Laser Surface Texturing of TiAl Multilayer Films—Effects of Microstructure and Topography on Friction and Wear

Laser surface texturing is an efficient way to control the friction and wear properties of materials. Although described in many papers, most previous work relates to a pure topographic view of laser-textured surfaces. As lasers are heat sources, their thermal impact during treatment can be high enough to modify the material’s microstructure or surface chemistry and affect tribological properties as well. This research took a closer look at the microstructure of laser-textured TiAl multilayers, besides topographic aspects. Direct laser interference patterning was used to create well-defined line-like surface textures in TiAl multilayers with differing lateral feature sizes in the micron range. High-resolution techniques such as TEM and XRD highlighted the effect of this method on microstructure, and in particular, the phase situation of the TiAl multilayer. Thermal simulations demonstrated that the maximum achievable temperatures were around 2000 K, thus being high enough to melt Ti and Al. Cooling rates on the order of 109 K/s depended on the lateral feature size, potentially leading to metastable microstructures. Finally, ball-on-disk tests on as-textured TiAl specimens showed a reduction in wear under dry conditions depending on the periodicity of the line-like textures used

Laser interference metallurgy of metallic surfaces for tribological applications

Tribological phenomena play a decisive role in diverse systems. For many years, researchers have sought to alleviate these problems and to understand their origin. There are many potential solutions to manipulate friction. In particular, the rapidly growing field of laser surface texturing has attracted a lot of attention in the last decades and shown to be an effective means of improving tribological properties. A possible approach of laser surface texturing to scrutinize the effects of various pattern geometries and lateral feature sizes in one single laser shot is the so called Laser Interference Metallurgy (LIMET) which will be applied within this thesis. The aim is to study the microstructural and topographic possibilities of LIMET concerning the tribological performance of laser-patterned thin film systems (Au and TiAl multilayer) and bulk aluminium as well as steel surfaces. It will be shown that depending on the laser fluence for example, distinct grain size arrangements and intermetallic phase composites can be created with superior tribological properties compared to the unpatterned reference situation. Moreover, a successful process combination of micro-coining and LIMET will be presented with an enhanced oil retainment capability under lubrication. Finally, the results of laser-textured steel surfaces and their ability to geometrically interlock will be shown. Depending on the relative alignment between the textured sliding surfaces and the selected pattern line-spacing, the frictional response can be significantly influenced. Most of the experimental results will be directly correlated to simulations in order to reveal the underlying phenomena.Reibung spielt eine zentrale Rolle in vielen Bereichen. Insbesondere die Steuerung von Reibung ist dabei von enormer Bedeutung. Zur Minimierung von Reibung sind in den vergangenen Jahrzehnten bereits unzählige Methoden für trockene und geschmierte Bedingungen entwickelt worden. Besonders laserstrukturierte Oberflächen scheinen hierbei vielversprechend für tribologische Anwendungen zu sein. Ein Ansatz, mikrostrukturell und topographisch ma geschneiderte Werkstoffe zu erzeugen, ist die Laserinterferenzmetallurgie (LIMET). Das Ziel der vorliegenden Arbeit ist die Untersuchung der erzielbaren mikrostrukturellen und topographischen Effekte durch LIMET und deren Auswirkungen auf die tribologischen Eigenschaften von metallischen Schichtsystemen (Au und TiAl-Multilagen) sowie massiven Aluminium- und Stahloberflächen. Hierbei wird gezeigt, dass es z.B. abhängig von der gewählten Fluenz möglich ist, Korngrößenarchitekturen oder intermetallische Phasenkomposite definiert zu erzeugen, deren Reibeigenschaften denen der unbehandelten Ausgangssituation überlegen sind. Des Weiteren wird die erfolgreiche Kombination des Mikroprägens mit der LIMETMethode vorgestellt. Die Ergebnisse zeigen, dass insbesondere die Ölspeicherfähigkeit in den hierarchischen Kavitäten unter geschmierten Bedingungen deutlich gegenüber einer unstrukturierten Oberfläche gesteigert ist. Schlie lich werden die tribologischen Auswirkungen von beidseitig strukturierten Stahloberflächen in Abhängigkeit von deren gegenseitiger Orientierung und den gewählten Strukturabständen näher untersucht. Je nach Ausrichtung und den genannten Strukturperiodizitäten lässt sich das Reibverhalten reproduzierbar in gewissen Grenzen manipulieren. Die experimentellen Ergebnisse werden mit Simulationen verknüpft, um dadurch die Wirkmechanismen näher zu beleuchten

Effect of Low Depth Surface Texturing on Friction Reduction in Lubricated Sliding Contact

Laser surface texturing is an interesting possibility to tailor materials’ surfaces and thus to improve the friction and wear properties if proper texture feature sizes are selected. In this research work, stainless steel surfaces were laser textured by two different laser techniques, i.e., the direct laser interference patterning by using a nanosecond pulsed Nd:YAG laser and additionally by an ultrashort pulsed femtosecond Ti:Sa. The as-textured surfaces were then studied regarding their frictional response in a specially designed linear reciprocating test rig under lubricated conditions with a fully formulated 15W40 oil. Results show that dimples with smaller diameter lead to a significant reduction in the coefficient of friction compared to the dimples with a larger diameter and surfaces with a grid-like surface pattern produced by direct laser interference patterning

