Browsing by Author "Bhattacharyya, D"
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- ItemCharacterization of complex carbide–silicide precipitates in a Ni–Cr–Mo–Fe–Si alloy modified by welding(Elsevier B.V., 2015-07-01) Bhattacharyya, D; Davis, J; Drew, M; Harrison, RP; Edwards, LNickel based alloys of the type Hastelloy-N™ are ideal candidate materials for molten salt reactors, as well as for applications such as pressure vessels, due to their excellent resistance to creep, oxidation and corrosion. In this work, the authors have attempted to understand the effects of welding on the morphology, chemistry and crystal structure of the precipitates in the heat affected zone (HAZ) and the weld zone of a Ni–Cr–Mo–Fe–Si alloy similar to Hastelloy-N™ in composition, by using characterization techniques such as scanning and transmission electron microscopy. Two plates of a Ni–Cr–Mo–Fe–Si alloy GH-3535 were welded together using a TiG welding process without filler material to achieve a joint with a curved molten zone with dendritic structure. It is evident that the primary precipitates have melted in the HAZ and re-solidified in a eutectic-like morphology, with a chemistry and crystal structure only slightly different from the pre-existing precipitates, while the surrounding matrix grains remained unmelted, except for the zones immediately adjacent to the precipitates. In the molten zone, the primary precipitates were fully melted and dissolved in the matrix, and there was enrichment of Mo and Si in the dendrite boundaries after solidification, and re-precipitation of the complex carbides/silicides at some grain boundaries and triple points. The nature of the precipitates in the molten zone varied according to the local chemical composition. © 2015 Elsevier Inc.
- ItemCharacterization of complex carbide–silicide precipitates in a Ni–Cr–Mo–Fe–Si alloy modified by welding(Materials Australian and The Australian Ceramic Society, 2015-02-09) Bhattacharyya, D; Davis, J; Drew, M; Harrison, RP; Edwards, LNickel based alloys of the type Hastelloy-N™ are ideal candidate materials for molten salt reactors, as well as for applications such as pressure vessels, due to their excellent resistance to creep, oxidation and corrosion. In this work, the authors have attempted to understand the effects of welding on the morphology, chemistry and crystal structure of the precipitates in the heat affected zone (HAZ) and the weld zone of a Ni–Cr–Mo–Fe–Si alloy similar to Hastelloy-N™ in composition, by using characterization techniques such as scanning and transmission electron microscopy. Two plates of a Ni–Cr–Mo–Fe–Si alloy GH-3535 were welded together using a TiG welding process without filler material to achieve a joint with a curved molten zone with dendritic structure. It is evident that the primary precipitates have melted in the HAZ and re-solidified in a eutectic-like morphology, with a chemistry and crystal structure only slightly different from the pre-existing precipitates, while the surrounding matrix grains remained unmelted, except for the zones immediately adjacent to the precipitates. In the molten zone, the primary precipitates were fully melted and dissolved in the matrix, and there was enrichment of Mo and Si in the dendrite boundaries after solidification, and re-precipitation of the complex carbides/silicides at some grain boundaries and triple points. The nature of the precipitates in the molten zone varied according to the local chemical composition. - Graphical abstract: Display Omitted - Highlights: • Ni-based alloy with Cr, Mo, Si, Fe and C was welded, examined with SEM, EBSD, and TEM. • Original Ni{sub 2}(Mo,Cr){sub 4}(Si,C) carbides changed from equiaxed to lamellar shape in HAZ. • Composition and crystal structure remained almost unchanged in HAZ. • Original carbides changed to lamellar Ni{sub 3}(Mo,Cr){sub 3}(Si,C) in some cases in weld metal. • Precipitates were mostly incoherent, but semi-coherent in some cases in weld metal.
