This study examines the influences of milling-induced surface topography and residual stresses on the fretting fatigue behaviour of high-strength steel 34CrNiMo6 + QT (AISI 4340) under flat–flat contact conditions. Various milling parameters (feed rate, cutting depth, and tool configuration) were systematically varied to characterize their influence on surface roughness and residual stress states, which ranged from tensile to compressive depending on tool stiffness and cutting conditions. Derived milling configurations were subsequently employed to produce specimens for plain fatigue and fretting fatigue experiments under actively controlled slip amplitude and defined contact pressure. The resulting S–N curves revealed a 78% reduction in fretting fatigue strength compared to plain fatigue attributable to tribological damage mechanisms. While lower surface roughness promotes the crack growth in the inclined section, compressive residual stresses appear to moderately improve the fretting fatigue limit by enhancing crack arrest, as indicated by marker load tests. Moreover, the breadth of the surface power spectrum, expressed by the Nayak parameter, exerts only a minor influence on the normalized number of load cycles. Instead, the fretting fatigue life is primarily affected by adhesive wear and mechanical interlocking influencing the crack initiation. Adhesion formation is largely governed by macroscopic surface waviness and mostly independent of residual stresses. These results indicate that the residual stresses mainly influence the fretting fatigue limit through crack arrest while the surface topography modifies the level and depth affected by contact stresses and primarily governs the specimen lifetime in the HCF regime.

Abstract Magnetically responsive carbon fibres that can be actively aligned during composite manufacturing are of interest for improving the load bearing applications of fibre-reinforced lightweight structures. This work investigates thermal and chemical pretreatment methods to remove the epoxy sizing layer and enable a uniform galvanic coating with Fe-Co. Since the epoxy-based sizing layer on commercial carbon fibres limits wettability and prevents uniform metal deposition, its removal is essential for successful coating. To address this, thermal pretreatment was carried out between 350 °C and 500 °C in air while chemical pretreatment involved acetone and nitric acid. Thermal treatment in air progressively improves fibre dispersibility with increasing temperature above 450 °C. Acetone treatment produces only minor improvements, whereas acid treatment enhanced dispersibility by oxidising the fibre surface and increasing its polarity. Limited coating coverage is obtained after low-temperature thermal treatment and acetone treatment, while fibres pretreated thermally at 450–500 °C show continuous and uniform coatings. Acid treatment further improves coating coverage compared with acetone but remains less effective than thermal desizing. The resulting Fe-Co coatings had an average thickness of approximately 1 μm with an average composition of 64% Fe and 36% Co. The magnetic properties of the Fe-Co coatings are described by its low coercivity (approximately 30 Oe) and high saturation magnetisation (approximately 80 emu/g). Overall, thermal desizing at 450 °C and above proved to be the most effective pretreatment for producing homogeneous magnetic Fe-Co coatings on carbon fibres.

The analysis of process signals is a key method for gaining experimental insight into the underlying layer formation mechanisms in plasma electrolytic oxidation (PEO). This is made possible by the simultaneous measurement of electrical and optical process signals with high temporal resolution. However, according to the current state of the art, the interaction between these signals is primarily discussed in qualitative terms. Therefore, this article presents a robust methodology for analysing the current signal, which makes it possible to categorise the charge electro-chemical and plasma-chemical dominated subprocesses and to quantify their respective contributions. The evaluation is performed by taking additional process signals into account. The experimental setup for measuring process voltage, current, and photovoltage, as well as the measurement routine, are briefly described. This is followed by a detailed description of the numerical procedure. This includes the application of fundamental mathematical methods to the time-discrete measurement data, the automated selection of the pulse segment to be examined and the identification of discharge initiation to determine the interval boundaries of the electro- and plasma-chemically dominated pulse subsegments. The description of the routine is primarily intended for experimental scientists and is meant to provide them with a tool for extracting additional information from their process data. These can then be used to better understand electro-chemical side reactions and parasitic subprocesses in PEO.

