Laser Peening für innovative Werkstoffe und Oberflächen

Laser peening (laser shock peening, LSP) is a mechanical surface treatment, increasingly applied for generating particularly deep residual compressive stresses close to the surface thus significantly increasing the service life of components. In order to meet the current challenges in the field of sustainability, this work investigates the enormous potential of this technology, from a materials science perspective, in the field of additive manufacturing / 3D printing for lifetime enhancement as well as surface functionalization. As an example, Ti6Al4V alloy, used for additively manufactured components for space applications, is used to demonstrate the introduction of 2.4 mm deep compressive residual stresses, leading to an increase in fatigue life by a factor 100, and also further explaining the deformation characteristics. A comparison is made with conventional shot peening and technically proven cast iron. Laser peening is used for the first time to overcome the near-surface tensile residual stresses typical in laser-based topographic functionalization and additionally opens the perspective for a multi-scale periodically structured surface. Laser polishing, direct laser interference patterning (DLIP) and laser peening will be presented as a novel process combination applied for the sustainable and tailored post-treatment of additively manufactured parts.Laser Peening (Laser Shock Peening, Laser Schock Verfestigung, LSP) repräsentiert ein zunehmend anwendungsrelevantes mechanisches Oberflächenbehandlungsverfahren zur Generierung besonders tiefer oberflächennaher Druck-Eigenspannungen für signifikante Lebensdauersteigerungen von Bauteilen. Um den aktuellen Herausforderungen im Bereich Nachhaltigkeit zu begegnen, untersucht die vorliegende Arbeit aus materialwissenschaftlicher Perspektive das enorme Potential dieser Technologie im Bereich additive Fertigung / 3D-Druck zur Lebensdauersteigerung sowie Oberflächenfunktionalisierung. Am Beispiel der für additiv gefertigte Bauteile in Weltraumanwendungen eingesetzten Legierung Ti6Al4V wird die Einbringung von 2,4 mm tiefen Druck-Eigenspannungen gezeigt, welche zu einer Steigerung der Lebensdauer um den Faktor 100 führen, sowie ein Beitrag zur Aufklärung der Deformationscharakteristik geleistet. Dabei erfolgt ein Vergleich zu konventionellem Kugelstrahlen und dem technisch bewährten Werkstoff Gusseisen. Laser Peening wird erstmals zur Überwindung der für laserbasierte topographische Funktionalisierungen typischen oberflächennahen Zug-Eigenspannungen genutzt und eröffnet die Perspektive für eine multiskalige, periodische Oberflächenstrukturierung. Die Verfahren Laserpolieren, direkter Laser-Interferenzstrukturierung (DLIP) und Laser Peening werden als neuartige Prozesskombination zur nachhaltigen und maßgeschneiderten Nachbehandlung additiv hergestellter Bauteile vorgestellt

Multipurpose setup used to characterize tribo-electrical properties of electrical contact materials

Electrical contacts are pervasively found on countless modern devices and systems. It is imperative that connecting components present adequate electrical, mechanical, and chemical characteristics to fulfill the crucial role that they play in the system. To develop an electrical contact material that is tailored for a specific application, different approaches are pursued (e.g., coatings, reinforced composites, alloyed metals, duplex systems, etc.). The manufacturing of electrical contact materials demand a thorough characterization of their electrical properties, mechanical properties, and their resistance to wear, as well as their resistance to atmospheric conditions. Accordingly, commissioning of a novel setup enables a more comprehensive study of the materials that are developed. Therefore, a complete understanding of the material's electrical and tribological characteristics are attained, allowing the production of a material that is compliant with the particular demands of the application for which it is intended. This multipurpose setup was built with higher precision stages and higher accuracy 3-axis force sensor, thus providing the following improvement over the preceding setup: • Elevated load-bearing capacity (double), higher precision and stability. • Tribo-electrical characterization (implementation of scratch and fretting tests). • Environmental control (climate and external vibration)

