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The microstructure of additively manufactured Ti-6Al-4V (Ti64) produced by a laser powder bed fusion process was studied during post-build heat treatments between 1043 K (770 °C) and just above the β transus temperature 1241 K (1008 °C) in situ using high-energy X-ray diffraction. Parallel studies on traditionally manufactured wrought and annealed Ti64 were completed as a baseline comparison. The initial and final grain structures were characterized using electron backscatter diffraction. Likewise, the initial texture, dislocation density, and final texture were determined with X-ray diffraction. The evolution of the microstructure, including the phase evolution, internal stress, qualitative dislocation density, and vanadium distribution between the constituent phases were monitored with in situ X-ray diffraction. The as-built powder bed fusion material was single-phase hexagonal close packed (to the measurement resolution) with a fine acicular grain structure and exhibited a high dislocation density and intergranular residual stress. Recovery of the high dislocation density and annealing of the internal stress were observed to initiate concurrently at a relatively low temperature of 770 K (497 °C). Transformation to the β phase initiated at roughly 913 K (640 °C), after recovery had occurred. These results are meant to be used to design post-build heat treatments resulting in specified microstructures and properties.

The evolution of the crystallographic texture and lattice strain of uranium 6-weight percent niobium alloy samples are tracked during multiple deformation and heat treating cycles in an effort to understand and control the mechanical properties of the material following thermo-mechanical processing. The heavily twinned microstructure and low-symmetry crystal structure of U-6Nb result in multiple sequential active deformation mechanisms associated with distinctive deformation textures in strain ranges from 0-0.15 true strain. It is found that heating into the high-temperature γ-phase erases much of the texture formed during deformation at room temperature in the α′′-phase and resets the active deformation mechanisms. Through a small number of deformation/heat treat cycles to moderate strains, i.e., ~ 0.13 per cycle, the flow strength of the material is recovered to its original value. However, on the fourth such cycle, a reduction of strength is observed and the sample failed.

Steels are ubiquitous due to their affordability and the landscape of useful properties that can be generated for engineering applications. But to further expand the performance envelope, one must be able to understand and control microstructure development by alloying and processing. Here we use multiscale, advanced characterization to better understand the structural and chemical evolution of AISI 4340 steel after quenching and tempering (Q&T), including the role of quench rate and short-time, isothermal tempering below 573 K (300 °C), with an emphasis on carbide formation. We compare the microstructure and/or property changes produced by conventional tempering to those produced by higher temperature, short-time “rapid” tempering. We underscore that no single characterization technique can fully capture the subtle microstructure changes like carbon redistribution, transition carbide and/or cementite formation, and retained austenite decomposition that occur during Q&T. Only the use of multiple techniques begins to unravel these complexities. After controlled fast or slow quenching, η transition carbides clearly exist in the microstructure, likely associated with autotempering of this high martensite start temperature (Ms) steel. Isothermal tempering below 598 K (325 °C) results in the relief of carbon supersaturation in the martensite, primarily by the formation of η transition carbides that exhibit a range of carbon levels, seemingly without substitutional element partitioning between the carbide and matrix phases. Hagg transition carbide is present between 300 °C and 325 °C. After conventional tempering at or above 598 K (325 °C) for 2 h, cementite is predominant, but small amounts of cementite are also present in other conditions, even after quenching. Previous work has indicated that silicon (Si) and substitutional elements partition between the cementite, which initially forms under paraequilibrium conditions, and the matrix. Phosphorous (P) may also be preferentially located at cementite/matrix interfaces after high temperature tempering. Slower quench rates result in greater amounts of retained austenite compared to those after fast quenching, which we attribute to increased austenite stability resulting from “autopartitioning”. Rapid, high temperature tempering is also found to diminish tempered martensite embrittlement (TME) believed to be associated with the extent of austenite decomposition, resulting in mechanical properties not attainable by conventional tempering, which may have important implications with respect to industrial heat treatment processes like induction tempering. Controlling the amount and stability of retained austenite is not only relevant to the properties of Q&T steels, but also next-generation advanced high strength steels (AHSS) with austenite/martensite mixtures.

Uranium-6 wt pct niobium (14 at pct niobium) displays the shape memory effect (SME), where deformation proceeds by twinning and twin rearrangement via boundary migration within the SME regime. In-situ neutron diffraction during deformation suggests that after SME strain is exhausted, deformation proceeds via another twinning mechanism that does not recover to the original parent orientation upon reheating and transformation. Here we show from in-situ tensile and compressive loading and unloading experiments that early post-SME twins partially reverse during unloading, which is evident by rapid texture evolution, and this reversion is responsible for the inelastic portion of the previously reported ~ 2 pct strain recovery.

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.