During plasma electrolytic oxidation (PEO), an electrochemical oxide layer formation is essential for the substrate passivation, both during the initial stage of the PEO process, prior to the onset of discharges, and at the bottom of discharge channels during ongoing PEO treatment. Therefore, the final properties of the PEO coating are linked to the electrochemical formation of the oxide layer. This study presents a two-dimensional simulation of the barrier layer formation during the initial stage of PEO on aluminium. The high-field model was used to calculate the oxide layer growth as a function of the transferred electric charge. The model was validated by comparing the simulated results with experimentally measured current–potential curves obtained from polarisation experiments and with oxide-layer thicknesses determined by electron microscopy. Good agreement between the simulation and the experimental results was achieved when the electron current contribution was taken into account. The maximum current density was found to be 2.35 A dm-2 in the experiment and 2.51 A dm-2 in the simulation. The resulting barrier layer thickness is (127 ± 4) nm according to the experiments and 128.6 nm according to the simulation.

Nickel and its alloys offer excellent chemical resistance and mechanical properties under elevated temperatures. This makes them suitable for high- and low-temperature applications. Microreactors, due to their microscale dimensions, pose challenges for conventional joining techniques. Diffusion bonding offers a promising approach to overcome these challenges, with bond strength influenced by temperature, time, contact pressure, and surface state. This study investigates how face-turning and diamond smoothing affect the surface state of pure nickel. Specimens are face-turned at cutting speeds from 50 m/min to 400 m/min, followed by diamond smoothing with forces of 100 N to 200 N. Surface properties are characterized, and the results indicate that increasing the cutting speed decreases surface roughness values, coarsens crystallites, and increases tensile residual stresses. Smoothing at all forces induces compressive residual stresses and minimizes the surface roughness values at 100 N and 150 N. The findings highlight the influences of turning and diamond smoothing on the surface state of pure nickel, providing a basis for selecting surface preparation parameters that are expected to enhance diffusion bonding performance. With this knowledge, the field of application of diffusion bonding can be improved by achieving the suitable surface state.

The layer thickness can be measured non-destructively by a variety of methods. However, there are limitations, such as, layer thickness < 300 nm, minimal roughness, optical transparency, or a required difference in the chemical composition between layer and substrate. The present study aims to provide a method that fills the gaps of the existing methods. By utilizing grazing-incidence X-ray diffraction and considering the effects of roughness and specimen curvature, a model is proposed, which can be used for layer thicknesses in the range of several tens of nanometers to several micrometers. The model can be applied for a crystalline layer on a crystalline substrate if the phase can be distinguished by X-ray diffraction. The model is validated for a martensitic layer on austenitic steel using electron backscatter diffraction and electrodeposited layers on curved substrates. Good agreement (average deviation < 10%) can be reached. The approach cannot replace thin-film characterization methods like ellipsometry, but it extends the usability of X-ray diffraction for layer-thickness determinations.

The characteristic heat accumulation within a burst of ultrashort pulses enables the formation of new types of surface alloys. The melt dynamics during irradiation provide the opportunity to change the surface texture in a controlled manner. However, there is still very limited information available on the influence of the topography of solidified melts of these novel surface alloys on the tribological properties of the metal matrix composite (MMC) surface. In this study, the authors report on the use of a burst-mode solid-state laser with an emitting wavelength of 1064 nm and a pulse duration of 10 ps for the surface treatment of the MMC cemented tungsten carbide. This treatment and texturing form a novel surface alloy with different topographies of the solidified melt. The characterization of the generated topographies and their tribological properties is conducted by means of pin-on-disk and nanoindenter hardness measurements of the remelted surfaces. Furthermore, x-ray diffraction analyses provide the basis for the discussion of newly formed phases. The results demonstrate that surface treatment with burst pulses has a significant influence on the tribological properties, which can be manifested in an increase or decrease in the coefficient of friction or wear.

PurposeAdditive manufacturing of polymer-metal components increases the freedom of design and avoids expensive tooling. Few studies investigated the direct printing of thermoplastics onto metal parts, and geometrically coarse form fits have been used to achieve adhesion. The suitability of anodizing and organosilicate coating of metal surfaces - performant adhesion promoting layers in conventional production - has not been tested. This study aims to test the hypothesis that these treatments are suitable if convenient printing parameters are used.Design/methodology/approachPolymers are printed onto aluminum parts using fused-filament-fabrication (FFF). The effects of anodizing in phosphoric acid at low voltages and of organosilicate coating bearing epoxy functionality on the joint strength are evaluated. Sufficient FFF parameters of the first printed layer were identified with PLA and then transferred for printing with the PA, ABS and PETG.FindingsLow interfacial pore content and thus high joint strength is achieved for excessively increased metal-surface temperatures and when subsequently ironing the first printed layer. The parameters print speed, layer height of the first layer, and nozzle temperature had negligible impact. For anodizing, joint strengths of 15.5 MPa, 8.7 MPa, 2.6 MPa and 2.5 MPa were determined for PLA, PA, ABS and PETG, respectively, whereas the organosilicate enabled joint strengths of 5.1 MPa, 9.2 MPa, 5.0 MPa and 4.4 MPa, respectively.Originality/valueTo the best of the authors' knowledge, it is shown for the first time that anodizing and organosilicate coating enable moderate joint strengths between aluminum and typical FFF polymers. Besides adhesion promotion, a significant added value of these treatments is the possible integration of further functionalities into the manufactured components, such as protection against wear by anodizing and corrosion protection by the organosilicate coating.

