Abstract An attempt is being made to develop novel Ni-Mo-W-Cr-Al-X alloys with ICME approach with critical experimental/simulations and processing/microstructural characterization/property evaluation and performance testing has been adopted. In this work, based on thermodynamic modeling five alloy compositions with varying Mo/W and two alloys with high tungsten modified with the addition of Al or Ti were selected and prepared. The newly developed alloys were evaluated for their response to thermal aging in the temperature range of 700 to 850 °C and corrosion in the KCl-NaCl-MgCl2 salt under suitable conditions. Thermally aged and post-corrosion test samples were characterized to ascertain phase transformations, microstructural changes and corrosion mechanisms. Al/Ti modified alloys showed significant change in hardness after 400 hours aging at 750°C, which was found to be due to the presence of fine γ’/γ” precipitates along with plate-shaped W/Mo-rich particles. These alloys show comparable molten salt corrosion resistance as commercial alloys at 750°C for 200-hour exposures. The good corrosion behavior of these alloys may be attributed to the formation of a protective multicomponent Al-or Ti-enriched oxide as well as the unique microstructure.

As super-saturated solid solutions of Al-Mg, 5XXX series aluminum alloys are susceptible to sensitization via intergranular precipitation of the anodic beta-phase, which promotes intergranular corrosion, exfoliation and stress corrosion cracking under environmental conditions. This study presents important updates to a Johnson-Mehl-Avarami-Kolmogorov (JMAK) type model for low-temperature sensitization, correlating the intergranular corrosion response to impingement of locally sensitized regions surrounding discrete beta-phase grain boundary precipitates. It is demonstrated that the sensitization response of these alloys can be approached as a combination of two independent contributions: the geometric configuration of grain boundaries passing through the microstructure that are most prone to sensitization, and the rate that these boundaries sensitize due to the formation of the beta-phase. This allows for the large sensitization response variations found between nominally identical materials produced by different suppliers, which originate due to a lack of constraints within current cold-rolled plate tempers, to be removed as a sample-dependent linear scaling factor that is separate of the rate kinetics. The JMAK model describes the kinetics of 5xxx series sensitization with excellent accuracy across all data available in the literature. The results of the model imply that sensitization at environmental temperatures proceeds via a site-saturated process, with the beta-phase forming on a set density of preferential nucleation sites. It is shown that site-saturation allows for extension of the JMAK model to non-isothermal aging profiles and supports a diffusion pathway dominated by pipe diffusion to the interface followed by precipitate growth via the collector plate mechanism.

Laser Shock Peening with (LSP) and without protective coating (LPwC) was applied to sensitized AA5083 followed by electrochemical analysis. Potentiodynamic tests indicated a region of increased passivity for the LPwC samples with lower corrosion current. Similarly, significantly reduced intergranular corrosion rate was observed during potentiostatic polarization after LPwC treatment while LSP samples showed only a negligible improvement. The results are attributed to the unique recast surface layer composed of a modified oxide film followed by an embedded oxygen-rich aluminum nanoparticles sub-surface layer without grain boundary β-phase created during laser pulse interaction with the surface when no coating was applied.

Aluminium alloy 5083 was subjected to Laser Shock Peening both with (LSP) and without protective coating (LPwC) at multiple pulse densities. A second LPwC treatment was conducted fully submersed under water, in addition to the standard laminar water flow condition. The results show that compressive residual stresses were generated in all cases, although their character varied depending on the peening strategy and method of confinement. In all cases, higher pulse density lead to an increase in compressive stresses with a saturation point of −325 MPa at 1089 p/cm2 for the LPwC treatments. Corrosion fatigue testing of sensitized samples then showed 59% and 69% improvement in fatigue strength after the LSP and LPwC treatments, respectively.