Fatigue behaviour of PBF additive manufactured TI6AL4V alloy after shot and laser peening

Additive manufacturing (AM) of metallic parts is a relatively new manufacturing procedure. Many industry sectors, such as the aerospace or automotive sectors, have started to apply this technology to produce some elements, thus reducing costs and weight. Several metallic alloys have been employed for AM. Due to the high strength-to-density ratio, Ti6Al4V alloy is probably the alloy most used for AM in the aerospace industry. This alloy usually shows good static strength properties. However, the presence of internal defects and the surface roughness result in a fatigue strength that is clearly lower than that of materials produced by traditional processes. Moreover, the scatter of the fatigue results is generally higher than in the case of wrought pieces. Different treatments have been proposed to improve the fatigue behavior by reducing internal defects and roughness or generating a favorable residual stress field. In this work, selected surface treatments were considered to improve the fatigue strength of AM parts, including shot and laser peening as well as a combination of shot peening plus chemical assisted surface enhancement (CASE®). Three groups of specimens, each with one of the surface treatments, were fatigue tested to compare the results produced by these treatments. The residual stresses, roughness and hardness produced by the treatments were analyzed. After testing, the fracture surfaces were also analyzed to better understand the fatigue process of the different groups of specimens. The results indicate that laser peening produced the best results, followed by shot peening plus CASE and shot peening. In all three cases, the fatigue strength was much higher than that of the reference group without surface treatment. It was also observed that all failures initiated from an interior defect in the shot peening plus CASE group, four out of six failures in the laser peened group, but only one failure in the case of shot peened group and none in the reference group. Failures of specimens with initiation from internal defects started from defects located deeper than the compressive residual stress layer produced by the treatments

Effect of surface treatment on the fatigue strength of additive manufactured Ti6Al4V alloy

Different alloys can be used for Additive Manufacturing (AM) with good structural strength. Among the titanium alloys, Ti6Al4V is the most used, especially for aerospace applications. There have been many analyses of the mechanical properties of additive manufactured Ti-6Al-4V with very good static strength results in general. However, there are still some difficulties to get fatigue properties close enough to the ones of specimens manufactured using traditional processes Considering the high effect of surface roughness on the fatigue strength of  AM specimens, this work deals with the effect produced by some surface treatments on the fatigue properties. Five treatments have been used for comparison. All specimens were annealed previously to reduce residual stresses, as well as sand blasted to reduce the roughness. The treatments considered are: 1) no treatment after annealing and sand blasting; 2) shot peening; 3) shot peening plus Chemical Assisted Surface Enhancement (CASE); 4) laser shock peening, and 5) HIP. After fatigue testing, a comparison of the results has been carried out. It was found that laser peening produced the best results, followed by shot peening plus CASE and shot peening, with the lowest strength produced by HIP as well as just sand blasting after thermal treatment

Fat tissue, aging, and cellular senescence

Fat tissue, frequently the largest organ in humans, is at the nexus of mechanisms involved in longevity and age-related metabolic dysfunction. Fat distribution and function change dramatically throughout life. Obesity is associated with accelerated onset of diseases common in old age, while fat ablation and certain mutations affecting fat increase life span. Fat cells turn over throughout the life span. Fat cell progenitors, preadipocytes, are abundant, closely related to macrophages, and dysdifferentiate in old age, switching into a pro-inflammatory, tissue-remodeling, senescent-like state. Other mesenchymal progenitors also can acquire a pro-inflammatory, adipocyte-like phenotype with aging. We propose a hypothetical model in which cellular stress and preadipocyte overutilization with aging induce cellular senescence, leading to impaired adipogenesis, failure to sequester lipotoxic fatty acids, inflammatory cytokine and chemokine generation, and innate and adaptive immune response activation. These pro-inflammatory processes may amplify each other and have systemic consequences. This model is consistent with recent concepts about cellular senescence as a stress-responsive, adaptive phenotype that develops through multiple stages, including major metabolic and secretory readjustments, which can spread from cell to cell and can occur at any point during life. Senescence could be an alternative cell fate that develops in response to injury or metabolic dysfunction and might occur in nondividing as well as dividing cells. Consistent with this, a senescent-like state can develop in preadipocytes and fat cells from young obese individuals. Senescent, pro-inflammatory cells in fat could have profound clinical consequences because of the large size of the fat organ and its central metabolic role

