High Entropy Alloys (HEA) are gaining increasing interest due to their unique combination of properties. Especially the combination of high mechanical strength and hardness with distinct ductility ...makes them attractive for numerous applications. One interesting alloy system that exhibits excellent properties in bulk state is AlCoCrFeNiTi. A high strength, wear resistance and high-temperature resistance are the necessary requirements for the application in surface engineering. The suitability of blended, mechanically ball milled and inert gas atomized feedstock powders for the development of atmospheric plasma sprayed (APS) coatings is investigated in this study. The ball milled and inert gas atomized powders were characterized regarding their particle morphology, phase composition, chemical composition and powder size distribution. The microstructure and phase composition of the thermal spray coatings produced with different feedstock materials was investigated and compared with the feedstock material. Furthermore, the Vickers hardness (HV) was measured and the wear behavior under different tribological conditions was tested in ball-on-disk, oscillating wear and scratch tests. The results show that all produced feedstock materials and coatings exhibit a multiphase composition. The coatings produced with inert gas atomized feedstock material provide the best wear resistance and the highest degree of homogeneity.
Abstract
Within this work, an entirely new electrolyte system for the electrochemical deposition of REACh-compliant Zn-W and Zn-W-Cu alloy layers was developed based on thermodynamic calculations. ...The required constants of complex formation were determined using potentiometric titrations. The layers were analyzed with regard to the layer microstructure (including coating thickness, chemical and phase composition), the optical properties (including gloss and color) and the passivation and corrosion behaviors. The Zn, Zn-W, and Zn-W-Cu layers are characterized by a decorative appearance, high uniformity, a nanocrystalline structure and natural passivation during the exposure in the climate chamber. Due to their particularly favorable optical properties and their pronounced natural passivation, the Zn-W alloy layers exhibit a great potential for industrial applications.
Abstract
The simulation of large-scale industrial electrodeposition of zinc is of major importance, since through the simulation, important data about the positioning of electrodes, thickness of ...layers, etc. can be generated. But the models used in practical applications indirectly assume small anodes and cathodes for which the electrical potential or the charge-transfer current are constant over the cathode, resp. anode. In this paper, a new type of model for the dissolution of zinc anodes is described. Furthermore, a numerical scheme to treat the model will be described and verified. The new model will be compared to a commonly known model. The paper gives an alternative model for the calculation of the current density on anodes and formulates a FEM for the approximation of Poisson equations on multiple domains with Robin-interfaces. Besides the application to the dissolution of zinc-anodes during electro-plating, the basic model and FEM can be applied to the dissolution of anodes made of a different material and to the modelling of corrosion processes.
Abstract
This paper presents a novel approach to enhance the corrosion resistance of cylinder-bore coatings for internal combustion engines by changing surface characteristics and microstructures of ...the coating and utilizing alternative materials. The approach of this study refers to the knowledge of the complex gas-flow conditions during the internal-diameter coating of cylinder-bores using a twin-wire arc-spray process. Selective influencing of the gas flow enables the preparation of sample coatings with inhomogeneous and more homogeneous microstructures and surfaces. The various coatings were exposed to corrosive environments using the Kesternich testing method and an alternating immersion test. Significant improvements in corrosion resistance have been demonstrated by up to 50 % through altering the microstructure of the coating and almost 100 % by additional changing the spraying material. The study reveals an increased protection of cylinder-bore coatings against corrosive attacks through a homogeneous microstructure prepared in oxygen-poor coating conditions.
In the recent decades, various process windows have been found for plasma anodising of aluminium surfaces to produce wear-resistant alumina coatings. The coatings offer a high hardness and provide an ...excellent bonding to the substrate material, thus preventing spallation under mechanical or tribological load. In the present study, coatings with a high abrasive wear resistance and a hardness of up to 12GPa were produced in an electrolyte of 5g/l sodium metasilicate and 5g/l potassium hydroxide at a current density of 30A/dm2. To understand the reasons for the high wear resistance, the morphology as well as the phase composition and distribution within the coating were examined globally and locally using X-ray diffraction with conventional and grazing incidence and electron backscatter diffraction. The analyses show that the coating globally is comprised of approximately one third of α-alumina, one third of γ-alumina and one third of amorphous alumina with locally varying phase content.
•Coatings with a compact microstructure have been produced by plasma anodising under bipolar current.•XRD with grazing incidence allows the local examination of the phase content.•The coatings are comprised of approx. one third of alpha-, gamma- and amorphous alumina each.•The coatings possess a high abrasive wear resistance despite of the low alpha-alumina content.•Morphology outweighs phase composition in terms of wear resistance.