Among metal additive manufacturing technologies, additive friction stir deposition stands out for its ability to create freeform and fully-dense structures without melting and solidification. Here, we employ a comparative approach to investigate the process-microstructure linkages in additive friction stir deposition, utilizing two materials with distinct thermomechanical behavior—an Al-Mg-Si alloy and Cu—both of which are challenging to print using beam-based additive processes. The deposited Al-Mg-Si is shown to exhibit a relatively homogeneous microstructure with extensive subgrain formation and a strong shear texture, whereas the deposited Cu is characterized by a wide distribution of grain sizes and a weaker shear texture. We show evidence that the microstructure in Al-Mg-Si primarily evolves by continuous dynamic recrystallization, including geometric dynamic recrystallization and progressive lattice rotation, while the heterogeneous microstructure of Cu results from discontinuous recrystallization during both deposition and cooling. In Al-Mg-Si, the continuous recrystallization progresses with an increase of the applied strain, which correlates with the ratio between the tool rotation rate Ω and travel velocityV. Conversely, the microstructure evolution in Cu is found to be less dependent on Ω, instead varying more with changes to V. This difference originates from the absence of Cu rotation in the deposition zone, which reduces the influence of tool rotation on strain development. We attribute the distinct process-microstructure linkages and the underlying mechanisms between Al-Mg-Si and Cu to their differences in intrinsic thermomechanical properties and interactions with the tool head.

The gamma-FCC (face-centered cubic) to epsilon-HCP (hexagonal close packed) phase transformation in a laser additively fabricated Co-29Cr-5Mo alloy was investigated. The microstructure of the as-built material was gamma--FCC featured with a sub-micron scale dislocation cell structure and stacking faults. Aging at 1073 K led to rapid transformation within 0.5 h to the epsilon-HCP structure in a massive mode, characterized by: (i) composition invariance, (ii) oriented grain face nucleation; and (iii) interface-controlled linear growth mechanism. Effective lowering of the carbon content in the gamma--FCC by partial tie-up as carbides along prior grain and dislocation cell boundaries and the diverse grain structure and interfaces are believed to promote the massive transformation. (C) 2020 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

This study reports an angular diffraction peak shift that scales linearly with the neutron beam path length traveled through a diffracting sample. This shift was observed in the context of mapping the residual stress state of a large U–8 wt% Mo casting, as well as during complementary measurements on a smaller casting of the same material. If uncorrected, this peak shift implies a non-physical level of residual stress. A hypothesis for the origin of this shift is presented, based upon non-ideal focusing of the neutron monochromator in combination with changes to the wavelength distribution reaching the detector due to factors such as attenuation. The magnitude of the shift is observed to vary linearly with the width of the diffraction peak reaching the detector. Consideration of this shift will be important for strain measurements requiring long path lengths through samples with significant attenuation. This effect can probably be reduced by selecting smaller voxel slit widths.

Finite element (FE) analysis was used to simulate the strain history of an α-uranium foil during cold straight-rolling, with the sheet modeled as an isotropic elastoplastic continuum. The resulting strain history was then used as input for a viscoplastic self-consistent (VPSC) polycrystal plasticity model to simulate crystallographic texture evolution. Mid-plane textures predicted via the combined FE→VPSC approach show alignment of the (010) poles along the rolling direction (RD), and the (001) poles along the normal direction (ND) with a symmetric splitting along RD. The surface texture is similar to that of the mid-plane, but with a shear-induced asymmetry that favors one of the RD split features of the (001) pole figure. Both the mid-plane and surface textures predicted by the FE→VPSC approach agree with published experimental results for cold straight-rolled α-uranium plates, as well as predictions made by a more computationally intensive full-field crystal plasticity based finite element model. α-uranium foils produced by cold-rolling must typically undergo a recrystallization anneal to restore ductility prior to their final application, resulting in significant texture evolution from the cold-rolled plate deformation texture. Using the texture measured from a foil in the final recrystallized state, coefficients of thermal expansion and the elastic stiffness tensors were calculated using a thermo-elastic self-consistent model, and the anisotropic yield loci and flow curves along the RD, TD, and ND were predicted using the VPSC code.

