A set of dispersion strengthened Ni-3 wt.% SiC samples have been prepared via a powder metallurgy route for an application in molten salt reactor (MSR) systems. A mixture of 97 wt.% Ni and 3 wt.% SiC powder was prepared by varying the ball-milling time (8, 24, 36 and 48 h). The ball-milling process was followed by powder consolidation using spark plasma sintering (SPS) and rapid cooling to room temperature. The samples were then annealed at different temperatures (300 degrees C, 700 degrees C and 850 degrees C). The fracture behaviour of the Ni-3 wt.% SiC samples was investigated using the Small Punch Test (SPT). A scanning electron microscope (SEM) with energy dispersive spectrometer (EDS) and electron back-scatter diffraction (EBSD), as well as transmission electron microscopy (TEM) were employed to examine the microstructure of the tested Ni-3 wt.% SiC samples. The obtained results show that the SPT fracture energy is strongly dependent on the grain size of Ni matrix, which is affected by ball-milling times and annealing temperature. It has been further found that the segregation of large SiC particles at grain boundaries promotes intergranular fracture and thus significantly reduces the fracture energy. The results indicate that the distribution and size of SiC particles at grain boundary is mainly affected by the ball-milling time. Hence, the ball-milling time governs the fracture toughness of Ni-3 wt.% SiC samples.

The fracture behavior of oxide dispersion strengthened (ODS) 410L stainless steels was investigated by means of small punch testing and scanning electron microscopy. The results showed that there are noticeable strengthening effects by the addition of 0.9 μm yttria into 410L steel. Small punch testing was also conducted on a specimen of ODS 410L steel with 50 nm yttria irradiated by helium ion beam with a dose of 2 × 10 16 ion.cm–2. The small punch test is an effective method to reveal the irradiation effects in the materials.

Current and future nuclear-technologies such as fission and fusion reactor-systems depend on well-characterized structural materials, underpinned by reliable material-models. The response of the material must be understood with science-based models, under operating and accident conditions which include irradiation, high temperature and stress, corrosive environments, and magnetic fields. Neutron beams offer methods of characterizing and understanding the effects of radiation on material behaviour such as yield and tensile strength, toughness, embrittlement, fatigue and corrosion resistance. Neutron-analysis techniques improve our understanding of radiation damage, which is essential in guiding the development of new materials.

A 45XD TiAl alloy possessing a lamellar microstructure was irradiated using 5 MeV helium ions to a fluence of 5 × 1021 ion m−2 (5000 appm) with a dose of about 1 dpa (displacements per atom). A uniform helium ion stopping damage region about 17 μm deep from the target surface was achieved by applying an energy degrading wheel. Radiation damage defects including helium-vacancy clusters and small helium bubbles were found in the microstructure of the samples irradiated at room temperature. With increasing irradiation temperature to 300 °C and 500 °C helium bubbles were clearly observed in both the α2 and γ phases of the irradiated microstructure. By means of nanoindentation significant irradiation hardening was measured. For the samples irradiated at room temperature the hardness increased from 5.6 GPa to 8.5 GPa and the irradiation-hardening effect reduced to approximately 8.0 GPa for the samples irradiated at 300 °C and 500 °C.

The transformation between the face centered cubic austenitic and hexagonal close‐packed martensitic phases during high‐pressure torsion processing was observed in a Fe–Mn–C–Al twinning‐induced plasticity steel. This phase transformation was not found in the same material processed by unidirectional compressive and tensile deformation. Initiated by the high‐pressure loading, the martensite phase initially increased with torsional strain but diminished subsequently. Texture evolution of the austenitic phase was compared with the ideal texture distribution of face‐centered cubic materials after shear deformation.

A Ti–45Al–2Nb–2Mn + 0.8 vol.% TiB2 (at.%) alloy with fully lamellar microstructure consisting of hexagonal-close-packed (hcp) α2 and face-centred-tetragonal (fct) γ phases was irradiated by implanting helium ions to different fluences. Microstructural examination showed that helium cavities are formed in both the α2 and γ phases after He-ion irradiation. However, the helium cavities and their size change with fluence are much larger in the α2 phase than those in the γ phase, indicating that the γ phase exhibits better tolerance to the He-ion irradiation than the α2 phase. Since α2 and γ phases have different crystal structures, they possess differences in helium solubility and interstitial migration. These differences are responsible for the variation in radiation damage behaviour between the two phases.

The results of linear elastic finite element analyses of stress concentration factor (SCF) and through-thickness stress distribution for 80 weld toe T-butt plate geometries are presented in parametric form for tension (membrane) loading. The closed-form solutions, which describe the stress state of the two-dimensional plane stress models studied in terms of weldment angle, weld toe radius, weld attachment width and plate thickness, are accurate and wide ranging. The SCF is presented in full parametric form and also as a simple reduced expression, quantifying the degree of error from raw data in each case. An expression for the stress distribution through the potential Mode I crack plane of the uncracked geometries is also presented in full parametric form. It is anticipated that these HBC equations will be particularly useful in the calculation of weight functions for stress intensity factors (SIFs) of fatigue cracks emanating from weld toes in T-butt welded joints, especially in the presence of known residual stresses, or those resulting from peening.

