Microstructural features of ductile cast iron (DCI), including graphite morphology and the pearlitic matrix, are influenced by solidification and subsequent eutectoid transformation and can be effectively tailored through the cooling conditions. While the relationship between pearlite characteristics and mechanical properties is well established for pearlitic steels, the specific contribution of the pearlitic matrix to the mechanical response of DCI has received limited attention. In this study, fully pearlitic DCIs were cast under various cooling rates between 0.1 to 0.34 K/s, enabling systematic variations in microstructure to be correlated with changes in mechanical properties. The resulting interlamellar spacing (ILS) of the pearlite matrix ranged from 291 to 564 nm and was associated with an approximately 70 MPa difference in yield strength. A modified Hall-Petch-type relationship was formulated to describe the dependence of yield strength on ILS. To support predictive capability, representative volume elements were generated from optical micrographs and micromechanical simulations were conducted to isolate the effect of varying ILS on yield strength. The simulation results showed excellent agreement with the experiments, confirming that the ILS predominantly governs the onset of plastic deformation and that pearlite refinement is a key controlling factor for the yield strength of pearlitic DCI.

Grey cast iron is a common, cost-efficient engineering material used in a wide range of technical applications due to its favourable mechanical properties including good wear resistance and high compressive strength. This investigation focuses on the development of a novel combination of austempering and cryogenic treatment of lamellar cast iron, aiming to enhance its mechanical properties. For this purpose, two materials with differing chemical compositions were casted as Y-block specimens and were subjected to austempering at five different temperatures followed by a cryogenic treatment. The microstructure, the graphite morphology, the hardness and the compressive strength of all specimens were investigated systematically. For the first material, a notable increase of hardness and compressive yield limit by approximately 50% respectively 60% compared to the as-cast condition was found, which is attributed to the presence of newly formed martensite. This was consistently proven by dilatometry, Electron Backscatter Diffraction (EBSD) and Transmission Kikuchi Diffraction (TKD), with the latter revealing martensitic regions being located close to phosphides and acicular ferrite. Contrarily, the second material exhibits a negligible effect by cryogenic treatment, which is attributed to a finer austenitic grain size, which suppresses the phase transformation.

The mechanical properties of a solid-electrolyte interphase (SEI), such as hardness and Young's modulus, influence the ion transport pathways through the SEI as well as affecting the dendrite formation processes. Moreover, the local composition of the SEI has a strong influence on mechanical variations at small scales, making a thorough understanding of such properties with high detail in depth and with high spatial resolution crucial. Within this contribution, in operando atomic force microscopy (AFM) and nanoindentation are used to investigate the mechanical properties of the SEI in conventional electrolytes in comparison to those in ionic liquids. While both methods have been shown to be powerful tools to investigate SEI formation, distinctive mechanical fingerprints are demonstrated for SEIs formed in carbonate electrolytes on lithium deposited on copper in AFM-based experiments. Such fingerprints change significantly when ionic liquids are used as electrolytes and depend critically on the exact composition. These results are correlated with nanoindentation, performed on freshly cleaved lithium surfaces in an inert atmosphere and carbonate solvents. Additionally, lithium surfaces treated with varying amounts of and exposure times to ionic liquids are studied. In both cases, AFM-based experiments and nanoindentation, higher stiffnesses and storage moduli are found, indicating a highly complex SEI structure.

For future fusion devices, tungsten is the main candidate materials for the application as plasma facing materials (PFMs). However, considering the challenging operational condition with high thermal loading/thermal stress combining plasma exposure and neutron irradiation/embrittlement, one of the major concern for tungsten as PFMs is its intrinsic brittleness. To avoid cracking and components failure, toughening tungsten is widely investigated, among which tungsten fiber reinforced tungsten composites (Wf/W) are developed using an extrinsic toughening mechanism. Recently, a new type of aligned long fiber Wf/W (L-Wf/W) with dedicated weak interface have been prepared by powder metallurgy process, combing the advantages of superb damage resilience with a much easier production compared to conventional chemical vapor deposition process. In this work, the newly developed material is characterized, including, mechanical tests, high heat flux tests, exposure to plasma for erosion and fuel retention tests. The l-Wf/W composite could improve significantly the damage resilience compared to pure W without altering much of other properties.

