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After α + β-zirconium has fully transformed into β-phase upon heating, the intensities of all β-Zr Bragg reflections decrease simultaneously as a function of time. It is shown that this effect represents a transition from the kinematic to the dynamic theory of diffraction due to the ever increasing crystal perfection driven by thermal recovery of the system. The best fitting coherent crystallite size of 30 μm and other microstructural features are verified by in situ laser scanning confocal microscopy. This effect of primary extinction in neutron diffraction has been employed to further investigate the crystal perfection kinetics. Upon further heating, crystal recovery is identified as a process of dislocation annihilation, suffering from lattice friction. Upon cooling, precipitating α-Zr induces strain into the perfect β-crystallites, re-establishing the kinematic diffraction intensities. An Avrami analysis leads to the estimations of nucleation time, consumption of nucleation sites and lower-dimensional growth. Such technique bears great value for further investigation on all metal systems annealed close to the melting temperature. [ABSTRACT FROM AUTHOR]

Near-interface chipping of the porcelain veneer is now widely accepted as the primary failure mode of Yttria Partially Stabilised Zirconia (YPSZ) prosthesis. The origin of these failures is believed to be the complex interaction between YPSZ phase transformation, thermal expansion mismatch and other microstructural effects which induce high magnitude residual stresses within the first few microns of the interface. Recent studies have also provided evidence that these stresses, in combination with the applied sintering temperatures, are sufficient to induce tensile creep (and the associated voiding damage) within the near interface porcelain region. In order to improve understanding of this creep rate behaviour, tensile creep has been performed on representative dental feldspathic porcelain (Vitablocs ® Mark II for Cerec ® ) at the temperatures (650–800 °C in 50 °C increments) and stresses (50–125 MPa in 25 MPa increments) typically encountered in the near interface porcelain. Limitations on porcelain sample size meant that conventional ceramic secondary creep rate testing could not be implemented in this study and therefore a new approach based on applying multiple stresses and temperatures to a single sample was developed. The four values of activation energy and stress rate exponent determined in this study were found to be consistent to within the 95% confidence intervals of each value. Average values and 95% confidence intervals for each parameter were determined to be Q = 243.0 ± 3.1 kJ mol − 1 and n = 1.32 ± 0.08. These values compare well with published values of creep rate behaviour in silica and alumina based ceramics. The quantitative values obtained in this study form a foundation for future studies into tensile creep induced voiding in porcelain as well as facilitating the development of improved models of the YPSZ-porcelain interface. The new single sample, tensile creep experimental approach also has potential for use in ceramic tensile creep testing of samples of limited size. [ABSTRACT FROM AUTHOR]

[Display omitted] • Load distribution in a γ ′ strengthened superalloy is measure by in-situ neutron diffraction. • The effect of particle size on Load distribution at cryogenic temperatures is studied. • Co-deformation of phases leads to intergranular load transfer between in matrix. • Coarse γ ′ microstructure experience both intergranular and intragranular load transfer. • Coarse particles initially behave elastically but yield at higher stresses. In-situ neutron diffraction was performed during tensile deformation of a Ni-based superalloy, Haynes 282, at 20, 100 and 300 K. Two distinct uni-modal microstructures with fine (20 nm) and coarse (200 nm) γ ′ particles were investigated. On the macro-scale yield strength increased and ductility decreased with decreasing temperature, although the most significant decrease in ductility occurred between 100 and 20 K. The work hardening differed between the two microstructures, but was independent of temperature for each microstructure. On the micro-scale intergranular elastic interactions mainly lead to a transfer of the load to grains with the 200 orientation parallel to the tensile axis. No further load re-distribution between matrix and particles occurred in the microstructure with fine γ ′ , where shearing of precipitates lead to co-deformation at all temperatures. In the coarse γ ′ microstructure, the load was transferred intragranularly from matrix to particles, in addition to the intergranular load transfer. The particles initially behaved elastically while the matrix deformed plastically, but at higher stresses a change in load partitioning indicated that also the γ ′ phase underwent plastic deformation as a result of the stress build-up from the load partitioning. The tendency for, and effect of, plastic deformation of γ ′ increased with decreasing temperature. [ABSTRACT FROM AUTHOR]