One of the primary barriers for adoption of additive manufacturing (AM) has been the uncertainty in the performance of AM parts due to residual stresses/strains. The rapid heating and cooling rates from the thermal history of the laser melting process result in high residual stresses/strains that produce significant part distortion. Efforts to mitigate residual stresses using post-process heat treatments can significantly impact the microstructures of the AM part which may lead to further issues. Therefore, the ability to accurately predict the residual stresses in as-built AM parts is crucial, and rigorous benchmark measurements are needed to validate such predictions. To fill this need, the AM-Bench aims to provide high-fidelity residual stress and strain benchmark measurements in well-characterized AM bridge-shaped parts. The measurements reported here are part of the residual elastic strain benchmark challenge CHAL-AMB2018-01-RS. Residual strains and stresses in this work were measured using neutron diffraction, synchrotron X-ray diffraction, and the contour method. Part deflection measurements were performed using a coordinate measurement machine after the part was partially separated from the build plate. These independently measured results show a high degree of agreement between the different techniques.

An experimental platform for multiscale studies of materials subjected to plane stress loads is presented. Coupling with far-field high-energy diffraction microscopy for grain-by-grain measurements of elastic strains and rotations provides an additional benefit; it enables the direct assessment of elastic vs. inelastic deformation of the gauge sections of cruciform specimens subjected to plane stress loadings, without any a priori assumptions of the form of constitutive relationships, resolving a long-outstanding challenge of multiaxial mechanical testing. Specifically, a planar biaxial mechanical load frame with four independent hydraulic actuators capable of applying arbitrary loading paths and ratios of tension and compression was designed and built for in situ diffraction experimentation. The load frame is integrated for use at the Argonne National Laboratory Advanced Photon Source (APS) synchrotron, Sector 1, 1-ID-E endstation and the Los Alamos Neutron Science Center (LANSCE) spallation neutron source, Spectrometer for Materials Research at Temperature and Stress (SMARTS) instrument. Cruciform specimen geometries were designed to experience loading ratios in the gauges commensurate with those applied at the grips, and to minimize interference with diffracted X-rays and neutrons. The finite element models used to design the cruciform specimen geometries were experimentally validated using stereo digital image correlation measurements. This complete planar biaxial in situ diffraction platform provides a new capability for studying multiaxial micromechanics of crystalline materials (e.g., elastic, slip, twinning, phase transformation) and their dependencies on grain size, location, texture, and neighborhood characteristics.

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 time-resolved synchrotron X-ray diffraction experiments were conducted to study the fine-scale phase evolution of U-6Nb. Upon rapid heating from 125 °C to 400 °C, a reverse martensitic transformation sequence, α″ → γo → γs, was observed in less than 4 seconds, which represents the first direct observation of the γo → γs transformation in diffraction-based measurements. Consistent with previous ex situ metallography experiments, our isothermal hold experiments at 526 °C, 530 °C and 565 °C reveal two distinct reactions for the phase separation, γs → α-U + γ1 (general precipitation) followed by (α-U + γ1) → α-U + γ1-2 (discontinuous precipitation). For the first-stage precipitation, the incubation time is determined to be ~ 50 and 100 seconds, respectively, for the isothermal aging at 526-530 °C and 565 °C. At this stage, the phase transformation is characterized by the simultaneous growth of α-U and γ1 at the expense of γs. As expected from the Arrhenius equation for the reaction rate, the determined times (~ 23 minutes) for the completion of the first-stage reaction at 526 ± 3 °C and 530 ± 3 °C are nearly twice longer than that at 565 ± 4 °C (~ 13 minutes). Over these periods of time, the Nb contents derived from a Vegard’s-type relationship for γ1 are in the 30.2 to 32.1 and 29.2 to 30.6 at. pct ranges, and the kinetics of the precipitation at 565 ± 4 °C can be described by the classic Avrami rate equation and one-dimensional growth of a surface or grain-boundary nucleation. During the second-stage precipitation, the γ1 phase continues to enrich in Nb as it gradually evolves toward the α + γ1-2 metastable state (up to 47 at. pct over a period of 172 minutes at 530 °C). These new and time-resolved measurements can be used to better constrain the time–temperature–transformation diagram, solute (Nb) redistribution, and transformation kinetics during the early stages of the diffusional phase transformation.

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.

We present a comprehensive study of the effects of internal boundaries on the accuracy of residual stress values obtained from the eigenstrain method. In the experimental part of this effort, a composite specimen, consisting of an aluminum cylinder sandwiched between steel cylinders of the same diameter, was uniformly heated under axial displacement constraint. During the experiment, the sample temperature and the reaction stresses in the load frame in response to changes in sample temperature were monitored. In addition, the local (elastic) lattice strain distribution within the specimen was measured using neutron diffraction. The eigenstrain method, utilizing finite element modeling, was then used to predict the stress field existing within the sample in response to the constraint imposed by the load frame against axial thermal expansion. Our comparison of the computed and measured stress distributions showed that, while the eigenstrain method predicted acceptable stress values away from the cylinder interfaces, its predictions did not match experimentally measured values near them. These observations indicate that the eigenstrain method is not valid for sample geometries with this type of internal boundaries.

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.