High-speed steels are commonly used for cutting tools requiring a high impact toughness and fatigue resistance. Both properties are significantly enhanced by employing the powder metallurgical (PM) production route using HIP as consolidation technique. However, the inherent oxides of the used powder may reduce the fatigue limit. Hence, subsequent forging is commonly required, which in turn precludes the possibility of near net shape production by PM. The purpose of this study is to investigate the efficiency of an isothermal holding stage that is introduced prior to the application of pressure to allow oxide size reduction during the HIP process and thereby increasing fatigue limit. The fatigue limit is assessed by accelerated fatigue testing, allowing its determination with a single specimen, which is particularly crucial for HIP processes with limited capsule volume. Good agreement is observed with results from conventional fatigue testing based on the staircase method.

Fatigue modelling of metals is essential for accurate prediction of fatigue strength and fatigue life which ensures structural integrity and reliability. The fatigue performance of additively manufactured metals, such as laser powder bed fusion (PBF-LB/M) 316L stainless steel (SS), is highly dependent on the microstructure, making microstructural sensitive models crucial for the modelling. To overcome the expensive computation by traditional incremental analysis, crystal plasticity enhanced direct cyclic analysis was performed to efficiently predict the shakedown limit, i.e. fatigue limit, of PBF-LB/M 316L SS in this work. Statistically equivalent representative volume elements (SERVEs) of the two materials produced with different preheating platform temperatures were generated considering the features of grains and lack of fusion defects. The model parameters were determined and calibrated at microscopic and macroscopic levels. The effect of different dislocation cells on the critical resolved shear stress (CRSS) was incorporated in the model. The statistics of the shakedown limit of the SERVEs show that the defects and the surrounding complex grain interaction resulting from the differences in orientations, shapes, and CRSS comprehensively determine the shakedown limit. The shakedown limit of the two materials is compared with respect to the hierarchical microstructure. A preliminary correlation between the modelled fatigue limit, the CRSS, and the material porosity is proposed. This work advances microstructural sensitive fatigue modelling to improve the fatigue limit prediction for PBF-LB/M 316L SS in aerospace, transportation and medical applications.

In this work, the sintering behavior of tapes prepared via tape casting from stainless-steel and zirconia powders is investigated by optical—as well as push-rod—dilatometry. Both methods are compared in terms of sample preparation, measurement conditions, and advantages and disadvantages. The experimental work shows the advantages of optical dilatometry in the characterization of the sintering behavior of load-free sintering tapes and the possibility of simultaneously observing sample warpage and deformation. Push-rod dilatometry requires a constant load on the sample, which influences measurement in the case of tapes with lower mechanical stability due to their sensitivity to deformation, but it has advantages because of its higher accuracy in measuring dimensional changes. In the case of warpage, shrinkage due to the sintering of the sample is superimposed by an irregular deformation process that can be separated by analytical methods. No in-plane shrinkage anisotropy of the tapes is observed for either type of tape. In the case of the push-rod dilatometer, an additional peak in the shrinkage rate is observed in the early stage of compaction, along with a slight shift and an increased maximum in the compaction rate. This is most likely due to the effects of the contact pressure of the push-rod.

LiNixCoyMn1-x-yO2 (NMC) is one of the most relevant lithium-ion battery cathode materials. In this study, micromechanical tests were used to examine the fracture behavior of LiNi0.8Co0.1Mn0.1O2 (NMC811) secondary particles. Furthermore, the grain boundary strength was measured and the grain boundary stiffness was estimated to 521 GPa mu m-1. Using an optimized push-to-pull sample geometry produced by focused ion beam (FIB) technology and measuring the displacement through digital image correlation (DIC), micro tensile tests were performed and validated against nanoindentation. A Weibull distribution characteristic tensile strength of 745 MPa followed by a brittle fracture behavior was measured. The fracture surface was examined and showed an intercrystalline fracture. Through electron backscatter diffraction (EBSD) analysis, less frequently occurring transcrystalline fracture was detected. Scanning transmission electron microscopy (STEM) showed a slight increase in dislocation density within the testing section in comparison to reference positions. The results can be used for a more detailed understanding of the mechanical degradation during the cycling of batteries as well as for building accurate simulation models.