CrCoNi-based medium- and high-entropy alloys display outstanding damage tolerance, especially at cryogenic temperatures. In this study, we examined the fracture toughness values of the equiatomic CrCoNi and CrMnFeCoNi alloys at 20 kelvin (K). We found exceptionally high crack-initiation fracture toughnesses of 262 and 459 megapascal-meters½ (MPam½) for CrMnFeCoNi and CrCoNi, respectively; CrCoNi displayed a crack-growth toughness exceeding 540 MPam½ after 2.25 millimeters of stable cracking. Crack-tip deformation structures at 20 K are quite distinct from those at higher temperatures. They involve nucleation and restricted growth of stacking faults, fine nanotwins, and transformed epsilon martensite, with coherent interfaces that can promote both arrest and transmission of dislocations to generate strength and ductility. We believe that these alloys develop fracture resistance through a progressive synergy of deformation mechanisms, dislocation glide, stacking-fault formation, nanotwinning, and phase transformation, which act in concert to prolong strain hardening that simultaneously elevates strength and ductility, leading to exceptional toughness. [ABSTRACT FROM AUTHOR]

The evolution of metallurgy is a fundamental aspect related to the knowledge of the technological level of ancient civilizations, for which the information was mostly part of an oral tradition. The ancient, preserved artefacts are the only keepers of this long gone knowledge. Most advanced non-invasive techniques provide us the key to access it. Neutron techniques are nowadays the only available approach for revealing, non-destructively and with good spatial resolution, the morphological and microstructural properties within the whole volume of densely composed artefacts such as bronze statues. Application of neutron methods allows us to learn about ancient artefact manufacturing methods and to study at a very detailed level the current conservation status in their different parts. As part of a research project dedicated to the study of ancient Asian bronzes led by the Rijksmuseum Metal Conservation Department, four statues from the Rijksmuseum Asian collection were analysed using non-invasive neutron techniques. In this work, we present the investigation of a South Indian bronze statuette depicting Shiva in the form of Chandrasekhara (AK-MAK-1291, c. 1000–1200 A.D.) by means of white beam tomography, energy-selective neutron imaging (performed on CONRAD-2 at HZB, DE, and on FISH at TU-Delft, NL), and neutron diffraction (on ENGIN-X at ISIS, UK). The application of neutron imaging revealed the inner structure of the statue and allowed us to investigate the conservation state and potential cracking on the surface and in the bulk, to understand the interconnection of the different sections of the statue, and to obtain clues about the manufacturing processes. These morphological and microstructural results were employed to guide neutron diffraction analyses that allowed us to precisely characterize compositional differences, the presence of dendrites and columnar growth peak structures related to casting. This work is a complete non-invasive analytical investigation on an archaeological bronze artefact, providing outstanding results: from a quantitative analysis of the composition and microstructure to an in-depth morphological analysis capable of unveiling details on the ancient casting methods of the statue. [ABSTRACT FROM AUTHOR]

Weld residual stress and fracture behavior of 316L electron beam weldments, which are of particular interest in power generation industry, were investigated in this work. Two butt‐weld joints were manufactured in stainless steel 316L plates of 6 mm and 25.4 mm thicknesses. Three complementary methods were used to measure the three orthogonal components of the residual stress in the weld coupons, and fracture tests were conducted on single edge notched bending specimens extracted from different regions of the welds and parent metals. The residual stress measurements showed a maximum value of 450 MPa in longitudinal direction, while it was less than 150 MPa in the other two orthogonal directions, revealing that in our material, and with the chosen weld parameters, the residual stresses were biaxial. The fracture resistance of the weldment and parent material was similar, with material microstructure differences being more significant than the measured residual stresses. The study suggests that 316L electron beam weldments are not susceptible to fracture failure due to their high ductility and ability to relieve residual stresses through gross plasticity. Electron beam welding may therefore be suggested as a reliable manufacturing technology for safety critical 316L components. [ABSTRACT FROM AUTHOR]

Tantalum-clad tungsten targets are a popular choice for spallation neutron production, due to the combination of high neutron yield and corrosion resistance. Such targets typically use the Hot Isostatic Press (HIP) process to bond the cladding to the core; this produces a strong bond but also introduces large residual stresses in the target and cladding. This is of particular interest at the ISIS neutron source, because cladding breaches are currently believed to limit the lifetime of ISIS TS2 targets. Two different and complementary methods were used to measure the residual strain in a tantalum-clad tungsten strip manufactured using the same HIP process as ISIS targets. The strip was produced with deliberately asymmetric cladding, causing it to deflect in proportion to the residual stress. FEA simulations were used to back-calculate the stress from the measured deflection. The strip was then placed on the ISIS instrument ENGIN-X, which allowed detailed through-thickness strain profiles to be measured via neutron diffraction. The results of both methods confirm the presence of large residual strains, and agree reasonably well with FEA simulations of the cladding process. [ABSTRACT FROM AUTHOR]