- ItemA comparative study of two nanoindentation approaches for assessing mechanical properties of ion-irradiated stainless steel(The Minerals, Metals & Materials Society, 2020-02-26) Bhattacharyya, D; Saleh, M; Xu, A; Zaidi, Z; Hurt, C; Ionescu, MNot available
- ItemComparison of implantation and diffusion behavior of Ti, Sb and N in ion-implanted single crystal and polycrystalline ZnO: a SIMS study(Elsevier, 2010-01-15) Lee, J; Metson, J; Evans, PJ; Pal, U; Bhattacharyya, DImplantation and diffusion behavior of Sb, Ti and N in ZnO single crystal and sputter deposited thin films were studied through secondary ion mass spectrometric studies on ion-implanted and thermally annealed samples. Sb was implanted and Ti and N were co-implanted into ZnO single crystals and polycrystalline thin films on Si substrates at room temperature. The implanted samples were then annealed at 800°C. Depth profiles of implant distributions before and after annealing were examined by Secondary Ion Mass Spectrometry (SIMS). As expected, implant range is sensitive to the mass of the dopants; and the dopant distribution is broadened as implanted elements migrate deeper into the film on thermal annealing. While diffusion of N in the ZnO thin film is not significant, Ti tends to diffuse deeper into the sample during annealing. For Ti and N co-implanted single crystal, annealing induced diffusion causes more redistribution of the lighter N than Ti. In general, implanted dopants diffuse more easily in thin films compared to the single crystal due to the presence of grain boundaries in the latter. © 2010, Elsevier Ltd.
- ItemDefect evolution in a NiMoCrFe alloy subjected to high-dose Kr ion irradiation at elevated temperature(Elsevier B.V., 2016-06-01) de los Reyes, M; Voskoboinikov, R; Kirk, MA; Huang, HF; Lumpkin, GR; Bhattacharyya, DA candidate NiMoCrFe alloy (GH3535) for application as a structural material in a molten salt nuclear reactor was irradiated with 1 MeV Kr2+ ions (723 K, max dose of 100 dpa) at the IVEM-Tandem facility. The evolution of defects like dislocation loops and vacancy- and self-interstitial clusters was examined in-situ. For obtaining a deeper insight into the true nature of these defects, the irradiated sample was further analysed under a TEM post-facto. The results show that there is a range of different types of defects formed under irradiation. Interaction of radiation defects with each other and with pre-existing defects, e.g., linear dislocations, leads to the formation of complex microstructures. Molecular dynamics simulations used to obtain a greater understanding of these defect transformations showed that the interaction between linear dislocations and radiation induced dislocation loops could form faulted structures that explain the fringed contrast of these defects observed in TEM. © 2016 Elsevier B.V.
- ItemDeformation behaviour of hexagonal- and circular-patterned Ni single-crystal 2D micro-lattices via in situ micro-tensile testing and computational analysis(Springer Nature Limited, 2022-04-22) Xu, A; Saleh, M; Bhattacharyya, DThe effects of hole shape and orientation on the mechanical properties of micro-scale 2D honeycomb structures, fabricated using a focused ion beam equipment, have been investigated using an in situ micro-mechanical testing machine inside the scanning electron microscope . The material used was single-crystal Ni oriented in the < 100 > direction, with the plane of the 2D micro-lattice having a {001} normal direction. The hole shapes explored were hexagonal and circular, while two different orientations of the hexagonal holes were also compared. One of these orientations had a horizontal arm (designated 0° orientation), while the other had a vertical arm (30° orientation) in each hexagon. The results indicate that there is substantial change in strength and ductility depending on the orientation and shape of the holes with respect to the tensile axis. The samples with 30° oriented hexagonal holes had the lowest strength and highest ductility, while the samples with circular holes showed the greatest yield and tensile strength. The samples with the 0° orientated hexagonal holes had much higher strength and lower ductility than the 30° orientated ones. Moreover, the samples with 0° orientated hexagonal holes, which had a similar hole pattern arrangement to the ones with circular holes, had a similar strength to those of the latter type. Thus, it is apparent from this study that the orientation or arrangement of the holes is more important in determining the properties of the 2D microlattice than the shape of the holes. Finite element simulation of the lattice structures utilised the GTN (Gurson, Tvergaard and Needleman) model to evaluate the failure modes under uniaxial tension. The lattice structure has been shown, in a previous paper by the authors, to exhibit composite like behaviour with strength differences in various parts arising from size effects. These size effect variations were incorporated into the model, and a generalised formulation for the GTN parameters was proposed on the basis of one of the experimental configurations and subsequently applied to the other geometries. The models were in good quantitative agreement with the experimental results with accurate representation of the flows stress and failure modes. © 2022, The Author(s), under exclusive licence to Springer Science Business Media, LLC, part of Springer Nature
- ItemEffect of double ion implantation and irradiation by Ar and He ions on nano-indentation hardness of metallic alloys(Elsevier, 2013-07-01) Dayal, P; Bhattacharyya, D; Mook, WM; Fu, EG; Wang, YQ; Carr, DG; Anderogluc, O; Mara, NA; Misra, A; Harrison, RP; Edwards, LIn 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.© 2013, Elsevier B.V.