Austenitic stainless steels such as 316L (1.4404) are widely used in chemical plant engineering applications because of their exceptional corrosion resistance. However, forming processes significantly affect the material's microstructure, which in turn influences its corrosion behavior. Depending on the chemical composition and forming history, 316L tends to martensite formation during forming, which strongly impacts the corrosion behavior in narrow zones close to the surface. In forming processes with tool contact, local martensite formation occurs at least on the surface up to a few micrometers into the bulk of the material. The residual stress state, phase fractions, crystallite sizes and microstrain are experimentally determined by x-ray diffraction and numerically predicted. This paper introduces a numerical approach to predict corrosion rates of 316L after cold rolling. The method extends conventional forming simulations with empirically calibrated models that factor in the component surface and the near-surface microstructure. This approach facilitates the optimization of workpiece designs and forming processes and is also adaptable to other materials and forming operations.

This work aims to clarify whether the individual advantages of the two commonly used silicate- and aluminate-based electrolytes for the plasma electrolytic oxidation (PEO) of steel can be combined in a two-step process. The first PEO step was carried out in an aluminate–phosphate electrolyte with pulsed voltage and anodic amplitudes between 150 V and 200 V. The second PEO step was carried out at an increased anodic voltage amplitude of 400 V in a silicate–phosphate electrolyte. As a reference, PEO was conducted in a single step in the same silicate–phosphate electrolyte at an increased anodic voltage amplitude of up to 400 V. The microstructural layer analysis was carried out using SEM and EDX analyses, Raman spectroscopy and XRD analysis. Heterogeneous layers containing iron oxide and iron phosphate form in the silicate–phosphate electrolyte at anodic voltage amplitudes up to 300 V by electrochemical reactions. Further increasing the anodic voltage amplitude up to 400 V results in heterogeneous layers, too. PEO in the aluminate–phosphate electrolyte at 150 V causes the formation of thin, amorphous layers mainly consisting of aluminum and iron oxides. At 200 V amplitude, a PEO layer with pronounced open porosity is formed, which primarily consists of the crystalline phases corundum and hercynite. During subsequent PEO in the silicate–phosphate electrolyte, the previously formed layers were replaced by a macroscopically homogeneous layer that is mostly nanocrystalline and may contain amorphous iron(-aluminum) phosphates and oxides as well as silicon oxide. It can be concluded that the two-step PEO process is suitable for the production of more homogeneous PEO layers.

Electroplated coatings, i.e. coatings formed by electrodepositons, play an important role in tribological and corrosion protection. Within the theory diffusion boundary layer models play an important part in investigations on electrodeposition. For direct current approaches, the model is applied and investigated directly in depth with great success. For pulse plating, uses exact solutions to Fick’s second law for certain pulse-forms or is more indirect and relies on identification with a direct-current model the modeling approach. The identification is then used to deduce from direct current to pulse plating, or uses relations from exact solutions to compute the limiting current density for pulse plating from the limiting current density for direct current. The article investigates if the used identification scheme, by averaging, holds true in general and finds that it does not hold true for high current distributions due to the identification of a physical model for direct current with an unphysical model for pulse plating. Motivated by this situation in the article models and their numerical treatment are derived, which grant physicality of the models and the limiting current distribution, independent from the pulse-form. Additionally, in the article a methodology to compute the maximal applicable current density for pulse plating is derived, in form of approximately solving an optimal control problem, without relying on the identification with direct current and exact solutions for the given pulse-form. Besides theoretical results, the article develops an easy to implement numerical methodology to simulate the models alongside the theoretical results.