Gear hobbing is one of the most established manufacturing processes for manufacturing external gears. Typically, gear hobbing tools are coated by means of physical vapor deposition (PVD). In this study the influence of chemical vapor deposition (CVD) hob coatings on tool wear under dry cutting conditions was investigated and compared to the wear behavior of typical PVD coatings. 20MnCr5 steel and C45 tempered steel were machined using the fly-cutting trial as an analogy process for gear hobbing. The gear module was mn = 2.557 mm, which represents a common gear size for a passenger car manual transmission. Sintered tungsten carbide-cobalt WC-Co K30 tools with a PVD AlCrN coating and with a CVD TiCN/α-Al2O3 were used and macro- and microscopically analyzed with regard to the result-ing tool life and wear behavior. To investigate different wear behaviors the cutting speed vc and axial feed rate fa were varied in the range of vc = 100-600 m/min and fa = 0.4-3 mm for the individual trials. In total, eight different trials were analyzed. For the CVD-coated tools, no stable cutting conditions could be found and the tools failed by breakout during machining the first part at each parameter combination. Characteristic chip values were calculated using the manufacturing simulation SPARTAPRO. Based on the simulation results the observed wear phenomena were inter-preted and analyzed with regard to their cause of occurrence. The trials showed a significant influence of the coating on the tool life. The mean tool life of the PVD-coated tools was 113 times longer than that of the CVD-coated tools.

As part of the energy transition, fluctuations in the energy supply occur repeatedly. For this reason, power plants are increasingly operated in load-following mode, which entails additional cyclic loads, often not considered in initial power plant design. Consequently, understanding the cyclic material properties of the components used – particularly their fatigue life – is of particular importance. Determining the latter with conventional constant amplitude tests involves significant experimental effort, which is associated with considerable time and cost. Modern lifetime prediction methods, however, enable the determination of fatigue life using a single load increase test in the HCF regime by calculating the incremental cyclic damage based on Palmgren-Miner. This study adapts these methods for use in the LCF regime based on the results of total strain-controlled strain increase tests, determining the incremental cyclic damage based on the dissipated strain energy at each strain level of the strain increase test. The newly proposed MiDAcStrain approach shows good agreement with conventional constant amplitude tests and outperforms the already established lifetime prediction method StrainLife, which requires at least two additional constant amplitude tests in conjunction with a single strain increase test. The material examined in this study is a metastable austenitic stainless steel of type AISI 347, which is frequently used in pressure retaining components of nuclear power plants

The staircase method is commonly employed in the characterization of metals to determine their fatigue limit. In this approach, the stress amplitude is systematically varied around the assumed fatigue limit in consecutive tests. However, its applicability for in-process optimization in alloy design and development is limited by the large number of specimens required-particularly for high-speed steels (HSSs), which exhibit pronounced scatter in fatigue limit-resulting in long testing times. To address this limitation, accelerated fatigue testing is applied to HSS for the first time in the present study. The stress amplitude is continuously increased within a single experiment while recording the specimen temperature, enabling the fatigue limit to be estimated from the dissipated energy of a single specimen and thereby reducing both material consumption and testing time. The applicability of the accelerated fatigue testing method is demonstrated for an ingot-cast HSS (AISI M2) and a powder-metallurgical (PM) HSS (AISI M3 Class 2) fabricated by hot isostatic pressing (HIP) as consolidation technique. In addition, the fatigue limits of both materials are determined using the conventional staircase method at various highly loaded volumes (HLVs) to characterize the defect distribution and to validate the results obtained from accelerated testing.

Nickel-based alloys are widely used in high-temperature applications due to their excellent mechanical strength and oxidation resistance. However, properties such as high-temperature strength and pronounced work-hardening make them difficult to machine. In this study, the mechanical behavior and strengthening mechanisms of conventionally heat-treated Inconel 718 alloy are investigated. Microstructural characterization is performed to identify and analyze the composition, morphology, and distribution of precipitates. Uniaxial compression tests are conducted at temperatures ranging from 20 to 1000C and strain rates from 0.002 to 20 . A phenomenological constitutive model based on the Johnson-Cook formulation is developed to better describe thermal softening and temperature-dependent strain rate sensitivity. The model is validated against experimental flow stress data, reducing yield strength deviations at 850C and strain rate of 0.002 from 88% to 13% and from 321% to 7% at 1000C. In addition, a physically based MatCalc model is used to simulate precipitation kinetics, yield strength, and flow stress. Overall, this study introduces an integrated experimental-computational framework that combines microstructural characterization with a physically based model and an improved flow stress model, enabling a more accurate and comprehensive understanding of the deformation and strengthening mechanisms of Inconel 718 under extreme thermomechanical conditions.