A titanium aluminide (TiAl) alloy 45XD has been irradiated by a He ion beam with an energy of 5 MeV on a tandem accelerator at the Australian Nuclear Science and Technology Organization (ANSTO). The total fluence of He ions was 5 × 1017 ion cm−2. A 17 μm uniform damage region from the material surface with a helium concentration of about 5000 appm was achieved by using an energy degrading wheel in front of the TiAl target. The micro-size test specimens from the damage layer were fabricated using a focused ion beam & scanning electron microscope (FIB-SEM) system. The in situ SEM micromechanical compressive testing was carried out inside an SEM and the results indicated irradiation embrittlement in the helium affected region. Electron back scatter diffraction (EBSD) analysis has been applied to reveal the orientation of the lamellae in the TiAl specimens, and used to understand the deformation processes in the sample. The irradiation damage of gallium ion beam from FIB on the surface of TiAl sample was also investigated.

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.

In this study, the authors have investigated the combined effect of a double layer of implantation on four different metallic alloys, ODS steel MA957, Zircaloy-4, Ti–6Al–4V titanium alloy and stainless steel 316, by ions of two different species – He and Ar – on the hardening of the surface as measured by nano-indentation. The data was collected for a large number of indentations using the Continuous Stiffness Method or “CSM” mode, applying the indents on the implanted surface. Careful analysis of the data in the present investigations show that the relative hardening due to individual implantation layers can be used to obtain an estimate of the relative hardening effect of a combination of two separate implanted layers of two different species. This combined hardness was found to lie between the square root of the sum of the squares of individual hardening effects, (ΔHA2+ΔHB2)0.5 as the lower limit and the sum of the individual hardening effects, (ΔHA+ΔHB) as the upper limit, within errors, for all depths measured.

Titanium aluminide (TiAl) alloys exhibit high specific strength, low density, good oxidation, corrosion, and creep resistance at elevated temperatures, making them good candidate materials for aerospace and automotive applications. TiAl alloys also show excellent radiation resistance and low neutron activation, and they can be developed to have various microstructures, allowing different combinations of properties for various extreme environments. Hence, TiAl alloys may be used in advanced nuclear systems as high-temperature structural materials. Moreover, TiAl alloys are good materials to be used for fundamental studies on microstructural effects on irradiation behavior of advanced nuclear structural materials. This article reviews the microstructure, creep, radiation, and oxidation properties of TiAl alloys in comparison with other nuclear structural materials to assess the potential of TiAl alloys as candidate structural materials for future nuclear applications.

The alpha-beta phase transformation behavior of Zr-2.5Nb (in mass%) has been characterized in real time during an in situ neutron diffraction experiment. The Zr-2.5Nb material in the current study consists, at room temperature, of alpha-Zr phase (hcp) and two beta phases (bcc), a Nb rich beta-Nb phase and retained, Zr rich, beta-Zr(Nb) phase. It is suggested that this is related to a quench off the equilibrium solubility of Nb atoms in the Zr bcc unit cells. Vegard's law combined with thermal expansion is applied to calculate the composition of the beta-phase, which is compared with the phase diagram, revealing the system's kinetic behavior for approaching equilibrium.

In the present work in situ neutron diffraction and acoustic emission were used concurrently to study deformation twinning in two ZM20 Mg alloys with significantly different grain sizes at room temperature. The combination of these techniques allows differentionation between the twin nucleation and the twin growth mechanisms. It is shown, that yielding and immediate post-yielding plasticity in compression is governed primarily by twin nucleation, whereas the plasticity at higher strains is governed by twin growth. The current results further suggest that yielding by twinning happens in a slightly different manner in the fine-grained as compared to the coarse-grained alloy.

Neutron diffraction and acoustic emission were used in a single in situ experiment in order to study the deformation twinning of two ZM20 Mg alloys with significantly different grain sizes at room temperature. The combination of these two techniques facilitates the distinction between twin nucleation and twin growth. It is shown that yielding and immediate post-yielding plasticity in compression along the extrusion direction is governed primarily by twin nucleation, whereas plasticity at higher strains is presumably governed by twin growth and dislocation slip. It is further shown that, in the fine-grained alloy, collaborative twin nucleation in many grains dominates yielding, whereas twin nucleation in the coarse-grained alloy is progressive and occurs over a larger strain range. In addition, it is shown that, despite twin nucleation stresses increasing with decreasing grain size, roughly the same overall volume fraction of twins is formed in both fine and coarse parent grains. This confirms the difficulty of the alternative deformation modes and suggests a negligible suppressive effect of grain size on twinning in the case of the strongly textured fine-grained alloy. The current results also show that twins in the coarse-grained alloy are born less relaxed with respect to surrounding polycrystalline aggregate than those in the fine-grained alloy. This is believed to lead to lower reversal stresses acting on twin grains in the coarse-grained alloy upon unloading and thus to less untwinning and thus to a smaller pseudoelastic-like hysteresis.

