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The aim of this work is to understand the evolutions of the β1metastable austenite phase of a CuAlBe Shape Memory Alloy at macroscopic and microscopic scales under mechanical solicitation by neutron diffraction. The tensile specimen, taken in the raw material is subjected to superelastic cycles at room temperature on SMARTS diffractometer. Before loading, the mater ial is fully austenitic. During loading, after elastic deformation of austenite, phase transformation starts, martensite variants appear. The material follows a law of pseudo elastic behavior. At the end of the first mechanical cycle after unloading, the macroscopic curve does not fully return into its original point. A macroscopic deformation is observed. The evolution of first order microdeformations during mechanical cycles shows a large deformation of {400} plane family. This deformation is linked to the presence of partial fibber characterizing the crystallographic texture of the material after elaboration. The FWHM of the (400) diffraction peak is also largely increased during loading. This increase is the signature of the generation of stacking faults during the transformation of β1metastable austenite into β1martensite.

Time-of-flight neutron measurements have been made at 20, 400 and 650oC on δ-processed Inconel 718 in order to measure the load sharing between the γ-phase matrix and the orthorhombic δ-phase. The strain response parallel and perpendicular to the applied stress was measured for seven γ-phase reflections and five δ-phase reflections. The latter were about 50 times weaker than the former suggesting a 2.0% concentration of the δ-phase. At all temperatures the δ-phase strain becomes strongly tensile parallel to the loading direction but also exhibits plastic deformation. However, the nature of the three orthorhombic strains changes with temperature.

Near-field high energy x-ray diffraction microscopy (nf-HEDM) and high energy x-ray micro-tomography (μT) have been utilized to characterize the pore structure and grain morphology in sintered ceramic UO2nuclear fuel material. μT successfully images pores to 2-3μm diameters and is analyzed to produce a pore size distribution. It is apparent that the largest number of pores and pore volume in the sintered ceramic are below the current resolution of the technique, which might be more appropriate to image cracks in the same ceramics. Grain orientation maps of slices determined by nf-HEDM at 25 μm intervals are presented and analyzed in terms of grain boundary misorientation angle. The benefit of these two techniques is that they are non-destructive and thus could be performed before and after processes (such as time at temperature or in-reactor) or even in-situ.

The high-resolution neutron diffraction and acoustic emission (AE) techniques have been used for in-situ investigation of deformation twinning and microstructure evolution in cast polycrystalline magnesium. The combination of these two techniques results in obtaining complementary information about the twinning mechanism and evolution of the dislocation structure during the straining. The dependence of the mechanisms of the plastic deformation on loading mode is discussed in detail. The microscopy investigations revealed a difference in twin number and size after tension and compression, respectively.

Neutron diffraction measurements of strain in austenitic stainless steel alloys are presented to examine whether there are contributions to the shifts from deformation induced stacking faults. Differences between successive orders of reflections are consistent with the presence of stacking faults for 316 stainless steel but not for a NiCrFe steel.

Neutron diffraction research has been limited to the "static" behavior of materials since the number of collected neutrons is insufficient to reach the adequate neutron counts in rapid changes of material state. In order to achieve the desired precision for the study of the transient material behavior, we propose an in-situ neutron-diffraction measurement method based on the quasi-steady state (QSS) phenomenon. The QSS principle was applied for the measurement of transient lattice spacing changes in a 6061-T6 aluminum alloy plate during thermo-mechanical processing.

Textured Mg alloys exhibit tension – compression strength asymmetry due to mechanical twinning. The distinction arises as the material deforms primarily by slip in one direction and by twinning in the other. In-situ neutron diffraction during cyclic loading in tension and compression of extruded bar allows study of the effect of twinning on subsequent load reversals. The diffraction data reveal the texture evolution and internal stress development as a function of deformation. De-twinning resulted in complete texture reversal during initial cycles, but eventually “fatigued” resulting in some residual twin component.

ULTIMET® alloy, a cobalt-based superalloy with good corrosion and wear resistant properties, exhibits a deformation-induced phase transformation from the face-centered-cubic (FCC) phase to the hexagonal-close-packed (HCP) phase. The HCP phase formation during monotonic tensile loading was investigated using in-situ neutron diffraction. The HCP phase is first observed at a stress level of 810 MPa, which is well beyond macroscopic yielding. Strain analysis is performed on the FCC phase diffraction data in order to relate the lattice-strain development with the evolution of the new HCP phase. A method of calculating the effective macroscopic stress associated with the measured lattice strains is presented here. The effective stress can then be compared to the applied macroscopic stress in order to draw conclusions about the load-partitioning behavior of the material as a new phase develops.

