Search

The robust determination of the threshold against fatigue crack propagation Δ K th is of paramount importance in fracture mechanics based fatigue assessment procedures. The standards ASTM E647 and ISO 12108 introduce operational definitions of Δ K th based on the crack propagation rate d a / d N and suggest linear fits of logarithmic Δ K – d a / d N test data to calculate Δ K th . Since these fits typically suffer from a poor representation of the actual curvature of the crack propagation curve, a method for evaluating Δ K th using a nonlinear function is proposed. It is shown that the proposed method reduces the artificial conservativeness induced by the evaluation method as well as the susceptibility to scatter in test data and the influence of test data density. [ABSTRACT FROM AUTHOR]

The fatigue behavior of bolted joints is critical to failure for many applications due to the high notch effect. Among other parameters, the lifetime is based on the influence of the surface system, consisting of corrosion protection and lubricant. With the intention of considering the surface system in the design and dimensioning process of bolted joints, experimental investigations are carried out systematically for an exemplary selected basecoat and various lubricant systems. The basis is given by fatigue tests supported by selected methods of material analysis for the fractographic evaluation. A reproducible method to determine the crack initiation as well as the crack propagation is developed and used for the evaluation of lubricant systems. Defined damage can be reproducibly assigned on the basis of a critical frequency change rate of the resonance test machine. A high durability of the friction in the load-bearing contact (e.g., greases) reduces the stress and delays the crack initiation. Lubricants which are able to creep (e.g., oil) slow down the crack propagation and increase the lifetime, which is proved by a higher number of cycles to failure and an increased fatigue strength. [ABSTRACT FROM AUTHOR]

Rotary components in turbine machinery such as gas turbine blades and discs or turbocharger wheels need to be designed so that high cycle fatigue (HCF) loads are well below the fatigue endurance limit to ensure safe operation. This requires an accurate measurement of the fatigue endurance limit and the related intrinsic fatigue crack growth (FCG) threshold. Furthermore, knowing the FCG threshold is crucial in order to assess the criticality of initial defects (e.g. cavities, carbide nests, etc.). In this study, the influence of the manufacturing route on the FCG threshold and the FCG behaviour at 650 °C in air of the nickel based superalloy IN718 is investigated. For this, a per Laser Powder Bed Fusion (LPBF) process manufactured version is compared to a conventionally wrought IN718 material state, both in the short and long crack regime. To measure crack growth increments of about 1 μm, an alternative pre-cracking and threshold test procedure is proposed for high temperature testing. To assess the behaviour of both material states in the short crack growth regime, cyclic R-curves have been generated taking the influence of two different R ratios into account. A further comparison of the FCG behaviour of the LPBF and the wrought material state is made on the basis of da/dN-ΔKI plots, with a focus on the Paris regime created from both classical FCG tests as well as continued threshold tests. The results observed are discussed in relation to the initial characterization of the two material states, which includes tensile tests at room temperature and at 650 °C as well as microstructural investigations. [ABSTRACT FROM AUTHOR]

In Parkinson's disease (PD) patients, visual misperceptions are a major problem within the non-motor symptoms. Pareidolia, i.e., the tendency to perceive a specific, meaningful image in an ambiguous visual pattern, is a phenomenon that occurs also in healthy subjects. Literature suggests that the perception of face pareidolia may be increased in patients with neurodegenerative diseases. We aimed to examine, within the same experiment, face perception and the production of face pareidolia in PD patients and healthy controls (HC). Thirty participants (15 PD patients and 15 HC) were presented with 47 naturalistic photographs in which faces were embedded or not. The likelihood to perceive the embedded faces was modified by manipulating their transparency. Participants were asked to decide for each photograph whether a face was embedded or not. We found that PD patients were significantly less likely to recognize embedded faces than controls. However, PD patients also perceived faces significantly more often in locations where none were actually present than controls. Linear regression analyses showed that gender, age, hallucinations, and Multiple-Choice Vocabulary Intelligence Test (MWT) score were significant predictors of face pareidolia production in PD patients. Montreal Cognitive Assessment (MoCA) was a significant predictor for pareidolia production in PD patients in trials in which a face was embedded in another region [ F (1, 13) = 24.4, p = <0.001]. We conclude that our new embedded faces paradigm is a useful tool to distinguish face perception performance between HC and PD patients. Furthermore, we speculate that our results observed in PD patients rely on disturbed interactions between the Dorsal (DAN) and Ventral Attention Networks (VAN). In photographs in which a face is present, the VAN may detect this as a behaviourally relevant stimulus. However, due to the deficient communication with the DAN in PD patients, the DAN would not direct attention to the correct location, identifying a face at a location where actually none is present. [ABSTRACT FROM AUTHOR]

