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Additively manufactured (AM) components offer superior design flexibility compared to their conventionally manufactured counterparts and require process parameter optimization to achieve high-quality depositions with desirable and predictable mechanical properties. This study was focused on 4340 steel fabricated using laser powder bed fusion (LPBF), and 42 laser power and scan speed combinations have been systematically investigated to optimize the melt pool geometry and ensure fully dense parts. The AM material was compared with a wrought 4340 equivalent and studied in both as-fabricated and heat-treated conditions. Two heat treatments were designed and used to optimize the materials for strength and toughness, respectively. Microstructure, tensile, and fractographic studies were conducted to assess build integrity and establish processing–structure–performance relationships. Tensile properties of the AM materials in all studied conditions were equivalent or better than the comparable wrought materials. The high performance of the AM materials was attributed to the absence of both manganese sulfide inclusions and rolling-induced banding, typically found in the wrought materials. The fine cellular substructure is thought to additionally contribute to the high strength of the as-fabricated AM material. Complementary to the knowledge that has emerged from the experimental investigations, the dataset was further leveraged to make recommendations for future design of experiments to optimize AM build parameters in other material systems. A statistical Monte Carlo analysis was used to predict the interpolation error produced when using reduced datasets and to enable informed processing parameters selection. These findings are discussed to make recommendations for the use of AM materials for high-integrity structural applications.

A solid state phase transformation of Ti-6Al-4V was studied using high speed in situ x-ray diffraction measurements made during rapid cooling of a cold metal transfer arc weld bead deposited onto a water cooled substrate. Analysis of body centered cubic (BCC) and hexagonal close packed (HCP) lattices revealed an abrupt, nonlinear shift in the lattice parameters of both phases just after the HCP phase had nucleated. Postmortem transmission electron microscopy confirmed that V diffusion was mostly suppressed during cooling. Together, these results indicate that at this cooling rate of approximately 104 K/s, which is representative of cooling rates of many additive manufacturing and welding processes, kinematic coherency of the BCC–HCP interfaces gives rise to the anomalous lattice expansion and contraction behaviors of both phases during the initial nucleation and growth stages of (mostly) martensitic transformation from BCC to HCP; the role of diffusion in such lattice anomalies is shown to be minimal.

Adoption of metal additive manufacturing (AM) components in property-critical applications requires predictable performance of fabricated metal AM parts. In-situ diagnostics coupled with material models provide a pathway for qualification of AM whereby a prime objective is to capture data that inform or validate models or theory. Part of this is to understand the solidification and cooling of the material through diagnostics in order to ensure the part is being built correctly and that microstructures and properties are predictable. We have utilized high-energy X-ray diffraction to provide a unique probe for bulk material characterization in-situ during additive manufacture. The current work is focused on presenting the opportunities and potential pitfalls associated with extracting microstructural information from diffraction data that is necessarily limited due to the dynamic nature of the process. We present diffraction measurements and Rietveld refinement of stainless steel wire-arc line depositions using 71 keV X-rays, providing information on temperature, phase evolution, and residual stress during the deposition of a single-layer of 308L stainless filler wire on a 304L stainless steel substrate. In addition to observing both the liquid/solid and solid-state phase transformations, this methodology can be used to map the extent of the melt pool, identify thermal gradients, and measure residual stresses in materials during deposition.

Additive manufacturing of metal components results in unique microstructures with, necessarily, mechanical properties that are distinct from conventionally produced components. In this work, four distinct microstructural features associated with directed energy deposition of 304L stainless steels, their stability, and their influences on flow strength were examined. These were (1) high dislocation density comparable with deformed materials, (2) increased ferrite content, (3) local chemical heterogeneity, and (4) tortuous grain morphology. In situ neutron diffraction measurements were used to monitor the evolution of the as-built microstructure during post-build heat treatment and relate the specific microstructural features to the strength behavior of the material following the heat treatment. The increased flow strength of the additively manufactured material relative to wrought counterparts is found to be due primarily to an increased dislocation density in the as-built material. However, the increased dislocation density does not completely account for the increased strength and it is hypothesized that some of the additional strength is related to the unique AM grain structure.

In situ high-energy X-ray diffraction measurements were completed during deposition of 308L stainless steel wire onto a 304L stainless steel substrate. Attempts were made to extract microstructural features such as phase fraction and internal stress, as well as temperature evolution immediately following the deposition. The limited data that could be collected during deposition and rapid solidification are critically examined. High-energy X-rays coupled with relatively slow detectors were utilized to enable determination of orientation-dependent lattice parameters accurately enough to comment on phase strain evolution between austenite and ferrite. Information about the hydrostatic and deviatoric stress states of the constituent phases was determined on time scales that are relevant to their development. However, the time resolution of the technique was insufficient to monitor phase evolution during the solid–solid phase transformation and, more so, during solidification. Moreover, the accurate and absolute determination of inherently statistical parameters, such as phase fraction, depends critically on the ability to sample a statistically significant numbers of grains in the microstructure.

Physics-based modeling of metal additive manufacturing (AM) processes is computationally challenging due to the very fine meshing required in both time and space. State-of-the-art numerical models that offer great insight into the process have been developed, but they require powerful computational resources and weeks of processing time. Thus, it is often more time-effective to fabricate multiple builds within the time it takes to complete one simulation prediction, further reinforcing the current trial-and-error approach to optimizing the build parameters. This study presents a simplified approach to the transient thermal modeling of the AM process. The numerical model is designed to run on a moderate laptop or desktop computer, without use of parallel processing. The method described in this study uses a unique approach to node creation which leverages the simplicity of the finite difference method to provide predictions in less time than it takes to build the part. Coarse meshing in both time and space along with simplifying assumptions about the solidification process are used in this numerical approach. Model predictions track well with experimental measurements. This approach is being developed for use in an industrial setting to inform deposition parameters based on a desired thermal profile.

The generation of high magnetic fields requires materials with high electric conductivity and good strength properties. Cu/Nb composites are considered to be good candidates for this purpose. In this work we aim to predict, from theory, the dependence of electric conductivity on the microstructure, most notably on the layer thickness and grain sizes. We also conducted experiments to calibrate and validate our simulations. Bimetal interfaces and grain boundaries are confirmed to have the largest impact on conductivity in this composite material. In this approach, a distribution of the layer thickness is accounted for in order to better model the experimentally observed microstructure. Because layer thicknesses below the mean free path of Cu significantly degrade the conductivity, an average layer thickness larger than expected may be needed to meet conductivity requirements in order to minimize these smaller layers in the distribution. We also investigate the effect of variations in volume fraction of Nb and temperature on the material's conductivity., 18 pages, 5 figures, 2 tables; v2 minor clarifications

A two-color pyrometer is aligned co-axially to the laser inside a Laser Engineered Net Shaping machine to gather thermal data during a single layer two-pass deposit. Several molten pool metrics are calculated from the pyrometer data, and anomalies in the data are used to flag potential defect locations. The depositions are scanned using x-ray Computed Tomography (XCT) with a 4.13 micron voxel, and void size and location are recorded. XCT void data is then compared to the thermal analysis to determine the efficacy of the anomaly detection technique. In this build, four voids > 40 microns in diameter were found with XCT. Three defects appeared in the interfacial region between the deposit and substrate and produced signatures that were detected by analyzing the in-situ pyrometer data.

Recent work in both 304L and 316L stainless steel produced by additive manufacturing (AM) has shown that in addition to the unique, characteristic microstructures formed during the process, a fine dispersion of sub-micron particles, with a chemistry different from either the powder feedstock or the expected final material, are evident in the final microstructure. Such fine-scale features can only be resolved using transmission electron microscopy (TEM) or similar techniques. The present work uses electron microscopy to study both the initial powder feedstock and microstructures in final AM parts. Special attention is paid to the chemistry and origin of these nanoscale particles in several different metal alloys, and their impact on the final build. Comparisons to traditional, wrought material will be made.

Accumulative roll bonded (ARB) Copper Niobium (Cu-Nb) nano-lamellar composite (NLC) panels were friction stir welded (FSWed) to evaluate the ability to join panels while retaining the nano-lamellar structure. During a single pass of the friction stir welding (FSW) process, the nano-lamellar structure of the parent material (PM) was retained but was observed to fragment into equiaxed grains during the second pass. FSW has been modeled as a severe deformation process in which the material is subjected to an instantaneous high shear strain rate followed by extreme shear strains. The loss of the nano-lamellar layers was attributed to the increased strain and longer time at temperature resulting from the second pass of the FSW process. Kinematic modeling was used to predict the global average shear strain and shear strain rates experienced by the ARB material during the FSW process. The results of this study indicate that through careful selection of FSW parameters, the nano-lamellar structure and its associated higher strength can be maintained using FSW to join ARB NLC panels.

In situ neutron diffraction measurements were completed during tensile and compressive deformation of stainless steel 304L additively manufactured (AM) using a high power directed energy deposition process. Traditionally produced wrought 304L material was also studied for comparison. The AM material exhibited roughly 200 MPa higher flow stress relative to the wrought material. Crystallite size, crystallographic texture, dislocation density, and lattice strains were all characterized to understand the differences in the macroscopic mechanical behavior. The AM material’s initial dislocation density was about 10 times that of the wrought material, and the flow strength of both materials obeyed the Taylor equation, indicating that the AM material’s increased yield strength was primarily due to greater dislocation density. Also, a ~50 MPa flow strength tension/compression asymmetry was observed in the AM material, and several potential causes were examined.

For additive manufacturing (AM) of metallic materials, the certification and qualification paradigm needs to evolve as there is currently no broadly accepted “ASTM- or DIN-type” additive manufacturing certification process or AM-produced material specifications. Accordingly, design, manufacture, and subsequent implementation and insertion of AM materials to meet engineering applications requires detailed quantification of the constitutive (strength and damage) properties of these evolving materials, across the spectrum of metallic AM methods, in comparison/contrast to conventionally-manufactured metals and alloys. For this study, cylindrical samples of 316L SS were produced using a LENS MR-7 laser additive manufacturing system from Optomec (Albuquerque, NM) equipped with a 1 kW Yb-fiber laser. The microstructure of the AM-316L SS was characterized in both the “as-built” AM state and following a heat-treatment designed to obtain full recrystallization to facilitate comparison with annealed wrought 316L SS. The constitutive behavior as a function of strain rate and temperature was characterized and is compared to that of annealed wrought 316L SS plate material. The dynamic shock-loading-induced damage evolution and failure response of all three 316L SS materials was quantified using flyer-plate impact driven spallation experiments at peak stresses of 4.7 and 6.5 GPa. The spall strength of AM-produced 316L SS and the recrystallized-AM-316L SS were found to decrease with increasing peak shock stress while the annealed wrought 316L SS spall strength remained essentially constant. The damage evolution, characterized using optical metallography and electron-backscatter diffraction (EBSD), was found to vary significantly across the three 316L SS microstructures while the three samples loaded to a peak shock stress of 6.5 GPa displayed only ∼12% differences in spall strength.

In-situ neutron diffraction measurements were performed during heat-treating and uniaxial loading of additively manufactured (AM) GP1 material. Although the measured chemical composition of the GP1 powder falls within the composition specifications of 17-4 PH steel, a fully martensitic alloy in the wrought condition, the crystal structure of the as-built GP1 material is fully austenitic. Chemical analysis of the as-built material shows high oxygen and nitrogen content, which then significantly decreased after heat-treating in a vacuum furnace at 650 °C for one hour. Significant austenite-to-martensite phase transformation is observed during compressive and tensile loading of the as-built and heat-treated material with accompanied strengthening as martensite volume fraction increases. During loading, the initial average phase stress state in the martensite is hydrostatic compression independent of the loading direction. Preferred orientation transformation in austenite and applied load accommodation by variant selection in martensite are observed via measurements of the texture development.

In order for metallic additive manufacturing (AM) to find application in industrial production environments, methods for quality control need to be developed. Presently, even precisely calibrated process parameters cannot prevent the stochastic occurrence of defects resulting from elements in the AM process which are difficult to control. This study utilizes low framerate (10 Hz) pyrometry to record in situ temperature measurements of the molten pool and surrounding substrate in LENSTM AM. The data is statistically analyzed in search of anomalous behavior which is compared to the actual population of voids and inclusions found using X-ray Computed Tomography. This statistical analysis technique was able to identify volumetric defects as small as 40 μm in diameter as well as inclusions such as powder contamination. This study shows that the thermal analysis parameters can be tuned specifically for detecting different anomalies in the build.

This work presents the effects of input processing parameters and strut thickness (in square struts) on microstructure and properties in laser powder bed fusion additively manufactured stainless steel 316L lattice-emulating structures. Lattice-emulating X-structures with square cross-sections of 1.5, 1.0, and 0.5 mm were fabricated using three different parameter sets with varying power, speed, and therefore, linear energy density. Grain size and morphology were shown to be dictated by epitaxial growth, which was dependent on weld pool morphology. Additionally, grain size and morphology were shown to change across the thickness direction of the struts (from the bottom inclined surface to the top inclined surface). The spatial variation in grain size was reflected by changes in hardness through the thickness of each strut. The 0.5 mm struts exhibited more significant grain elongation in the strut direction and larger sub-grain solidification cell diameters than their thicker counterparts. The larger sub-grain solidification cell diameters in the 0.5 mm samples resulted in correspondingly lower hardness values when compared to samples of higher thicknesses.

Charpy test specimens were additively manufactured (AM) on a single stainless steel plate from a 17–4 class stainless steel using a powder-bed, laser melting technique on an EOS M280 direct metal laser sintering (DMLS) machine. Cross-hatched mesh support structures for the Charpy test specimens were varied in strut width and density to parametrically study their influence on the build stability and accuracy as the DMLS process has been known to generate parts with large amounts of residual stress. Neutron diffraction was used to profile the residual stresses in several of the AM samples before and after the samples were removed from the support structure for the purpose of determining residual stresses. The residual stresses were found to depend very little on the properties of the support structure over the limited range studied here. The largest stress component was in the long direction of each of the samples studied and was roughly 2/3 of the yield stress of the material. The stress field was altered considerably when the specimen was removed from the support structure. It was noted in this study that a single Charpy specimen developed a significant tear between the growth plate and support structure. The presence of the tear in the support structure strongly affected the observed stress field: the asymmetric tear resulted in a significantly asymmetric stress field that propagated through removal of the sample from the base plate. The altered final residual stress state of the sample as well as its observed final shape indicates that the tear initiated during the build and developed without disrupting the fabrication process, suggesting a need for in-situ monitoring.

The ability of additive manufacturing to directly fabricate complex shapes provides characterization challenges for part qualification. The orientation of the microstructures produced by these processes will change relative to the surface normal of a complex part. In this work, the microscopy and x-ray tomography of an AlSi10Mg alloy hemispherical shell fabricated using powder bed metal additive manufacturing are used to illustrate some of these challenges. The shell was manufactured using an EOS M280 system in combination with EOS-specified powder and process parameters. The layer-by-layer process of building the shell with the powder bed additive manufacturing approach results in a position-dependent microstructure that continuously changes its orientation relative to the shell surface normal. X-ray tomography was utilized to examine the position-dependent size and distribution of porosity and surface roughness in the 98.6% dense part. Optical and electron microscopy were used to identify global and local position-dependent structures, grain morphologies, chemistry, and precipitate sizes and distributions. The rapid solidification processes within the fusion zone (FZ) after the laser transit results in a small dendrite size. Cell spacings taken from the structure in the middle of the FZ were used with published relationships to estimate a cooling rate of ~9 × 105 K/s. Uniformly-distributed, nanoscale Si precipitates were found within the primary α-Al grains. A thin, distinct boundary layer containing larger α-Al grains and extended regions of the nanocrystalline divorced eutectic material surrounds the FZ. Subtle differences in the composition between the latter layer and the interior of the FZ were noted with scanning transmission electron microscopy (STEM) spectral imaging.

This study utilizes in situ thermal imaging to monitor the melt pool during a LENS additive manufacturing (AM) process. A software tool is created which gathers metrics for each frame and summarizes them over every build. Plotted metrics allow a user to visually inspect the data, but the software tool also automatically identifies anomalies and flags them for further review. Anomalies are then correlated to physical locations in the build which are inspected for defects. This type of process monitoring could lead to fast detection of defects during a build, thus increasing the confidence in production quality and eliminating the acceptance of parts with abnormalities. An anomalous event was identified by the software tool and investigated with X-ray computed tomography. Defects were observed in the location identified by the software tool.

We examine recrystallization and grain growth during processing of accumulative roll-bonded (ARB) Cu-Nb and Zr-Nb composites. Throughout the ARB process, from initial millimeter thick layers down to nanometer thick layers, the mechanism for recrystallization and grain growth is the motion of high-angle grain boundaries (HAGBs). However, the driving forces for these phenomena change as the densities of different types of defects evolve during the process. The creation and redistribution of dislocations, grain boundaries, and phase boundaries has significant effects on recrystallization and grain growth and, thus, on microstructural evolution. Both Cu-Nb and Zr-Nb exhibit a distinct transition in recrystallization and growth behavior at around 500-nm average layer thicknesses. For the thicker layered materials, the microstructure evolution during recrystallization and growth is determined by the density and distribution of dislocations and HAGBs. For layers less than 500 nm, the layers are largely one-grain thick and the grains are nearly dislocation free; coarsening of grains within layers at the nanoscale is due to reduction in phase boundary energy.

This work presents a new method to determine the flow strengths of the constituents in nanolayered composites, by coupling finite element simulations of nanoindentation with experimental hardness and micropillar compression data. This enhances the capability of separate nanoindentation and micropillar compression tests, which provide only bulk values of flow strength. This expanded capability is critical to understanding how interfaces mediate dislocation nucleation and propagation in each phase. The new method is validated using in-situ diffraction studies of deforming Cu/Ni nanolayered composites with [0 0 1] interfaces. Here, 20 nm thick Ni layers are shown to have ∼3 times the flow strength of neighboring 20 nm Cu layers. These flow strengths are comparable to those for pure electrodeposited nanocrystalline (d = 20 nm) Cu and Ni, respectively. A Tabor factor of 2.7—often assumed in the literature—may be inappropriate if the ratio of constituent flow strengths is large (>1.5:1).

It was recently demonstrated that bulk two-phase 50/50 Zr–Nb nanolayered composites with 90 nm individual layers can be fabricated from an initial coarse-layered composite with 1 mm layers via the severe plastic deformation process of accumulative roll bonding. During the deformation, the Zr phase retained its hcp crystal structure and the Zr–Nb interface remained sharp. Here we use a combination of neutron diffraction and dislocation-based polycrystal plasticity constitutive modeling to assess the evolution of texture and deformation mechanisms over a four order-of-magnitude range in layer thickness. The phase textures in the nanocomposite strongly deviate from that of Zr or Nb rolled in monolithic form, becoming highly peaked and intense. The model suggests that texture development in the Nb phase is associated with multiple slip and contributions from both {1 1 2}〈1 1 0〉 slip and {1 1 0}〈1 1 0〉 slip. In the Zr phase the model suggests that the texture develops due to a predominance of prismatic 〈a〉 and basal 〈a〉 slip.

International audience; It was recently shown that the crystals in an already nanocrystalline alloy (Pd-10% Au) became highly oriented under extreme shearing. No such self-ordering is seen in the coarse-grained counterpart under the same conditions. Here we use phase field dislocation dynamics and polycrystalline plasticity modeling to explore the possible causes that enabled this unusual crystallographic alignment. The results suggest that full-dislocation slip and preservation of grain boundary misorientation with at least one neighbor grain can cause the highly oriented texture observed experimentally.

The problem of calculating the inverse pole figure (IPF) is analyzed from the perspective of the application of time-of flight neutron diffraction toin situmonitoring of the thermomechanical behavior of engineering materials. On the basis of a quasi-Monte Carlo (QMC) method, a consistent set of grain orientations is generated and used to compute the weighting factors for IPF normalization. The weighting factors are instrument dependent and were calculated for the engineering materials diffractometer VULCAN (Spallation Neutron Source, Oak Ridge National Laboratory). The QMC method is applied to face-centered cubic structures and can be easily extended to other crystallographic symmetries. Examples include 316LN stainless steelin situloaded in tension at room temperature and an Al–2%Mg alloy, substantially deformed by cold rolling andin situannealed up to 653 K.

Strain localization is a common deformation-induced instability in many metallic metals. How it happens is related to both microstructure and the way in which plasticity is mediated prior to localization. Both aspects can fundamentally change in a face-centered cubic metal when it becomes nanostructured; the propensity for deformation twinning increases and the behavior is dominated by dislocation–interface interactions. Here we carry out a transmission electron microscopy investigation to elucidate the collaborative role of deformation twinning and dislocation transmission on the onset of strain localization in nanolayered composites. Two material systems are examined, Cu–Ag and Cu–Nb, and for each system, two interface structures are examined, one prone to dislocation transmission and the other not. We show that dislocation transmission favors crystallographic band formation, whereas dislocations that do not transmit cause interface tilting and are associated with (non-crystallographic) shear band formation.

Severe plastic deformation (SPD) is a common method to fabricate nano-grained metals. However for Zr, a structural metal for nuclear applications, obtaining a nanoscale grain structure via SPD has ...

Advantages of neutron diffraction for metallurgical studies are highlighted with research examples performed on the High Pressure - Preferred Orientation diffractometer at the Los Alamos Neutron Science Center. The previously inconclusive crystallographic structure of the Fe–Al ϵ-phase, stable between 1095 and 1231°C, was determined by in situ neutron diffraction to have the formula Fe5Al8 with a body centred cubic structure of the Hume–Rothery Cu5Zn8 type at 1120°C. As a second example, the effect of variations in accumulative roll bonding processing parameters on interfacial structure, hardness, and thermal stability are explored for lamellar Cu–Nb multilayers with individual layer thicknesses of 20 nm. Furthermore, we derive an explanation for observed texture memory effects during the α→γ→α transformation cycle in a 0·1%C–1%Mn hot rolled steel sheet from the double Kurdjumov–Sachs relationship. Finally, we present in situ results of a Zr–2·5Nb sample heated into the β-field and subsequently co...

Cu-Nb nanolayered material was produced through an accumulative roll bonding (ARB) technique. Using this technique, two different rolling schedules were employed to produce a normal and transverse rolled material. This resulted in specimens with differing microstructures within the 135nm thick nanolayers and interface structures between the layers. The dynamic response of these bulk Cu-Nb nanocomposites was then investigated under planar shock loading. It was observed in dynamically fractured specimens that the characteristics of ductile failure features formed on the fracture surface after dynamic loading were dependent upon the processing route of the nanocomposite. Specifically, grain shape differences due to dissimilar rolling passes are linked with differences in the failure response, particularly kinetics of fracture. In addition, incipient failure immediately below the primary fracture surface was also observed. Numerous nanovoids were nucleated and aligned linearly in the middle of Cu layers within the shocked Cu-Nb nanocomposites. These observations indicate relative stability of Cu-Nb interfaces produced by the ARB methods utilized in this study under dynamic loading conditions.

Large strain deformation is used to make fine nanolayered two-phase composites from stacks of conventional polycrystalline sheets. The final materials made by this technique possess a crystallographically highly oriented structure containing nearly atomically perfect interfaces prevailing ubiquitously throughout the material. How this ordered structure evolves with strain from the coarser, more disordered state is not known. Here, using microstructural analysis and computational modeling, we discover a local interface-affected zone (IAZ) possessing the same crystallographically sharp structure in coarse layered composites as the final nanolayered composites. This means that this strongly oriented interface “zone” survives the mechanical work and overtakes the structure as it refines to the nanoscale. In essence, through the formation of this interface zone, the crossover to a highly oriented nanostructure occurs. Using microstructural analysis and crystal plasticity simulations, we show that the IAZ is a consequence of slip accommodation at the interface. This insight is valuable for developing processing strategies for superior interface-dominated materials.

In this work, we examine the microstructural development of a bimetal multilayered composite over a broad range of individual layer thicknesses h from microns to nanometers during deformation. We observe two microstructural transitions, one at the submicron scale and another at the nanoscale. Remarkably, each transition is associated with the development of a preferred interface character. We show that the characteristics of these prevailing interfaces are strongly influenced by whether the adjoining crystals are deforming by slip only or by slip and twinning. We present a generalized theory that suggests that, in spite of their different origins, the crystallographic stability of their interface character with respect to deformation depends on the same few basic variables.

Initial efforts to friction-stir weld (FSW) Cu–Nb nanolamellar composite plates fabricated via accumulative roll bonding are reported in this study. Parent material layers within the composite were nominally 300 nm and exhibited a hardness of 2.5 GPa. After FSW, two types of microstructures were present: a refined layered structure, and an equiaxed nanocrystalline microstructure with grain diameters on the order of 7 nm. The type of microstructure was dependent on location within the FSW nugget and related to varying amounts of strain. Material hardness increased with refinement, with the equiaxed microstructure reaching a maximum hardness of 6.0 GPa.