Key differences in the textures of cold-, warm-, and hot-rolled Mg alloy AZ31 sheets and plates are identified. It is shown that incorporation of compression twinning within Visco-Plastic Self-Consistent (VPSC) polycrystal plasticity simulations reproduces key features of the cold-rolling texture that have not previously been predicted. Discussion of recent observations of recrystallization and grain growth provide explanations for the hot-rolled texture. Finally, it is demonstrated that starting with the correct initial texture is essential to produce observed features in all the rolling textures, including warm-rolling.

An empirical model for the evolution of β-phase (Mg2Al3) along grain boundaries in aluminium alloy AA5083 (Al-Mg-Mn) during isothermal exposures is proposed herein. Developing a quantitative understanding of grain boundary precipitation is important to interpreting intergranular corrosion and stress corrosion cracking in this alloy system. To date, complete ab initio models for grain boundary precipitation based upon fundamental principles of thermodynamics and kinetics are not available, despite the critical role that such precipitates play in dictating intergranular corrosion phenomena. Empirical models can therefore serve an important role in advancing the understanding of grain boundary precipitation kinetics, which is an approach applicable beyond the present context. High resolution scanning electron microscopy was to quantify the size and distribution of β-phase precipitates on Ga-embrittled intergranular fracture surfaces of AA5083. The results are compared with the degree of sensitisation (DoS) as judged by nitric acid mass loss testing (ASTM-G67-04), and discussed with models for sensitisation in 5xxx series Al-alloys. The work herein allows sensitisation to be quantified from an unambiguous microstructural perspective.

Starting with electron backscattered diffraction (EBSD) data obtained from a warm clock-rolled alpha-uranium deformation microstructure, a Potts Monte Carlo model was used to simulate static site-saturated recrystallization and test which recrystallization nucleation conditions within the microstructure are best validated by experimental observations. The simulations support prior observations that recrystallized nuclei within alpha-uranium form preferentially on non-twin high-angle grain boundary sites at 450 degrees C. They also demonstrate, in a new finding, that nucleation along these boundaries occurs only at a highly constrained subset of sites possessing the largest degrees of local deformation. Deformation in the EBSD data can be identified by the Kernel Average Misorientation (KAM), which may be considered as a proxy for the local geometrically necessary dislocation (GND) density. (C) 2017 Elsevier B.V. All rights reserved.

Polycrystalline elastic moduli and stiffness tensor components of g-phase U - 8 wt% Mo have been determined by resonant ultrasound spectroscopy in the temperature range of 25-650 degrees C. The ambient temperature elastic properties are compared to results measured via other experimental methods and show reasonable agreement, though there is considerable variation of these properties within the literature at both the U - 8 wt% Mo composition and as a function of Mo concentration. The Young's modulus of U - 8 wt% Mo measured in this study decreases steadily with temperature at a rate that is slower than trends previously observed at similar Mo concentrations, though the difference is not statistically significant. This first measurement of the temperature dependent elastic stiffness tensor of a polycrystalline U-Mo alloy clarifies that the behavior of the Young's modulus is due to a strongly weakening C-11 polycrystalline stiffness tensor component, along with milder decreases in C-12 and C-44. The unique partially auxetic properties recently predicted for single-crystalline U-Mo are discussed in regard to their possible impact on the polycrystalline behavior of the alloy. (c) 2017 Elsevier B.V. All rights reserved.

The texture of recrystallized straight-rolled α-uranium foils, a component in prospective irradiation target designs for medical isotope production, has been measured by neutron diffraction, as well as X-ray diffraction using both Cu and Mo sources. Variations in the penetration depth of neutron and X-ray radiation allow for determination of both the bulk and surface textures. The bulk α-uranium foil texture is similar to the warm straight-rolled plate texture, with the addition of a notable splitting of the (001) poles along the transverse direction. The surface texture of the foils is similar to the bulk, with an additional (001) texture component that is oriented between the rolling and normal directions. Differences between the surface and bulk textures are expected to arise from shear forces during the rolling process and the influence that distinct strain histories have on subsequent texture evolution during recrystallization.

