SS 316LN with varying nitrogen content is subjected to thermal aging for 20,000 h at 650 °C to assess long-term structural integrity under operational conditions in nuclear reactors. While the ...annealing twins and heterogeneous grain evolution by bimodal division are independent of chemical composition, the type, size, and morphology of evolving secondary phases are characteristic of nitrogen concentration. Color contrast in bright field optical microscopy combined with transmission electron microscopy reveals the presence of three major precipitate phases; M
23
(C, N)
6
, Fe
2
Mo intermetallics, and Cr
2
N. Contiguously formed hetero-structures of Fe
2
Mo/Cr
2
N are quantified, and extensive formation has been observed in steels with high nitrogen content (0.14 wt. % and 0.22 wt. %). In addition to the grain boundary carbo-nitrides, the morphological derivatives of intra-granular M
23
(C, N)
6
precipitates with cube-on-cube orientation relationship such as (1) isolated cubes, (2) primary stringers/strings of cubes, (3) secondary stringers/clusters of branched primary strings, and (4) clusters of laths are identified. The stringers and laths are preferentially grown in {111}/ < 110 > γ. The growth plane and crystallographic variants of primary and secondary stringers are exclusively identified from optical micrographs. All varieties of M
23
(C, N)
6
are prominent in the sample with 0.22 wt. % nitrogen whereas, clustering of stringers and laths are absent in steels with lower nitrogen concentration. Overall mechanical properties reform by the precipitation strengthening effect due to the excess nitrogen content.
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•Identified the fine features appear in diffraction patterns of ω forming β alloy.•Comparison of simulated diffraction patterns with SADP has revealed the uncoupling of diffuse arcs ...with ω variants.•Predicted the possibility of P3m1 space group for trigonal ω by simulation experiments.•Trigonal ω is imaged in three various zone axes ( β, β and β) solely by phase contrast microscopy.•Experimental evidence for variation in degree of collapse for various ω particles is given with simulation support.•By addressing the de Fontaine’s model, it is rectified that the sphere of intensity will not fit in fcc lattice.•Refined the de Fontaine’s model by using hollow sphere of patterned intensity.
Initial stage of ω phase formation and associated anomalous features that appear in diffraction patterns of a metastable β transition metal alloy have been investigated in this study with the aid of transmission electron microscopy, simulation and modeling. The paper explores discrete features that emerge in selected area diffraction patterns of quenched Ti-15wt%Mo alloy and analyzes the correlation between ω reflections and diffuse arcs by considering all variants of ω phase as per the formation kinetics of ω phase in β matrix while quenching. Superimposed simulated diffraction patterns have been compared with experimental counterparts and it is deduced that there is lack of congruence between ω reflections and diffuse arcs even after considering trigonal ω with varying degrees of displacement. Direct lattice imaging of trigonal ω in β matrix has been demonstrated by phase contrast microscopy coupled with Fourier filtering techniques. By investigating the nature of ω reflections and diffuse arcs with the aid of electron diffraction pattern calculations and phase contrast microscopy, it is shown that, existing model of three-dimensional (3D) reciprocal space of ω forming alloy at quenched stage is not complete. A new model incorporating a patterned intensity distribution is fitted at the octahedral sites of an fcc reciprocal lattice whose planar intersections with Ewald’s sphere show a better fit with the observed experimental diffraction patterns.
