Solid oxide cell technologies play a pivotal role in the realm of renewable energy storage, guiding us through the journey toward decarbonization. Understanding how electrocatalytic materials behave under high‐temperature conditions is an absolute necessity to push these technologies forward. Operando spectroscopic investigations, such as near‐ambient pressure X‐ray photoelectron spectroscopy (NAP–XPS), offer insights into the chemical nature of active working electrodes, including the dynamic response of redox states and adsorbate chemistry to changing electrochemical conditions. Mixed ceramic–metallic electrodes exhibit a limited region with electrochemically active triple‐phase‐boundary (TPB) sites, which are located close to the electrolyte/electrode interface. To monitor this specific region spectroscopically, metallic (Ni) and bimetallic (NiCu) network‐like structures are synthesized on a yttria‐stabilized zirconia electrolyte and the electrochemical state and performance are studied by using operando NAP–XPS. In the experiments, the surface oxidation states under different polarizations are revealed, the gas composition dependent Nernst shift is confirmed, electrocatalytic activities are unraveled, and hydrogen evolution is correlated with the applied potential. The findings demonstrate, the effectiveness of thin‐film model cells with spectroscopically accessible TPB regions for probing interfacial states and electrochemical processes. The obtained fundamental knowledge can provide valuable insights for the advancement of renewable energy storage technologies.

WC-Co hardmetals are utilized as tool materials in metal cutting applications in which they are exposed to high mechanical cyclic loads and elevated temperatures. A better understanding of the failure mechanisms of WC-Co hardmetals under these application conditions and the ability to diagnose the damage evolution state are key factors to understand the limits of endurable cyclic load at a certain temperature. The aim of the current work was the experimental determination of stress-strain-hysteresis loops for the investigation of damage indicators in uniaxial cyclic tests at a stress ratio of R = sigma(min)/sigma(max) = -1 for two WC-10 wt% Co hardmetals at 700 degrees C and 800 degrees C in vacuum. An increase in the stress-strain-hysteresis loop area and tension-compression-strain asymmetry was recorded with increasing number of load cycles at 800 degrees C, with earlier failure than at 700 degrees C. The relationship between the stress-strain-hysteresis loop parameters and the damage evolution state at the microstructure level, as well as the deformation behavior of WC- and Co-phases with increasing number of load cycles, were analyzed. To this end, the microstructure for one WC-Co hardmetal grade was analyzed by scanning electron microscopy and electron backscatter diffraction after cyclic testing up to defined numbers of load cycles at 800 degrees C. It was observed that the hysteresis loop area and strain asymmetry coincide with the formation of nanopores at WC/WC interfaces and WC/Co phase boundaries, which enlarge to form larger cavities with increasing number of load cycles. Additionally, electron backscatter diffraction data showed that the fcc Co-phase partially transformed into hcp Co under cyclic loading. All specimens, in which an increase in the stress-strain hysteresis loop area or strain asymmetry was observed, ultimately failed when a sufficiently high number of load cycles was applied. Thus, these results indicate that the investigated parameters are reliable indicators for bulk material damage.

The aim of the current work was the experimental determination of limit stresses in the uniaxial cyclic compression test that lead to advancing ratcheting in different WC-Co hardmetal grades at elevated temperature. At stresses below the limit stress the plastic strain per cycle reduces and plastic strain accumulation stops after a characteristic number of load cycles. Special attention was paid to the microstructural influence on the onset of advancing ratcheting and the associated damage development at the microstructure level. WC-Co hardmetals are used in various areas such as forming and forging tools, where they are exposed to high temperatures and pressure loads. Their good high-temperature properties allow them to be used under these conditions, but these properties are influenced by the microstructure. Investigations of the mechanical properties of hardmetals had been carried out under monotonously increasing loads and cyclic tests at room temperature and elevated temperatures. In these tests, the effect of different stress ratios R = sigma(min)/sigma(max) on the fatigue behaviour of hardmetals were studied, However, no studies are known for WC-Co hardmetals and their limit stresses in relation to strain ratcheting under cyclic compressive loading at elevated temperature. Hence, in the current work the influence of increasing stresses as a function of microstructure and their effect on the evolution of the strain of six different WC-Co hardmetal grades are discussed. For this purpose, the materials were investigated by uniaxial cyclic compression tests at a stress ratio of R = -infinity at 700 degrees C and 800 degrees C in vacuum. The investigated hardmetal grades differ on the one hand in their WC grain size, which varies between 0.4 mu m and 2.0 mu m, and on the other hand in their Co-content, which varies between 6 wt% and 12 wt%. The residual strain value epsilon(res) at zero applied stress was observed to stabilize with increasing number of load cycles at low applied stress ranges. Strain ratcheting occurred above a critical stress range, referred to as the limit stress for strain ratcheting. Strain ratcheting is the accumulation of plastic strain with increasing number of load cycles in which no strain stabilization occurs. Further, for all investigated hardmetal grades, the limit stresses were observed to decrease with increasing temperature. In the following, the microstructure of one hardmetal grade was analysed after loading below and above the limit stress by scanning electron microscopy and electron backscatter diffraction (EBSD). The influence of strain stabilization and ratcheting was analysed with regard to damage development and deformation behaviour of the WC and Co-phases. Strain ratcheting was observed to result in the formation of cavities and nanopores at phase boundary triple points and WC/Co interfaces. Additionally, the EBSD data showed that the fcc Co phase was transformed into hcp Co. Therefore, it is assumed that on the one hand, a certain strain value needs to be exceeded for strain ratcheting to occur and, on the other hand, that besides dislocation movement, microdefect formation and phase transformation significantly contribute to the increase in strain.