Ein großes Potenzial zur Verringerung der THG-Emissionen und der Effizienzsteigerung von Verbrennungsmotoren liegt in der Nutzung von Abgaswärme. In Abgaswärmenutzungssystemen soll dabei die Abgaswärme im Rankine-Prozess zumindest partiell wieder nutzbringend in mechanische Energie zurückgeführt werden. Arbeitsmedien und Materialien werden in solchen Systemen thermisch und korrosiv hochbeansprucht. Am Zentrum für Konstruktionswerkstoffe der TU Darmstadt wurden im FVV-Vorhaben Nr. 1184 relevante Medien und Werkstoffe hinsichtlich ihrer chemischen und thermischen Beständigkeit bewertet. [ABSTRACT FROM AUTHOR]

Austenitic stainless steel of type X6CrNiNb18-10 exhibits advantageous mechanical and chemical properties and is a common material for numerous applications in the nuclear power plant and chemical industries. Besides the mechanical strain induced by high pressure, the fatigue life in welded pipelines is affected by additional thermomechanical strains due to thermal loading. The welding process mainly determines the geometry and metallurgical constitution of the welded joint. Therefore, the butt welds additionally influence the strain gradient along the component and reduce its lifetime. While the base and weld material are similar, they show different softening and hardening behavior, especially at ambient temperature. Cyclic hardening occurs in the base material, whereas cyclic softening can be observed in the weld material. The hardness distribution along the welded joint reveals no clear differentiation of the base material, the heat affected zone, and the weld material. The attributes of the individual materials cannot be transferred to the welded joint automatically. Thus, the analysis of the interaction between the materials along the welded joint is a main topic of this research. To this end, digital image correlation (DIC) is used for different kinds of specimens and load conditions. The position along the testing area at which fatigue failure occurs depends on the specimen type and the load condition but not on the temperature. Further, isothermal and anisothermal fatigue tests on welded cruciform specimens are presented. The common practice of the effective strain is discussed for the analyzed conditions. [ABSTRACT FROM AUTHOR]

To make powder bed fusion (PBF) via laser beam (-LB) for metals (/M) available for highly regulated components such as pressure equipment according to the Pressure Equipment Directive, system-specific qualification methods need to be established to deal with process- and geometry-dependent inhomogeneous material behavior. Therefore, the material properties of austenitic stainless steel (316L) and their influences on normative acceptable qualification strategies were investigated in this study. Flat tensile test specimens were produced by two manufacturing systems identical in construction and were compared to specimens produced from conventionally rolled sheet material. Specimens were compared in the horizontal and vertical building directions in relation to different slope angles, wall thicknesses and cross-sectional areas. Despite identical process setups, parameters and powder feedstock, differences in mechanical behavior could be seen. Furthermore, the mechanical properties, surface roughness and density showed dependencies on the wall thickness and slope angle. In particular, the influence of wall thickness has not been covered in publications about PBF-LB/M before. These results suggest that geometry- and system-dependent components can be designed based on associated data from qualification processes. Therefore, a new qualification method based on wall structure properties is suggested for standard qualification processes of components with wall structures, such as pressure equipment. [ABSTRACT FROM AUTHOR]