Introduction: Computed Tomography Angiography (CTA) is useful for evaluating and diagnosing conditions related to blood vessels, such as aneurysms, stenosis (narrowing of vessels), vascular ...malformations, and blockages. It provides valuable information for planning and guiding interventions or surgeries. It is also important to measure patient doses during CTA operations to evaluate and optimise the technique and balance the benefits compared to radiation hazards. Aim: To calculate the CT Dose Index (CTDI), Dose Length Product (DLP), and effective dose for CT brain angiography and CT pulmonary angiography, and also to compare whether the measured values are within the International Commission on Radiological Protection (ICRP) recommended levels. Materials and Methods: A retrospective descriptive study was conducted in the Department of Radiodiagnosis at Yenepoya Medical College Hospital Mangaluru, Karnataka, India, from September 2022 to September 2023. A total of 52 data points were collected for CT brain and CT pulmonary angiography examinations, which were acquired before October 2022. Information on CTDI and DLP was collected, and the effective dose was calculated using the conversion factor. The values were then compared with the ICRP reference level. Descriptive statistics, mean, and standard deviation for continuous variables, and frequency and percentage for categorical variables were used. Results: There was a significantly lower value of CTDI, DLP, and effective dose for CT brain angiography and CT pulmonary angiography compared to the ICRP recommended reference levels. The mean CTDI and DLP for CT brain angiography were 111.56 mGy and 1153.31 mGy·cm, and the mean CTDI and DLP for CT pulmonary angiography were 24.56 mGy and 713.74 mGy·cm, respectively. The mean effective dose for CT brain and CT pulmonary angiography was 2.46 mSv and 9.94 mSv, respectively. Conclusion: The measured values were within the recommended values of ICRP regulations. It is recommended that CT brain angiography and CT pulmonary angiography examinations are safer for diagnostic purposes. Optimising scanning protocols, utilising low-dose techniques, and implementing dose monitoring and control are important clinical aspects. Compliance with the guidelines helps to enhance patient care and reduce the risk of radiation-related complications.
The trigonal/bcc orientation relationships (ORs) and their likelihood of occurrence are extensively studied using dispersed Y4Zr3O12 (δ) nano-precipitates in bcc Fe (α) matrix by means of ...transmission electron microscopy, image simulations and a crystallographic model. Two orientation relationships related by a rotation: 12̄0δ||111α with (212̄)δ||(1̄10)α and 12̄0δ||111α with (003̄)δ||(1̄10)α, are established and periodic arrays of misfit dislocation doublets are identified at the strained interface in (110)α for both ORs. Further eighteen energetically feasible ORs in Y4Zr3O12/bcc system are deduced by combining stereographic projections, which include the two predominant ORs in this study and other ORs in literature. The orientation relationship which generates interface with a minimum number of dislocation doublets is the most frequent. The precipitate size dependence of ORs and the role of predominant OR in strengthening mechanism are discussed.
Atomistic origin of stacking faults in non-close packed systems is a fundamentally distinct mechanism from the well-known close packed structures with ABC stacking, and represents an uncharted ...territory in material research. According to experimental data, stacking faults in simple hexagonal WC happen in {1-100} planes that are packed rectangularly and have ABAB stacking. This work identified the type of the defect and crystallographic behaviour by creating energetically relaxed potential atomistic models of stacking faults in WC. Experimental evidence supporting the rotation axis along stacking fault caused by variation in carbon ordering at the interstitial site has been established, in accordance with the theoretical model.
•Side bands in diffraction and striations in real space were recorded from Ti-15Mo.•Evidence for phase separation by spinodal decomposition has been established.•Spinodal waves of 1.3 nm appear in ...Mo-enriched regions.•The ω phase forms in regions without undulation, presumably Mo-lean regions.•Two different types of nano instabilities occur simultaneously in quenched Ti-15Mo.
Electron diffraction effect associated with nano-scale periodic modulations observed in a quenched Ti-15 wt%Mo alloy within ω phase forming regime has been investigated in this study by analyzing selected area diffraction patterns and high-resolution phase contrast images. Crystallographic direction of the side bands in electron diffraction associated with the periodic modulation of wavelength 1.3 nm is established as 001β which is an elastically soft direction for the body-centered cubic lattice. Characteristics of the side bands in the diffraction patterns, such as the correlation of spacing of satellite spots with real-space modulation wavelength and the constancy in the direction of satellites and modulations are interpreted as the proof of phase separation by spinodal decomposition. The striations associated with spinodal decomposition form only in Mo-enriched regions of dimensions ˜ 20 nm distributed throughout the β matrix. Accordingly, in this study, two varieties of compositional modulations that appear in the matrix are experimentally illustrated: (1) Mo-depleted and Mo-enriched domains of 10–20 nm size, and (2) The anisotropic compositional modulation by spinodal decomposition in 001β direction with a modulation wavelength of 1.3 nm occurring in Mo-enriched pockets. It is confirmed that the structural modulations and ω phase formation occurs only in the regions without striations (Mo-lean regions). By analyzing the diffraction spots, it is also shown that the ω phase does not undergo any phase separation by spinodal decomposition.