WC-Co hardmetals are popular tool materials, which are used in applications such as metal milling or turning. In these applications, elevated temperatures occur in the tools during the machining process, although they are also cooled. This results in a complex interaction of thermal and mechanical loads in the tools. Within this current work, a strain asymmetry of a WC-10 wt% Co hardmetal after tensile and compression uniaxial step-loading creep tests is described. Two types of tests were performed: Firstly, specimens were deformed to certain strain limits at 700 ?C and 800 ?C. Strain asymmetry was observed for tensile and compression stresses above 600 MPa at 700 ?C and above 250 MPa at 800 ?C. In the second type of test, the specimens were stepwise loaded up to a stress of 300 MPa under tensile and compressive load at 800 ?C. The aim of test 2 was to identify the physical reason for the strain asymmetry from the first tests at 800 ?C. The material?s microstructure was analyzed for the specimens from test 2 by scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). The influence of the loading type was analyzed with regard to damage development and deformation behaviour of the WC- and Co-phase. SEM images showed that the faster increase in strain over time under tensile than under compressive loading was caused by the formation of cavities at WC-WC interfaces and at WC-Co phase boundaries. Due to the larger number of observed microdefects under tension than under compression, it was assumed that this was the physical reason for the strain asymmetry. In addition, EBSD data showed that during the compression and tension creep tests, the fcc Co-phase was partially transformed into the hcp Co-phase.

At elevated temperatures, the material behaviour of WC-Co hardmetals shows differences under similar loading conditions depending on WC grain size and Co-content. Variations in the chemical composition and microstructure in hardmetals cause different material properties such as strength or creep resistance. In the current work, the influence of WC grain size on creep mechanism and creep resistance was investigated for WC-12 wt% Co hardmetals with 0.4 mu m, 0.7 mu m and 2.0 mu m average WC grain size. Specimens were tested in uniaxial tensile and compression step-loading creep tests at 700 degrees C and 800 degrees C under vacuum conditions. Time-dependent creep behaviour with steady-state secondary creep was observed for all hardmetal grades investigated, with specimens creeping faster under tensile than under compressive loading. At 700 degrees C, the medium-grained hardmetal grade exhibited the highest minimal creep rates epsilon min compared to the submicron and ultrafine-grained grades. In contrast, the ultrafine-grained hardmetal grade showed higher epsilon min at low stresses and 800 degrees C, because of the high amount of grain boundary area per unit volume, which is advantageous for vacancy diffusion at grain boundaries. Therefore, the epsilon min of the medium-grained hardmetal grade was less affected by temperature than that of the finer-grained grade. Also two stress exponent n-ranges were observed at 700 degrees C and 800 degrees C: At low stress levels, n was in the range of about 1. Above a critical stress level, n reached values between about 4 and 6. Beside the influence of the WC grain size on the creep mechanism and creep resistance, damage evolution with increasing stress levels was analysed for the ultrafine-grained grade at 800 degrees C. The microstructures of three compression step-loading creep tested specimens were examined after maximum stress levels of -350 MPa, -950 MPa and -1350 MPa. Microstructural investigations performed via scanning electron microscopy showed that more and larger cavities had formed at WC/WC interfaces and WC/Co phase boundaries in the specimen tested up to -1350 MPa compared to the ones tested up to -350 MPa and -950 MPa.

