Heat Input Effect on Microstructure and Mechanical Properties of Electron Beam Additive Manufactured (EBAM) Cu-7.5wt.%Al Bronze

Electron beam additive wire-feed deposition of Cu-7.5wt.%Al bronze on a stainless-steel substrate has been carried out at heat input levels 0.21, 0.255, and 0.3 kJ/mm. The microstructures formed at 0.21 kJ/mm were characterized by the presence of both zigzagged columnar and small equiaxed grains with 10% of Σ3 annealing twin grain boundaries. No equiaxed grains were found in samples obtained at 0.255 and 0.3 kJ/mm. The zigzagged columnar ones were only retained in samples obtained at 0.255 kJ/mm. The fraction of Σ3 boundaries reduced at higher heat input values to 7 and 4%, respectively. The maximum tensile strength was achieved on samples obtained with 0.21 kJ/mm as tested with a tensile axis perpendicular to the deposited wall’s height. More than 100% elongation-to-fracture was achieved when testing the samples obtained at 0.3 kJ/mm (as tested with a tensile axis coinciding with the wall’s height).

Formation of Dislocations and Stacking Faults in Embedded Individual Grains during In Situ Tensile Loading of an Austenitic Stainless Steel

The formation of stacking faults and dislocations in individual austenite (fcc) grains embedded in a polycrystalline bulk Fe-18Cr-10.5Ni (wt.%) steel was investigated by non-destructive high-energy diffraction microscopy (HEDM) and line profile analysis. The broadening and position of intensity, diffracted from individual grains, were followed during in situ tensile loading up to 0.09 strain. Furthermore, the predominant deformation mechanism of the individual grains as a function of grain orientation was investigated, and the formation of stacking faults was quantified. Grains oriented with [100] along the tensile axis form dislocations at low strains, whilst at higher strains, the formation of stacking faults becomes the dominant deformation mechanism. In contrast, grains oriented with [111] along the tensile axis deform mainly through the formation and slip of dislocations at all strain states. However, the present study also reveals that grain orientation is not sufficient to predict the deformation characteristics of single grains in polycrystalline bulk materials. This is witnessed specifically within one grain oriented with [111] along the tensile axis that deforms through the generation of stacking faults. The reason for this behavior is due to other grain-specific parameters, such as size and local neighborhood.

Tensile Properties of -Oriented Nanotwinned Cu with Different Columnar Grain Structures

We performed tensile tests on highly <111>-oriented nanotwinned copper (nt-Cu) foils with different columnar grain structures. For a systematic study, we altered the microstructure of the foils by tuning the electroplating electrolyte and annealing temperatures under a nitrogen atmosphere. The results show that the yield strength ranges from 300 to 700 MPa, and elongation spans from 5% to 25%. Knowing the measured twin spacing and average grain size, and combining the confined layer slip with the Hall–Petch equation, we calculated the theoretical yield strength of the nt-Cu with different microstructures, and the theoretic values match the experiment results. Owing to the unique crystal orientation properties of <111>-oriented columnar grains, dislocations induced by slip are very limited. The Schmid factor of grains along the tensile axis direction is highly identical, so the plastic deformation is much more suitably explained by the Schmid factor model. Thus, we replace the Taylor factor with the Schmid factor in the slip model of nt-Cu.

CRYSTAL LATTICE ROTATIONS DURING PLASTIC DEFORMATION OF TWO-DIMENSIONAL POLYCRYSTALLINE Al SAMPLES

Theoretical studies of feasible rotations of the crystal lattice during the deformation of samples with an FCC structure under uniaxial tension are carried out. The results of the experimental determination of the magnitudes of these rotations for various grains of two-dimensional polycrystalline aluminum samples after their deformation by the same strain value are presented. For the first time, it has been theoretically shown and experimentally confirmed that under uniaxial tension of a specimen under the conditions of operation of only one slip system, regardless of the scheme of rotation, the magnitude of the rotation is determined only by the angle between the direction of the tensile axis and the slip direction before deformation of the specimen.

Compression-induced anti-nematic order in glassy and semicrystalline polymers

The glassy and semicrystalline polymers under extension align with the tensile axis and exhibit a nematic order, whereas under compression polymers reorganize to lie in planes perpendicular to the compressive axis resulting in the emergence of a novel anti-nematic order.

