controlled and instrumented tests and international standards. A framework is required therefore that can be applied to these different situations to characterise the high t...
Abstract This work presents a critical assessment of wear volume determination methods for ball-o... more Abstract This work presents a critical assessment of wear volume determination methods for ball-on-flat linear reciprocating sliding tribological tests. It revealed that the ASTM D7755-11 standard leads to the highest relative errors (up to 106%) and deviations (up to 27%) depending on the regularity of the wear track shape. The present study suggests improvements for the ASTM D7755-11 wear computation, which can reduce errors from 106% to 17% when analysing irregularly shaped wear tracks. In addition, a five-year period review of two relevant tribology journals revealed that the most used methods for wear determination, namely three-dimensional (3D) profilometry (46%) and nonstandard profile-based methods (36%), are overall reported with incomplete procedural information for wear computation. Furthermore, as many as 8% of the papers specify no data regarding the computation method and only 3% explicitly cited and followed the existing standards (ASTM D7755-11 or G133-05). The present study highlights the importance of the correct selection, implementation, and reporting of wear volume computation method and quantifies the potential errors.
Laser material processing is an innovative technology that generates surface functionalities on t... more Laser material processing is an innovative technology that generates surface functionalities on the basis of optical, mechanical, or chemical properties [...]
High-power piezo-electric motors with power densities of 1.4 kW/kg display a potential for substi... more High-power piezo-electric motors with power densities of 1.4 kW/kg display a potential for substituting hydraulic actuators. For this application, two novel tribometers of the same type have been designed using commercially available components for sliding motion at 40 kHz with amplitudes between 2.5 m and 5 m. The tribometers are equipped with means to measure amplitude, frequency, power required to keep the samples in motion and load applied. The effective motion between the two contacting bodies is monitored in each of the tribometers. These data are used to evaluate the coefficient of friction. The wear rate was determined after the tests. The setups were tested using well-known 100Cr6H (AISI 52100) samples before investigating novel, non-commercial substrates such as AlFeCrTi-alloys and tungsten carbide-based coatings as well as Magnéli-type coatings (Ti n−2 Cr 2 O 2n−1 and Ti n O 2n−1). This paper presents the principle of the ultra-high frequency tribometers and first tribological quantities of materials and coatings tested up to and above 10 11 cycles. Very low wear rates in the range 10 −8 mm 3 /Nm down to 10 −10 mm 3 /Nm were determined under dry oscillation in air.
For the production of raw materials, the generation of energy and for their mobility, the industr... more For the production of raw materials, the generation of energy and for their mobility, the industrialized countries strongly depend on the import of fossil resources. Second generation resources, such as Jatropha, grow on arid soils and produce non-edible oils. Thus, their cultivation does not compete with food production for farmland. Oils of such plants are therefore suggested as sustainable, CO2-neutral and regenerative alternatives to fossil fuels and lubricants. The present work establishes one of the first functional profiles of second generation oils with properties relevant for the use as fuel or lubricants in order to validate the potential for substituting fossil resources. It concentrates on the characterization of oil gained from the Jatropha Curcas plant to be used as fuel and lubricant. Properties were determined such as pour point, flash point, lubricity of diesel-like fuel in high frequency reciprocating rig, high-temperature/high-shear viscosity, and viscosities as function of temperature, extreme pressure behavior, oxidation resistance as well as its toxicity and bio-degradability. These properties are compared to those of currently used plant oils and fossil oils. The fatty acid chain length distribution of Jatropha oil was determined and found to be close to that of palm oil. This qualifies Jatropha oil as a substitute, thus releasing the pressure on the prices of food based oils. First tribological characterizations were carried out and are presented here, showing impressive performance of the as pressed filtered pure Jatropha plant oil. In oil dilution tests carried out on piston-ring/cylinder-liner test rigs, the performance of oils processed from plants such as Jatropha are compared to ester-based, polyalkylene glycol based, and hydrocarbon-based oils. Finally, functional properties of Jatropha were compared to further possible second generation bio-oils and aspects of availability and costs are discussed.