- ItemHigh spin polarization in the disordered quaternary Heusler alloy FeMnVGa(American Physical Society, 2023-07-25) Gupta, S; Chakraborty, S; Bhasin, V; Pakhira, S; Dan, S; Barreteau, C; Crivello, JC; Jha, SN; Avdeev, M; Greneche, JM; Bhattacharyya, D; Alleno, E; Mazumdar, CIn this paper, we report the successful synthesis of a Fe-based highly spin-polarized quaternary Heusler alloy FeMnVGa and its structural, magnetic, and transport properties probed through different experimental methods and theoretical techniques. Density functional theory (DFT) calculations performed on different types of structures reveal that the structure with Ga at 4a, V at 4b, Mn at 4c, and Fe at 4d (space group F¯43m) possess minimum energy among all the ordered variants. Ab initio simulations in the most stable ordered structure show that the compound is a ferromagnet having a large spin-polarization (89.9%). Neutron diffraction reveals that the compound crystallizes in disordered type-2 structure (space group Fm¯3m) in which Ga occupies at 4a, V 4b and Fe/Mn occupy 4c/4d sites with 50:50 proportions. The structural disorder is further confirmed by x-ray diffraction, extended x-ray absorption fine structure, 57Fe Mössbauer spectrometry results, and DFT calculations. Magnetization studies suggest that the compound orders ferromagnetically below TC∼293 K and the saturation magnetization follows the Slater-Pauling rule. Mössbauer spectrometry, along with neutron diffraction, suggest that Mn is the major contributor to the total magnetism in the compound, consistent with the theoretical calculations, which also indicates that spin polarization remains high (81.3%), even in the presence of such large atomic disorder. The robustness of the half-metallic ferromagnetic (HMF) property in the presence of disorder is a quite unique characteristic over other reported HMF in literature and makes this compound quite promising for spintronics applications. ©2023 American Physical Society.
- ItemHigh spin-polarization in a disordered novel quaternary Heusler alloy FeMnVGa(Cornell University, 2023-03-15T12:51:40Z) Gupta, S; Chakraborty, S; Bhasin, V; Pakhira, S; Dan, S; Barreteau, C; Crivello, JC; Jha, SN; Avdeev, M; Greneche, JM; Bhattacharyya, D; Alleno, E; Mazumdar, CIn this work, we report the successful synthesis of a Fe-based novel half-metallic quaternary Heusler alloy FeMnVGa and its structural, magnetic and transport properties probed through different experimental methods and theoretical technique. Density functional theory (DFT) calculations performed on different types of structure reveal that Type-2 ordered structure (space group: F-43m, Ga at 4a, V at 4b, Mn at 4c and Fe at 4d) possess minimum energy among all the ordered variants. Ab-initio simulations in Type 2 ordered structure further reveal that the compound is half-metallic ferromagnet (HMF) having a large spin-polarization (89.9 %). Neutron diffraction reveal that the compound crystalizes in disordered Type-2 structure (space group: Fm-3m) in which Ga occupy at 4a, V at 4b and Fe/Mn occupy 4c/4d sites with 50:50 proportions. The structural disorder is further confirmed by X-ray diffraction (XRD), extended X-ray absorption fine structure (EXAFS),57Fe Mossbauer spectrometry results and DFT calculations. Magnetisation studies suggest that the compound orders ferromagnetically below TC ~ 293 K and the saturation magnetization follows Slater-Pauling rule. Mossbauer spectrometry, along with neutron diffraction suggest that Mn is the major contributor to the total magnetism in the compound consistent with the theoretical calculations. First principle calculations indicate that spin-polarization remain high (81.3 %) even in the presence of such large atomic disorder. The robustness of the HMF property in presence of disorder is a quite unique characteristic over other reported HMF in literature and make this compound quiet promising for spintronics applications.