It is well known that producing bulk metallic glasses requires very high cooling rates during processing. This limits the sizes of elements produced by casting methods and is why the alternative technology, additive manufacturing, is explored as a development method for bulk metallic glass with no geometry restrictions. Among the tested alloys with high glass ability, Co-based alloys have not yet been printed successfully. This work investigated the possibility of developing a fully amorphous sample from Co-based alloy with high glass-forming ability using selective laser melting focusing on alloy Co47.6B21.9Fe20.4Si5.1Nb5. This study contains literature analyses and experimental tests of selective laser melting (SLM). After printing, the samples were analyzed by optical microscopy, scanning electron microscopy, scanning transmission microscopy, differential thermal analysis, X-ray diffraction, and nanohardness testing. The best set of parameters was established: laser power of 65 W and scanning speed of 500 mm/s. Other parameters, constant during the experiment, were laser spot diameter of 0.11 mm, hatch spacing 77 µm, and layer thickness 25 µm. The main finding is that it is possible to develop fully amorphous samples from Co-based alloys by selective laser melting and samples printed from Co47.6B21.9Fe20.4Si5.1Nb5 are the first fully amorphous samples of Co-based alloy printed by SLM. Furthermore, an extensive discussion of the results was conducted with conclusions for further optimization of the process to enhance the quality of the samples, namely reducing the porosity and cracking phenomena. This study contributes to the area of bulk metallic glasses printing, especially in the case of a group of alloys based on cobalt.

Surface properties significantly influence the performance of machined parts. However, they cannot be measured directly during machining. For surface conditioning based on a soft sensor, it is necessary to monitor process characteristics like temperatures and forces, which influence the surface state. Soft-sensor development in machining requires a robust methodology, which is adaptable to different materials and machining processes. In addition, a measurement system that combines hardware sensors to measure temperatures and process forces has to be implemented into the machine tool. In the present study, a suitable methodology is proposed and tested using a tool-workpiece thermocouple and a dynamometer to determine the thermomechanical workpiece load during turning of the aluminum alloys EN AW-2017 and EN AW-7075. Experimental investigations are performed according to a D-optimal statistical design of experiments. For this, the machining parameters cutting speed, feed, depth of cut, as well as the flank wear land width are varied on four levels. Subsequent measurements of residual stresses and the surface roughness are used to correlate the surface state with input parameters and their resulting thermomechanical workpiece load by multiple regression based on analysis of variance (ANOVA). It is found that the methodology is applicable and allows for the prediction of surface states. The developed soft sensors enable an in-process control of machining parameters, which enables a robust prediction and targeted conditioning of the addressed surface properties during machining.

Amorphous metals have been of interest to researchers since the 1960s of the twentieth century. In recent years, interest has been focused on the development of amorphous metals using selective laser melting (SLM) technology, because it guarantees very high cooling rates and allows the production of a theoretically unlimited size of elements. However, no studies have considered the development of SLM alloys with a high glass ability based on cobalt. This work offers one of the first investigations into the possibility of developing amorphous samples from Co42B26.5Fe20Ta5.5Si5Cu1 using SLM technology. The study involves two-stage experimental parameters testing and testing obtained samples by optical and scanning electron microscopy, transmission electron microscopy (TEM), X-ray diffraction analyzes, energy dispersive spectroscopy by TEM mapping, nanoindentation, and microhardness testing. This paper has shown that the optimal energy density (ED) window for printing Co42B26.5Fe20Ta5.5Si5Cu1 is between 41 and 50J/mm3 and samples with the best structure form carried out experiment were developed with a laser power of 75W and a scanning speed of 800mm/s (ED 48.7J/mm3). However, the Rietveld analysis of the crystal phase in his sample points out the 54% crystal phase (Co5Si2B and TaB2) in this sample, which makes it a bulk metallic glass composite.

Eutectic high-entropy alloys (EHEAs) with a fine-lamellar structure and homogenous property profile are of particular interest for wear and corrosion protection coatings. High cooling rates in the laser metal deposition (LMD) process can induce microstructure refinement and allow the formation of a supersaturated solid solution in EHEAs. A subsequent solution annealing can create the equilibrium state. In the present study, LMD coatings with an ultrafine-grained Widmanstätten structure were produced from the EHEA Al 0.3 CoCrFeNiMo 0.75 gas atomized powder. High cooling rates during deposition led to a supersaturated solid solution with face-centered cubic (FCC) structure. The LMD coating exhibits the highest average hardness of 734 HV0.5, which drops to approx. 200 HV0.5 due to an increased microstructural domain size after heat treatment. Under oscillating wear, the formation of oxidized wear debris promotes material removal in the heat-treated condition. Corrosion tests reveal a deterioration of the passivation behavior. LMD processes exhibit great potential to create supersaturated solid solutions with refined structure in EHEAs to enhance the property profile.