Additive manufacturing (AM) technology provides unique opportunities for producing net-shape geometries at the macroscale through microscale processing. This level of control presents inherent trade-offs necessitating the establishment of quality controls aimed at minimizing undesirable properties, such as porosity and residual stresses. Here, we perform a parametric study into the effects of laser scanning pattern, power, speed, and build direction in powder bed fusion AM on residual stress. In an effort to better understand the factors influencing macroscale residual stresses, a destructive surface residual stress measurement technique (digital image correlation in conjunction with build plate removal and sectioning) has been coupled with a nondestructive volumetric evaluation method (i.e., neutron diffraction). Good agreement between the two measurement techniques is observed. Furthermore, a reduction in residual stress is obtained by decreasing scan island size, increasing island to wall rotation to 45 deg, and increasing applied energy per unit length (laser power/speed). Neutron diffraction measurements reveal that, while in-plane residual stresses are affected by scan island rotation, axial residual stresses are unchanged. We attribute this in-plane behavior to misalignment between the greatest thermal stresses (scan direction) and largest part dimension.

The present paper focuses on the development of a fully implicit, incrementally objective integration algorithm for a hypoelastic formulation of $$J_{2}$$ -viscoplasticity, which employs the mechanical threshold strength model to compute the material’s flow stress, taking into account its dependence on strain rate and temperature. Heat generation due to high-rate viscoplastic deformation is accounted for, assuming adiabatic conditions. The implementation of the algorithm is discussed, and its performance is assessed in the contexts of implicit and explicit dynamic finite element analysis, with the aid of example problems involving a wide range of loading rates. Computational results are compared to experimental data, showing very good agreement.

The recovery of deformed beryllium was studied with mechanical testing and in situ neutron diffraction measurements. The initial texture of the material and the deformation rate were manipulated to produce four distinct deformation microstructures. The dislocation density was determined from line profile analysis of the neutron diffraction data collected as a function of temperature during annealing to a maximum homologous temperature of 0.53 following deformation. Mechanical testing was completed after the in situ annealing to determine the extent of the recovery of the flow stress. Both the dislocation density and flow stress recovered significantly by a relatively low homologous temperature of 0.3. A comparison with model calculations using a dislocation-based hardening law indicates that it is forest-type dislocations that annihilate during the relatively low temperature anneal; the dislocation substructure was stable at these temperatures. Finally, the motion of the dislocations during annealing prevented the development of intergranular thermal stresses due to the crystallographically anisotropic thermal expansion of beryllium.

We report results from neutron diffraction experiments where partitioning of applied tensile load between the inner and outer wires of seven-wire parallel and quasi-parallel wire strands were measured while 1-all wires were undergoing elastic deformation, 2-where one wire within the bundle was undergoing plastic flow and, 3-when one or more wires fractured under load. The results indicate that mechanical interference and friction mechanisms have similar contributions to the load transferred to fractured wires, and both mechanisms should be included in analytical or numerical formulations of strain partitioning in quasi-parallel wire cables.

Time-of-flight neutron diffraction is widely used in characterizing the microstructure and mechanical response of heterogeneous systems. Microstructural characterization techniques include spatial or temporal mapping of the phases and determination of grain size, dislocation structure, and grain orientations (texture) within these phases. Mechanical response analysis utilizes the crystallographic selectivity of the diffraction process to measure the partitioning of strain within the system. The microstructural and mechanical response information is then used to develop more realistic constitutive models. In this article we review some examples of such measurements, based on our experiences at the Lujan Center of Los Alamos National Laboratory.

Elastic residual strains were measured in a laser welded commercially pure titanium ring using a non-destructive neutron diffraction technique in order to determine the resolution of this method for the characterization of small laser welds. In addition, these measurements were used to validate calculations made using residual strain data obtained from simulation of the residual stress near the weld. The measured strains were in good agreement with the simulated results.

The large strain deformation of polycrystalline uranium 6 wt pct niobium (U6Nb) was studied in situ during uniaxial tensile and compressive loading by time-of-flight neutron diffraction. Diffraction patterns were recorded at incremental strains to a maximum of approximately 0.13 tensile and 0.15 compressive true strain. A discrete reorientation of the crystallographic texture under tensile straining between 0.04 and 0.08 true strain is consistent with a previously unobserved mechanical deformation twinning mechanism, identified as either a (100) or (010) mechanical twin system. Beyond this, a continuous texture reorientation towards an (010) crystal orientations indicates that a slip mechanism is likely predominant. An analogous mechanical twin system was not observed in compression at large strain.

Precipitate strengthening effects toward the improved creep behavior have been investigated in a ferritic superalloy with B2-type (Ni,Fe)Al precipitates. In situ neutron diffraction has been employed to study the evolution of the average phase strains, (hkl) plane-specific lattice strains, interphase lattice misfit, and grain-orientation texture during creep deformation of the ferritic superalloy at 973 K (700 °C). The creep mechanisms and particle-dislocation interactions have been studied from the macroscopic creep behavior. At a low stress level of 107 MPa, the dislocation-climb-controlled power-law creep is dominant in the matrix phase, and the load partition between the matrix and the precipitate phases remains constant. However, intergranular stresses develop progressively during the primary creep regime with the load transferred to 200 and 310 oriented grains along the axial loading direction. At a high stress level of 150 MPa, deformation is governed by the thermally activated dislocation glide (power-law breakdown) accompanied by the accelerated texture evolution. Furthermore, an increase in stress level also leads to load transfer from the plastically deformed matrix to the elastically deformed precipitates in the axial direction, along with an increase in the lattice misfit between the matrix and the precipitate phases.