- ItemIn situ micro tensile testing of He+ ion irradiated single crystal nickel film(Australian Microscopy and Microanalysis Society, 2015-11-01) Bhattacharyya, D; Reichardt, A; Ionescu, M; Davis, J; Hosemann, P; Harrison, RP; Edwards, LIntroduction : Radiation damage can cause increase in strength and decrease in ductility, thus reducing the service life of structural parts in reactors. Ion beam irradiation has been a method of choice to simulate the effects of neutron irradiation in a reactor for some time now [1], since it enables the attainment of reasonable doses within hours, instead of years inside a reactor. A major problem in this method is that the damaged region is very shallow, and mechanical testing of such thin layers is extremely difficult. In this study, we have used in situ micro-tensile testing in the scanning electron microscope (SEM) to understand the effects of high energy ion beam irradiation on the mechanical properties of a single crystal nickel thin film. Experiments Single crystal Nickel foils, ~12.8-13.1 μm thick, were irradiated with 6 MeV He+ ions in the Tandetron “STAR” accelerator at ANSTO. The samples were irradiated to two different fluences – (i) 2 x 1017 ions/cm2 (peak damage of ~ 10 displacements per atom or dpa), and (ii) 3.8 x 10 17 ions/cm2 (peak damage of ~19 dpa). Damage profiles calculated using the SRIM software [2], showed that there is a long, low tail of the profile beginning at the entry face and extending to approximately 9-10 μm depth, after which the damage rises sharply (Fig. 1(a)). Micro-tensile samples of approximate dimensions 25-30 μm (l) x 10 μm (w) x 12-13 μm (h) were fabricated using a Zeiss® Auriga 60™ Cross-Beam™ instrument. The free end of the sample was milled to obtain a rectangular hole which was used as a grip. The end of the tensile device, shaped as an L shaped hook, was inserted into the aforementioned rectangular hole. The sample was then subjected to tension by applying a voltage to a piezo-electric device attached to the tensile head, causing it to move at a rate of ~20 nm/sec. SEM images were taken at regular intervals, and the strain measured using two fiducial markers, one on each side of the gauge length. Results : An image of a typical tensile sample used in these tests is shown in Figure 1(b), before the start of the test. The SEM image in Figure 1(c) shows the unirradiated sample after a tensile strain of e ~ 56%. The sample had a Y.S. of ~70- 100 MPa, and an U.T.S. of ~240 MPa (see Fig. 2). There was significant strain hardening up to the U.T.S., and subsequently it underwent plastic strain with large slip bands passing on two major sets of planes in an alternate manner. The formation of these slip bands was accompanied by small drops in the stress and increases in strain. A post- test SEM image of a sample irradiated with 6 MeV He+ ions to a fluence of ~2e17 ions/ cm2 and a peak damage of ~ 10 dpa is presented in Fig. 1(d), showing slip bands passing through the whole thickness of the sample and fracture at the lower surface, which in this case is the “exit surface” of the ions. This sample had a Y.S. of ~ 195-230 MPa, and a peak strength of ~358 MPa before first rupture at the surface near peak damage, at a strain of about 1.9% (Fig. 2). A post-test SEM image of the sample fabricated from the foil irradiated with He+ ions to a total fluence of 3.8e17 ions/ cm2 and a peak damage of ~ 19 dpa is shown in Figure 1(e). This sample showed a Y.S. of ~ 400 MPa and a peak strength of ~ 500 MPa before first rupture at the exit surface of the ions, which is the top surface in this case. Conclusions: The effect of He+ ion irradiation on the tensile strength of Ni single crystals was measured successfully by in situ micro- tensile testing of FIB-fabricated samples which included the damaged layers. The results showed increase in average strength of up to ~118 MPa for a total fluence of 2e17 ions/ cm2 and ~260 MPa for a peak damage of ~3.8e17 ions/cm2. Brittle fracture was observed in the irradiated samples at the surface nearer to the peak damage layer.