Copyright of Praxis (16618157) is the property of Aerzteverlag medinfo AG and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Laser powder bed fusion (LPBF) has indisputable advantages when designing new components with complex geometries due to toolless manufacturing and the ability to manufacture components with undercuts. However, fatigue properties rely heavily on the surface condition. In this work, in-process surface parameters (three differing contour parameter sets) and post-process surface treatments, namely turning and shot peening, are varied to investigate the influence of each treatment on the resulting fatigue properties of LPBF-manufactured specimens of the aluminium–magnesium–scandium alloy Scalmalloy®. Therefore, metallographic analysis and surface roughness measurements, as well as residual stress measurements, computer tomography measurements, SEM-analyses, tensile and fatigue tests, along with fracture surface analysis, were performed. Despite the fact that newly developed in-process contour parameters are able to reduce the surface roughness significantly, only a minor improvement in fatigue properties could be observed: Crack initiation is caused by sharp, microscopic notches at the surface in combination with high tensile residual stresses at the surface, which are present on all in-process contour parameter specimens. Specimens using contour parameters with high line energy show keyhole pores localized in the subsurface area, which have no effect on crack initiation. Contours with low line energy have a slightly positive effect on fatigue strength because less pores can be found at the surface and subsurface area, which even more greatly promotes an early crack initiation. The post-process parameter sets, turning and shot peening, both improve fatigue behaviour significantly: Turned specimens show lowest surface roughness, while, for shot peened specimens, the tensile residual stresses of the surface radially shifted from the surface towards the centre of the specimens, which counteracts the crack initiation at the surface. [ABSTRACT FROM AUTHOR]

Purpose -- This paper aims to develop a set of process parameters tailored for lattice structures and test them against standard process (SP) parameters. Selective laser melting (SLM) is a commonly known and established additive manufacturing technique and is a key technology in generating intricately shaped lattice structures. However, SP parameters used in this technology have building time and accuracy disadvantages for structures with a low area-to-perimeter ratio, such as thin struts. Design/methodology/approach -- In this research work, body-centred cubic structure specimens are manufactured using adapted process parameters. Central to the adapted process parameters is the positioning of the laser beam, the scan strategy and the linear energy density. The specimens are analysed with X-ray micro-computed tomography for dimensional accuracy. The final assessment is a comparison between specimens manufactured using adapted process parameters and those using SP parameters. Findings -- Standard parameters for lattice structures lead to a significant shift from the nominal geometry. An extensive manufacturing and computation time due to several exposure patterns (e.g. pre-contours, post-contours) was observed. The tailored process parameters developed had good dimensional accuracy, reproducible results and improved manufacturing performance. Research limitations/implications -- The results are based on a distinctive geometry of the lattice structure and a specific material. Future research should be extended to other geometries and materials. Practical implications -- Optimisation of process parameters for the part geometry is a critical factor in improving dimensional accuracy and performance of SLM processes. Originality/value -- This study demonstrates how application-tailored process parameters can lead to superior performance and improved dimensional accuracy. The results can be transferred to other lattice structure designs and materials. [ABSTRACT FROM AUTHOR]

Background The use of human acellular dermis (hAD) to close open abdomen in the treatment process of severe peritonitis might be an alternative to standard care. This paper describes an investigation of the effects of fluids simulating an open abdomen environment on the biomechanical properties of Epiflex® a cell-free human dermis transplant. Methods hAD was incubated in Ringers solution, blood, urine, upper gastrointestinal (upper GI) secretion and a peritonitis-like bacterial solution in-vitro for 3 weeks. At day 0, 7, 14 and 21 breaking strength was measured, tensile strength was calculated and standard fluorescence microscopy was performed. Results hAD incubated in all five of the five fluids showed a decrease in mean breaking strength at day 21 when compared to day 0. However, upper GI secretion was the only incubation fluid that significantly reduced the mechanical strength of Epiflex after 21days of incubation when compared to incubation in Ringer's solution. Conclusion hAD may be a suitable material for closure of the open abdomen in the absence of upper GI leakage and pancreatic fistulae. [ABSTRACT FROM AUTHOR]

