How to catch a shear band and explain plasticity of metallic glasses with continuum mechanics.

Capturing a shear band in a metallic glass during its propagation experimentally is very challenging. Shear bands are very narrow but extend rapidly over macroscopic distances, therefore, characterization of large areas at high magnification and high speed is required. Here we show how to control the shear bands in a pre-structured thin film metallic glass in order to directly measure local strains during initiation, propagation, or arrest events.

Unveiling the mechanism of deformation-induced supersaturation.

A Cu-6at%Ag cast alloy was deformed by means of high-pressure torsion to different applied strain levels until a steady-state regime is reached. The continuous structural refinement is attended by the successive dissolution of the Ag precipitates in the Cu matrix. The results show that the Ag regions need to fall below a phase size of ~ 5 nm to fully dissolve.

Deformation Induced Structure and Property Changes in a Nanostructured Multiphase CrMnFeCoNi High-Entropy Alloy.

A nanocrystalline CrMnFeCoNi high-entropy alloy produced using severe plastic deformation using high-pressure torsion was annealed at selected temperatures and times (450 °C for 1 h and 15 h and at 600 °C for 1 h), causing a phase decomposition into a multi-phase structure. The samples were subsequently deformed again by high-pressure torsion to investigate the possibility of tailoring a favorable composite architecture by re-distributing, fragmenting, or partially dissolving the additional intermetallic phases. While the second phase in the 450 °C annealing states had high stability against mechanical mixing, a partial dissolution could be achieved in the samples subjected to 600 °C for 1 h.

Can Severe Plastic Deformation Tune Nanocrystallization in Fe-Based Metallic Glasses?

The effects of severe plastic deformation (SPD) by means of high-pressure torsion (HPT) on the structural properties of the two iron-based metallic glasses FeCuNbSiB and FeCoSiBPCu have been investigated and compared. While for FeCuNbSiB, HPT processing allows us to extend the known consolidation and deformation ranges, HPT processing of FeCoSiBPCu for the first time ever achieves consolidation and deformation with a minimum number of cracks. Using numerous analyses such as X-ray diffraction, dynamic mechanical analyses, and differential scanning calorimetry, as well as optical and transmission electron microscopy, clearly reveals that FeCoSiBPCu exhibits HPT-induced crystallization phenomena, while FeCuNbSiB does not crystallize even at the highest HPT-deformation degrees applied.

Phase Transformation Induced by High Pressure Torsion in the High-Entropy Alloy CrMnFeCoNi.

The forward and reverse phase transformation from face-centered cubic (fcc) to hexagonal close-packed (hcp) in the equiatomic high-entropy alloy (HEA) CrMnFeCoNi has been investigated with diffraction of high-energy synchrotron radiation. The forward transformation has been induced by high pressure torsion at room and liquid nitrogen temperature by applying different hydrostatic pressures and large shear strains. The volume fraction of hcp phase has been determined by Rietveld analysis after pressure release and heating-up to room temperature as a function of hydrostatic pressure.

Manufacturing of Textured Bulk Fe-SmCo Magnets by Severe Plastic Deformation.

Exchange-coupling between soft- and hard-magnetic phases plays an important role in the engineering of novel magnetic materials. To achieve exchange coupling, a two-phase microstructure is necessary. This interface effect is further enhanced if both phase dimensions are reduced to the nanometer scale.

Soft Magnetic Properties of Ultra-Strong and Nanocrystalline Pearlitic Wires.

The paper describes the capability of magnetic softening of a coarse-grained bulk material by a severe deformation technique. Connecting the microstructure with magnetic properties, the coercive field decreases dramatically for grains smaller than the magnetic exchange length. This makes the investigation of soft magnetic properties of severely drawn pearlitic wires very interesting.

A Perspective to Control Laser-Induced Periodic Surface Structure Formation at Glancing-Incident Femtosecond Laser-Processed Surfaces.

Unlabelled: The favorable combination of high material removal rate and low influence on the material beneath the ultra-short pulsed laser-processed surface are of particular advantage for sample preparation. This is especially true at the micrometer scale or for the pre-preparation for a subsequent focused ion beam milling process. Specific surface features, the laser-induced periodic surface structures, are generated on femtosecond laser-irradiated surfaces in most cases, which pose an issue for surface-sensitive mechanical testing or microstructural investigations.

Microstructural Effects on the Interfacial Adhesion of Nanometer-Thick Cu Films on Glass Substrates: Implications for Microelectronic Devices.