The microstructural evolution and deformation mechanisms of 316L stainless steel (SS) have been investigated at 297, 173, 50 and 15 K by in situ neutron diffraction during tensile loading and correlative transmission electron microscopy (TEM). The yield strength and ultimate tensile strength of 316L stainless steel are significantly improved at cryogenic temperatures. In contrast to room temperature, deformation-induced martensitic transformation was observed at all cryogenic temperatures. The γ-austenite (FCC) content decreases and α′-martensite (BCC) increases with increasing strain, a fraction of this γ to α′ transformation is accompanied by the transient appearance of ε-martensite (HCP) as an intermediate phase. The maximum volume fraction of ε-martensite increases with decreasing deformation temperature and reaches 13% for deformation at 15 K. TEM results confirm that γ → ε → α′ and γ → α′ martensitic transformations occur during cryogenic deformation, while mechanical twins were observed only at 173 K. The evolution of lattice strain, phase volume fraction, stacking fault probability (SFP) and stacking fault energy (SFE) were quantified to investigate the correlation between deformation mechanisms and mechanical behaviour of 316L SS as a function of deformation temperature. [ABSTRACT FROM AUTHOR]

In this work we present a preliminary investigation by means of neutron diffraction experiment to determine the residual stress state in three different iron meteorites (Chinga, Sikhote Alin and Nantan). Because of the very peculiar microstructural characteristic of this class of samples, all the systematic effects related to the measuring procedure - such as crystallite size and composition - were taken into account and a clear differentiation in the statistical distribution of residual stress in coarse and fine grained meteorites were highlighted. Moreover, the residual stress state was statistically analysed in three orthogonal directions finding evidence of the existence of both type I and type II residual stress components. Finally, the application of von Mises approach allowed to determine the distribution of type II stress. [ABSTRACT FROM AUTHOR]

Magnetic and nonmagnetic shape memory alloys (SMAs) exhibit thermoelastic martensitic transformations (MTs) which are hysteretic due to their first‐order nature. According to the thermodynamic Landau theory of phase transitions, which assumes ideal thermoelastic equilibrium at each point of the MT interval, the hysteresis is explained by the different limits of stability for austenite and martensite in the phase diagram. No interactions on the phase boundaries are taken into account. In the real alloys, the hysteresis of MT is related not only to the stability intervals of two phases but also to the processes of nucleation and growth of the resultant phase inside the parent phase. In turn, the features of these processes are related to the heights of energy barriers caused by the incompatibility of austenitic and martensitic lattices, crystal defects and some other physical factors. However, the defects, normally, play a minor role in the width of MT hysteresis if compared to the thermodynamic and crystallographic factors. A reduction of hysteresis of MT in SMAs, being crucial for technology, presents a challenging problem for science. A decrease of hysteresis width of MT was observed recently for the single crystals of ferromagnetic SMAs such Ni–Fe(Co)–Ga and Fe–Pd on approaching of their transformation paths to the critical point in stress–temperature phase diagram. Moreover, the superelastic and shape memory properties characterized by the nearly‐zero hysteresis width were observed in the postcritical transformational regime. Here we show that both the Landau‐type theory of ferroelastic phase transitions and neutron diffraction experiments carried out under axial compression describe the essential features of these properties. We also interpret the experimentally observed anhysteretic phenomena in Ni–Mn–Ga thin films and nanobeam actuators in terms of their postcritical state. [ABSTRACT FROM AUTHOR]

A FeCoCrNiMo 0.23 high entropy alloy was processed by powder metallurgy with two conditions: hot extruded and annealed. In situ neutron diffraction, together with electron microscopy, was used to study the deformation mechanisms and concomitant microstructural evolution for both conditions. The as-extruded alloy has a single face-centered-cubic structure with a calculated stacking fault energy of ∼19 mJ/m 2 . When the alloy is tensile deformed, nano-twins and microbands are induced, resulting in an excellent combination of strength and ductility (784 MPa ultimate tensile strength and over 50% elongation). Annealing at 800 °C for 72 h increases the strength of the alloy but decreases its ductility. This is due to the decomposition of the alloy after annealing, causing the formation of Mo-rich intermetallic particles and a decrease of the stacking fault probability. These results highlight that combined mechanisms (i.e. solute strengthening and twin/microband induced plasticity) can effectively improve both the strength and ductility of high entropy alloys. [ABSTRACT FROM AUTHOR]