The damping behavior of a model ferroelastic-reinforced–metal matrix composite (FR-MMC) system was examined through the incorporation of barium titanate (BaTiO3) particles into a Cu-10 wt pct Sn (bearing bronze) matrix. The damping properties of the resulting FR-MMC were investigated vs frequency, temperature (above and below the Curie temperature of the ferroelastic reinforcement), and number of strain cycles. Dynamic mechanical analysis (DMA) indicates that the incorporation of the ferroelastic-capable reinforcement significantly augments the damping capability relative to the matrix alone, and also with respect to the damping that would result from the presence of passive composite reinforcements. Neutron diffraction data demonstrate a strong correlation of domain reorientation activity to imposed stress level and demonstrate a degree of reversibility important to the potential practical application of this mechanism of damping.

The hydride-phase formation and its influence on the fatigue behavior of a Zircaloy-4 alloy charged with hydrogen gas are investigated. First, the microstructure and fatigue crack propagation rate of the alloy in the as-received condition are studied. Second, the formation and homogeneous distribution of the delta zirconium hydride in the bulk and its effect on the fatigue crack propagation rate are presented. The results show that in the presence of hydrides, the zirconium alloy exhibits reduced toughness and enhanced crack growth rates. Finally, the influence of a preexisting fatigue crack in the specimen and the subsequent hydride formation are examined. The residual lattice strain profile around the fatigue crack tip is measured using neutron diffraction. It is observed that the combined effects of residual strains and hydride precipitation on the fatigue behavior are more severe leading to propagation of the crack under near threshold loading.

Twinning is an important deformation mode in hexagonal metals to accommodate deformation along the c-axis. It differs from slip in that it accommodates shear by means of crystallographic reorientation of domains within the grain. Such reorientation has been shown to be reversible (detwinning) in magnesium alloy aggregates. In this paper we perform in-situ neutron diffraction reversal experiments on high-purity Zr at room temperature and liquid nitrogen temperature, and follow the evolution of twin fraction. The experiments were motivated by previous studies done on clock-rolled Zr, subjected to deformation history changes (direction and temperature), in the quasi-static regime, for temperatures ranging from 76 K to 450 K. We demonstrate here for the first time that detwinning of $$\left\{ {10\overline 1 2} \right\}\left\langle {10\overline 1 \overline 1 } \right\rangle $$ tensile twins is favored over the activation of a different twin variant in grains of high-purity polycrystalline Zr. A visco-plastic self-consistent (VPSC) model developed previously, which includes combined slip and twin deformation, was used here to simulate the reversal behavior of the material and to interpret the experimental results in terms of slip and twinning activities.

For a duplex alloy being subjected to deformation, the different mechanical behaviors of its constituent phases may lead to a nonuniform partition of stresses between phases. In addition, the grain-orientation-dependent elastic/plastic anisotropy in each phase may cause grain-to-grain interactions, which further modify the microscopic load partitioning between phases. In the current work, neutron diffraction experiments on the spectrometer for materials research at temperature and stress (SMARTS) were performed on an austenite-ferrite stainless steel for tracing the evolution of various microstresses during tensile loading, with particular emphasis on the load sharing among grains with different crystallographic orientations. The anisotropic elastic/plastic properties of the duplex steel were simulated using a visco-plastic self-consistent (VPSC) model that can predict the phase stress and the grain-orientation-dependent stress. Material parameters used for describing the constitutive laws of each phase were determined from the measured lattice strain distributions for different diffraction {hkl} planes as well as the laboratorial macroscopic stress-strain curve of the duplex steel. The present investigations provide in-depth understanding of the anisotropic micromechanical behavior of the duplex steel during tensile deformation.

Lattice parameters for both hcp α-Sc and bcc β-Sc were determined between 1200 °C and 1400 °C from time-of-flight (TOF) neutron diffraction data collected from an elemental Sc sample vacuum sealed inside a niobium crucible. On heating, the high-temperature β-Sc phase first appeared between 1340 °C and 1350 °C, close to the reported transition temperature of 1337 °C. The lattice constants of hcp α-Sc were found to vary between a = 3.3522(4) A, c = 5.3807(7) A at 1200 °C and a = 3.3579(6) A, c = 5.398(1) A at 1340 °C. The lattice constants of bcc β-Sc were found to vary between a = 3.752(2) A at 1350 °C and a = 3.7572(8) A at 1400 °C. The average thermal expansion coefficient for the bcc β-Sc phase was 1.61 × 10−5 °C−1 over the temperature range 1360 °C to 1400 °C. The average thermal expansion coefficient along the a-axis of hcp α-Sc between 1200 °C and 1340 °C was 1.46 × 10−5 °C−1. The average thermal expansion coefficient along the c-axis of hcp α-Sc between 1200 °C and 1340 °C was 2.22 × 10−5 °C−1.