- ItemIn situ micro tensile testing of He+2 ion irradiated and implanted single crystal nickel film(Elsevier B.V., 2015-11-01) Reichardt, A; Ionescu, M; Davis, J; Edwards, L; Harrison, RP; Hosemann, P; Bhattacharyya, DThe effect of ion irradiation on the tensile properties of pure Ni single crystals was investigated using an in situ micro-mechanical testing device inside a scanning electron microscope. A 12.8 μm-thick Ni film with {0 0 1} plane normal was irradiated with 6 MeV He+2 ions to peak damage of 10 and 19 displacements per atom (dpa). Micro-tensile samples were fabricated from the specimens parallel to the plane of the film using a focused ion beam (FIB) instrument, and tested in tension along [1 0 0] direction, up to fracture. The peak strength increased from ∼230 MPa for the unirradiated material to about 370 MPa and 500 MPa for the 10 dpa and 19 dpa samples respectively, while the ductility decreased with increasing dose. The surface near the peak damage regions fractured in a brittle manner, while the regions with smaller dose underwent significant plastic deformation. Slip bands extended to the peak-damage zone in the sample with a dose of 19 dpa, but did not propagate further. Transmission electron microscopy confirmed the stopping of the slip bands at the peak-damage region, just before the high He concentration region with voids or bubbles. By removing the peak damage region and the He bubble region with FIB, it was possible to attain propagation of slip bands through the entire remaining thickness of the sample. This material removal also made it possible to calculate the irradiation hardening in the region with peak hardness – thus enabling the separation of hardening effects in the high and low damage regions. © 2015 Elsevier Ltd.
- ItemInvestigating bulk mechanical properties on a micro-scale: micro-tensile testing of ultrafine grained Ni–SiC composite to determine its fracture mechanism and strain rate sensitivity(Elsevier, 2020-03-15) Xu, A; Yang, C; Thorogood, GJ; Bhattacharyya, DIn this study, in-situ micro-tensile testing technique was used to investigate the mechanical properties of ultrafine grained Ni-3wt% SiC composite the size effect on the mechanical properties of the ultrafine grained Ni-3wt% SiC composite, and to further reveal the reasons for the low ductility of the bulk Ni-3wt%SiC composite. Dog-bone micro-tensile samples were manufactured using a Focused Ion Beam (FIB) milling machine to 15 μm length with a cross sectional area of 5 μm by 5 μm. The micro-tensile samples are pulled in tension at a quasi-static strain rate of 0.000087/s (LSR) and a relatively faster strain rate of 0.011/s (HSR). Analysis of experimental stress-strain plots for the LSR tests measured yield stress, ultimate tensile stress and modulus values that approach values previously reported for bulk/macro-level tensile tests. However, the elongation and fracture energy at the micro-level is approximately half that at the bulk scale. This discrepancy is attributed to the presence of unwanted carbon and silicon oxide impurities ∼1.5 μm in diameter which act as stress concentrators especially given their large size relative to the width of the tensile specimens. The composition of these impurities was validated by transmission electron microscopy, and they seem to be the most likely cause of low ductility of the Ni-3wt% SiC composite. In all, the study undertaken here was able to replicate mechanical properties observed at the macro scale as well as reproduce a strain rate effect. Furthermore, the failure mode of Ni-3wt% SiC composite was identified and analysed in detail. Crown Copyright © 2019 Published by Elsevier B.V
- ItemInvestigating bulk mechanical properties on a micro-scale: micro-tensile testing of ultrafine grained Ni–SiC composite to determine its fracture mechanism and strain rate sensitivity(The Minerals, Metals & Materials Society, 2020-02-25) Bhattacharyya, D; Xu, A; Yang, C; Thorogood, GJIn this study, in-situ micro-tensile testing technique was used to investigate the mechanical properties of ultrafine grained Ni-3wt% SiC composite the size effect on the mechanical properties of the ultrafine grained Ni-3wt% SiC composite, and to further reveal the reasons for the low ductility of the bulk Ni-3wt%SiC composite. Dog-bone micro-tensile samples were manufactured using a Focused Ion Beam (FIB) milling machine to 15 μm length with a cross sectional area of 5 μm by 5 μm. The micro-tensile samples are pulled in tension at a quasi-static strain rate of 0.000087/s (LSR) and a relatively faster strain rate of 0.011/s (HSR). Analysis of experimental stress-strain plots for the LSR tests measured yield stress, ultimate tensile stress and modulus values that approach values previously reported for bulk/macro-level tensile tests. However, the elongation and fracture energy at the micro-level is approximately half that at the bulk scale. This discrepancy is attributed to the presence of unwanted carbon and silicon oxide impurities ∼1.5 μm in diameter which act as stress concentrators especially given their large size relative to the width of the tensile specimens. The composition of these impurities was validated by transmission electron microscopy, and they seem to be the most likely cause of low ductility of the Ni-3wt% SiC composite. In all, the study undertaken here was able to replicate mechanical properties observed at the macro scale as well as reproduce a strain rate effect. Furthermore, the failure mode of Ni-3wt% SiC composite was identified and analysed in detail.