In-situ neutron diffractometry is performed to study the visco-plasticity in a nickel-base single crystal superalloy during in-situ cooling from high temperatures. It is found that visco-plastic deformation has two contributions from creep and stress relaxation, which are subject to the accumulation of dislocation activity and dislocation annihilation, respectively. Use has been made of the lattice strain evolution of the (200) γ+γ′ peak to confirm this effect. The decrease in lattice strain and macro-stress during in-situ cooling has been observed and confirms that there was softening taking place before thermal strain dominates at lower temperatures. Therefore, in-situ isothermal cyclic loading and relaxation tests under strain control, akin to thermal contraction during casting, have been carried out. A visco-plasticity law was then developed based on macro-strain development during creep and lattice strain evolution during stress relaxation within an appropriate timescale, where transient effects are captured. The constitutive law developed has been used to independently determine the evolution of stress and strain during in-situ cooling. The implementation of these findings into thermo-mechanical modelling during cooling from solidification is also discussed. [ABSTRACT FROM AUTHOR]

High manganese steels are promising candidates for applications in cryogenic environments. In this study, we investigate the mechanical and microstructural responses of a high manganese twinning induced plasticity (TWIP) steel at a low-temperature range (from 373 to 77 K) via in situ neutron diffraction qualification and correlative microscopy characterization. During plastic deformation, stacking fault probability and dislocation density increased at a faster rate at a lower temperature, hence, higher dislocation density and denser mechanical twins were observed, confirmed by microscopic observation. Stacking fault energy was estimated, dropping linearly from 34.8 mJm−2 at 373 K to 17.2 mJm−2 at 77 K. A small amount of austenite transferred to martensite when deforming at 77 K. The contributions to flow stress from solutes, grain boundary, dislocation, and twinning were determined at different temperatures, which shows that the high work strain hardening capacity of the TWIP steel originates from the synergetic strengthening effects of dislocations and twin-twin networks. These findings reveal the relationship among stacking fault energy, microstructure, and deformation mechanisms at the low-temperature range, paving a way in designing TWIP steels with the superb mechanical performance for cryogenic applications. Image, graphical abstract [ABSTRACT FROM AUTHOR]

In situ neutron diffraction and synchrotron X-ray diffraction, combined with image correlation analysis of 2D optical and 3D X-ray tomography datasets, have been used to investigate the relationship between elastic lattice strain and total strain during deformation of Gilsocarbon (IM1-24) polygranular nuclear grade graphite. The specimens were flat-end Brazilian discs under diametral loading, such that a compressive-tensile biaxial stress state was developed in the central region. The X-ray study was at ambient temperature, and the neutron diffraction was conducted at temperatures from ambient to 850 °C. When under compression, there is a temperature-insensitive linear relationship between the total strain and the lattice strain that is measured perpendicular to the graphite basal planes. However, when under tensile stress, the total strain and elastic strain relationship is temperature sensitive: below 600 °C, the lattice tensile strain saturates with increasing total tensile strain; above 600 °C, significantly higher tensile lattice strains are sustained. The saturation in tensile lattice strain is attributed to microcracking in the graphite microstructure. Improved resistance to microcracking and damage tolerance at elevated temperature explains the increase in tensile strength of polygranular graphite. Image 109604 [ABSTRACT FROM AUTHOR]

By time-of-flight (TOF) neutron diffraction experiments, the influence of segregation-induced microstructure bands of austenite (γ) and martensite (α′) phases on the partitioning of stress and strain between these phases was investigated. Initially, tensile specimens of a Co-added stainless steel were heat treated by quenching and partitioning (Q&P) processing. Tensile specimens were subsequently loaded at 350 °C parallel to the length of the bands within the apparent elastic limit of the phase mixture. Lattice parameters in both axial and transverse directions were simultaneously measured for both phases. The observation of a lattice expansion for the γ phase in the transverse direction indicated a constraint on the free transverse straining of γ arising from the banded microstructure. The lateral contraction of α′ imposed an interphase tensile microstress in the transverse direction of the γ phase. The multiaxial stress state developed in the γ phase resulted in a large deviation from the level of plastic strain expected for uniaxial loading of single phase γ. Since segregation-induced banded microstructures commonly occur in many engineering alloys, the analysis of stress and strain partitioning with the present Q&P steel can be used to interpret the observations made for further engineering alloys with two-phase microstructures. [ABSTRACT FROM AUTHOR]

