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Plastic effects during sheet metal forming can lead to undesirable distortions in formed components. Here, the three-stage work hardening and plastic strain recovery (“springback”) in a cold-rolled, α-phase commercially pure titanium is examined. Interrupted standard tensile tests with in situ x-ray diffraction and quasi-in situ electron backscatter diffraction show that twinning plays a minor role in both of these phenomena. The experiments give evidence that the observed work hardening plateau is the result of an abrupt activation and multiplication of 〈 c + a 〉 slip and a subsequent redistribution of load between grain families. The springback can be attributed to inelastic backwards motion and annihilation of dislocations, driven by backstresses from dislocation-based hardening during loading. The peak broadening behavior, observed by x-ray diffraction, suggests that the internal stress state is highest in the rolling direction, resulting in consistently higher springback magnitude along this direction.

This work reports on the microstructure and mechanical properties of porous silver films produced with different sintering parameters. The microstructure is investigated by high-resolution ptychographic X-ray computed tomography and scanning electron microscopy. The mechanical properties are obtained from constant strain rate tensile tests. It is found that for this class of samples both grain size and ligament diameter have little effect on the magnitude of the yield stress. Instead, a clear correlation is found between strength and porosity.

Three-dimensional finite element simulations of nano-porous silver structures are performed to understand the correlation between the porous morphology and the mechanical behavior. The nanostructures have been obtained from ptychographic X-ray computed tomography. The simulations allow distinguishing between the interplay and role of the ligament size, the pore morphology and the porosity, and therefore provide a better comprehension of the experimental observations. We show that the proposed model has a predictive character for mechanical behavior of nano-porous silver.

Precursors of failure are dislocation mechanisms at the nanoscale and dislocation organization at the mesoscale responsible for long-range internal stresses and lattice rotation. Detailed information on the link between both scales is missing, computationally and experimentally. Here we present a method based on x-ray Laue diffraction scanning providing time and sub -micron spatially resolved evolution of geometrical necessary dislocations in volumes that are similar to what advanced computational models can achieve. The approach is used to follow dislocation patterning during accumulation of fatigue cycles using a newly developed miniaturized shear device. Performed on Cu during cyclic shear, it reveals early dislocation patterning influenced by pre-existing dislocation structures. The quantitative information on non -homogeneous structure formation and its evolution corresponds to the need for synergies with continuum dislocation plasticity simulations of fatigue or any other type of plastic deformation. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. This is an open access article under the CC BY -NC ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Dynamic recovery in nanocrystalline Ni and Ni50Fe50 with respective grain sizes of 65 rim and 15 nm is studied using stress reduction tests during in situ X-ray diffraction. The results are compared with a previous study on NC Ni with 35 nm grain size. Defect recovery by means of grain boundary processes plays an important role in controlling the strength evolution resulting in a constant flow stress during uniaxial deformation. The relative contributions of dislocation and grain boundary accommodation mechanisms are discussed in terms of grain size and alloying. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

An in situ method to study the behavior of alloys during rapid heating and cooling combining laser heating with synchrotron micro X-ray diffraction and high-speed imaging is presented. Near-spherical Ti-48Al specimens were melted using a laser-based heating system consisting of two diode lasers and subsequently rapidly solidified using a Cu support structure. The Al-rich Ti-48Al forms a fine grained dual phase alpha(2) + gamma microstructure. Upon solidification, the formation of the beta-phase is fully suppressed. Time-resolved peak evolution and temperature-corrected micro X-ray diffraction data provides clear observations of solidification and solid state phase transformations under non-equilibrium conditions similar to beam-based additive manufacturing. (C) 2015 Elsevier Ltd. All rights reserved.

The microstructure of porous silver layers produced under different low temperature pressure-assisted sintering conditions is characterized and linked with the mechanical behavior studied insitu during X-ray diffraction. Peak profile analysis reveals important strain recovery and hardening mechanism during cyclic deformation. The competition between both mechanisms is discussed in terms of porosity and grain size. (C) 2015 Acts Materialia Inc. Published by Elsevier Ltd. All rights reserved.

The role of misfit stress in kinematic hardening under reversed straining of a Type 316H austenitic stainless steel has been investigated by using neutron diffraction combined with in situ deformation. Initial misfit stresses, often referred to an intergranular internal stresses, were created by the tensile pre-straining at high temperature. The misfit stresses at the length-scale of grain families, measured by neutron diffraction, were shown to be a function of the magnitude of the tensile pre-strain. The pre-strained specimens were further subjected to either continued (tensile) straining or reversed (compressive) straining at room temperature. In situ neutron diffraction measurements were undertaken to monitor the change of the misfit stresses during loading. The macroscopic stress–strain behaviour was used to derive isotropic and kinematic hardening stresses developed in the pre-strained specimens. Results show that the change of the transient softening stress towards a zero value is accompanied by a decrease in the change of the misfit stresses. A multi-scale self-consistent model has been developed to assist in understanding the measured change of the misfit stresses when subjecting the material to strain reversal. An important conclusion is that the origin of the kinematic hardening of Type 316H austenitic stainless steel arises from the misfit stress between grains.