Improving the interface stability for nanosized thin films on brittle substrates is crucial for technological applications such as microelectronics because the so-called brittle-ductile interfaces limit their overall reliability. By tuning the thin film properties, interface adhesion can be improved because of extrinsic toughening mechanisms during delamination. In this work, the influence of the film microstructure on interface adhesion was studied on a model brittle-ductile interface consisting of nanosized Cu films on brittle glass substrates.

Geometrical model for calculating the effect of surface morphology on total x-ray output of medical x-ray tubes.

Purpose: Correlation of characteristic surface appearance and surface roughness with measured air kerma (kinetic energy released in air) reduction of tungsten-rhenium (WRe) stationary anode surfaces.

Methods: A stationary anode test system was developed and used to alter nine initially ground sample surfaces through thermal cycling at high temperatures. A geometrical model based on high resolution surface data was implemented to correlate the measured reduction of the air kerma rate with the changing surface appearance of the samples.

Hydrogen Trapping in bcc Iron.

Fundamental understanding of H localization in steel is an important step towards theoretical descriptions of hydrogen embrittlement mechanisms at the atomic level. In this paper, we investigate the interaction between atomic H and defects in ferromagnetic body-centered cubic (bcc) iron using density functional theory (DFT) calculations. Hydrogen trapping profiles in the bulk lattice, at vacancies, dislocations and grain boundaries (GBs) are calculated and used to evaluate the concentrations of H at these defects as a function of temperature.

Electron Irradiation Effects on Strength and Ductility of Polymer Foils Studied by Femtosecond Laser-Processed Micro-Tensile Specimens.

The influence of irradiation on mechanical properties of polymer foils used in spacecraft applications has widely been studied via macroscopic tensile samples. An increase in the local resolution of this investigation can be achieved by reducing the sample's dimensions. A femtosecond laser enables a fast fabrication of micro-samples with dimensions from tens of μ m to the mm range, with ideally no influence on the material.

Magnetic Binary Supersaturated Solid Solutions Processed by Severe Plastic Deformation.

Samples consisting of one ferromagnetic and one diamagnetic component which are immiscible at the thermodynamic equilibrium (Co-Cu, Fe-Cu, Fe-Ag) are processed by high-pressure torsion at various compositions. The received microstructures are investigated by electron microscopy and synchrotron X-ray diffraction, showing a microstructural saturation. Results gained from microstructural investigations are correlated to magnetometry data.

Internal stress and defect-related free volume in submicrocrystalline Ni studied by neutron diffraction and difference dilatometry.

A combined study of neutron diffraction and difference dilatometry on submicrocrystalline Ni prepared by high pressure torsion aims at studying the anisotropic behaviour during dilatometry and its relation to internal stress and structural anisotropy. Macroscopic stresses were undetectable in the dilatometer samples. Along with specific tests such as post cold-rolling, this shows that an observed anisotropic length change upon annealing is not caused by internal stress, but can be explained by the inherent microstructure, i.

In situ atomic-scale observation of oxidation and decomposition processes in nanocrystalline alloys.

Oxygen contamination is a problem which inevitably occurs during severe plastic deformation of metallic powders by exposure to air. Although this contamination can change the morphology and properties of the consolidated materials, there is a lack of detailed information about the behavior of oxygen in nanocrystalline alloys. In this study, aberration-corrected high-resolution transmission electron microscopy and associated techniques are used to investigate the behavior of oxygen during in situ heating of highly strained Cu-Fe alloys.

Femtosecond laser machining for characterization of local mechanical properties of biomaterials: a case study on wood.

The standard preparation technique for micro-sized samples is focused ion beam milling, most frequently using Ga ions. The main drawbacks are the required processing time and the possibility and risks of ion implantation. In contrast, ultrashort pulsed laser ablation can process any type of material with ideally negligible damage to the surrounding volume and provides 4 to 6 orders of magnitude higher ablation rates than the ion beam technique.

From powders to bulk metallic glass composites.

One way to adjust the properties of materials is by changing its microstructure. This concept is not easily applicable on bulk metallic glasses (BMGs), because they do not consist of grains or different phases and so their microstructure is very homogeneous. One obvious way to integrate inhomogeneities is to produce bulk metallic glass composites (BMGCs).

Fatigue crack closure: a review of the physical phenomena.

Plasticity-induced, roughness-induced and oxide-induced crack closures are reviewed. Special attention is devoted to the physical origin, the consequences for the experimental determination and the prediction of the effective crack driving force for fatigue crack propagation. Plasticity-induced crack closure under plane stress and plane strain conditions require, in principle, a different explanation; however, both types are predictable.

Electrochemical and biocompatibility examinations of high-pressure torsion processed titanium and Ti-13Nb-13Zr alloy.

The purpose of this study was to estimate the electrochemical behavior and biocompatibility of ultrafine-grained (UFG) commercially pure titanium (CPTi) and Ti-13Nb-13Zr (TNZ) alloy obtained by high-pressure torsion process. Electrochemical behavior of materials in artificial saliva at 37°C was evaluated by potentiodynamic polarization tests and electrochemical impedance spectroscopy (EIS), and the obtained results indicated that UFG TNZ alloy showed corrosion current density (j  = 53 ± 5 nA cm ) which was 2 times lower compared to coarse-grained (CG) TNZ alloy (j  = 110 ± 12 nA cm ) and higher corrosion resistance, while UFG CPTi and CPTi showed approximately the same corrosion rate (mean j ∼ 38-40 nA cm ). Static immersion test in artificial saliva, performed in this study, showed that the released ion concentrations from UFG materials were more than 10 times lower than the permitted concentration (the highest released Ti ion concentration from UFG CPTi and UFG TNZ alloy was 1.

The effect of severe grain refinement on the damage tolerance of a superelastic NiTi shape memory alloy.

Nickel-titanium (NiTi) shape memory alloys are widely used for medical components, as they can accommodate large strains in their superelastic state. In order to further improve the mechanical properties of NiTi, grain refinement by severe plastic deformation is applied to generate an ultrafine-grained microstructure with increased strength. In this work comprehensive fracture and fatigue crack growth experiments were performed on ultrafine-grained NiTi to assess its damage tolerance, which is essential for the safe use of this material in medical applications.

A novel setup for wafer curvature measurement at very high heating rates.

The curvature evolution of a thin film layer stack containing a top Al layer is measured during temperature cycles with very high heating rates. The temperature cycles are generated by means of programmable electrical power pulses applied to miniaturized polysilicon heater systems embedded inside a semiconductor chip and the curvature is measured by a fast wafer curvature measurement setup. Fast temperature cycles with heating duration of 100 ms are created to heat the specimen up to 270 °C providing an average heating rate of 2500 K/s.

On nanostructured molybdenum-copper composites produced by high-pressure torsion.

Nanostructured molybdenum-copper composites have been produced through severe plastic deformation of liquid-metal infiltrated Cu30Mo70 and Cu50Mo50 (wt%) starting materials. Processing was carried out using high-pressure torsion at room temperature with no subsequent sintering treatment, producing a porosity-free, ultrafine-grained composite. Extensive deformation of the Cu50Mo50 composite via two-step high-pressure torsion produced equiaxed nanoscale grains of Mo and Cu with a grain size of 10-15 nm.

Ultra-strong and damage tolerant metallic bulk materials: A lesson from nanostructured pearlitic steel wires.

Structural materials used for safety critical applications require high strength and simultaneously high resistance against crack growth, referred to as damage tolerance. However, the two properties typically exclude each other and research efforts towards ever stronger materials are hampered by drastic loss of fracture resistance. Therefore, future development of novel ultra-strong bulk materials requires a fundamental understanding of the toughness determining mechanisms.

The importance of fracture toughness in ultrafine and nanocrystalline bulk materials.

The suitability of high-strength ultrafine and nanocrystalline materials processed by severe plastic deformation methods and aimed to be used for structural applications will strongly depend on their resistance against crack growth. In this contribution some general available findings on the damage tolerance of this material class will be summarized. Particularly, the occurrence of a pronounced fracture anisotropy will be in the center of discussion.

Thermally Activated Deformation Behavior of ufg-Au: Environmental Issues During Long-Term and High-Temperature Nanoindentation Testing.

For testing time-dependent material properties by nanoindentation, in particular for long-term creep or relaxation experiments, thermal drift influences on the displacement signal are of prime concern. To address this at room and elevated temperatures, we tested fused quartz at various contact depths at room temperature and ultra-fine grained (ufg) Au at various temperatures. We found that the raw data for fused quartz are strongly affected by thermal drift, but corrected by use of dynamic stiffness measurements all the datasets collapse.