Nickel-based hardfacing alloy bushes are used in dynamic moving components inside fast breeder reactors. Due to the difficulties associated with their fabrication through casting or weld deposition, ...laser rapid manufacturing (LRM) was attempted. In this work, microstructure development and phase selection in laser additive manufactured Ni-based hardfacing alloy bushes are investigated. The as-fabricated bushes had a uniform, defect-free microstructure perpendicular to the material build direction, whereas microstructural heterogeneity could be detected parallel to the build direction due to coarsening of precipitates. Overall microstructure was dominated by
γ
-Ni,
γ
-Ni + Ni
3
B anomalous and lamellar eutectic and Ni–B–Si lamellar eutectic constituents. In addition, Cr-rich borides and carbides were also found. Phase property diagrams and Scheil’s non-equilibrium solidification simulated using ThermoCalc® provided supporting insights into the phase selection phenomena under rapid cooling conditions. Microstructure of LRM Ni-based hardfacing alloy bushes was quite distinct from weld deposited ones and is analyzed in terms of a non-equilibrium eutectic solidification reaction occurring in Ni–Cr–B–C–Si–Fe multicomponent alloy system due to rapid cooling.
The trigonal/bcc orientation relationships (ORs) and their likelihood of occurrence are extensively studied using dispersed Y4Zr3O12nano-precipitates in bcc Fe matrix by means of transmission ...electron microscopy, image simulations, and a crystallographic model. Two orientation relationships related by a rotation:1-20||111 with (21-2)||(-110) and 1-20||111 with (00-3)||(-110), are established and periodic arrays of misfit dislocation doublets are identified at the strained interface in (110) for both ORs. Further eighteen energetically feasible ORs in Y4Zr3O12/bcc system are deduced by combining stereographic projections, which include the two predominant ORs in this study and other ORs in literature. The orientation relationship which generates the interface with a minimum number of dislocation doublets is the most frequent.
Type 316LN stainless steel (SS) with varying nitrogen content (0.07, 0.14 and 0.22 wt%) was thermally aged at 873 K and 923 K for 20,000 h. The microstructures of thermally aged steels revealed ...secondary phases such as M23C6 carbides and Fe–Cr–Mo intermetallics at all the nitrogen contents and Cr2N nitrides additionally at 0.14 and 0.22 wt% N. The amount of precipitates increased with increase in nitrogen content and aging temperature. The effect of thermal aging on the tensile properties of 316LN SS was evaluated using automated ball indentation (ABI) technique at 298 K. The flow curves of the steels aged at 873 K were lower than those obtained under unaged condition. Whereas due to ageing at 923 K, the flow stress response gradually increased above the unaged condition with increasing nitrogen content. The ultimate tensile strength varied similarly at 873 K aging condition for all nitrogen levels and was observed to recuperate upon aging at 923 K, except for 0.07 wt% N. Yield strength was not strongly affected by thermal ageing, except the considerable increase in 316LN SS with 0.22 wt% N aged at 923 K. The addition of nitrogen generally imparted interstitial solid solution strengthening to 316LN SS. The higher the nitrogen content and ageing temperature, the higher is the precipitation strengthening due to ageing, which was reflected in the tensile behavior. Transmission electron microscopy examination of ABI deformed zone revealed dislocation-precipitate interactions, precipitate-shear band interaction and pile-up of dislocations at precipitates, influencing the tensile properties.
•Combined effect of ageing temperature and nitrogen content on 316LN SS was investigated using ABI technique.•The addition of nitrogen generally imparted interstitial solid solution strengthening to 316LN SS.•Evolution of precipitates on ageing 316LN SS at 873 K and 923 K for 20000 h are presented.•Higher the nitrogen content and ageing temperature, higher is the precipitation strengthening.•TEM studies on the plastic zone deformed under tip of ABI indenter are presented.
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