The Deformation Behavior of Oxygen-Modified Ti-29Nb-13Ta-4.6Zr(wt.%)

A series of Ti-29Nb-13Ta-4.6Zr(wt.%) {TNTZ} alloys containing either 0.1, 0.3 or 0.7(wt.%) oxygen (O) were room-temperature tensile tested inside a scanning electron microscope to evaluate the effect of O on the deformation evolution. The deformation modes observed for TNTZ-0.1O, which exhibited the largest elongation-to-failure and lowest strength of all the alloys, were deformation-induced α”-martensitic transformation, {332}<113> twinning, and <111> slip. For the other two alloys, <111> slip was the dominant deformation mode, where TNTZ-0.7O exhibited more homogeneous and extensive slip, a higher frequency of cross slip, and a higher work-hardening rate, all of which contributed to both its strength and elongation-to-failure being greater than that for TNTZ-0.3O. TNTZ-0.3O exhibited the greatest tendency for cracking, which generally occurred on grain boundaries perpendicular to the tensile axis, leading to the lowest elongation-to-failure of all the alloys.

Anomalous Twinning as the Macroscopic Deformation Mechanism for AZ31 Magnesium Alloy

In order to study the plastic deformation mechanism of AZ31 magnesium alloy, in situ texture measurement during uniaxial tensile deformation is conducted by using neutron diffraction. The specimen is prepared from a rolled sheet so that the deformation axis is parallel to the rolling direction. By increasing strain, the alignment of <10-10> along the tensile axis is strengthened, which is due to the activation of the prism slip system. The basal pole concentration at the prior sheet normal direction is slightly decreased by the deformation and the new texture component is formed at the transvers direction. This can be understood by activation of the {10-12} tension twinning. These results indicate that the tension twinning plays an important role even when the tensile deformation is applied parallel to the basal plane.

Role of Hydrogen-Charging on Nucleation and Growth of Ductile Damage in Austenitic Stainless Steels

Hydrogen energy is a possible solution for storage in the future. The resistance of packaging materials such as stainless steels has to be guaranteed for a possible use of these materials as containers for highly pressurized hydrogen. The effect of hydrogen charging on the nucleation and growth of microdamage in two different austenitic stainless steels AISI316 and AISI316L was studied using in situ tensile tests in synchrotron X-ray tomography. Information about damage nucleation, void growth and void shape were obtained. AISI316 was found to be more sensitive to hydrogen compared to AISI316L in terms of ductility loss. It was measured that void nucleation and growth are not affected by hydrogen charging. The effect of hydrogen was however found to change the morphology of nucleated voids from spherical cavities to micro-cracks being oriented perpendicular to the tensile axis.

A study on extruded filament bonding in fused filament fabrication

Purpose The performance of parts produced by fused filament fabrication is directly related to the printing conditions and to the rheological phenomena inherent to the process, specifically the bonding between adjacent extruded paths/raster. This paper aims to study the influence of a set of printing conditions and parameters, namely, envelope temperature, extrusion temperature, forced cooling and extrusion rate, on the parts performance. Design/methodology/approach The influence of these parameters is evaluated by printing a set of test specimens that are morphologically characterized and mechanically tested. At the morphological level, the external dimensions and the voids content of the printed specimens are evaluated. The bonding quality between adjacent extruded paths is assessed through the mechanical performance of test specimens, subjected to tensile loads. These specimens are printed with all raster oriented at 90º relative to the tensile axis. Findings The best performance, resulting from a compromise between surface quality, dimensional accuracy and mechanical performance, is achieved with a heated printing environment and with no use of forced cooling. In addition, for all the conditions tested, the highest dimensional accuracy is achieved in dimensions defined in the printing plane. Originality/value This work provides a relevant result as the majority of the current printers comes without enclosure or misses the heating and envelope temperature control systems, which proved to be one of the most influential process parameter.

Micromechanical Modeling of the Elasto-Viscoplastic Behavior and Incompatibility Stresses of β-Ti Alloys

Near β titanium alloys can now compete with quasi-α or α/β titanium alloys for airframe forging applications. The body-centered cubic β-phase can represent up to 40% of the volume. However, the way that its elastic anisotropy impacts the mechanical behavior remains an open question. In the present work, an advanced elasto-viscoplastic self-consistent model is used to investigate the tensile behavior at different applied strain rates of a fully β-phase Ti alloy taken as a model material. The model considers crystalline anisotropic elasticity and plasticity. It is first shown that two sets of elastic constants taken from the literature can be used to well reproduce the experimental elasto-viscoplastic transition, but lead to scattered mechanical behaviors at the grain scale. Incompatibility stresses and strains are found to increase in magnitude with the elastic anisotropy factor. The highest local stresses are obtained toward the end of the elastic regime for grains oriented with their <111> direction parallel to the tensile axis. Finally, as a major result, it is shown that the elastic anisotropy of the β-phase can affect the distribution of slip activities. In contrast with the isotropic elastic case, it is predicted that {112} <111> slip systems become predominant at the onset of plastic deformation when elastic anisotropy is considered in the micromechanical model.