The constant flow stress reached during uniaxial deformation of electrodeposited nanocrystalline Ni reflects a quasi-stationary balance between dislocation slip and grain boundary (GB) accommodation mechanisms. Stress reduction tests allow to suppress dislocation slip and bring recovery mechanisms into the foreground. When combined with in situ X-ray diffraction it can be shown that grain boundary recovery mechanisms play an important role in producing plastic strain while hardening the microstructure. This result has a significant consequence for the parameters of thermally activated glide of dislocations, such as athermal stress and activation volume, which are traditionally derived from stress/strain rate change tests. (C) 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Deformation mechanisms in nanocrystalline electrodeposited Ni (26 nm) and Ni-Fe (12 nm) are studied by strain rate sensitivity experiments and in situ mechanical testing during X-ray diffraction. We find a relatively low strength for Ni-Fe, which may be ascribed to a weakening of dislocation pinning points. Furthermore, the strain rate sensitivity of Ni-Fe is relatively low. The in situ studies allow the macroscopic mechanical response of Ni to be divided into three different deformation regimes: elastic, microplastic and macroplastic. For Ni-Fe, recovery mechanisms seem particularly important, resulting in an extended microplastic regime and necking before a state of homogeneous deformation can be reached. (C) 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

We investigate various microstructural features of nanocrystalline electrodeposited Ni-Fe with a nominal iron content of 50% and compare them with the well-known nanocrystalline Ni system. In-depth electron microscopy analysis reveals the existence of large strain variations in the grain interior. Three-dimensional atom probe studies demonstrate no significant segregation to grain boundaries. However, significant deviations from a perfect chemically disordered system are found, which can be related to compositional variations of 5% over length scales of only a few nanometres. Finally, X-ray diffraction measurements suggest higher dislocation and twin density in Ni-Fe compared to Ni. (C) 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

In-situ mechanical testing during X-ray diffraction is performed on electro-deposited nanocrystalline Ni. It is found that the evolution of inter-granular stresses with plastic deformation is altered compared to what is usually found for coarse-grained metals. The results are rationalized by insights gained from molecular dynamics and quantized crystal plasticity modelling.

A change in strain path may have a significant effect on the mechanical response of metals. In order to understand or even predict the macroscopic behaviour under such conditions a detailed knowledge on the microstructural evolution is crucial. Yet relatively little work has been done to quantify and understand how the inter- and intragranular strains are affected during a change in strain path. In this work we present a new multiaxial deformation rig that allows performing in situ proportional and non proportional loading under neutron diffraction. We demonstrate the capabilities of this new setup for the case of a 316 L stainless steel. We show that the nature and magnitude of intergranular strain strongly depends on the applied stress state and demonstrate that micro yielding and internal strain recovery are responsible for the observed transient softening during a 90 strain path change. We anticipate that this new characterization method will provide previously inaccessible microstructural data that can serve as input for benchmarking current state-of-the-art crystal plasticity models. (C) 2015 Acta Materialia Inc. Published by Elsevier Ltd.

In situ Laue analysis during microcompression is carried out on Mo-alloy pillars containing defects due to focused ion beam milling or pre-strain. Independently of how the defects are introduced, if the diffraction peaks are streaked prior to deformation, slip starts in the direction matching the observed streaking, even if this corresponds to a low Schmid factor. The amount of pre-strain influences the deformation behaviour in terms of hardening and strain bursts. (C) 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

In situ Laue analysis during microcompression reveals plasticity in [0 0 1]-oriented, directionally solidified Mo alloy pillars to start with slip on the {1 1 2} system having the highest Schmid factor followed by slip on the (1 1 0) plane containing the same Burgers vector. The results are interpreted in terms of the microstructure analyzed by scanning transmission electron microscopy and 3-D atom probe. (C) 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

The mechanical properties of electrodeposited nanocrystalline Ni–50 wt.% Fe are compared with those of electrodeposited Ni. Load–unload experiments and strain rate jump tests demonstrate the presence of a yield point after a change in strain rate in the plastic regime. The strain rate sensitivity is considerably reduced in Ni–Fe, in spite of the smaller grain size.

Neutron and synchrotron X-ray diffraction spectra have been acquired during room temperature tensile deformation of a creep-resistant bainitic 1% CrMoV steel, in order to study the evolution of internal microstresses and load-sharing mechanisms between the ferrite matrix and the various carbides. Cementite takes load from the plastifying matrix at the onset of macroscopic plasticity resulting in residual interphase stresses. Single peak fitting indicates an elastic anisotropic behaviour of cementite.

White beam Laue micro-diffraction was performed on directionally solidified, single-crystal Mo pillars in the as-grown state, after focused ion beam (FIB) milling and after pre-straining. The Laue diffraction peaks from the as-grown pillars are very sharp and show no broadening, similar to those from single-crystal Si wafers. Significant broadening and streaking of the peaks occurred after FIB milling and pre-straining, indicative of the damage these treatments induce in the nearly perfect crystal structure of the directionally solidified Mo pillars.