A transmission-electron-microscope-based orientation mapping technique that makes use of beam precession to achieve near-kinematical conditions was used to map the phase and crystal orientations in nanolamellar Cu/Nb composites with average layer thicknesses of 86, 30 and 18 nm. Maps of high quality and reliability were obtained by comparing the recorded diffraction patterns with pre-calculated templates. Particular care was taken in optimizing the dewarping parameters and in calibrating the frames of reference. Layers with thicknesses as low as 4 nm were successfully mapped. Heterophase interface plane and character distributions (HIPD and HICD, respectively) of Cu and Nb phases from the samples were determined from the orientation maps. In addition, local orientation relation stereograms of the Cu/Nb interfaces were calculated, and these revealed the detailed layer-to-layer texture information. The results are in agreement with previously reported neutron-diffraction-based and precession-electron-diffraction-based measurements on an accumulated roll bonding (ARB)-fabricated Cu/Nb sample with an average layer thickness of 30 nm as well as scanning-electron-microscope-based electron backscattered diffraction HIPD/HICD plots of ARB-fabricated Cu/Nb samples with layer thicknesses between 200 and 600 nm.

A combination of accumulative roll bonding and rolling is used to fabricate bulk sheets of multilayer Cu-Nb bimetallic composites. Alterations in the processing sequence are made in comparison with prior studies in order to expand the processing window available for bimetallic multilayer composites. Cu-Nb composites with layer thicknesses ranging from 45 μm to 10 nm with accompanying total strains of 3.8 to 12.21 are characterized via neutron diffraction, electron back scatter diffraction, and transmission electron microscopy. These characterization methods provide microstructural information such as layer morphology and grain morphology as well as orientation information such as texture and interface plane normal distribution. The evolution of these microstructural characteristics is collected as a function of increasing strain. These results can provide guidance, inputs, and validation for multiscale predictive models that are being developed on materials with interfacially-driven properties. Finally, synthesis pathways are presented that allow the fabrication of nanoscale multilayer composites with predominant interfacial structures. These fabricated materials are ideal for exploring the relative importance between inter-phase interfacial density and atomic interfacial structure in determining material properties.

The deformation and failure of bulk Cu–Nb nanocomposites with a nominal layer thickness of 135 nm was investigated under planar shock loading. It was observed that little substructural evolution was evident after shock compression to a peak stress of 7 GPa, while specimens were fully spalled after loading to 7 GPa under free surface conditions. In these fully spalled specimens, the characteristics of ductile failure that formed on the fracture surface were dependent upon the processing route of the nanocomposite. Specifically, process-induced grain-shape differences due to dissimilar rolling passes are linked with differences in the failure response. In addition, incipient failure was also observed. Numerous nanovoids, 20 nm or less in size, nucleated and aligned in a row in the middle of Cu layers. Due to the reflection of the shock wave at the Cu–Nb interfaces, incipient voids tend to nucleate within the Cu phase, which has a higher impedance and lower spall strength than Nb. This occurs rather than nucleation along the Cu–Nb interfaces or in the Nb phase. This finding contradicts the general thinking of failure starting from interfaces, and indicates that the Cu–Nb interfaces are stable under dynamic loading. It is postulated that numerous voids nucleate in the Cu layers under shock loading, then lead to failure through their growth and coalescence.

The deformation behavior of a wrought, cobalt-based superalloy, Haynes 25, was studied using a combination of experimental techniques and crystal plasticity modeling. The microstructure was examined by transmission electron microscopy and electron backscattered diffraction to determine the deformation and hardening mechanisms contributing to the mechanical behavior of the alloy. A high density of stacking faults within the grains, consistent with planar glide, was found to be the predominant defect mechanism with no evidence of deformation twinning observed. A strain-rate and temperature-sensitive hardening law that includes effects of planar glide was developed for the material and implemented in a self-consistent homogenization scheme. The hardening of individual crystals is based on the evolution of dislocation densities per plane and includes the effects of strain rate and temperature through thermally activated recovery and dislocation interactions. The model is validated on a comprehensive set of compression tests performed at temperatures ranging from 298 to 673 K and strain rates ranging from 10 −3 to 2600 s −1 and found capable of reproducing the stress–strain response and texture for all tests with a unique set of single-crystal hardening parameters.