- ItemLarge strain deformation of bimodal layer thickness Cu/Nb nanolamellar composites(Elsevier, 2013-03-01) Wynn, TA; Bhattacharyya, D; Hammon, DL; Misra, A; Mara, NANanolayered composites have garnered much attention due to their ability to withstand deformation to large strains, shock deformation, and irradiation induced microstructural damage. These behaviors have been attributed to high densities of bimetal interfacial content. Although they exhibit yield strengths approaching theoretical limits, multilayered materials with layer thicknesses less than 10 nm have shown limited ductility in rolling. In this study, bimodal 4 nm/40 nm Cu/Nb multilayers are rolled to 30% thickness reduction without the onset of shear instability. The stacking order used allows focus to be drawn specifically to the ductility by the boundary crossing mechanism exhibited in multilayered materials with layer thicknesses below 10 nm. Through the geometric constraint offered by alternating 4 nm and 40 nm layer thickness modes, the onset of localized shear is avoided and the 4 nm layers can be rolled to large strains. © 2015, Elsevier B.V.
- ItemLoad partitioning and evidence of deformation twinning in dual-phase fine-grained Zr-2.5%Nb alloy(Elsevier, 2012-03-01) Muránsky, O; Daymond, MR; Bhattacharyya, D; Zanellato, O; Vogel, SC; Edwards, LIn situ neutron diffraction loading experiments were carried out on a cold-rolled dual-phase (α-phase, ∼10% β-phase) Zr–2.5%Nb alloy at room temperature. The specimens were cut at different angles from the rolling direction (RD) towards the transverse direction (TD), thus the loading axis changes gradually from the rolling to transverse direction. Due to the strong texture of the studied alloy, and unidirectional nature of deformation twinning, the changing loading direction with respect to initial texture has a significant impact on the collaborative slip-twinning deformation mode in the hexagonal close-packed (hcp) α-phase. The present neutron diffraction results provide direct evidence of {1−1.2}〈1−1.−1〉 “tensile” twins in the α-phase of dual-phase Zr–2.5%Nb alloy at room temperature. Additionally, TEM analysis was employed to confirm the presence of “tensile” twins, and determine if other type of twins were present. It is further clear from the neutron diffraction results that applied load is gradually transferred from the plastically softer α-phase to the plastically harder β-phase which acts as a reinforcing phase having a yield strength in the range 750–900 MPa depending on the loading direction. © 2012, Elsevier B.V.
- ItemMartensitic phase transformation and deformation behavior of Fe–Mn–C–Al twinning-induced plasticity steel during high-pressure torsion(Wiley Online Library, 2014-02-05) Yan, K; Bhattacharyya, D; Lian, Q; Kabra, S; Kawasaki, M; Carr, DG; Callaghan, MD; Avdeev, M; Li, HJ; Wang, Y; Liao, XZ; Langdon, TG; Liss, KD; Dippenaar, RJThe 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.© 2014, WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
- ItemMicrostructural evolution of an ion irradiated Ni–Mo–Cr–Fe alloy at elevated temperatures(Materials Transactions, 2014-01-01) de los Reyes, M; Edwards, L; Kirk, MA; Bhattacharyya, D; Lu, KT; Lumpkin, GRThe irradiation behavior of a Ni–Mo–Cr–Fe alloy, of the type currently being considered for use in future molten salt cooled reactors, has been investigated in situ using 1 MeV Kr ions at temperatures of 723 and 973 K. When irradiated to 5 dpa, experimental observations reveal the instantaneous formation and annihilation of point defect clusters, with such processes attributed to the long range elastic interactions that occur between defects through multiple intra-cascade overlap. Corresponding differences in the defect cluster density and size distribution suggest that changes to the microstructure were dependent upon temperature and dose, affecting the growth, accumulation and mobility of irradiation-induced defect clusters under these conditions. © 2014,The Japan Institute of Metals and Materials.