The martensitic phase transformation in an ultra fine grained (UFG) TRIP (transformation induced plasticity) steel with combination of high strength and high elongation was investigated during room temperature tensile test using in situ neutron diffraction. Two types of specimens, namely coarse grained (grain size of about 50 μm) and ultra-fine-grained (grain size of about 350 nm) specimens were examined. The lattice strain evolution of the austenite and martensite phases was observed and the load partitioning between the phases was identified.

Plastic deformation in cubic metals is relatively simple due to the high crystallographic symmetry of the underlying structure. Typically, one unique slip mode can provide arbitrary deformation. This is not true in lower symmetry hexagonal metals, where prismatic and basal slip (the usual favored modes) are insufficient to provide arbitrary deformation. Often, either pyramidal slip and/or deformation twinning must be activated to accommodate imposed plastic deformation. The varied difficulty of activating each of these deformation mechanisms results in a highly anisotropic yield surface and subsequent mechanical properties. Further, the relative activity of each deformation mode may be manipulated through control of the initial crystallographic texture, opening new opportunities for the optimization of mechanical properties for a given application.

The use of severe plastic deformation techniques such as equal channel angular pressing, has been shown to refine metal microstructures giving advantageous mechanical properties. Metals and alloys subjected to ECAP procedures can have very high yield strengths while maintaining substantial ductility, a unique and attractive combination. However, the implicitly large deformations (the application of repeated shear strains of 1 are typical) make prediction of the resulting mechanical properties difficult. In particular, modeling the polycrystalline texture evolution and microstructural strain response is challenging. In this paper, results are presented from a neutron diffraction study on aluminum, copper, nickel and beryllium processed by ECAP. Specific attention is given to the evolution of the bulk texture after one pass and the effect of the initial texture. The neutrons probed volumes on the order of cubic centimeters and therefore provided texture and strain information averaged over the bulk of the sample. The results are discussed in the context of a visco-plastic self- consistent model.

We present a study of residual stresses associated with the welding of beryllium rings. Using novel analysis techniques, information about residual stresses and plastic deformation of the base metal were obtained. In the post-welded state, the rings have a strong tensile circumferential residual stress and show evidence of significant plastic deformation.

Successful application of metal matrix composites often requires strength and lifetime predictions that account for the deformation of each phase. Yet, the deformation of individual phases in composites usually differs significantly from their respective monolithic behaviors. An approach is presented that quantifies the deformation parameters of each phase using neutron diffraction measurements before, during, and after failure under tensile loading in model composites consisting of a single alumina fiber embedded in an aluminum matrix. The evolution of residual strains after loading was examined including the effects of fiber failure.

Bulk metallic glasses (BMGs) are potentially superb structural materials due to a unique combination of properties such as a large elastic strain limit, high strength and good fracture toughness. However, most BMGs are prone to catastrophic failure during unconstrained loading due to high concentration of shear deformation in the form of a shear band. This problem has been addressed by the development of BMG-matrix composites that suppress this failure mode. In this study we have utilized neutron diffraction measurements to investigate the load sharing in such a BMG-matrix composite, where the second phase is formed in-situ during quenching. The properties of the second phase itself have also been investigated in the monolithic form. The diffraction data has been compared to the predictions of self-consistent models resulting in good agreement.

Measurements of internal strain development during in-situ deformation of a textured magnesium alloy plate represent the first direct observations of intergranular (type II) strains, which allow for definitive statements about the magnitude of stresses within (i) parent grains when mechanical twins are beginning to form, (ii) the mechanical twins themselves as they are being formed, and (iii) the development of stresses within twins during subsequent deformation. These data will be extremely valuable for developing accurate constitutive models incorporating twinning.

We have completed a comparative X-ray diffraction (XRD) and Finite Element Analysis (FEA) study of Inconel 718 clad Tungsten tubes, of relevance to the Accelerator Production of Tritium (APT) program at the Los Alamos National Laboratory (LANL). Because the Inconel cladding must be in intimate contact with the tungsten at operating temperatures, the materials are diffusion bonded by Hot Iso-static Pressing (HIP) at 1080°C. However, the difference in thermal expansion coefficients of inconel 718 and tungsten produce large residual stresses upon cooling. The classical XRD (d vs. sin 2 ψ) technique was used to determine the stresses in the outer layer of inconel 718. These results are used to benchmark Finite Element Analysis (FEA) calculations, and a direct comparison is made in this paper.