Deformation mechanisms of high entropy alloys (HEAs) at cryogenic temperatures have attracted extensive research interest. We used in situ neutron diffraction to study the tensile behavior of a face-centered-cubic HEA at 77 and 15 K and compared its stacking fault energy (SFE) at ambient and cryogenic temperatures. The SFE dropped from 28 mJm−2 at 293 K to 11 mJm−2 at 15 K, leading to the transition of deformation mechanism from deformation-induced twinning to martensite phase transformation. As a result, excellent balance of strength and ductility was achieved at both temperatures. This finding highlights the importance of SFE for cryogenic alloy design. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Cold spray (CS) is a solid-state additive material deposition technique, which has gained attention in the aerospace industry as a potentially viable technology for structural repair of high-value parts made of high-strength alloys such as Ti-6Al-4V (Ti-64). Residual stresses build up in the substrate and deposited materials resulting from the CS process can influence the integrity of a coating or repair. However, the nature, magnitude and distribution of residual stresses in Ti-64/Ti-64 CS repairs are currently unknown. This study aims to evaluate the effects of geometrical variables (i.e. the number of CS layers, CS layer thickness, and substrate thickness) and track pattern on the magnitude and distribution of residual stresses in CS deposit-substrate assemblies. Through-thickness stress distributions were measured experimentally by neutron diffraction and contour method. Furthermore, a comparison among different residual stress build-up mechanisms induced by CS processes has been discussed for different combinations of substrate and deposit assemblies. An analytical model based on the force and moment equilibrium requirements was used to interpret the experimental stress profiles and to predict the residual stress distribution. It was found that residual stresses are highly tensile near the free surface of the Ti-64 deposits as well as towards the bottom of the substrate, and compressive near the interface region. Although all the specimens showed similar stress distribution, the magnitudes were found to be higher in one or more of the following cases: specimens with a higher number of CS layers, lower substrate thickness, higher layer thickness (i.e. at lower scanning speed), and deposited with a horizontal track pattern. • Residual stresses induced by cold spraying of Ti-6Al-4 V were evaluated using neutron diffraction and contour method. • A parametric study was performed on the influence of geometrical and process variables on residual stresses. • An analytical method was used to interpret the experimental results and to compare different stress build-up mechanisms. [ABSTRACT FROM AUTHOR]

The deformation responses at 77 and 293 K of a FeCoNiCr high-entropy alloy, produced by a powder metallurgy route, are investigated using in situ neutron diffraction and correlative transmission electron microscopy. The strength and ductility of the alloy are significant improved at cryogenic temperatures. The true ultimate tensile strength and total elongation increased from 980 MPa to 45% at 293 K to 1725 MPa and 55% at 77 K, respectively. The evolutions of lattice strain, stacking fault probability, and dislocation density were determined via quantifying the in situ neutron diffraction measurements. The results demonstrate that the alloy has a much higher tendency to form stacking faults and mechanical twins as the deformation temperature drops, which is due to the decrease of stacking fault energy (estimated to be 32.5 mJ/m 2 and 13 mJ/m 2 at 293 and 77 K, respectively). The increased volume faction of nano-twins and twin-twin intersections, formed during cryogenic temperature deformation, has been confirmed by transmission electron microscopy analysis. The enhanced strength and ductility at cryogenic temperatures can be attributed to the increased density of dislocations and nano-twins. The findings provide a fundamental understanding of underlying governing mechanistic mechanisms for the twinning induced plasticity in high entropy alloys, paving the way for the development of new alloys with superb resistance to cryogenic environments. [ABSTRACT FROM AUTHOR]

Objectives Recent studies of the yttria partially stabilised zirconia–porcelain interface have revealed the presence of near-interface porcelain nanovoiding which reduces toughness and leads to component failure. One potential explanation for these nanoscale features is thermal creep which is induced by the combination of the residual stresses at the interface and sintering temperatures applied during manufacture. The present study provides improved understanding of this important phenomenon. Methods Transmission electron microscopy and small angle neutron scattering were applied to a sample which was crept at 750 °C and 100 MPa (sample C), a second which was exposed to an identical heat treatment schedule in the absence of applied stress (sample H), and a reference sample in the as-machined state (sample A). Results The complementary insights provided by the two techniques were in good agreement and log-normal void size distributions were found in all samples. The void number density was found to be 1.61 μm −2 , 25.4 μm −2 and 98.6 μm −2 in samples A, H and C respectively. The average void diameter in sample A (27.1 nm) was found to be more than twice as large as in samples H (10.2 nm) and C (11.6 nm). The crept data showed the highest skewness parameter (2.35), indicating stress-induced growth of larger voids and void coalescence that has not been previously observed. Significance The improved insight presented in this study can be integrated into existing models of dental prostheses in order to optimise manufacturing routes and thereby reduce the significant detrimental impact of this nanostructural phenomenon. [ABSTRACT FROM AUTHOR]