The austenitic stainless steel 316L is used for numerous components due to its excellent corrosion resistance. However, forming of components influences the microstructure and can thus change the corrosion resistance of the steel. In this context, the corrosion rate of the steel 316L is determined for the case of uniform corrosion of various cold-rolled conditions by ageing tests in 0.5 M H 2 SO 4 . The microstrain, the martensite fraction, and the residual stress state are quantified using X-ray diffraction. The surface roughness is measured by laser scanning microscopy. Three different model equations are derived by means of multiple regression to predict the corrosion rate as a function of the specimen properties. The analysis shows that a particularly simple model equation, which predicts the corrosion rate only via the plastic strain, shows insufficiently large deviations from the experimentally determined corrosion rates. However, a low divergence to the experimental results with a mean deviation of less than 4% is achieved by using a model equation that takes microstructural parameters and the surface ratio into account. Within this model equation, an increased corrosion rate is achieved with higher microstrain and residual compressive stress of the austenite phase as well as a higher surface-area ratio. A higher fraction of martensite is found to lower the corrosion rate.

The grain size of a metallic coating or the surface layer after the machining of metallic parts strongly impacts corrosion and wear properties along with fatigue behavior. By measuring the combined electrical resistance of this layer and the substrate using the four-point probe method, the grain size of the layer can be determined. For different grain shapes, models are derived based on an analytical approach. The parameters in the models can be determined by appropriate calibration measurements. As a result, the grain sizes can be determined quickly with a non-destructive method, which can be applied to ensure consistent coating or machining results as part of quality control routines in industrial processes.

Depassivation processes known by literature detected by electrochemical methods during polarization experiments of Mg substrates in alkaline silicate PEO electrolytes below the ignition voltage were investigated in more detail by SEM images of the generated reaction layers. Remarkable crater structures were discovered on the Mg alloy AZ31 that do not form on the aluminum AlMgSi1 substrate under identical experimental conditions. The formations of these structures were described using the concepts of the high-field model. Through systematic comparative investigations of PEO processes on the two studied substrates by means of in situ process diagnostics, electrochemical subprocesses in the plasma electrolytic oxidation of magnesium were identified by analyzing electrical and photoelectric process signals. A negative influence on the morphology of PEO layers on magnesium was attributed to subprocesses in the context of the depassivation mechanism below the ignition voltage as well as microstructure images of the generated PEO layers.

Potentiodynamic and potentiostatic polarization tests in the potential range between open circuit potential (OCP) − 0.1 V and OCP + 4 V were carried out in aluminate–phosphate electrolytes with an aluminate concentration of 0.2 mol/L and varying phosphates contents between 0 and 0.1 mol/L. The pH was adjusted between 11.5 and 12.0 due to phosphate and optional KOH addition. A high-strength, dual-phase steel, which is relevant for lightweight construction, served as the substrate material. The layer microstructure was investigated by optical and scanning electron microscopy. Energy-dispersive X-ray spectroscopy and Raman spectroscopy were used for element and phase analyses. We found that iron hydroxides or oxides are initially formed independently of the electrolyte composition at low potentials. At around 1 V vs. standard hydrogen electrode (SHE), the current density suddenly increases as a result of oxygen evolution, which causes a significant reduction in the pH value. Precipitation leads to the formation of porous layers with thicknesses of 10 µm to 20 µm. In the case of a pure aluminate solution, the layer mainly consists of amorphous alumina. When adding phosphate to the electrolyte, the layer additionally contains the hydrous phosphate evansite. At the highest phosphate content in the electrolyte, the highest P content and the most pronounced crack network were observed.

The limiting current density is one of to the most important indicators in electroplating for the maximal current density from which a metal can be deposited effectively from an electrolyte. Hence, it is an indicator of the maximal deposition speed and the homogeneity of the thickness of the deposited metal layer. For these reasons, a major interest in the limiting current density is given in practical applications. Usually, the limiting current density is determined via measurements. In this article, a simple model to compute the limiting current density is presented, basing on a system of diffusion–reaction equations in one spatial dimension. Although the model formulations need many assumptions, it is of special interest for screenings, as well as for comparative work, and could easily be adjusted to measurements.