Diamond-like carbon (DLC) coatings are perceived as part of a strategy for low frictional tribosy... more Diamond-like carbon (DLC) coatings are perceived as part of a strategy for low frictional tribosystems. Especially the automotive industry anticipates a benefit in applying such coatings in association with the lightweight construction of mechanical parts, for instance in gear and engine components. Therefore, in previous investigations amorphous carbon (a-C) and tetragonal amorphous carbon (ta-C) coatings were inspected. For up to ten million cycles at Hertzian contact pressures P 0max of 2.9 GPa it was shown that these coatings are slip-rolling resistant not only at room temperature in the presence of unaddivated paraffin oil, but also up to 120 • C oil temperature. The steel substrates in this investigation were made of the hardened and tempered steels 100Cr6H and Cronidur 30. The aim of the current work is manifold. The Hertzian contact pressures should be increased up to P 0max of 4.2 GPa by using new steel metallurgies as substrates for thin film coatings. These steel metallurgies are also assessed, if they can compete as uncoated couples. Two high toughness spring steels and an ultra-high toughness aerospace steel were tested in a twin disc tribometer of the Amsler type as well as in an Optimol 2Disk test rig under mixed/boundary conditions in a factory fill SAE 0W-30 engine oil. Different factors such as influences of the lubrication, surface chemistry and wear behaviour were investigated.
In this contribution, chemical, structural, and mechanical alterations in various types of femtos... more In this contribution, chemical, structural, and mechanical alterations in various types of femtosecond laser-generated surface structures, i.e., laser-induced periodic surface structures (LIPSS, ripples), Grooves, and Spikes on titanium alloy, are characterized by various surface analytical techniques, including X-ray diffraction and glow-discharge optical emission spectroscopy. The formation of oxide layers of the different laser-based structures inherently influences the friction and wear performance as demonstrated in oil-lubricated reciprocating sliding tribological tests (RSTTs) along with subsequent elemental mapping by energy-dispersive X-ray analysis. It is revealed that the fs-laser scan processing (790 nm, 30 fs, 1 kHz) of near-wavelength-sized LIPSS leads to the formation of a graded oxide layer extending a few hundreds of nanometers into depth, consisting mainly of amorphous oxides. Other superficial fs-laser-generated structures such as periodic Grooves and irregular Sp...
Commercial grade-1 titanium samples (Ti, 99.6%) were treated using three alternative methods, (i)... more Commercial grade-1 titanium samples (Ti, 99.6%) were treated using three alternative methods, (i) femtosecond laser processing, (ii) thermal heat treatment, and (iii) electrochemical anodization, respectively, resulting in the formation of differently conditioned superficial titanium oxide layers. The laser processing (i) was carried out by a Ti:sapphire laser (pulse duration 30 fs, central wavelength 790 nm, pulse repetition rate 1 kHz) in a regime of generating laser-induced periodic surface structures (LIPSS). The experimental conditions (laser fluence, spatial spot overlap) were optimized in a sample-scanning setup for the processing of several square-millimeters large surface areas covered homogeneously by these nanostructures. The differently oxidized titanium surfaces were characterized by optical microscopy, micro Raman spectroscopy, variable angle spectroscopic ellipsometry, and instrumented indentation testing. The tribological performance was characterized in the regime of mixed friction by reciprocating sliding tests against a sphere of hardened steel in fully formulated engine oil as lubricant. The specific tribological performance of the differently treated surfaces is discussed with respect to possible physical and chemical mechanisms.
ABSTRACT This paper shows how Angle-Resolved Scattering can reveal wear on engineered surfaces. T... more ABSTRACT This paper shows how Angle-Resolved Scattering can reveal wear on engineered surfaces. The samples studied, three discs made of steel 100Cr6H used in gear wheels in the automotive industry, were assessed after they had undergone ball-on-disc tests. Scattering maps recorded for spatial frequencies from 0.1 µm−1 to 2.7 µm−1 show a contrast inversion around 0.36 µm−1 revealing the wear trace. Besides measurements of rms roughness, where mean values are 20 nm and 24 nm depending on the locations considered, stationarity and isotropy, we demonstrate the ability of the technique to reveal localized wear on this type of surface in a rapid, robust and convenient way. We show that the tool trace is influenced by the load magnitude rather than by the number of oscillation cycles and highlight the key role played by surface roughness in how the sample responds to wear tests.
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Papers by D. Spaltmann