The effects of strain rate on the mechanical behaviour and microstructure evolution of extruded Mg AZ31 alloy are investigated here for strain rates ranging from 0.0001 s −1 to 4000 s −1 . High strain rate compression testing was performed using a split Hopkinson pressure bar apparatus. The microstructure and texture evolution were characterised by using electron backscatter diffraction (EBSD) and neutron diffraction. The results show that the yield strength increases by roughly 55% from the quasi-static to the high strain rate regime while the plateau stress increases by roughly 35%. After compression along the extrusion direction, the deformed textures of both quasi-static and high strain rate loading samples are similar, showing that a large portion of grains have been reoriented through the activation of tensile twinning. However, a detail EBSD analysis suggests that there is a higher fraction of secondary compressive twins in high strain rate deformed specimens at 16% strain. A visco-plastic self-consistent (VPSC) model, which incorporates the composite grain scheme to account for twinning, is employed to model the mechanical response and texture evolution, and to elucidate the collaborative nature of the slip-twinning deformation. Using only a single set of parameters, the VPSC model successfully reproduces the stress-strain curves at all tested strain rates, and more importantly, captures the texture and twin volume fraction evolutions. The simulation results suggest that under quasi-static and high strain rate loadings, the dominant slip systems are different in both untwinned grains and tensile twins. The results also suggest that twins are formed at a lower strain at high strain rates when compared to quasi-static loading. [ABSTRACT FROM AUTHOR]

This article reports on in situ macroscopic scale imaging of NiO-YSZ (YSZ is yttria-stabilized zirconia) reduction under applied stress - a phase transition taking place in solid oxide electrochemical cells in a reducing atmosphere of a hydrogen/nitrogen mixture and at operation temperatures of up to 1073 K. This process is critical for the performance and lifetime of the cells. Energy-resolved neutron imaging was applied to observe the phase transition directly with time and spatial resolution. Two different approaches are presented for using this imaging technique for the investigation of chemical and physical processes requiring controlled atmosphere and elevated temperature. The first type of measurement is based on alternating stages of short-term partial chemical reaction and longer neutron image acquisition, and the second type is a real in situ neutron imaging experiment. Results of applying energy-resolved neutron imaging with both approaches to the NiO-YSZ reduction investigation indicate enhancement of the reduction rate due to applied stress, which is consistent with the results of the authors' previous research. [ABSTRACT FROM AUTHOR]

Manufacturing austenitic stainless steels (ASSs) using additive manufacturing is of great interest for cryogenic applications. Here, the mechanical and microstructural responses of a 316L ASS built by laser powder bed fusion were revealed by performing in situ neutron diffraction tensile tests at the low-temperature range (from 373 to 10 K). The stacking fault energy almost linearly decreased from 29.2 ± 3.1 mJm−2 at 373 K to 7.5 ± 1.7 mJm−2 at 10 K, with a slope of 0.06 mJm−2K−1, leading to the transition of the dominant deformation mechanism from strain-induced twinning to martensite formation. As a result, excellent combinations of strength and ductility were achieved at the low-temperature range. [Display omitted] [ABSTRACT FROM AUTHOR]

The intergranular lattice strains in the near-β titanium alloy Ti-β21S have been measured in the longitudinal and transverse directions during tensile loading using neutron diffraction. The obtained results have been modelled and explained using a two-phase elasto-plastic self-consistent model. We first identified the best set of the main model parameters (single crystal elastic constants, critical resolved shear stresses) and investigated the influence of these parameters on the behaviour of both the polycrystal and the diffracting volume. Good agreement between the experimental results and those predicted by the model was found for the macroscopic stress-strain dependencies and lattice strain developments of Ti-β21S. [ABSTRACT FROM AUTHOR]

