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Rare earth elements are promising alloying element candidates for magnesium alloys used as biodegradable devices in biomedical applications. Rare earth elements have significant ...effects on the high temperature strength as well as the creep resistance of alloys and they improve magnesium corrosion resistance. We focused on lanthanum, neodymium and cerium to produce magnesium alloys with commonly used rare earth element concentrations. We showed that low concentrations of rare earth elements do not promote bone growth inside a 750μm broad area around the implant. However, increased bone growth was observed at a greater distance from the degrading alloys. Clinically and histologically, the alloys and their corrosion products caused no systematic or local cytotoxicological effects. Using microtomography and in vitro experiments, we could show that the magnesium–rare earth element alloys showed low corrosion rates, both in in vitro and in vivo. The lanthanum- and cerium-containing alloys degraded at comparable rates, whereas the neodymium-containing alloy showed the lowest corrosion rates.
In the scope of the present study, microstructural and mechanical characterizations of duplex stainless steel UNS S31803 processed by selective laser melting (SLM) are conducted. The findings shed ...light on the phase arrangement evolving in the as-built condition and in several heat-treated conditions. In the as-built condition, austenite formation is almost suppressed due to process-related high cooling rates. Therefore, several heat treatments ranging from 900°C to 1200°C for 5min each were performed in order to adjust to the desired austenitic-ferritic microstructure. Results generated by transmission electron microscopy (TEM) reveal a high dislocation density induced during SLM fabrication, such that a recrystallized microstructure prevails after the heat treatment. Tensile tests display the severe impact of the heat treatment on the resulting mechanical response. The nearly complete ferritic as-built specimens obtain a higher ultimate tensile strength and a reduced elongation at fracture compared to the heat-treated specimens.
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•Successful fabrication of duplex stainless steel via selective laser melting is reported.•A nearly balanced austenite-ferrite arrangement is obtained after suitable heat treatment.•High dislocation density in the as-built condition provokes recrystallization during further heat-treatment.
This paper presents a fully coupled three-dimensional finite element model for the simulation of a tube manufacturing process consisting of roll forming and high-frequency induction welding. The ...multiphysics model is based on the dual mesh method. Thus, the electromagnetic field, the temperature field, the elasto-plastic deformation of the weld bead, and the phase transformations within the material can be simulated for a moving tube without remeshing. A comparison with measurements shows that the geometry of the welded tube and the weld bead, the force on the squeeze rolls, the temperature along the band edges, and the hardness distribution within the heat-affected zone can be simulated realistically.
Reactive air brazing (RAB) is a cost‐effective way to produce ceramic–ceramic or ceramic–metal brazed joints in air, without applying a protective gas atmosphere or a vacuum. In addition to ...conventional furnace technology, the brazing with induction heating can also be used effectively. Within the scope of this study the shrinkage and wetting behavior of self‐developed brazing pastes with different CuO contents and two qualities of silver powders with coarse and fine particle size are investigated by optical dilatometry on alumina (Al2O3, 99.7% purity). Thereby, the fine silver powder quality reveals a significant swelling effect at high temperatures, leading to an expansion of densified powder compacts caused by evolving gases. Joining tests are performed on ceramic–steel brazed joints using a muffle furnace and induction heating for short brazing cycles. The brazing seams and interfaces of the joints are investigated using scanning electron microscopy (SEM) and energy‐dispersive X‐ray spectroscopy (EDS). As a result, correlations between the brazing filler metal composition, the steel, and the brazing conditions are obtained.
Reactive air brazing (RAB) is a cost‐effective way to produce ceramic–ceramic or ceramic–metal brazed joints in air without protective gas atmosphere or a vacuum. Pore‐free brazing seams between filler metal and steel of metal–ceramic joint are achieved by selected steel and filler composition by induction heating in a conventional muffle furnace under air.
There are several manufacturing processes, in which the employment of solid lubricants is limited. In addition, ecological damage and higher production costs are further consequences of using such ...solid lubricants. This work aims at using the great potential of thin film technology to deposit adaptive, self-lubricating coatings as an alternative to conventional solid lubricants. Using magnetron sputtering process several titanium aluminum vanadium nitride coatings (TiAlVN) were developed in this study. These quaternary coatings possess the ability of forming lubricious oxides, known as Magnéli phases, at elevated temperatures, which significantly reduces the friction coefficient and surface wear.
•Successful deposition of a novel quartary TiAlVN wear resistant coating.•Optimization of deposition process parameters.•Approving of self-lubrication effect of TiAlVN coating.•Dependency of deposition rate on heating rate of the chamber.•Dependency of wear resistance/friction coefficient on nitrogen gas flow.
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•Heat treating increases the hardness of 17–4 PH from 24 to 39 HRC and improves the load-carrying capacity.•The diamond-like carbon coatings reduce the friction and wear of binder jet ...printed 17–4 PH.•The plastic deformation wear of the entire substrate/coating system is reduced by a harder 17–4 PH substrate.
Diamond-like carbon (DLC) coatings deposited on additively manufactured steel greatly improve the tribological properties. However, a high substrate hardness is crucial to sustaining high mechanical loads in the tribological contact. Herein, the heat treatment of binder jet printed 17–4PH enhances the hardness from 24 to 39 HRC. Binder jet printed 17–4 PH substrates are coated by DLC of the types hydrogen-free amorphous carbon (a-C) of ∼23 GPa and hydrogenated amorphous carbon (a-C:H) of ∼20 GPa. The influence of the heat treatment on the tribo-mechanical properties of the DLC coatings is investigated. 17–4 PH demonstrates high friction and wear against steel counterparts, but the wear rate is reduced from 693 ± 43 × 10–6 mm3/Nm to 492 ± 41 × 10-6 mm3/Nm by heat treating the steel. Both a–C and a–C:H are effective in reducing the friction and wear with wear rates below 0.3 × 10–6mm3/Nm. The a–C and a–C:H coatings demonstrate lower plastic wear on heat treated 17–4 PH due to the higher substrate hardness. Consequently, the heat treatment is an essential process step to ensure maximum tribological functionality of the DLC coating on additively manufactured 17–4PH steel.