An in-situ neutron diffraction technique was used to investigate the lattice-strain distributions and plastic deformation around a crack tip after overload. The lattice-strain profiles around a crack tip were measured as a function of the applied load during the tensile loading cycles after overload. Dislocation densities calculated from the diffraction peak broadening were presented as a function of the distance from the crack tip. Furthermore, the crystallographic orientation variations were examined near a crack tip using polychromatic X-ray microdiffraction combined with differential aperture microscopy. Crystallographic tilts are considerably observed beneath the surface around a crack tip, and these are consistent with the high dislocation densities near the crack tip measured by neutron peak broadening.

Tensile tests and neutron diffraction measurements of the residual elastic strain response to applied uniaxial stress have been made on samples taken from a ZIRCALOY-4 (Zr-4) weld in the as-welded condition. The samples were taken from the parent plate, and the weld metal and time-of-flight neutron diffraction measurements were made parallel and perpendicular to the applied stress direction, which corresponds to the weld direction and the transverse direction in the plane of the plate. Measurements were made on all crystallographic reflections permitted by the texture, and this allowed strains to be measured over the entire of the stereographic projection. The strains can be understood qualitatively in terms of what is already known for other zirconium alloys and with the aid of the elasto-plastic self-consistent model.

Mechanical twinning in polycrystalline quartz was investigated in situ with time-of-flight neutron diffraction and a strain diffractometer. Dauphine twinning is highly temperature sensitive. It initiates at a macroscopic differential stress of 50–100 MPa and, at 500°C, saturates at 400 MPa. From normalized diffraction intensities the patterns of preferred orientation (or texture) can be inferred. They indicate a partial reversal of twinning during unloading. The remaining twins impose residual stresses corresponding to elastic strains of 300–400 microstrain. Progressive twinning on loading and reversal during unloading, as well as the temperature dependence, can be reproduced with finite element model simulations.

Strain measurements by neutron diffraction are employed as an in situ technique to obtain insight into the deformation modes of crystalline domains in a deformed semi-crystalline polymer. The SMARTS (Spectrometer for MAterials Research at Temperature and Stress) diffractometer has been used to measure the crystalline lattice displacements in polytetrafluoroethylene (PTFE) for crystalline phase IV (at room temperature) in tension and compression and for crystalline phase I (at 60°C) in compression. The chemical structure of PTFE, -(C2F4)-n, makes it ideally suited for investigation by neutron methods as it is free of hydrogen that results in limited penetration depths and poor diffraction acquisition in most polymers. Deformation parallel to the prismatic plane normals is shown to occur by inter-polymer chain compression with a modulus ∼10× bulk, while deformation parallel to the basal plane normal occurs by intra-polymer chain compression with a modulus ∼1000× bulk, corresponding with theoretical values for a PTFE chain modulus. Deformation parallel to the pyramidal plane normals is accommodated by inter-polymer chain shear.

Bulk metallic glasses (BMGs) are an emerging class of materials whose unique properties make them excellent choices for many applications. As with crystalline metals, the processing and forming techniques used to produce BMG components necessarily result in residual stresses. However, traditional diffraction stress analysis is difficult to apply to BMG components, because they lack the long-range order necessary to produce sharp diffraction patterns, and thus, the internal strains for BMG have not been examined until recently. In this work, in-situ neutron scattering was used to measure the local elastic internal strain distribution in a Zr57Nb5Cu15.4Ni12.6Al10 BMG as a function of applied stress. Various techniques were used to evaluate the internal strain. The strain was determined in real space, by measuring changes in the atomic pair distribution function (PDF). These results can be used to help understand the elastic deformation of BMGs as well be to evaluate current models of BMG deformation.

The in-situ strain response of WC-Ni cemented carbides (5, 10, and 20 wt pct Ni) to uniaxial compressive load was measured using neutron diffraction. Strain was measured in both phases parallel and transverse to the loading axis of cylindrical samples. Plasticity is observed in the Ni binder from the lowest levels of applied load. The plasticity occurs locally in the Ni phase, on the scale of the microstructure, and leads to continuous curvature of the WC-Ni stress-strain curves and significant toughness of the material. The plasticity results from the interaction of the thermal residual microstresses created during sample production with the applied macrostress. It also leads to anisotropic relaxation of the initial residual stress and the creation of a residual stress state with cylindrical symmetry in the material. This process was observed over three load-unload cycles. Analysis enables phase-specific stress strain curves to be constructed. Finally, strain distributions were observed through peak breadth responses.