Additive manufacturing (AM) offers numerous possibilities for toolmaking, such as the integration of internal cooling structures, easy fabrication of complex tool geometries, or hybrid manufacturing. Another important aspect is the minimization of necessary post-processing steps through near-net-shape manufacturing, which enables needed cost and effort savings, especially for difficult-to-machine, carbide-rich tool steels. Previous studies have investigated laser powder bed fusion (PBF-LB/M) as a possible process. However, PBF-LB/M is not applicable to all steels. In this study, AISI A11 was successfully processed using metal binder jetting and electron beam melting both with optional hot isostatic pressing (HIP). The resulting microstructures were characterized depending on the AM process. Mechanical investigations enable appropriate microstructure-property correlations for fatigue performances. For additively manufactured A11, the high cycle fatigue (HCF, N G = 107) strengths are statistically evaluated under rotation bending tests. Those results are compared to conventional A11 PM produced via HIP and subsequent hot working. The results show that AM toolmaking of high vanadium alloyed, carbide-rich tool steels is a promising alternative to conventional steelmaking.

Hard physical vapor deposition (PVD) coatings are widely used as protective layers on cemented carbide tools due to their exceptional mechanical properties. However, these coatings can be susceptible to damage and cracking. Gaining a deeper understanding of how the coating microstructure influences the cracking behavior is essential. A precise micromechanical simulation of cracks could improve the understanding of crack initiation and propagation under external loads, and its contribution to tool wear in real cutting applications. This study combines experiments and micromechanical simulations to investigate the crack behavior of two TiAlCrN PVD coatings with different coating thicknesses. Initially, nanoindentations coupled with inverse FEM simulations guided by an automatic optimization algorithm were conducted to determine the Young's modulus and plastic Ludwik-Hollomon model parameters for both coatings. These properties were then applied to simulate crack behavior under microindentation. Scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD) were applied to characterize the grain morphology and microstructure of the coating. Numerical simulations of the local crack initiation and growth were performed based on a microstructure-based model as well as the extended finite element method (XFEM). The simulated crack lengths showed good agreement with the experimental results.

The incorporation of nitrogen as an alloying element in stainless steels can significantly improve both mechanical properties and corrosion resistance. The conventional production of high nitrogen-alloyed steels (HNS) is hampered by the limited solubility of nitrogen in the steel melt. This study investigates a new powder metallurgical process to produce HNS by mixing stainless steel powder with Si3N4 powder, followed by hot isostatic pressing (HIP) of the mixture, in which the Si3N4 particles dissolve in the solid austenitic phase, enriching the matrix with nitrogen and exploiting the higher solubility of nitrogen in the solid phase compared to the liquid phase. The innovative aspect of this approach is the use of HIP with integrated gas quenching, which allows simultaneous powder consolidation and heat treatment. This method exploits the austenite-stabilising effect of isostatic pressure, which increases the solubility of nitrogen in the austenitic phase, to achieve previously unattainable nitrogen-supersaturated matrices. The amount of Si3N4 to be added is determined based on CALPHAD calculations considering both pressure and temperature during HIP. The study evaluates the potential for producing HNS using two different base alloys: X2CrNi18-9 and X1Cr20. The X2CrNi18-9 steel produces a highly nitrogen-supersaturated austenitic state. The X1Cr20 alloy produces an almost fully austenitic condition in which only nitrogen is the austenite stabilising element. Micro-structural analysis is performed by secondary electron microscopy, electron backscatter diffraction and energy dispersive spectroscopy.

Newly developed hot isostatic pressing (HIP) units with integrated rapid cooling systems that are capable of operating at gas pressures up to 200 MPa provide the opportunity to densify and harden the metallic materials in a single step. For the application of these advanced HIP units in producing steels with defined microstructure, a crucial factor is the austenite grain size, which strongly influences the phase transformation during cooling and is effectively affected by the pressure during HIP. To study the effects of pressure, temperature and holding time on the growth of austenite grains and subsequently the final microstructure, a series of interrupted HIP experiments on hot work steel AISI H13 were conducted using such an advanced HIP unit. The austenite grain growth during HIP was analysed by metallographic microstructural investigations after rapid cooling. Thereafter, the effect of the austenite grain size on the phase transformation was studied using quenching dilatometry. Following this, the relationship between austenite grain size and martensitic/bainitic phase transformation temperature was determined, which indirectly indicates the influence of temperature, pressure and holding time on the final microstructure. By implementing this relationship into numerical models, the effect of HIP parameters on the microstructure of large-scale components, particularly those that experience large temperature gradients during the heating and cooling stages, can be predicted in the future.