Influence of Different Shaping and Finishing Processes on the Surface Integrity of WC-Co Cemented Carbides

Investigation of four different surface-shaping and finishing sequences is carried out on the surface integrity of a WC-10Co hardmetal grade. The surface conditions include grinding, electrical discharge machining and grinding, followed by mechanical and dry-electrochemical polishing using the DryLyte® technology. The evaluation includes the measurement of roughness, residual stresses, the Vickers hardness, indentation fracture toughness determination and the damage induced by conical contact response. By scanning electron microscopy, a systematic and detailed examination of the residual imprints is carried out to determine the critical loads for damage initiation and development across the different surface conditions. The results indicate that the use of dry-electrochemical polishing enables the attainment of polished surfaces without any corrosive damage to the metallic binder. Moreover, it retains the mechanical attributes reminiscent of the core material, comprising 85% that were initially induced via grinding

Microstructure versus topography: the impact of crystallographic substrate modification during ultrashort pulsed direct laser interference patterning on the antibacterial properties of Cu

Introduction: Topographic surface patterning in the micro- and nanometer scale has evolved into a well applied approach in surface functionalization following biomimetic blueprints from nature. Depending on the production process an additional impact of process-related substrate modification has to be considered in functional surface optimization. This is especially true in case of antimicrobial applications of Cu surfaces where a modification of the substrate properties might impact bactericidal efficiency. Methods: In this regard, the effect of ultrashort pulsed direct laser interference patterning on the microstructure of pure Cu and resulting antimicrobial properties was investigated alongside line-like patterning in the scale of single bacterial cells. Results and Discussion: The process-induced microstructure modification was shown to play an important role in corrosion processes on Cu surfaces in saline environment, whereas the superficial microstructure impacts both corrosive interaction and ion emission. Surprisingly, antimicrobial efficiency is not predominantly following deviating trends in Cu ion release rates but rather depends on surface topography and wettability, which was shown to be impacted by the substrate microstructure state, as well. This highlights the need of an in-depth understanding on how different surface properties are simultaneously modulated during laser processing and how their interaction has to be designed to acquire an effective surface optimization e.g., to agitate active antimicrobial surface functionalization

Microstructure versus topography: the impact of crystallographic substrate modification during ultrashort pulsed direct laser interference patterning on the antibacterial properties of Cu

Introduction: Topographic surface patterning in the micro- and nanometer scale has evolved into a well applied approach in surface functionalization following biomimetic blueprints from nature. Depending on the production process an additional impact of process-related substrate modification has to be considered in functional surface optimization. This is especially true in case of antimicrobial applications of Cu surfaces where a modification of the substrate properties might impact bactericidal efficiency.Methods: In this regard, the effect of ultrashort pulsed direct laser interference patterning on the microstructure of pure Cu and resulting antimicrobial properties was investigated alongside line-like patterning in the scale of single bacterial cells.Results and Discussion: The process-induced microstructure modification was shown to play an important role in corrosion processes on Cu surfaces in saline environment, whereas the superficial microstructure impacts both corrosive interaction and ion emission. Surprisingly, antimicrobial efficiency is not predominantly following deviating trends in Cu ion release rates but rather depends on surface topography and wettability, which was shown to be impacted by the substrate microstructure state, as well. This highlights the need of an in-depth understanding on how different surface properties are simultaneously modulated during laser processing and how their interaction has to be designed to acquire an effective surface optimization e.g., to agitate active antimicrobial surface functionalization