- ItemObservation of charge transfer induced large enhancement of magnetic moment in a structurally disordered inverse Heusler alloy Fe2RuGe(American Physical Society (APS), 2023-12-01) Chakraborty, S; Gupta, S; Bhasin, V; Pakhira, S; Barreteau, C; Crivello, JC; Jha, SN; Bhattacharyya, D; Avdeev, M; Paul-Boncour, V; Greneche, JM; Alleno, E; Mazumdar, CWe report the successful synthesis of a new 4d-based polycrystalline inverse Heusler alloy Fe2RuGe by an arc melting process and have studied in detail its structural, magnetic and transport properties complemented with first-principles calculations. X-ray and neutron diffraction, extended x-ray absorption fine structure, and 57Fe Mössbauer spectroscopic studies confirm the single-phase nature of the system where the Fe and Ru atoms are randomly distributed in the 4c and 4d Wyckoff positions in a ratio close to 50:50. The formation of the disordered structure is also confirmed by the theoretical energy minimization calculation. Despite the random cross-site disorder of Fe and Ru atoms, magnetic measurements suggest not only a high Curie temperature of ∼860 K, but also a large saturation magnetic moment ∼4.9µB per formula unit at 5 K, considerably exceeding the theoretical limit (4 µB per formula unit) predicted by the Slater-Pauling rule. Only a few Fe-based inverse Heusler alloys are known to exhibit such high Curie temperatures. Neutron diffraction analysis coupled with the isothermal magnetization value indicates that the magnetic moments in Fe2RuGe are associated with Fe atoms only, which is also confirmed by Mössbauer spectrometry. Interestingly, in comparison to the cubic or hexagonal phase of the parent compound, Fe3Ge, the Curie temperature of Fe2RuGe has increased significantly despite the substitution of the nonmagnetic yet isoelectronic element Ru in this structurally disordered compound. Our theoretical calculation reveals that the large Fe moment (∼2.8µB/Fe) on the 4b site can be attributed to a charge transfer from this Fe site towards its Ru neighbors while a significant moment (∼2µB/Fe) is kept on the other Fe sites. Instead of expected Slater-Pauling value of 4µB/f.u., the substantially increased observed total magnetic moment of ∼4.9µB/f.u. is due to these electron charge transfers, which have not been previously reported in other ferromagnetic Heusler systems. © 2024 American Physical Society.
- ItemThe observation of slip phenomena in single crystal Fe samples during in situ micro-mechanical testing through orientation imaging(Cambridge University Press, 2014-05-28) Bhattacharyya, D; Wheeler, RW; Harrison, RP; Edwards, LThis paper reports a study of local orientation change occurring within micro-scale tensile samples as a function of strain. These samples were fabricated from a thin film of single crystal bcc Fe and deformed in tension using an in situ micro-mechanical testing device inside a scanning electron microscope. Samples were loaded along the <110> direction parallel to the specimen axis, strained to different levels, and then subjected to electron backscatter diffraction scans over the entire area of the gauge section. Analysis of the surface orientation data shows that, within a necked zone of the micro-sample gauge section, there are two distinct regions of significant orientation change, in which local crystal rotations occur in opposite directions. These two regions are separated by an intermediate band that shows minimal misorientation from the original state. Crystal rotations within the two regions that develop opposite orientations are found to be consistent with classic single crystal slip, where the slip direction rotates toward the tensile axis. It is shown that increasing tensile strain causes an increasing degree of rotation away from the starting orientation. The tests also illustrate the occurrence of slip on at least two different slip systems, based on the slip traces and orientation change. © 2014 Microscopy Society of America.
- ItemRelationship between damage and hardness profiles in ion irradiated SS316 using nanoindentation–experiments and modelling(Elsevier, 2016-11) Saleh, M; Zaidi, Z; Hurt, C; Ionescu, M; Short, KT; Daniels, JE; Bhattacharyya, D; Munroe, P; Edwards, LIn this work, the authors apply the “top-down” nanoindentation testing method to assess the mechanical property changes in ion-irradiated metallic alloys for three different ion energies in order to understand the relationship between ion energy, damage peak depth and hardness peak depth. The samples were irradiated with He+2 ions having 1, 2 and 3 MeV beam energies respectively. The curves for ΔH (radiation induced hardness) have been obtained by calculating the difference of the irradiated and unirradiated hardness curves after these were corrected for indentation size effect. Three-dimensional analytical and numerical models have been developed to obtain greater insight into the mechanisms involved in the nanoindentation processes, the nature of the plastic zone, and how these affect the hardness results, including the full hardness profiles with respect to depth. This is particularly valuable in situations where the damage profile is non-uniform, as in the present case, and provides the means to predict expected hardness peak positions and values for a given irradiation dose. Copyright © 2017 Elsevier B.V.