Copyright of Heilberufe is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Alzheimer's disease (AD) and Parkinson's disease (PD) lead to a cholinergic deficit in the brain which is not only related to dementia, but may also lead to a disturbed neurovascular coupling. We investigated the effect of cholinergic decline on neurovascular coupling in PD patients. Patients with idiopathic PD were divided in groups without (n=59; 65 ± 9 y) or with moderate dementia as specified by Mini-Mental State Examination. The demented patients were assigned to groups with (n=55; 73 ± 6 y) or without (n=61; 72 ± 8 y) acetylcholinesterase inhibitor treatment. Neurovascular coupling was assessed by a simultaneous electroencephalography-Doppler technique applying a contrast-based visual stimulation task. Visually evoked potential amplitudes (N75-P100) and parameters of the hemodynamic response in the posterior cerebral artery were obtained using a control system approach (resting flow velocity, gain, attenuation, rate time, and natural frequency). Data were compared to a healthy control group of a similar age range (n=20; 63 ± 8 yr). Compared to controls, patient groups presented no differences in evoked potential amplitudes or neurovascular coupling parameters. The reported 30% decline in acetylcholinesterase activity in PD patients did not lead to measurable changes in neurovascular coupling. In AD patients additional factors might explain the uncoupling and higher cerebrovascular risk detected in clinical studies. [ABSTRACT FROM AUTHOR]

In the European standards specifying disc spring manufacturing, geometry, shape and characteristic, an edge rounding is prescribed. Common methods for the calculation of disc spring characteristics, even in these standards, are based on a rectangular cross-section. This discrepancy can lead to a considerable divergence of the computed characteristic from the characteristic determined by testing. In literature, this divergence has not yet been examined with regard to rounded edges. In this paper, a new method addressing this problem is introduced. For this purpose, the geometry of idealized disc springs is parameterized. Based on four edge radii and two angles of the inner and outer faces, equations to compute the initial cone angle and the lever arm are introduced. These equations are used to formulate an algorithm to adapt other computation methods to non-rectangular cross-sections and rounded edges. The method is applied to the formulas by Almen–Laszlo, Curti–Orlando, Zheng and those by Kobelev. FE simulations of disc springs with rounded edges and a non-rectangular cross-section were used to verify the new formulas. The results show that the introduced method can be applied to known characteristic computation methods and result in a model expansion taking cross-section variations into account. The adjusted characteristics show more accurate alignment to the FE simulation for the cross-section variations investigated. These findings not only close the geometric gap between the manufacturing guidelines and the computation on an analytical basis, they also define a new parameter space for designs of disc springs and a corresponding force computation method to optimize spring characteristics. [ABSTRACT FROM AUTHOR]

The majority of lifetime models associate the failure of thermal barrier coatings (TBCs) to oxidation of the bond coat (BC). A thickening of the thermally grown oxide (TGO) leads to a conversion of stresses at the undulated ceramic-metal interface, supporting the propagation of existing microcracks. However, in plasma-sprayed multilayer TBCs consisting of gadolinium zirconate (GZO) and yttria-stabilized zirconia (YSZ) a shift of the failure site from the ceramic-metal interface to the GZO-YSZ interface has been observed. Thus, an exclusively oxide-based formulation is not sufficient to describe the damage transition phenomena. Therefore, this paper outlines a mechanism-based approach for assessing the structural integrity, considering all relevant thermally activated processes as well as the interaction between thermal and elastic misfits. Oxidation of BC, creep of composite materials and sintering of ceramics are modeled in terms of temperature and exposure time. Finite element analysis of GZO-YSZ pairings with different microstructures reveal a strong influence of the initial porosities on the sintering behavior and thus on the resulting mechanical stresses and potential crack driving forces at the bimaterial interfaces. [ABSTRACT FROM AUTHOR]

