Could face-centered cubic titanium in cold-rolled commercially-pure titanium only be a Ti-hydride?

A face-centered cubic (FCC) phase in electro-polished specimens for transmission electron microscopy of commercially pure titanium has sometimes been reported. Here, a combination of atom-probe tomography, scanning transmission electron microscopy and low-loss electron energy loss spectroscopy is employed to study both the crystal structural and chemical composition of this FCC phase. Our results prove that the FCC phase is actually a TiHx (x>1) hydride, and not a new allotrope of Ti, in agreement with previous reports. The formation of the hydride is discussed

The origin of jerky dislocation motion in high-entropy alloys

© 2022 Springer Nature Limited. Dislocations in high-entropy alloys encounter pinning during glide resulting in jerky motion. Here the authors demonstrate that the density of high local Peierls force is proportional to the critical stress required for their glide and mobility. Dislocations in single-phase concentrated random alloys, including high-entropy alloys (HEAs), repeatedly encounter pinning during glide, resulting in jerky dislocation motion. While solute-dislocation interaction is well understood in conventional alloys, the origin of individual pinning points in concentrated random alloys is a matter of debate. In this work, we investigate the origin of dislocation pinning in the CoCrFeMnNi HEA. In-situ transmission electron microscopy studies reveal wavy dislocation lines and a jagged glide motion under external loading, even though no segregation or clustering is found around Shockley partial dislocations. Atomistic simulations reproduce the jerky dislocation motion and link the repeated pinning to local fluctuations in the Peierls friction. We demonstrate that the density of high local Peierls friction is proportional to the critical stress required for dislocation glide and the dislocation mobility.11Nsciescopu

Publisher correction: unveiling the Re effect in Ni-based single crystal superalloys

An amendment to this paper has been published and can be accessed via a link at the top of the paper

Chemical Partitioning at Crystalline Defects in PtAu as a Pathway to Stabilize Electrocatalysts

Dissolution of electrocatalysts during long-term and dynamic operation is a challenging problem in energy conversion and storage devices such as fuel cells and electrolyzers. To develop stable electrocatalysts, we adopt the design concept of segregation engineering, which uses solute segregation prone to electrochemical dissolution at internal defects, i.e., grain boundaries and dislocations. We showcase the feasibility of this approach by stabilizing a model Pt catalyst with an addition of more noble Au (approximately 5 atomic percent). We characterized the defects' nanoscale structure and chemistry, and monitored the electrochemical dissolution of Pt and PtAu alloys by online inductively coupled plasma mass spectrometry. Once segregated to defects, Au atoms can stabilize and hence passivate the most vulnerable sites against electrochemical dissolution and improve the stability and longevity of the Pt electrocatalysts by more than an order of magnitude. This opens pathways to use solute segregation to defects for the development of more stable nanoscale electrocatalysts, a concept applicable for a wide range of catalytic systems

Deformation-Induced Martensite: A New Paradigm for Exceptional Steels

Atom-probe tomography (APT) and synchrotron X-ray diffraction (XRD) were combined to study the carbon supersaturation of ferrite for two pearlitic steel-wire compositions, eutectoid and hypereutectoid. The samples were cold-drawn at different strains up to true drawing strains for the eutectoid steel and the hypereutectoid steel, respectively. The wire diameters range from 1.7 mm down to 0.058 mm for the eutectoid steel and from 0.54 mm down to 0.02 mm for the hypereutectoid steel. The findings reveal that cold-drawing of pearlitic steel wires leads to a carbon-supersaturated ferrite causing a spontaneous tetragonal distortion of the ferrite unit cell through a strain-induced deformation driven martensitic transformation. We fi nd that the drawing process induced a significant increase in the carbon content inside the originally nearcarbon-free ferrite until a steady state is approached at drawing strains larger than ca. 4 for the wires. The change of carbon concentration in the ferrite grains during the drawing process is closely related to the tetragonal distortion of the ferrite unit cell

Sensing Molecules with Metal–Organic Framework Functionalized Graphene Transistors

Graphene is inherently sensitive to vicinal dielectrics and local charge distributions, a property that can be probed by the position of the Dirac point in graphene field-effect transistors. Exploiting this as a useful sensing principle requires selectivity; however, graphene itself exhibits no molecule-specific interaction. Complementarily, metal–organic frameworks can be tailored to selective adsorption of specific molecular species. Here, a selective ethanol sensor is demonstrated by growing a surface-mounted metal–organic framework (SURMOF) directly onto graphene field-effect transistors (GFETs). Unprecedented shifts of the Dirac point, as large as 15 V, are observed when the SURMOF/GFET is exposed to ethanol, while a vanishingly small response is observed for isopropanol, methanol, and other constituents of the air, including water. The synthesis and conditioning of the hybrid materials sensor with its functional characteristics are described and a model is proposed to explain the origin, magnitude, and direction of the Dirac point voltage shift. Tailoring multiple SURMOFs to adsorb specific gases on an array of such devices thus generates a versatile, selective, and highly sensitive platform for sensing applications

Effect of annealing on the size dependent deformation behavior of thin cobalt films on flexible substrates

The effect of film thickness as well as the influence of heat treatment on the deformation behavior of thin cobalt films 50 2000 nm on polyimide substrates was investigated using various tensile tests. Straining under an optical light microscope provides information about the fracture strain and cracking behavior. The annealed films exhibit enhanced crack onset strains between 4 and 7 compared to the as deposited films with fracture strains of 1 2 . This is partly achieved by a mechanically induced martensitic phase transformation of cobalt from the face centered cubic FCC to the hexagonal closed packed HCP phase. Thereby, it was shown that the heat treatment can be used to increase the amount ofmetastable FCC phase. Complementary synchrotron diffraction experiments were used to determine the lattice strains which initially increase during straining. After reaching a maximum, the lattice strains decrease in the case of the as deposited films due to crack formation and in the case of the annealed films due the strain induced phase transformation and localized plastic deformation in the form of necks. At higher engineering strains, the formation of cracks is also observed in the heat treated samples. Additionally, a decrease of the maximum lattice strain could be found for the HCP phase below a film thickness of 200 nm and grain size of 50 nm in the as deposited films which is caused by crackin