Interface-Mediated Twinning-Induced Plasticity in a Fine Hexagonal Microstructure Generated by Additive Manufacturing

The grain size is a determinant microstructural feature to enable the activation of deformation twinning in hexagonal close-packed (hcp) metals. Although deformation twinning is one of the most effective mechanisms for improving the strength–ductility trade-off of structural alloys, its activation is reduced with decreasing grain size. This work reports the discovery of the activation of deformation twinning in a fine-grained hcp microstructure by introducing ductile body-centered cubic (bcc) nano-layer interfaces. The fast solidification and cooling conditions of laser-based additive manufacturing are exploited to obtain a fine microstructure that, coupled with an intensified intrinsic heat treatment, permits to generate the bcc nano-layers. In situ high-energy synchrotron X-ray diffraction allows tracking the activation and evolution of mechanical twinning in real-time. The findings obtained show the potential of ductile nano-layering for the novel design of hcp damage tolerant materials with improved life spans.Fil: Barriobero Vila, Pere. German Aerospace Center.; AlemaniaFil: Vallejos, Juan Manuel. Universidad Nacional del Nordeste. Facultad de Ingeniería; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste; ArgentinaFil: Gussone, Joachim. German Aerospace Center.; AlemaniaFil: Haubrich, Jan. German Aerospace Center.; AlemaniaFil: Kelm, Klemens. German Aerospace Center.; AlemaniaFil: Stark, Andreas. German Aerospace Center.; AlemaniaFil: Schell, Norbert. German Aerospace Center.; AlemaniaFil: Requena, Guillermo. German Aerospace Center.; Alemani

Laser powder bed fusion of Ti-22Al-25Nb at low and high pre-heating temperatures

Titanium alloys based on the orthorhombic Ti2AlNb phase are being considered as potential structural lightweight alloys since the early 1990s due to their favourable mechanical performance, i.e., balanced strength and ductility at room and high temperatures as well as high oxidation and creep resistance. With the emergence of additive manufacturing these alloys become particularly interesting again as the microstructures and properties differ considerably from conventionally processed materials. In our work, we consider the whole process chain including the powder production and explain the microstructure formation of the orthorhombic alloy Ti-22Al-25Nb and the effects of in situ and intrinsic heating during laser powder bed fusion with differing energy densities at low and high pre-heating temperatures by means of state-of-the-art characterization techniques such as in situ high energy synchrotron X-ray diffraction and advanced electron microscopy. Fast cooling rates during low-temperature LPBF lead to metastable weakly ordered β phase. For high-temperature LPBF a Widmanstätten microstructure was observed with lenticular O phase precipitates within the β matrix

Engineering alloys for 3D printing

The alloys used nowadays for metal-based additive manufacturing (AM) -colloquially termed 3D printing- are mostly based on compositions inherited from conventional production techniques. The strong anisotropy exhibited by alloys that solidify with cubic lattices (e.g. conventional compositions of Ni- or Ti-based alloys) represents a deep-rooted drawback during AM. The reason is that thermo-mechanical processing as implemented in traditional manufacturing for breaking up anisotropy, as well as controlling grain size and texture, is not considered in AM owing to the attractiveness of near net-shape fabrication. In this work, a phase transformation path opens up an alternative to avoid the typical coarse anisotropic microstructures obtained upon AM of titanium alloys and provides new windows for alloy design of other metallic systems

Assessment of Michaelis-Menten parameters by analysis of single time courses of enzyme-catalyzed reactions

Schleeger M, Heberle J, Kakorin S. Assessment of Michaelis-Menten parameters by analysis of single time courses of enzyme-catalyzed reactions. In: EBEC Abstract Book. Biochimica et Biophysica Acta (BBA) - Bioenergetics. Vol 1797. Elsevier; 2010

Vasomotor assessment by camera-based photoplethysmography

Camera-based photoplethysmography (cbPPG) is a novel technique that allows the contactless acquisition of cardio-respiratory signals. Previous works on cbPPG most often focused on heart rate extraction. This contribution is directed at the assessment of vasomotor activity by means of cameras. In an experimental study, we show that vasodilation and vasoconstriction both lead to significant changes in cbPPG signals. Our findings underline the potential of cbPPG to monitor vasomotor functions in real-life applications

5-[(1R,2R,4R)-2-Methoxy-1,7,7-trimethylbicyclo[2.2.1]hept-2-yl]-1H-tetrazole

The title compound, C12H20N4O, undergoes a phase transition on cooling. The room-temperature structure is tetragonal (P43212, Z′ = 1), with the methoxybornyl group being extremely disordered. Below 213 K the structure is orthorhombic (P212121, Z′ = 2), with ordered molecules. The two independent molecules (A and B) have very similar conformations; significant differences only occur for the torsion angles about the Cbornyl—Ctetrazole bonds. The independent molecules are approximately related by the pseudo-symmetry relation: xB = −1/4 + yA, yB = 3/4 - xA and zB = 1/4 + zA. In the crystal, molecules are connected by N—H...N hydrogen bonds between the tetrazole groups, forming a pseudo-43 helix parallel to the c-axis direction. The crystal studied was a merohedral twin with a refined twin fraction value of 0.231 (2)