The strategy of antibiotic use in critically ill neutropenic patients

Suspicion of sepsis in neutropenic patients requires immediate antimicrobial treatment. The initial regimen in critically ill patients should cover both Gram-positive and Gram-negative pathogens, including Pseudomonas aeruginosa. However, the risk of selecting multidrug-resistant pathogens should be considered when using broad-spectrum antibiotics for a prolonged period of time. The choice of the first-line empirical drugs should take into account the underlying malignancy, local bacterial ecology, clinical presentation and severity of acute illness. This review provides an up-to-date guide that will assist physicians in choosing the best strategy regarding the use of antibiotics in neutropenic patients, with a special focus on critically ill patients, based on the above-mentioned considerations and on the most recent international guidelines and literature

The reliability and efficiency of power companies

One of the key indicators of heat supply organizations is the reliability of energy facilities. The index of reliability of heat supply organization is of interest to potential investors, to assess the risks of investing projects. We propose a method of determining the reliability of heat supply organizations with the use of SAW (simple additive weighting method). We are developing a versatile program and the analysis of heat supply organizations on the example of the Republic of Tatarstan. This criterion is of significant interest for potential investors to assess the risks of investing projects. All values for the calculation of the reliability of heat supply organization founded and are publicly available. The method of determining the reliability of heat supply organizations with the use of SAW. Developed a versatile program allows you to analyze the performance reliability of any heat supply organizations

Direct Laser Interference Patterning: Tailoring of Contact Area for Frictional and Antibacterial Properties

Surface functionalization by topographic micro- and nano-structures in order to achieve unique properties, like super-hydrophobicity or ultrahigh light absorption, is a common strategy in nature. In this paper, direct laser interference patterning (DLIP) is presented as a promising tool allowing for the generation of such surface patterns on technical surfaces in order to mimic these biological surfaces and effects. Friction optimization and antibacterial effects by DLIP are exemplarily described. Topographic surface patterns on the micro- and nano-scale demonstrated a significant reduction in the coefficient of friction and bacterial adhesion. It was shown that in both cases, the control of the contact area between surfaces or between surface and bacteria is of utmost importance

Automated Identification and Tracking of Deformation Twin Structures in Molecular Dynamics Simulations

Deformation twinning significantly influences the microstructure, texture, and mechanical properties of metals, necessitating comprehensive studies of twin formation and interactions. While experimental methods excel at analyzing individual samples, they often lack the capability for temporal analysis of twinned structures. Molecular dynamics simulations offer a temporal dimension, yet the absence of suitable tools for automated crystal twin identification has been a significant limitation. In this article, we introduce a novel computational tool integrated into the visualization and analysis software OVITO. Our tool automates the identification of coherent twin boundaries, links related twin boundaries, validates twin structures through orientation analysis, and tracks twins over time, providing quantifiable data and enabling in-depth investigations. Validation on a copper single crystal under shear loading demonstrates successful tracking of various twins, revealing their genesis and growth over multiple timesteps. This innovative approach promises to advance the computational materials science domain by facilitating the study of deformation twinning, offering profound insights into the behavior and mechanical performance of materials

Microstructural and Chemical Characterization of the Tribolayer Formation in Highly Loaded Cylindrical Roller Thrust Bearings

Zinc dithiophosphates (ZDDP) have been widely applied in automobile industry for over 70 years as a lubricant additive for wear protection. Tribolayers have been described as blue- and brown-colored layers on surfaces observed by microscopical observation or even bare eye presumably as a consequence of layer thickness or chemical composition. However, the reaction pathways of ZDDP tribolayers are still not yet fully understood. In the present study, the difference between the blue- and brown-colored tribolayers has been revealed by high resolution methods in cylindrical roller thrust bearings at relatively high contact pressures of around 1.92 GPa. After running a FE8 standard bearing test with a normal load of 80 kN and a temperature of 60 °C, said tribolayers could be identified on the bearing surfaces. By using Raman spectroscopy, it could be shown that the blue-colored layers are enriched by FeS and ZnS whereas the brown-colored layers show a significant amount of Fe3O4. This is an interesting finding as it clearly shows a correlation between the color appearance of the films and the chemical composition besides potential film thickness variations. Finally, transmission electron microscopy verified the amorphous nature of the formed tribolayer which is in a good agreement with literature

A Framework for Ex-Ante Economic Analysis of Tourism Investments: An Application to Haiti

This study develops a linked regional computable general equilibrium and micro-simulation (RCGE-MS) model to assess the regional economy-wide and poverty impacts of a US$36 million investment in tourism in the south of Haiti. The first social accounting matrix for Haiti with a base year of 2012/2013 was constructed to calibrate the model. This research addresses three key gaps identified in the tourism impact assessment literature. First, a destination-specific tourism demand and value chain analysis was used to calibrate the shocks implemented in the model. Second, the RCGE-MS approach moves beyond the representative household configuration to enable more robust analysis of tourism investment impacts on poverty and income inequality. Third, results of this modelling were used to inform a social cost-benefit analysis to provide greater transparency in the evaluation of trade-offs between investment alternatives. Results of this analysis showed a positive impact on sectoral activity, especially for the hotel and restaurant sector (182.1% in 2040) and a 2.0% increase in Gross Regional Product by 2040. The South's exports fell 4.7% below baseline and imports were 6.1% higher due to the inflow of foreign exchange, the appreciation of the regional real exchange rate, increased demand for most goods and services, and limited regional productive capacity. The rate of unemployment fell from 26% to 23%. The investment helped lift some of the region¿s poorest out of poverty, reducing the poverty headcount by 1.6 percentage points. Driving this result was an increase in employment, wages and non-labor income. The linked RCGE-MS approach proves to be a powerful tool for assessing how tourism investments affect regional economic activity and revealing the mechanisms through which tourism can contribute to increased employment opportunities and poverty reduction