ABSTRACT The ability to assess the risk of corrosion of metallic structures in particular environments holds considerable significance in the field of automotive industry. In recent years, machine learning has evolved into a crucial tool to evaluate the complex and multidimensional corrosion phenomena. In this paper, the special case of non‐aqueous alcoholate pitting corrosion of AA1050 in ethanol‐blended fuels with water and chloride contamination is examined via supervised machine learning techniques in order to distinguish between safe and unsafe conditions. The data space was created by conducting dedicated experiments with varying ethanol–fuel–water ratios, temperatures, and surface preparations. The classifier's performance rating of 0.87 (balanced accuracy) indicates an outstanding predictive ability and highlights the model's usefulness as decision support for subsequent experiments. [ABSTRACT FROM AUTHOR]

Due to the challenging operational conditions occurring during drilling, e.g., in the oil and gas industry, the corrosion fatigue (CF) behavior of materials used in drillstring components needs to be well understood. The combination of cyclic mechanic loads and a corrosive environment can affect significantly the integrity of a material, which has to be taken into account when selecting and qualifying materials for drilling equipment. Nickel alloys such as the precipitation-hardenable alloy 718 (UNS N07718) are widely used in many industrial applications including subterranean drilling. In the present study, the fatigue and CF behavior of alloy 718 in three different metallurgical conditions was investigated. The CF behavior of the different conditions was determined using customized rotating bending machines enabling testing in a simulated drilling environment at 125 °C. Results have shown that the fatigue and CF strength of alloy 718 is affected by its microstructural particularities, for instance, the amount of strengthening phases and δ-phase. [ABSTRACT FROM AUTHOR]

In this study, we investigate the influence of control type and strain rate on the lifetime of specimens manufactured from 50CrMo4. This influence is described by a strain rate dependent method that uses cyclic stress strain curves to correct displacement-controlled cyclic test results. The objective of this correction is to eliminate the stress related differences between displacement-controlled cyclic test results and force-controlled cyclic test results. The method is applied to the results of ultrasonic fatigue tests of six different combinations of heat treatment, specimen geometry (notch factor) and atmosphere. In a statistical analysis, the corrected results show an improved agreement with test results obtained on conventional fatigue testing equipment with similar specimens: the standard deviation in combined data sets is significantly reduced (p = 4.1%). We discuss the literature on intrinsic and extrinsic strain rate effects in carbon steels. [ABSTRACT FROM AUTHOR]

For the generation of fatigue curves by means of fatigue tests, an ultimate number of cycles must be chosen. This ultimate number of cycles also limits the permissible range of the fatigue curve for the design of components. This introduces extremely high costs for testing components that are to be used in the Very High Cycle Fatigue regime. In this paper, we examine the influence of the ultimate number of cycles of fatigue tests on lifetime prediction for compression springs manufactured from VDSiCr class spring wire. For this purpose, we propose a new kind of experiment, the Artificial Censoring Experiment (ACE). We show that ACEs may be used to permissibly extrapolate the results of fatigue tests on compression springs by ensuring that a batch-specific minimum ultimate number of cycles has been exceeded in testing. If the minimum ultimate number of cycles has not been exceeded, extrapolation is inadmissible. Extrapolated results may be highly non-conservative, especially for models assuming a pronounced fatigue limit. [ABSTRACT FROM AUTHOR]

In this paper, a novel algorithm for the determination of Walker damage in loaded disc springs is presented. The algorithm takes a 3D-scan of a disc spring, measured residual stresses, material parameters, and spring loads as inputs. It outputs a distribution of Walker damage over the surface area of the input disc spring. As the algorithm allows a fully automated determination of the Walker damage, it can be used by disc spring manufacturers to reduce the working time spent on this task by specialized engineers significantly. Compared to spreadsheet applications using analytical formulas and finite element models using idealized geometry, this approach offers a superior description of the stress states in disc springs. [ABSTRACT FROM AUTHOR]