Sensitization of marine grade AA5xxx aluminum alloys results from precipitation of the intermetallic beta phase along grain boundaries and is typically assessed by the destructive ASTM G67 procedure. Recently it has been shown that a Johnson-Mehl-Avarami-Kolmogorov model of grain boundary precipitation kinetics can be used to predict sensitization under isothermal aging conditions. This paper addresses the viability of expanding the isothermal model to cases with thermal history functions, utilizing parameters determined from controlled isothermal cases. Some fundamental assumptions required for non-isothermal expansion are examined using the special case of cyclic thermal treatments, suggesting the model may be applied to more complex thermal histories, especially in the form of environmental daily cycles. In this extended investigation, it is demonstrated that the grain boundary precipitation model predicts the kinetic behavior of sensitization with a remarkable (R-2) over bar = 0.965, although experimental deviations in microstructure and application of the ASTM Standard G67 contribute to a relatively large variability in the raw sensitization measurements. The model is then compared to one contemporary case study, confirming a direct correlation with beta-phase grain boundary coverage (R-2 = 0.985) that substantiates certain fundamental assumptions.

Using first principles calculations, it is demonstrated that solute segregation during U-Mo solidification can be modeled using the classic Brody-Fleming limited diffusion framework. The necessary supporting equations specific to the U-Mo alloy, along with careful verification of the assumptions underpinning the Brody-Fleming model are developed, allowing for concentration profile predictions as a function of alloy composition and cooling rate. The resulting model is compared to experimental solute concentration profiles, showing excellent agreement. Combined with complementary modeling of dendritic feature sizes, the solute segregation model can be used to predict the complete microstructural state of individual U-Mo volume elements based upon cooling rates, informing ideal processing routes.

The a-phase transformation kinetics of as-cast U - 8 wt% Mo below the eutectoid temperature have been established by in situ neutron diffraction. alpha-phase weight fraction data acquired through Rietveld refinement at five different isothermal hold temperatures can be modeled accurately utilizing a simple Johnson-Mehl-Avrami-Kolmogorov impingement-based theory, and the results are validated by a corresponding evolution in the g-phase lattice parameter during transformation that follows Vegard's law. Neutron diffraction data is used to produce a detailed Time-Temperature-Transformation diagram that improves upon inconsistencies in the current literature, exhibiting a minimum transformation start time of 40 min at temperatures between 500 degrees C and 510 degrees C. The transformation kinetics of U - 8 wt% Mo can vary significantly from as-cast conditions after extensive heat treatments, due to homogenization of the typical dendritic microstructure which possesses non-negligible solute segregation. (C) 2016 Elsevier B.V. All rights reserved.

Sensitization of marine grade Al-Mg alloys originates from grain boundary precipitation of the intermetallic beta-phase and is typically assessed by destructive nitric acid mass loss testing (NAMLT). This paper presents a simple model based upon beta-phase precipitation kinetics that can predict the NAMLT values of Al-Mg alloys as a function of isothermal aging temperature and time, directly relating beta-phase grain boundary coverage to industry standards and providing a pathway for non-destructive sensitization measurement. (C) 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Hand portability of non-contact optical profilometers represents a significant technological breakthrough for wide-area industrial processes such as grit blasting, capable of replacing mechanical styluses and providing real time assessment of surface roughness without damaging sampled areas. This paper demonstrates the possibility of building depth from defocus profilometers using off the shelf components, allowing for improved portability, affordability, and customization compared to similar table-top commercial products. An outlined demonstration device is proven to be capable of matching the performance of an ISO/NIST standardized mechanical profilometer for isotropic rough surfaces in the 2–10 μm Ra range with R2 > 0.96, and important considerations for each component of the assembly are addressed in detail. A prototype for a next generation liquid-lens based depth from defocus optical profilometer is also presented along with the technological obstacles found to be associated with such devices.