Sustainability is the key concept in the management of products that reached their end-of-life. We propose that end-of-life products have—besides their value as recyclable assets—additional value for producer and consumer. We argue this is especially true for the machining industry, where we illustrate an automatic characterization of worn cutting tools to foster value co-creation between tool manufacturer and tool user (customer) in the future. In the work at hand, we present a deep-learning-based computer vision system for the automatic classification of worn tools regarding flank wear and chipping. The resulting Matthews Correlation Coefficient of 0.878 and 0.644 confirms the feasibility of our system based on the VGG-16 network and Gradient Boosting. Based on these first results we derive a research agenda which addresses the need for a more holistic tool characterization by semantic segmentation and assesses the perceived business impact and usability by different user groups.

In service, milling tools have to cope with severe levels of thermal and mechanical load. Especially temperature influences the damage behavior of a tool’s cutting edge by influencing material properties and thermally induced stresses. It is therefore of relevance to gain quantitative information on the thermal tool load situation. Information on temperatures in milling tools is not readily available today. Therefore, extensive experimental effort was necessary to determine temperatures in-situ during milling in the axial center of a rotating end mill and in a Ti6Al4V workpiece near the milled surface. The used end mill was a WC-Co hard metal tool protected by a TiAlN coating. Since the damage-relevant cutting edge temperature is not directly accessible by experimental means, a simulation was employed. The transient temperature field in the tool was calculated by an iterative and synergetic use of two-dimensional finite element cutting models, three-dimensional finite element end mill models and two-dimensional workpiece models. The simulation allows for the description of the time-dependent temperature distribution from the chip formation site at the cutting edge to the axial tool center and into the workpiece, where thermocouples were placed in experiments. Validation of the calculated cutting edge temperatures was performed for 5000 individual consecutive cuts via comparison of results for tool core temperature in experiment and simulation. The model yields a very pronounced concentration of the thermal load maximum of T>650 °C near the cutting edges in a very small volume of only 1 ppm of the tool’s volume. In particular, the model’s spatial discretization is able to resolve the gradient of temperature in the hard coating towards the coating/substrate interface, showing temperature shielding effects of the hard coating.

Milling processes are characterized by interrupted cutting, resulting in cyclic thermo-mechanical loading conditions affecting the milling tool's service life. In the current paper, a numerical method is built to predict the transient temperature and stress fields inside coated milling inserts during a dry milling application. The investigated milling tools are hard coated WC-Co hard metal milling inserts, the cut workpiece material is 42CrMo4. The thermal shielding of the substrate by three different hard coating layers, each with a thickness of 7 pm is quantitatively evaluated numerically. The compared coatings are: (i) a TiAlN single layer, (ii) a TiCN/alpha-Al2O3 bilayer and (iii) a TiAlN/alpha-Al2O3 bilayer. The deformation behavior and thermal properties of the hard metal substrate and the hard coatings were considered as a function of temperature by experimentally parameterized material models. A remarkable new feature of the presented model is that the simulated dry milling process includes an unprecedented number of 100 load cycles. The synergetic combination of 2D and 3D finite element models gives insight into the cyclic thermo-mechanical tool load that causes stresses and inelastic strains in the substrate. The applied modeling approach considers that the heat flux between the workpiece and the milling tool is changing as the tool heats up during milling. During successive milling cycles, a decreasing heat flux into the tool is taken into account. A comparison of hard coatings with different inherent thermal properties showed a damage-relevant reduction in substrate plasticization with decreasing thermal conductivity of the coatings.

The special properties of titanium and titanium alloys, such as their high strength-to-weight ratio, their corrosion resistance, and their biocompatibility are of high importance for aerospace, medical and other industrial applications. However, components made of these difficult-to-cut materials entail major challenges for machining processes. High thermo-mechanical tool load results in rapid tool wear, and the already significant machining costs are further increased by premature tool exchange to avoid tool breakage, damaging the valuable workpieces. Both, tool wear progress and risk of tool breakage can be reduced by gaining extensive knowledge about the thermo-mechanical tool load over the tool life time. In this paper, the influence of different machining parameters on the end milling tools’ core temperature and the resulting active force affecting the tool are investigated over tool life time. To measure thermal and mechanical tool loads, an adapted sensory tool holder was used. The results show a strong interdependence between tool load, tool core temperature, machining parameters and tool wear.

Difficult-to-cut materials, such as titanium- and nickel base alloys, are of great importance for the aerospace industry. However, they entail major challenges for machining processes, due to the high thermo-mechanical tool load. To meet these challenges, various lubrication and cooling strategies have been developed, but their effect on the load collective has not been sufficiently investigated. In this paper, the influence of different lubrication/cooling strategies on the end milling tools’ core temperature and the resulting active force affecting the tool while milling Ti6Al4V are investigated. Therefore, an adapted sensory tool holder with wireless data transmission was used.