High material penetration by neutrons allows for experiments using sophisticated sample environments providing complex conditions. Thus, neutron imaging holds potential for performing in situ nondestructive measurements on large samples or even full technological systems, which are not possible with any other technique. This paper presents a new sample environment for in situ high resolution neutron imaging experiments at temperatures from room temperature up to 1100°C and/or using controllable flow of reactive atmospheres. The design also offers the possibility to directly combine imaging with diffraction measurements. Design, special features, and specification of the furnace are described. In addition, examples of experiments successfully performed at various neutron facilities with the furnace, as well as examples of possible applications are presented. This covers a broad field of research from fundamental to technological investigations of various types of materials and components. [ABSTRACT FROM AUTHOR]

High manganese steels are emerging as promising structural materials for cryogenic applications due to their low production cost and great potential in achieving excellent strength-ductility combinations. Micro-alloying serves as a desirable method in tailoring stacking fault energy (SFE) of the steels and thus tailoring the mechanical performance. In this study, we investigated the dedicate role of Cu addition played on the mechanical and microstructural responses of high manganese steels at the low-temperature range (293, 173, and 77 K) via in situ neutron diffraction and microscope characterizations. The addition of 1 wt%Cu to the steel not only effectively improved the yield strength (YS) and elongation but also increased the SFE thus postponing the martensite formation. For both high Mn steels, as deformation temperature decreased, the tensile strength was increased linearly, the formation of stacking faults and dislocation was promoted, and the SFE almost linearly decreased with a slope of about 0.06 mJm−2·K−1. The contributions to YS and flow stress from lattice friction, grain boundary, dislocation, deformation twins, and phase transformation were determined based on neutron diffraction results and previously validated models. The work revealed the critical roles of Cu micro-alloying in tailoring the SFE of TWIP steels and the resulting deformation mechanisms, paving the way in adapting new high manganese steels for cryogenic applications. • Cryogenic mechanical properties of two TWIP steels were measured. • Stacking fault energy (SFE) was determined theoretically and experimentally. • Deforming mechanisms were studied at cryogenic temperatures. • Adding Cu can enhance yield strength, tailor SFE, and change deformation behaviors. • Strengthening effects from a variety of hardening mechanisms were determined. [ABSTRACT FROM AUTHOR]

A time-of-flight (TOF) neutron strain scanner is a white-beam instrument optimized to measure diffractograms at precise locations within bulky specimens, typically along two perpendicular sample orientations. Here, a method is proposed that exploits the spatial resolution (~1 mm) provided by such an instrument to determine in a nondestructive manner the crystallographic texture at selected locations within a macroscopic object. The method is based on defining the orientation distribution function (ODF) of the crystallites from several incomplete pole figures, and it has been implemented on ENGIN-X, a neutron strain scanner at the ISIS facility in the UK. This method has been applied to determine the texture at different locations of Al alloy plates welded along the rolling direction and to study a Zr2.5%Nb pressure tube produced for a CANDU nuclear power plant. For benchmarking, the results obtained with this instrument for samples of ferritic steel, copper, Al alloys and Zr alloys have been compared with measurements performed using conventional X-ray diffractometers and more established neutron techniques. For cases where pole figure coverage is incomplete, the use of TOF neutron transmission measurements simultaneously performed on the specimens is proposed as a simple and powerful test to validate the resulting ODF. [ABSTRACT FROM AUTHOR]

Abstract: In-situ neutron diffraction was employed to monitor the evolution of nano-bainitic ferrite during low temperature isothermal heat treatment of austenite. The first 10 peaks (austenite, γ and ferrite, α) were monitored during austenization, homogenisation, rapid cooling and isothermal holding at 573K. Changes in the α-110 and γ-111 peaks were analysed to determine the volume fraction changes and hence the kinetics of the phase transformation. Asymmetry and broadening in the α-200 and γ-200 peaks were quantified to lattice parameter changes due to carbon redistribution as well as the effects of size and dislocation density. Atom Probe Tomography was then used to confirm that, despite the presence of 1.5 mass% Si, carbide formation was evident. This carbide formation is the cause of poor ductility, which is lower than expected in such steels. [Copyright &y& Elsevier]

Neutron and high-energy X-ray diffraction methods have been used to investigate deformation mechanisms (slip and twinning activities) during uniaxial tensile tests of Grade 1 commercially pure titanium (Ti-α). These two diffraction techniques have provided valuable and complementary information. The predictions made by an Elasto-Plastic Self-Consistent (EPSC) model, taking into account grain reorientation and stress relaxation induced by twinning activity, have been compared with the experimental data. Results clearly demonstrate that there is a good agreement between simulations and diffraction measurements. The EPSC model enables accurate predictions of: (i) the lattice strains developed in variously oriented {hk.l} grain families within the bulk material, (ii) the grain reorientation induced by twinning activity and (iii) the macroscopic stress-strain response. Two different textured products were studied in order to evaluate the influence of texture on the mesoscopic and macroscopic responses of Ti-α alloy. [ABSTRACT FROM AUTHOR]