Commercial Co/WC/diamond composites are hard metals and very useful as a kind of tool material, for which both ductile and quasi-brittle behaviors are possible. This work experimentally investigates ...their damage evolution dependence on microstructural features. The current study investigates a different type of Co/WC-type tool material which contains 90 vol.% Co instead of the usual <50 vol.%. The studied composites showed quasi-brittle behavior. An in-house-designed testing machine realizes the in-situ micro-computed tomography (μCT) under loading. This advanced equipment can record local damage in 3D during the loading. The digital image correlation technique delivers local displacement/strain maps in 2D and 3D based on tomographic images. As shown by nanoindentation tests, matrix regions near diamond particles do not possess higher hardness values than other regions. Since local positions with high stress are often coincident with those with high strain, diamonds, which aim to achieve composites with high hardnesses, contribute to the strength less than the WC phase. Samples that illustrated quasi-brittle behavior possess about 100–130 MPa higher tensile strengths than those with ductile behavior. Voids and their connections (forming mini/small cracks) dominant the detected damages, which means void initiation, growth, and coalescence should be the damage mechanisms. The void appears in the form of debonding. Still, it is uncovered that debonding between Co-diamonds plays a major role in provoking fatal fractures for composites with quasi-brittle behavior. An optimized microstructure should avoid diamond clusters and their local volume concentrations. To improve the time efficiency and the object-identification accuracy in μCT image segmentation, machine learning (ML), U-Net in the convolutional neural network (deep learning), is applied. This method takes only about 40 min to segment more than 700 images, i.e., a great improvement of the time efficiency compared to the manual work and the accuracy maintained. The results mentioned above demonstrate knowledge about the strengthening and damage mechanisms for Co/WC/diamond composites with >50 vol.% Co. The material properties for such tool materials (>50 vol.% Co) is rarely published until now. Efforts made in the ML part contribute to the realization of autonomous processing procedures in big-data-driven science applied in materials science.
This paper presents an experimental electro-thermo-mechanical simulation of high-frequency induction (HFI) welding to investigate the effect of temperature and contact normal stress on the weld seam ...quality. Therefore welding experiments at different temperatures and contact pressures are performed using flat specimens of 34MnB5 steel sheet. In order to characterize the weld seam strength of the welded specimens, tensile and bending tests are performed. To obtain a relative weld seam strength, the bending specimens were additionally hardened prior to testing. With the hardened specimens, it can be shown that the weld seam strength increases with increasing temperature and contact normal stress until a kind of plateau is formed where the weld seam strength remains almost constant. In addition to mechanical testing, the influence of the investigated process parameters on the weld seam microstructure is studied metallographically using light optical microscopy, scanning electron microscopy, EBSD and hardness measurements. It is shown that the weld seam strength is related to the amount of oxides in the bonding line.
Due to the rising demand and carcinogenic effect of cobalt, alternative metal matrixes need to be developed for hot-pressed diamond tools. Due to this reason High-Entropy alloys without cobalt were ...calculated via phase fraction diagrams. Three alloys of the Al–Cu–Fe–Mn–Ni system Al30Cu30Fe5Mn25Ni10, Al11.25Cu35Fe5Mn20Ni28.75 and Al5Cu20Fe25Mn25Ni25 were chosen due to their different crystal structures ranging from pure bcc, eutectic fcc-bcc to pure fcc crystal structure. Cr5Cu20Fe25Mn25Ni25 was chosen to verify the change of one element on the consolidation properties. The alloys were mechanically alloyed and hot-pressed at 800 °C for 3 min without and at 900 °C for 3 min with diamonds. Porosity increased with the fraction of bcc solid solution in the investigated alloys of the Al–Cu–Fe–Mn–Ni system. Samples consisting of Cr5Cu20Fe25Mn25Ni25 showed the lowest porosity, which was attributed to precipitation of a second copper-rich fcc solid solution around the remaining pores. At a process temperature of 800 °C and 3 min isothermal hold the samples featured a porosity of only 2.72%. Within the XRD patterns and SEM images of the hot-pressed samples with diamonds no graphitization or formation of carbides could be observed. Therefore, Cr5Cu20Fe25Mn25Ni25 was identified as a promising cobalt free metal-matrix candidate for diamond tools.
This paper investigates if the polar groups induced by a plasma treatment can increase the lap shear strength of laser-joined metal and plastic hybrids. Optimal laser joining parameters for ...cold-rolled AISI304–polyamide 6.6 and sandblasted AISI304–polypropylene hybrids were developed at 2.85 MPa and 4.22 MPa, respectively. The surface free energy was doubled for all used plasma gases to a value of ca. 80 mN m−1 at 180 s. The plasma-treated samples were joined and tested. The arithmetic means of the plasma-treated hybrids’ lap shear strength with polyamide 6.6 varied slightly, but all measured values were within the range of the untreated samples. Residue on the sheared metal samples indicated covalent bonds between AISI304 and polyamide 6.6. The lap shear strengths of the plasma-treated polypropylene hybrids were significantly reduced between −30.8% and −53.3%, depending on the used plasma gas. This was attributed to the over-aging and development of low-molecular-weight oxidized materials, which led to a weak boundary layer. No residue of polypropylene was found on treated or untreated lap shear samples. No correlation between the surface free energy and lap shear strength could be found.
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