The influence of the stirring pin and pressing tool shoulder on the microstructural softening during friction-stir processing (FSP) and subsequent natural aging behavior was investigated for a 6061-T6 aluminum alloy. The evolution of hardness profiles in various characteristic regions of the FSP plates was investigated as a function of time from 4 to 5760 hours after the FSP through the thickness of the plates and correlated to the microstructure and residual strain profiles measured by a neutron-diffraction technique. The results show that the microstructural softening and the natural aging observed in the dynamic recrystallized zone and thermomechanically affected zone are mainly caused by the frictional heating from the tool shoulder, resulting in dissolution and reprecipitation of strengthening precipitates. On the other hand, the softening in the heat-affected zone is due to the dissolution/growth of the precipitates and is not followed by the natural aging under the current processing condition. The kinetics of the natural aging behavior is also discussed.

We studied the phase-transition induced texture changes and strengthening mechanism for zirconium metal under quasi-hydrostatic compression and uni-axial deformation under confined high pressure using the deformation-DIA (D-DIA) apparatus. It is shown that the experimentally obtained texture for ω-phase Zr can be qualitatively described by combining a subset of orientation variants previously proposed in two different models. The determined flow stress for the high-pressure ω-phase is 0.5–1.2 GPa, more than three times higher than that of the α-phase. Using first-principles calculations, we investigated the mechanical and electronic properties of the two Zr polymorphs. We find that the observed strengthening can be attributed to the relatively strong directional bonding in the ω phase, which significantly increases its shear plastic resistance over the α-phase Zr. The present findings provide an alternate route for Zr metal strengthening by high-pressure phase transformation.

The strain-induced martensitic phase transformation during quasi-static uniaxial compression testing of a 304L stainless steel was investigated at 300 and 203 K using time-of-flight neutron diffraction to study the evolution of transformation texture. A number of specimens were precompressed to different strain levels at 300 and 203 K and the texture was investigated. At 203 K, the newly formed martensites are bcc and hcp phases and the texture analysis shows that the martensites are highly textured due to the grain-orientation-dependent phase transformation. The bcc {100} planes are mostly oriented with their plane-normal parallel to the loading direction at the beginning of the phase transformation and this texture is weakened during the subsequent compressive deformation. In the case of fcc to hcp transformation, it is less dependent on the grain orientation, although the fcc grains with {111} plane-normal at an angle close to 40 deg to the loading direction transform easier and the {0001} plane-normal of the newly formed hcp phase tends to rotate toward the loading direction during the texture evolution. The final texture of bcc and hcp martensites is the result of the interaction between deformation texture and transformation texture.

The work-hardening behavior of hexagonal-close-packed (hcp) metals, such as hafnium, is influenced by temperature, strain rate, chemistry, and texture. In the case of hafnium, while slip on the prism and pyramidal planes is dominant during deformation, the propensity of deformation twinning is known to increase with decreasing temperature and increasing strain rate. In this study, hafnium was prestrained quasi-statically in compression at liquid nitrogen temperature (77 K), creating a heavily twinned microstructure. The specimens were then reloaded in compression at room temperature (298 K). Yield stress, flow stress, and work-hardening behaviors of the prestrained specimens were higher than room-temperature compression test data typical of the as-annealed material. The microstructure of each specimen was characterized optically and using a transmission electron microscope (TEM). Texture was measured by neutron diffraction and the texture evolution due to twinning, and the interaction of slip with the twins was seen to lead to higher work-hardening rates and flow stresses in the cold prestrained specimens.

Weakly textured hot-pressed (HP) beryllium and strongly textured hot-rolled beryllium were compressed using a split-Hopkinson pressure bar (SHPB) (strain rate ∼4500 s−1) to a maximum of 20 pct plastic strain as a function of temperature. The evolution of the crystallographic texture was monitored with neutron diffraction and compared to polycrystal plasticity models for the purpose of interpretation. The macroscopic response of the material and the active deformation mechanisms were found to be highly dependent on the orientation of the load with respect to the initial texture. Specifically, twinning is inactive when loaded parallel to the strong basal fiber but accounts for 27 pct of the plastic strain when loaded transverse to the basal fiber. In randomly textured samples, 15 pct of the plastic strain is accomplished by twinning. The role of deformation mechanisms with components out of the basal plane (i.e., twinning and pyramidal slip) is discussed.

The deformation of polycrystalline beryllium to strains of ±0.8 pct in uniaxial tension and compression was studied by neutron diffraction and modeled using an elasto-plastic self-consistent (EPSC) model. The beryllium response is asymmetric with respect to tension and compression in both the macroscopic behavior, as displayed in the stress/strain curve, and the microscopic lattice response. The EPSC model qualitatively reproduces the lattice strain curves in tension and compression with the assumption of pyramidal slip being active, in addition to prism and basal slip and with the inclusion of thermal residual stresses developed during processing. Although it underpredicts the magnitude of the observed strains, it demonstrates that accounting for residual stresses of thermal origin is crucial for understanding the evolution of lattice strains during uniaxial loading.