• FCC retained phase can be transformed under mechanical loading. • FCC to HCP phase transformation is activated by plasticity. • Temperature delayed the activation of the strain-induced phase transformation. Thermal and mechanical effects on the phase transformation of polycrystalline two-phase HCP/FCC cobalt have been studied in coupled and decoupled ways. This experimental work has involved in situ X-ray and neutron diffraction analysis to determine phase proportions under various thermomechanical conditions, those which are not referenced in the litterature. A quantitative analysis is proposed to better understand phase transformation in a cobalt rolled sheet. New experimental results show that the metastable FCC retained phase can be transformed into HCP phase by a mechanical loading. In accordance with the theory and the literature, the prominent phase (HCP) can subsequently be transformed with an increase of temperature above 743 K. [ABSTRACT FROM AUTHOR]

An amendment to this paper has been published and can be accessed via a link at the top of the paper. [ABSTRACT FROM AUTHOR]

An amendment to this paper has been published and can be accessed via a link at the top of the paper. [ABSTRACT FROM AUTHOR]

Primary creep regeneration (PCR) is observed during cyclic creep deformation in many engineering alloys. PCR is a phenomenon in which reverse inelastic strain fully, or partially, resets the early creep strain hardening memory of the material. The current understanding regarding the origin of the PCR behaviour in engineering alloys is limited to the phenomenological observations from the changes in dislocation structures whereas a good mechanistic understanding of the PCR behaviour is crucial for developing robust plasticity-creep predictive models. In this study, we investigated the micromechanical origin of PCR behaviour in type 316H stainless steel at 650 °C using high-temperature mechanical testing and neutron diffraction. A cyclic creep experiment was conducted in-situ at a neutron diffraction beamline, during which various degrees of unloading and reverse loading were applied to the specimen, followed by creep deformation under a load above the material's yield strength. Partial PCR was observed after reverse plastic loading for all the creep dwells, which is contrary to current high-temperature lifetime assessment's procedures advice which is to account for full recovery of primary creep after any reverse plastic loading. The extent of PCR is observed to be proportional to the magnitude of reverse plastic strain up to a level of 0.5% reverse plastic strain. From the measured neutron diffraction data, a strong correlation was observed between the changes in magnitude of the accumulated intergranular residual lattice strains and the macroscopic primary creep strain. Moreover, the increases of lattice strain to saturation and transition from primary creep to secondary regime occur at the same time. Based on these correlations it can be postulated that the PCR behaviour observed due to cyclic loading in type 316H stainless steel at elevated temperature originates from the accumulation of intergranular residual lattice strains during the reverse plastic loading and those time-dependent changes during the creep dwells. [ABSTRACT FROM AUTHOR]

We successfully prepared an Fe 22 Co 20 Ni 19 Cr 20 Mn 12 Al 7 alloy consisting of a face-center cubic (fcc) phase and body-center cubic (bcc) phase that exhibits an outstanding combination of true strength of 1430 MPa and ductility of 19.9% at room temperature (RT). The micromechanical behavior at RT and 77 K for the studied alloy during tensile deformation was investigated using in situ time-of-flight (TOF) neutron diffraction in combination with synchrotron-based high-energy X-ray diffraction (HE-XRD). Here, the striking finding of a large elastic strain of 7.0% and 5.6% is reported for the {200} bcc crystal plane, which was achieved at RT and 77 K, respectively. Such a large lattice distortion observed in the bcc phase was attributed to a new type of stress-induced confined martensitic transformation. We attributed the physical origin of this specific martensitic transformation to the intrinsic microstructural feature of a nano-scale continuous distribution of an ordered-to-disordered crystal structure within the bcc phase, i.e., the disordered A2-structure was distributed continuously in the ordered B2-structure matrix. The stress-induced martensitic transformation from the metastable nano-sized disordered A2-phase was confined by the stable B2-ordered matrix. The new findings in this study provide additional understanding of the deformation mechanisms of high-entropy alloys and insights into alloy design for further enhancement of the mechanical properties of high-performance structural materials used at cryogenic temperatures. [ABSTRACT FROM AUTHOR]