Additive manufacturing (AM) is an advanced manufacturing process that provides the opportunity to build geometrically complex and highly individualized lightweight structures. Despite its many advantages, additively manufactured components suffer from poor surface quality. To locally improve the surface quality and homogenize the microstructure, friction stir processing (FSP) technique was applied on Al-Si12 components produced by selective laser melting (SLM) using two different working media. The effect of FSP on the microstructural evolution, mechanical properties, and corrosion resistance of SLM samples was investigated. Microstructural investigation showed a considerable grain refinement in the friction stirred area, which is due to the severe plastic deformation and dynamic recrystallization of the material in the stir zone. Micro-hardness measurements revealed that the micro-hardness values of samples treated using FSP are much lower compared to SLM components in the as-built condition. This reduction of hardness values in samples treated with FSP can be explained by the dissolution of the very fine Si-phase network, being characteristic for SLM samples, during FSP. Surface topography also demonstrated that the FSP results in the reduction of surface roughness and increases the homogeneity of the SLM microstructure. Decreased surface roughness and grain size refinement in combination with the dissolved Si-phase network of the FSP treated material result in considerable changes in corrosion behavior. This work addresses the corrosion properties of surface treated additive manufactured Al-Si12 by establishing adequate microstructure-property relationships. The corrosion behavior of SLM-manufactured Al-Si12 alloys is shown to be improved by FSP-modification of the surfaces. [ABSTRACT FROM AUTHOR]

Metal laser powder bed fusion (PBF-LB/M) allows for high degrees of design freedom and the manufacture of high-temperature Ni-based materials, such as IN738LC. The PBF-LB/M microstructure is dependent on several factors, including process parameters, component geometry, build orientation and postprocessing steps (e.g., heat treatment). The correlation between the resulting microstructure and these parameters is material specific and not yet fully understood. In this study, the development of a specimen extraction cube (SEC), based on a generic component with design aspects related to turbomachinery applications, is presented. The SEC allows for the extraction of three samples, one for each of the build orientations: 0 deg (perpendicular to build direction), 45 deg (diagonal) and 90 deg (parallel to build direction). Specimens extracted from the SEC are mechanically tested and compared to witness samples manufactured in 0 deg, 45 deg, and 90 deg build orientation. Particular focus is placed on correlating measured properties and their variations with heat treated microstructures. Creep testing was performed using 240 MPa and a temperature of 850 °C. Microstructural differences and hence differences in mechanical properties are found in extracted and witness samples. [ABSTRACT FROM AUTHOR]

Rising demands on material performance at high temperature in components under complex loading such as steam- and gas turbine housings require an increase in versatility and precision of component life modeling approaches. However, the database to calibrate those models is commonly derived from uni-axial testing. The impact of multi-axial loading, both proportional and nonproportional, is usually addressed theoretically by the use of equivalent stress/strain formulations or reduction ratios derived from few specific validation tests. Therefore, a research program which systematically investigates the fatigue life of a 1Cr-cast steel both experimentally and theoretically has been initiated recently. For the experimental part, cruciform specimens are tested in a servohydraulic biaxial test rig equipped with an induction heating device. Each experiment is accompanied with finite element simulations before and after the test to parametrize the loading condition and derive equivalent loading parameters at hot-spot locations. When assessing cycles until crack initiation in the experiments using the von Mises equivalent strain range, a reoccurring sequence in the impact of the axis ratio can be observed. Beside the fatigue life in terms of cycles to crack initiation, the multi-axial loading conditions may also affect the deformation behavior, in detail cyclic softening. Such effects are discussed by comparing the produced experimental evidence with results gained from a unified constitutive material model. Furthermore, different lifetime parameters are applied in order to judge their accuracy and suitability for design applications. [ABSTRACT FROM AUTHOR]