Ductile cast irons (DCIs) offer a unique combination of excellent mechanical properties, low cost, and high geometric flexibility, making them particularly suitable for large-scale complex components. However, their heterogeneous microstructure, consisting of defects like microshrinkage pores and graphite nodules embedded in an iron matrix, exhibits strong variations throughout large structural components due to thermal gradients caused by changes in wall thickness of cast components. These microstructural variations lead to local and global differences in mechanical properties. Combined with intrinsic residual stresses present in the microstructure, this uncertainty in mechanical properties hinders efficient design and often results in overdimensioned components. To address this uncertainty, the present work introduces a simulation-based framework that incorporates second-order residual stresses into a subsequent shakedown analysis to evaluate their effect on the fatigue properties of SSF-DI. The results show that second-order residual stress fields significantly influence the predicted fatigue limit obtained from the shakedown analysis. Neglecting second-order residual stresses leads to a slight overestimation of the yield strength under tensile loading but a pronounced overestimation of the fatigue limit. The study demonstrates that reliable simulation models within process-structure-property-performance simulations require careful consideration of the interactions between microstructure and residual stresses.

In situ alloying via laser-based powder bed fusion of metals (PBF-LB/M) has gained attention as an alternative to prealloyed powders. In this study, H13 tool steel is in situ alloyed with titanium carbides (TiC) in amounts up to 30 wt.%. This approach offers the advantage that the carbides melt only partially during processing, preventing excessive carbon enrichment of the steel matrix. Using suitable process parameters, samples with up to 15 wt.% TiC were successfully fabricated with relative density above 99.6 vol.%. The resulting microstructure consists of coarse, undissolved and fine, reprecipitated carbides, leading to grain refinement and an isotropic microstructure. By varying the scanning speed, the energy input and thus the degree of carbide dissolution can be controlled. As-built hardness values for powder mixtures with 10 wt.% TiC reach 590 HV30, which is higher than the maximum hardness achieved through subsequent hardening. The secondary hardness peak is reached with direct tempering for 4 h at 500 degrees C with 659 HV30.

The high-speed steel PM HS3-3-4 was investigated to assess the influence of an isothermal holding stage within the transformation gap during quenching on the interfacial strength between the matrix and carbides. The interfacial strength was assessed by micro-tensile testing using push-to-pull geometries fabricated via focused ion beam (FIB) milling. During indentation, the gauge section was continuously recorded by scanning electron microscopy (SEM) and strain analysis was conducted by digital image correlation (DIC). Tensile strengths of 2150-2500 MPa, unaffected by the isothermal holding stage, were measured together with significant plastic deformation in the martensitic matrix. Fracture occurred within the matrix in close proximity to the interface.

As an inevitable post-treatment of the binder jetting (BJT) process, sintering strongly influences the dimensional accuracy of the final components. The main challenge for precise dimension control lies in the anisotropic shrinkage during densification which is prompted by printing-induced heterogeneous particle configurations. To address this, we investigated anisotropic sintering behavior of BJT-printed 17-4PH stainless steel at the mesoscale by integrating simulated anisotropic powder configurations with a modified kinetic Monte Carlo (KMC) Potts model. Anisotropic representatives of printed parts were generated by rational particle deletion of isotropic discrete element method (DEM) packings. The obtained anisotropic packings were incorporated into a KMC Potts model modified with an Arrhenius-type temperature-dependent probability, enabling tracking of powder and pore evolutions during sintering. It was revealed that porous channels govern the anisotropic shrinkage and elevated temperature accelerates the transition from anisotropic to isotropic sintering. The predicted pore morphologies agree well with those under optical microscope, which validates the modelling strategy. Furthermore, as an initial feasibility test toward cross-scale sintering modeling, stereology-derived constitutive parameters like sintering stress and effective viscosity extracted from the KMC results were supplied to macroscale finite element method (FEM) modelling. The feasibility was proved by an accurate prediction of the relative density evolution.