A single weld bead deposited on a flat plate is a deceptively simple problem that is in practice a challenge for both measurement and prediction of weld residual stresses. Task Group 1 of the NeT collaborative network has examined this problem in an extensive programme of measurement and simulation extending from 2002 to 2008. As a result, the NeT bead on plate forms an ideal benchmark problem for the development of weld residual stress simulation techniques. One of the conclusions of NeT Task Group 1 is that the most accurate predictions of weld residual stresses in austenitic steels are achieved using mixed isotropic-kinematic material constitutive models. However, the use of these models can require both extensive materials data, and compromises in fitting either the monotonic or cyclic responses. This paper reports a detailed matrix of sensitivity studies aimed at optimising the behaviour of mixed hardening models in welding simulation, using the Lemaitre-Chaboche formulation in the ABAQUS finite element code. Predicted stresses and strains in the NeT bead on plate specimen are compared with the extensive database of residual stress measurements. Further studies examine sensitivity to the handling of high temperature inelastic strains, using a novel two-stage annealing functionality implemented within ABAQUS. The results show that, overall, the most accurate predictions are made if the Lemaitre-Chaboche parameters are optimised to fit the monotonic response over the first 2% of plastic strain. However, further improvements in prediction could be achieved if the constitutive model were capable of independently fitting both the monotonic and saturated cyclic response of the material.

The plastic deformation behavior of twinning-induced plasticity steels of composition Fe-25Mn-3Si-3Al are investigated by means of in situ synchrotron high-energy X-ray diffraction and compared to self-consistent simulations. It is the first time the alternating interaction of {1 1 1} <1 1 0> slip and {1 1 1} <1 1 2> twinning have been directly observed in situ while undergoing uniaxial tension. The deformation texture is determined mainly by dislocation gliding, while deformation twinning impedes the reinforcement of texture. (C) 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

In situ neutron diffraction has been used to investigate the deformation twinning and untwinning during cyclic uniaxial straining of hydrostatically extruded AZ31 magnesium alloy. The development of the internal stresses and microstructure in the polycrystalline alloy when twinning takes place is explained on the basis of the two pairs of parent {10.0}||, {11.0}|| and twin {00.2}||, {10.3}|| grain families. The experimentally observed pseudoelastic-like behaviour in stress–strain cycles is interpreted as being due to the activation of reversal twinning processes during loading–unloading cycles. It is proposed that the driving force for the observed untwinning is the existence of high tensile stresses in favourably oriented grains which result from significant twinning activity prior to unloading from the peak stress.

Zircaloy-4 (Zr-4) is a zirconium alloy that has been used extensively within the nuclear industry in both power generation and research reactors. The potential for welded reactor core components to undergo embrittlement during neutron irradiation is an important materials property issue to be considered throughout the service life of the reactor. Of particular interest is the performance of welded joints which depend on the properties of both the weld heat-affected zone (HAZ) and the parent metal. For this work Zr-4 HAZ was simulated using a Gleeble weld simulator to rapidly bring the material into the β-Zr zone at peak temperatures of 1200 and 1400°C. The small punch (SP) test was then used to investigate the variation in fracture behavior of these narrow zones of the weld and compare them with the parent metal. A finite element analysis (FEA) model of the SP test was developed which can be used to predict the deformation and fracture behavior of Zr-4 welds and is compared with the experimental data obtained.

A single weld bead deposited on a flat plate is a deceptively simple problem that is, in practice, a significant challenge for both measurement and prediction of weld residual stresses. Task Group 1 of the NeT collaborative network has examined this problem in an extensive programme of measurement and simulation extending from 2002 to 2008. Thus, the NeT bead on plate forms an ideal benchmark problem for the development of weld residual stress simulation techniques.It is often difficult to separate the influence of different analysis variables in a large collaborative study such as NeT Task Group 1. This paper examines sensitivity to mesh design, element type, and heat source characteristics in a closely controlled study using several different mesh designs, element types (both tetrahedral and hexahedral), and heat sources, but the same material constitutive model and finite element analysis code. It complements a companion paper that varies material constitutive models.A dedicated heat source modelling tool with a semiautomatic interface to the ABAQUS finite element code has been used to vary the heat source characteristics, thus facilitating rapid and controlled sensitivity studies without the need for bespoke heat source coding within ABAQUS.