The deformation of polycrystalline uranium 6 wt pct niobium (U6Nb) was studied in situ during uniaxial tensile loading by time-of-flight neutron diffraction. Diffraction patterns were recorded at incremental stresses to a maximum of 450 MPa (∼4 pct macroscopic strain). Consistent with reorientation of the martensite variants by twinning, significant changes in the diffraction peak intensities, which were proportional to the plastic contribution of the macroscopic strain, were observed. Both the lattice parameters (a, b, c, and γ) and interplanar spacings (dhkl) were determined as a function of applied stress. Phenomenologically, the highly anisotropic stress response of the lattice parameters as well as the individual lattice spacings can be related to deformation twinning. Preliminary transmission electron microscopy (TEM) studies identified the (\(\bar 1\)30) and (\(\bar 1\)72) as active deformation twinning systems of U6Nb in tension.

The Hylebos Waterway is an industrialized waterway ofCommencement Bay, Tacoma, Washington, that is severelycontaminated with aromatic and chlorinatedhydrocarbons in the sediment. Juvenile chinook (Oncorhynchus keta) and chum salmon (O.tshawytscha) inhabit this waterway for a few days orweeks during their outmigration from freshwaterstreams to saltwater. The purpose of thisinvestigation was to determine to what degree juvenilechum and chinook salmon captured from the HylebosWaterway might bioaccumulate organic contaminants. These levels of exposure will be compared to previousstudies where such exposures have been linked tobiological dysfunction in juvenile salmon. Theresults showed that juvenile chum and chinook salmonfrom the Hylebos Waterway take up a wide range ofchemical contaminants, compared to fish fromhatcheries or reference estuaries. These contaminantsinclude high and low molecular weight polycyclicaromatic hydrocarbons (PAHs), polychlorinatedbiphenyls (PCBs, including the toxic congeners 105 and118), hexachlorobutadiene (HCBD), hexachlorobenzene(HCB), DDTs, heptachlor, and several pesticides. Immunohistochemical examination of the gill and gut injuvenile chum salmon from the Hylebos Waterway showedthe induction of the P450 metabolizing enzyme. Moreover, concentrations of contaminants in juvenilechinook and chum salmon from the Hylebos Waterway arecomparable to levels previously shown to be associatedwith biological injury in juvenile chinook salmon,such as impaired growth, suppression of immunefunction as demonstrated by reduced B cell function,and increased mortality following pathogen exposure.

HAYNES 230 is a solid solution strengthened, face centered cubic (FCC), nickelbased superalloy, with a small amount (1–5 vol. %) of semi-coherent FCC carbides. Neutron diffraction experiments were performed to study the interaction of the carbides with the matrix during tensile and compressive loading. The behavior of the elastic lattice strains during in situ loading clearly showed a tension-compression asymmetry. Although the volume percentage is small, the interaction between the carbides and the matrix had a significant effect on the load sharing. In compression, the carbides began load sharing at the macroscopic yield point, while the tension test suggests no load sharing. Debonding at the carbide-matrix interface is proposed to explain the lack of load sharing during the tensile loading based on the disparities observed between the experimental results and the finite element models.

The development of lattice strain was studied using in-situ time-of-flight neutron diffraction during constant-load tensile creep deformation of an austenitic 316FR stainless steel at 180, 240, and 300MPa at 873K (a power-law creep regime) with time resolution of 900 seconds. The macroscopic (global) and mesoscopic (lattice) strains were measured simultaneously during creep using an extensometer and neutron diffraction, respectively. The hkl-specific lattice strains were measured to gain insights into the plastic anisotropy at various stages of creep deformation (i.e., primary, secondary, and tertiary regimes). Furthermore, the creep-induced lattice strain behavior was compared to the result obtained from a quasistatic tension test at 873K. The lattice strain evolution in the axial direction (direction parallel to the tensile loading axis) during the primary and secondary creep (dislocation creep) is quite similar to the quasistatic case (slip). However, in the tertiary creep regime, the creep-induced lattice strain accumulation is smaller than the quasistatic case at a given total strain, except the (111) reflection.

In-situ, time-of-flight neutron diffraction was performed to investigate the martensitic phase transformation during quasi-static uniaxial compression testing of 304L stainless steel at 300K (room temperature) and 203K. In-situ neutron diffraction study enabled the bulk measurement of intensity evolution for each hkl atomic plane during the austenite (fcc) to martensite (hcp and bcc) phase transformation. The neutron diffraction patterns show that the martensite phases started to develop at about 2.5% applied strain (600 MPa applied stress) at 203K. However, at 300K, the martensite formation was not observed throughout the test. Furthermore, from changes in the relative intensities of individual hkl atomic planes, the selective phase transformation can be well understood and the grain orientation relationship between the austenite and newly-forming martensite phases can be determined. The results show that the fcc grain families with {111} and {200} plane normals parallel to the loading axis are favored for the “fcc to hcp” and “fcc to bcc” transformations, respectively.