This study focuses on the influence of microstructure and ductility on the short crack behavior and the fatigue crack growth (FCG) threshold. For this, an additively manufactured batch of the nickel-based alloy IN718, made via Laser Powder Bed Fusion (LPBF) process, is compared to both conventionally wrought and cast IN718 material. An initial characterization revealed significant differences in grain structure, from regular fine grained wrought material to large grains of several millimeters in diameter in the cast variant and a chessboard-like grain structure typical for LPBF. The ductility parameters of IN718-LPBF and wrought IN718 are comparable at room temperature, but at 650 °C the LPBF-variant shows macroscopic brittle fracture. The fatigue crack behavior both in the short and long crack regime is investigated in air at 650 °C. To produce minimal crack growth increments of about 1 µm, a compressive precracking and subsequent threshold test procedure with stepwise load increase has been adapted for high temperature testing. To assess the short crack behavior, cyclic R-curves have been generated taking the influence of three different stress ratios (R = -1, 0, and 0.5) into account. As expected, increasing crack closure mechanisms at higher stress ratios lead to higher stress intensity amplitudes KI necessary to initiate crack growth. The crack growth resistance of the LPBF-processed variant is higher compared to wrought IN718. In the long crack regime, the wrought alloy yields higher crack growth rates compared to LPBF and cast IN718. An expected R-ratio dependency is observed for all material states. [ABSTRACT FROM AUTHOR]

The use of magnesium alloys has enormous potential in terms of weight saving, resource availability and sustainability. This contrasts with the need to protect the surface from wear and corrosion, which is necessary to increase the depth of application of this promising material in industrial applications. The general requirements for the surface protection and surface functionalization can be fulfilled in particular by PVD coatings. However, so far there are no industrial PVD coatings available that meet the requirements for corrosion protection of the magnesium substrate. Common PVD coatings cannot be applied to magnesium due to the risk of severe galvanic corrosion between substrate and coating. In previous studies, TiMgN was identified as a prospective layer material for the corrosion protection of magnesium alloys as well as for the functionalization of the surface with regard to wear resistance and decoration. In the present work, the TiMgN coating concept has been applied to an industrial 4-cathode magnetron sputter unit of the type Cemecon CC800/9-HiPIMS. As substrate material the magnesium alloy AZ31hp was used. In addition to pure TiMgN, the rare earth elements Y and Gd were alloyed to the TiMgN coating in order to improve the corrosion properties. The influences of coating composition, target design and sputtering mode ( D irect C urrent — DC and Hi gh P ower I mpulse M agnetron S puttering — HiPIMS) were examined with regard to the chemical, mechanical and structural properties as well as the corrosion properties. It will be shown, that the corrosion properties of the TiMgN coated magnesium alloys depend significantly on the deposition conditions and on the coating microstructure, while the defect density seems to be of minor influence. Alloying of Gd to the coating leads to a further increase in corrosion resistance to more than 300 h in the salt spray test, while alloying of Y shows no positive effect. [ABSTRACT FROM AUTHOR]

A key indicator for the design of cold extrusion technology and materials is the force and pressure required to perform the process under different production conditions. Hence, this work is concerned with finding force and pressure functions of Aluminum 1350 for backward cold extrusion using regression method of experimental data. In order to find force and pressure functions considered, different mathematical formulas are used to obtain the optimum relations where several variables such as cavity diameter, semi-finished sizes, and extrusion strain are taken into account. Lack of data necessary for the calculation of the functions considered, depending on the different technological and construction parameters such as extrusion process, processed material, degree of deformation, form and dimensions of the part, semi-finished product and active elements of the molds requires the continuation of studies and research in this field. Analytical formulas, obtained using regression method, are considered essential for design and optimization purposes concerning backward extrusion for Aluminum 1350. Three different mathematical formulas have been developed for both pressure and force where good agreement has been found when compared to experimental records. Furthermore, cavity diameter and extrusion strain are found to be influential factors that affect the coefficients of force and pressure functions of cold backward extrusion [ABSTRACT FROM AUTHOR]