From mirco-mechanical properties to tribological performance

Abrasive contacts are still too complex to allow reliable predictions of part performance. There is not a single material model with satisfying generality, yet. However, it should be a combination of the contact body’s relative elastic and plastic properties as well as the loading condition.1 In industry carbide- and boride-reinforced, metal matrix composites are often cladded on a base part with welding processes to counter abrasive wear. These composites generally pose structural features at a multitude of length scales. A millimeter thick coating is reinforced with carbides of 100 µm diameter. Precipitates of 1 to 10 µm decorate the matrix and during the major solidification, a metal-stable carbide-metal eutectic forms with domains widths of 1 µm and 100 – 200 nm lamella spacing. Please click Additional Files below to see the full abstract

Reconstruction and subsurface lattice distortions in the (2 × 1)O-Ni(110) structure: A LEED analysis

LEED analysis of the reconstructed (2 × 1)O-Ni(110) system clearly favors the “missing row” structure over the “saw-tooth” and “buckled row” models. By using a novel computational procedure 8 structural parameters could be refined simultaneously, leading to excellent R-factors (RZJ = 0.09, RP = 0.18). The adsorbed O atoms are located 0.2 Å above the long bridge sites in [001] direction, presumably with a slight displacement ( 0.1 Å) in [1 0] direction to an asymmetric adsorption site. The nearest-neighbor Ni---O bond lengths (1.77 Å) are rather short. The separation between the topmost two Ni layers is expanded to 1.30 Å (bulk value 1.25 Å), while that between the second and third layer is slightly contracted to 1.23 Å. The third layer is, in addition, slightly buckled (±0.05 Å). The results are discussed on the basis of our present general knowledge about the structure of adsorbate covered metallic surfaces

Abrasive and adhesive wear behaviour of metallic bonds in a synthetic slurry test for wear prediction in reinforced concrete

The understanding of the tribological system and the corresponding wear behaviour of metallic materials is, especially in wet condition and in presence of abrasive particles, of high importance. This particularly applies for construction applications, like core drilling and sawing in reinforced concrete, where the knowledge about adhesive wear but also abrasive micro- and macro-mechanisms is limited. If it comes to material removal in reinforced concrete, adhesive wear between the metal matrix and the reinforcement steel is observed, besides abrasive wear as a result of the metal matrix–concrete interaction. To differentiate adhesive and abrasive wear, a new approach for testing metal materials with varying counter parts and different sliding speeds in a wet-slurry test is presented. A for this work modified B611 - 13 test is used to test two different metal compositions to investigate their change in mass, micro-hardness and the microstructure at the sliding interface zone. Additionally, the wear pattern is identified by optical microscope and under the scanning electron microscope. To differentiate the main wear mechanisms, a S355 steel and a silicon carbide ceramic are used as a counterbody. The results show that it is possible to separate the wear behaviour while testing in different conditions

Filament extrusion-based additive manufacturing of 316L stainless steel: Effects of sintering conditions on the microstructure and mechanical properties

Filament extrusion-based additive manufacturing of metals offers an alternative to the widespread beam-based counterparts. The microstructure obtained from extrusion-based techniques differs greatly from the ones obtained by beam-based additive manufacturing, as a sintering process is used, in contrast to the rapid solidification of a melt pool. In this study, the microstructure of 316L stainless steel fabricated by filament extrusion is investigated as a function of debinding and sintering conditions. High-speed nanoindentation correlated with energy-dispersive X-ray mapping is employed for microstructural characterization. High sintering temperatures of 1350 °C, an atmosphere of pure H2, and a cooling rate of 60 K/m are found to result in the optimal microstructure. High densities are obtained due to accelerated densification, enabled by the introduction of diffusion paths due to δ-ferrite formation. At the same time, hard phases like oxides or σ-precipitates with detrimental effects on the mechanical properties can be avoided. It is shown that the porosity can be quantified by analysis of hardness and modulus data from nanoindentation mapping. The values obtained are in good agreement with optical and Archimedes immersion method measurements. Tensile tests of 3D-printed and sintered specimens show excellent ductility and strength in comparison to literature. We demonstrate that 3D printing of 316L filaments and sintering with the optimized conditions results in material properties comparable to bulk values.ISSN:2214-860

Silver triflate catalyzed tandem heterocyclization/alkynylation of 1-((2-tosylamino)aryl)but-2-yne-1,4-diols to 2-alkynyl indoles

Don't cross me! 2-Alkynyl indoles were prepared efficiently by the AgOTf-catalyzed tandem heterocyclization/alkynylation of 1-(2-tosylamino)aryl)but-2-yne-1,4-diols under mild conditions (see scheme). The attractiveness of this approach lies in the fact that both the indole ring and alkyne side chain of the N-heterocycle are sequentially formed from low cost, readily available, and ecologically benign starting materials. It also provides the first route to this synthetically valuable class of compounds that is not based on a cross-coupling strategy