Pseudoelasticity in monocrystalline Fe3Al (23 at.% Al) was investigated by room-temperature mechanical testing along the tensile and compressive axes. In tension, up to ∼10% strain is recoverable whereas only ∼5% strain is recoverable in compression. Straight, parallel, surface step lines were seen to appear/disappear as the specimens were pseudoelastically loaded/unloaded. In contrast, in the plastic region (ε >10%), wavy slip lines appeared on the specimen surfaces which did not disappear upon unloading. In-situ neutron diffraction was performed during compressive straining and the intensities of several diffraction peaks increase/decrease reversibly during loading/unloading. These changes are consistent with a deformation twin which produces large crystal rotations. They could also be indicative of a phase transformation. Unfortunately, we were able to sample only a limited range of 2θ in the present investigation and, within this range, none of the new peaks that appeared during the pseudoelastic deformation were disallowed peaks for the D03 crystal structure. Therefore we are unable at this time to distinguish between the two possible mechanisms, twinning and phase transformation.

The deformation of polycrystalline uranium 6 wt. % niobium (U6Nb) was studied in-situ during uniaxial tensile and compressive deformation by time-of-flight neutron diffraction. Diffraction patterns were recorded at incremental strains to roughly 4% total deformation. The asymmetry in the crystallographic response of the lattice is discussed.

Concentrations of selected anthropogenic chemical contaminants and levels of pollution-related biological effects were measured during three consecutive years (1990–1992) in hardhead catfish (Arius felis), Gulf killifish (Fundulus grandis), longnose killifish (F. majalis), and red drum (Scieaenops ocellatus) from 12 subtidal and intertidal sites in Tampa Bay and nearby Sarasota Bay. Each species was collected from at least four sites. Compared to nonindustrialized sites, concentrations of PCBs, DDTs, and alpha-chlordane in liver, and of fluorescent aromatic compounds in bile, were highest in fish from sites in or near Hillsborough Bay, the most industrialized portion of Tampa Bay. The results of analyses for two biochemical markers of contaminant-induced effects in fish, hepatic cytochrome P4501A activities and levels of hepatic DNA adducts, also showed the highest levels to be in all four fish species from sites in the vicinity of Hillsborough Bay. Liver lesions, considered to be pollution-associated in several other bottom-feeding fish species, were found in hardhead catfish and longnose killifish, exclusively from sites in Hillsborough Bay. Overall, concentrations of selected contaminants and their derivatives in the four target fish species generally reflected concentrations of these contaminants found in sediment. The biochemical and histopathological responses demonstrated that chemical contaminant concentrations in the vicinity of Hillsborough Bay are sufficiently high to cause adverse effects in indigenous fish species. The results, collectively, showed that the extent of contaminant exposure and biological effects in fish from sites in Tampa Bay were low to moderate compared to more urbanized coastal sites of the United States. *** DIRECT SUPPORT *** A01BY073 00009

Winter flounder (Pseudopleuronectes americanus) were sampled from three sites located near Norwalk, New Haven, and Niantic, Connecticut, in Long Island Sound during February 1987, to evaluate the degree of chemical contamination and to determine possible effects of contaminant exposure. At each site, sediment and infaunal invertebrates were also collected and analyzed for trace metals and organic chemicals. Specimens of liver and kidney from winter flounder were examined for histopathological conditions, including the presence of macrophage aggregates in liver tissue. Liver samples were also analyzed for DNA damage (i.e., the formation of adducts between DNA and chemical contaminants). Blood samples were collected and analyzed for erythrocyte micronuclei. The sampling site near New Haven was determined to be the most affected site, from the standpoints of greater chemical contamination and possible effects on winter flounder. Concentrations of aromatic hydrocarbons (AHs) and polychlorinated biphenyls (PCBs) were highest in sediment from this site, and the highest prevalences of the histopathological changes and DNA alterations were also found in the livers of winter flounder from this site. No differences in the concentrations of contaminants in fish or in frequencies of erythrocyte micronuclei in fish blood were found between sites. None of the sites sampled had contaminant levels or prevalences of lesions as high as previously found at other East Coast locations (e.g., Boston Harbor, Massachusetts, Raritan Bay, New York). Overall, our results indicate moderate levels of pollution at two of the urban sites in Long Island Sound and provide a framework for expanded studies to better define the extent and impact of chemical pollution in Long Island Sound.

Petroleum is composed of a complex mixture of hydrocarbons that readily undergo chemical and biological conversions on entering aquatic environments. These conversions lead to the formation of a host of oxygenated products, some of which are potentially toxic to marine life and to the consumer of fishery products. State-of-the-art analytical methods, as employed in our laboratories, utilize glass-capillary gas chromatography in conjunction with mass spectrometry to analyze environmental samples containing trace amounts of aliphatic and aromatic petroleum hydrocarbons. These procedures are applied on a routine basis to the analysis of seawater, sediments and tissues of marine organisms. Despite this analytical proficiency, a need exists for analyzing oxygenated and other polar petroleum products in environmental samples. For example, techniques such as high-performance liquid chromatography (HPLC), in conjunction with on-line fluorometric assay techniques and mass spectrometry, make possible the analysis of polar oxygenated compounds resulting from both chemical and biological conversions. These methodologies are first steps toward the development of routine assay procedures for environmental samples. Current techniques for hydrocarbon analyses and new methods for analyzing polar aromatic compounds are discussed.