In order to achieve the desired properties, the microstructure of metals is often modified by heat treatments. A suitable combination of high strength and good ductility can be achieved by adjusting ...the amounts of martensite and retained austenite through a Quenching and Partitioning (Q&P) process. Controlling these material properties offers new potentials in the production of light weight steel parts. This paper presents a basic study of heat treatment conditions with subsequent microstructural characterization of quenched and partitioned commercial 0.54C-1.45Si-0.71Mn spring steel. Beginning from full austenitization, different quenching and partitioning parameters were applied. Microstructural characterization was performed using optical microscopy in combination with different etching methods as well as Scanning Electron Microscopy (SEM) and Electron Backscattered Diffraction (EBSD). It is shown that the intended dual phase microstructure with a specific phase fraction of austenite can be produced. Those results and consideration of hardness measurements show that the investigated commercial spring steel is a promising candidate for improving mechanical properties by a Q&P process.
The quality of laser welded joints is dependent on different factors like the process-parameters, weld configuration and the cleanliness of the joint area. Filmic contaminations on the joint area can ...be oil, grease and other lubricants, which are used for machining, corrosion protection or component assembly. Residuals of lubricants can vaporize during the laser welding process and may lead to weld smoke as well as spatters and results in welding defects like cracks and pores in the weld seam. Laser-induced breakdown spectroscopy (LIBS) was investigated successfully and applied to detect contaminants and finally avoid these welding defects. 1.7131 steel was used as model-substrate. The ground sample surfaces were characterized by means of surface energy as well as fluorescence-intensity and LIBS spectra of the cleaned surfaces were recorded. The effect of the laser pulse energy and the delay time between laser pulse and the spectra recording was investigated. Furthermore, a forming lubricant was applied on the sample surfaces and reflectometry was successfully used for the film thickness measurements. LIBS spectra of the contaminated surfaces are presented and the impacts of the oil film thickness on the appearance of the spectra are outlined. Additionally, the examination presents the evaluation of the spectra with the linear correlation and the peak intensity ratio.
The present study is focused on the influence of equal-channel angular pressing (ECAP) on the mean stress sensitivity of the fatigue strength. Systematic work has been done comparing the two ...precipitation-hardening aluminum alloys 6082 and 6060 in peak-aged and ECAP-processed condition, respectively. The fatigue strength was determined at alternating compression-tension and tension stresses with load ratios of R = -1, 0 and 0.1. Both aluminum alloys in peak-aged condition exhibit a strong dependence of the fatigue strength on the load ratio; i.e. and therefore on the applied mean stress. An increase in load ratio, which implies an increase in mean stress, results in a decrease of the fatigue strength amplitude. In contrast, ECAP-processing neutralizes the mean stress sensitivity of the fatigue strength for both aluminum alloys. The fatigue strength for the ECAP-processed conditions is not influenced by the load ratio: the fatigue strength amplitudes at tension mean stresses (R = 0 and 0.1) are just as high as for zero mean stress at alternating compression-tension stresses (R = -1). The neutralization of the mean stress sensitivity of two aluminum alloys due to ECAP-processing is shown for the first time in this study.
Abstract
The interlaminar strength of mechanically interlocked polymer-metal-interfaces strongly depends on the metal surface topography. Hence, this contribution assesses standardized surface ...roughness parameters as well as fractal dimension for interlaminar strength prediction of EN AW-6082/polyamide 6 polymer-metal-hybrids. Seven different metal surface topographies generated by mechanical blasting, alkaline etching, thermal spraying as well as laser structuring are investigated. Interlaminar strength testing is carried out with regard to tensile and shear strength using butt-bonded hollow cylinder specimens. The surface roughness profiles are recorded with a tactile stylus profiler. The fractal dimension of the metal surface is derived from cross-sectional images. The measured interlaminar strength values show good correlation to the fractal dimension, moderate correlation to the root mean square slope of the surface roughness profile and no correlation to surface roughness height parameters.
Abstract
Organo-functional silane coupling agents are widely used to promote adhesion in between inorganic and organic materials. Amino-functional silanes can improve bonding with polyamide. Aiming ...on a mechanically performant aluminum-polyamide joints, the effect of six amino silanes of different chemical structure, namely number and type of amine groups and alkyl spacers lengths, on the joint strength is investigated by means of lap-shear testing. Higher shear strengths are found along with a more pronounced capability of the amine group to form hydrogen bonds with polyamide. The results show that an additional amine group within the organo-functional group can increase joint strength, whereas long alkyl spacers reduce the observed joint strength. It is shown that high lap-shear strengths, in maximum about 15 MPa for N-(2-aminoethyl)-3-aminopropyltrimethoxysilane are achieved and that the high reproducibility can be assured when using right processing routines.
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