Single-crystal face-centered cubic metal pillars synthesized using a focused ion beam are reported to be stronger when compressed in smaller volumes. Using in situ Laue diffraction and crystal plasticity simulations it is shown that plastic deformation is initially controlled by the boundary constraints of the microcompression tests, followed by classical crystal plasticity for uniaxial compression. Taking the stress at which the change between the two modes occurs as strength of the pillar instead of the flow stress at a fixed amount of strain, the “smaller is stronger” trend is considerably reduced, if not eliminated, and what remains is a size dependence in strain hardening. The sizedependent increase in flow stress is a result of the early activation of multiple slip systems and thus the evolution of the microstructure during compression.

Stress-dip experiments followed by creep have been performed on nanocrystalline Ni during in situ X-ray diffraction. The signatures of the peak profile at different creep stress levels demonstrate the presence of a creep mechanism that broadens the diffraction peak width and of a creep mechanism that reduces the peak width. The balance between the two mechanisms is discussed in terms of the applied creep stress.

White beam Laue microdiffraction has been performed to investigate the initial microstructure of undeformed Au, Ni, Cu, and NiTi micropillars fabricated by focused ion beam milling. Various microstructural features have been shown, from which it is known that they contribute to classical hardening.

X-ray diffraction techniques allow the determination of mean grain size, root-mean-square strain and dislocation/twin content through peak profile analysis and the Williamson–Hall approach. The analysis is, however, based on assumptions that are questionable when applied to nanocrystalline (nc) structures. In the present work, two-theta X-ray diffraction profiles are calculated from multi-million atom computer-generated nc-Al samples containing a well-defined twin or dislocation content. The Williamson–Hall plots are compared with those obtained from in situ X-ray experiments performed on electrodeposited nc-Ni and on nc-Cu data available in the literature.

Ultra short pulsed laser ablation is applied for preparing samples suitable for micromechanical testing. Laue microdiffraction shows that the micromachining hardly damages the initial microstructure. The technique has the potential to be a promising alternative to focused ion beam preparation for micromechanical objects since it is relatively fast, efficient and implants no ions. (C) 2015 Elsevier B.V. All rights reserved.

Unique mechanical properties have been measured in submicrometer freestanding nanocrystalline Al films, where discontinuous grain growth results in a fundamental change in the way in which the material deforms. In contrast to the limited ductility normally associated with nanocrystalline metals, these nanocrystalline films exhibit extended tensile ductility. In situ X-ray diffraction and postmortem transmission electron microscopy point to the importance of stress-assisted room temperature grain growth in transforming the underlying processes that govern the mechanical response of the films: nanoscale deformation mechanisms give way to microscale plasticity.

Molecular statics is used to study the crack propagation in model nanocrystalline Ni with a mean grain size of 10 nm. It is shown that the crack propagates intergranularly, creating nano-voids ahead of the crack which coalesce gradually. Plasticity in the neighborhood of the crack tip is observed to be mediated by dislocation activity. The sequential emission of partials results in the observation of full dislocations and twinning.

The free volume in nanostructured Ni, synthesized by different techniques, was measured by electron microscopy and positron lifetime spectroscopy. Even in the fully dense samples 1–2 nm sized pores as well as smaller nanovoids were observed indicating that these nanovoids are an intrinsic property of the microstructure of nanostructured materials.

The mechanical behaviour of nanocrystalline austenitic steels with and without yttria particles was investigated using in situ synchrotron diffraction during tensile deformation. Two different strain-hardening regimes were found. The first regime can be assigned predominantly to a martensitic phase transformation, the second to deformation twinning in the fragmented retained austenite. The kinetics of martensitic phase transformation is remarkably enhanced in the nanocrystalline structure. (C) 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Cu/Nb/Cu conductors composed of a multiscale Cu matrix embedding Nb nanotubes were studied using in situ tensile testing during neutron diffraction. The evolution of lattice strains during deformation revealed the different elastoplastic regimes in the multiscale Cu matrix and the Nb nanotubes. The Cu nanofilaments embedded in the Nb nanotubes behaved as whiskers with a strong size dependence. The results are compared with Cu/Nb nanofilamentary wires and differences in strengthening mechanism are explained in terms of microstructure.

A multi-scale elastic-plastic finite element and fast Fourier transform based approach is proposed to study lattice strain evolution during uniaxial and biaxial loading of stainless steel cruciform shaped samples. At the macroscale, finite element simulations capture the complex coupling between applied forces in the arms and gauge stresses induced by the cruciform geometry. The predicted gauge stresses are used as macroscopic boundary conditions to drive a mesoscale elasto-viscoplastic fast Fourier transform model, from which lattice strains are calculated for particular grain families. The calculated lattice strain evolution matches well with experimental values from in-situ neutron diffraction measurements and demonstrates that the spread in lattice strain evolution between different grain families decreases with increasing biaxial stress ratio. During equibiaxial loading, the model reveals that the lattice strain evolution in all grain families, and not just the 311 grain family, is representative of the polycrystalline response. A detailed quantitative analysis of the 200 and 220 grain family reveals that the contribution of elastic and plastic anisotropy to the lattice strain evolution significantly depends on the applied stress ratio. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd.