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Precipitation of the secondary phase is a key factor that influences the strengthening effect of nickel-based superalloy. The precipitation behaviours of the M23C6 carbide and γ′-Ni3(Ti, Al) phase in Inconel 617B alloy aged at 700°C for different times were studied by scanning electron microscopy, transmission electron microscopy and atom probe tomography. Plate-like carbide nucleated in the interior of grain and irregular shape carbide precipitated at grain boundary respectively during the early stage of ageing. γ′ particle co-precipitated around carbide is a common microstructure feature during ageing for 5–160 h. After ageing for 160 h, γ′ phase is the main secondary phase. The carbide only distributes on the grain boundary, high density γ′ particle homogeneously distributes in the matrix after a longer ageing time. Elemental partitioning to the secondary phases and composition profiles across different phases was quantitatively analysed. Enrichments of Ti and Al at the carbide/γ interface are directly observed, which act as the nucleation site of γ′ particles during ageing. Enrichments of B, Si and Co at different interfaces are also detected. Based on the experimental results, the precipitation mechanisms of γ′ particles and carbide were discussed. [ABSTRACT FROM AUTHOR]

The mechanical property and microstructures of the 15-5PH stainless steel aged at 500 °C for different times have been studied in detail by using transmission electron microscopy and atom probe tomography. The precipitation-hardening effect is significant during aging and the peak hardness occurs at 2 h, but prolonged aging decreases the hardness significantly. The peak hardness is attributed to the formation of a large number of Cu-rich precipitates of 3-6 nm in diameter, with the Ni and Mn atoms segregating around the Cu-rich precipitates and forming a core–shell structure. The over-aging process increases the size of Cu-rich precipitates and causes Si and Nb atoms to segregate to the vicinity of Ni and Mn atoms, forming Nb-rich and NbN-rich particles. The formation of various phase precipitates, including possible G-phase particles, and their effects on mechanical property are discussed. [ABSTRACT FROM AUTHOR]

The precipitation behavior and ageing response of Al-Mg alloys with minor Cu/Si additions was investigated at 170 °C with dwell time up to one month. The microstructure and chemistry of precipitates are systematically characterized by transmission electron microscope (TEM) and atom probe tomography (APT). It is shown that strengthening is predominantly controlled by β-type (β″) and Q-type (L 1) particles rather than S phase or its precursor. Furthermore, a novel hybrid precipitate along <100> Al direction is observed and designated as L 1 , which possesses a distinct shell-core configuration. In this structure, Cu segregates within the shell in the form of either GPB zones or Cu sub-unit clusters, whereas the core region is eventually isostructural with β′ after severe over-ageing, albeit its orientation relative to the Al matrix is different. The L 1 phase with hybrid precipitate structures demonstrates remarkable thermal stability, maintaining a length of 5 nm and a width of 1.2 nm even after ageing for one month. This stability is attributed to the multiple interfacial structures including Cu segregation layers, C/L phases and GPB zones. This finding provides a novel design approach for heat-resistant aluminum alloys by promoting the formation of precipitates with hybrid structures and segregation layers at the matrix/interface through strategic microalloying and heat treatment. [ABSTRACT FROM AUTHOR]

This study investigates the precipitation behavior and phases stability in Al-Cu-Mg-Li-Sc alloy during aging, using scanning electron microscopy (SEM), high- resolution transmission electron microscopy (HRTEM), and atom probe tomography (APT). Results show that, besides the precipitation of S-phase (Al 2 CuMg) and θ-phase (Al 2 Cu), numerous Al 3 Sc phases, Al 3 Li phases, and Al 3 Li (Al 3 Sc) core-shell structures—L1 2 -type ordered and fully coherent with the α-Al matrix—form in the alloy after aging in the presence of Li and Sc elements. With increasing aging time, both Al 3 Sc and Al 3 Li (Al 3 Sc) core-shell structures maintain their morphology and structure, while also facilitating the formation of the alloy's primary strengthening phase, S. APT analysis further reveals that some Li atoms replace Mg atoms in the S phase, producing an S-like phase Al 2 CuMg 2/3 (Mg Li) 1/3. • The precipitation behavior of precipitated phases of Al-Cu-Mg-Li-Sc alloys at 490 °C/1 h+ 190 °C/ (2, 14, 24) h was investigated. • Theoretical structural models of the Al 3 (Li, Sc) core-shell structure precipitated during heat treatment of Al-Cu-Mg-Li-Sc alloys have been investigated using HRTEM and APT characterization techniques. • Using APT characterization, it was found that some Li atoms in the Al-Cu-Mg-Li-Sc alloy replace some of the Mg atoms in the S-phase (Al 2 CuMg) to form the S-like phase of Al 2 CuMg 2/3 (Mg Li) 1/3. [ABSTRACT FROM AUTHOR]

The mechanical properties of precipitation-strengthened Co-based superalloys are determined by the γ/γ′ two-phase microstructure features. This study investigates the precipitation behavior of multimodal γ′ phases in a Co-based superalloy from both thermodynamic and kinetic perspectives. The effects of secondary and tertiary γ′ phases were examined using different cooling methods from 900 °C to 1000 °C. The results reveal that water cooling from 900 °C inhibited the precipitation of tertiary γ′ phase, whereas other samples exhibited nanoscale tertiary γ′ phases within the γ matrix channels. Finally, the influence of tertiary γ′ phase on chemical composition, microstructure evolution, and mechanical properties in Co-based superalloys is elucidated. [ABSTRACT FROM AUTHOR]

Natural aging (NA) is unavoidable in Al-Mg-Si alloys during actual manufacturing. Revealing the reasons for the alloy strength reduction caused by the negative NA effect is of great significance to research and practice. In this work, atom probe tomography (APT) and transmission electron microscopy (TEM) were employed simultaneously to study the effect of NA on precipitates and their contributions to the strength of Al-Mg-Si alloys. It was found that the numerous clusters formed after significant NA are unstable and will dissolve into the matrix during initial AA. However, a few stable clusters are undissolved and will result in abnormal growth of β″, which then transforms to β′. Due to the decrease of nucleation sites resulting from the abnormal growth of precipitates, more solute atoms remain in the matrix. The calculation results show that the strengthening of the solid solution atoms is much smaller than that of large-sized β′, which is much less than that of fine β″. Therefore, lengthy NA causes a significant reduction in AA strength of the Al-Mg-Si alloy. [ABSTRACT FROM AUTHOR]

In-situ Small-Angle Neutron Scattering (SANS) is used to determine the time evolution of the chemical composition of precipitates at 650 °C and 700 °C in three micro-alloyed steels with different vanadium (V) and carbon (C) concentrations. Precipitates with a distribution of substoichiometric carbon-to-metal ratios are measured in all steels. The precipitates are initially metastable with a high iron (Fe) content, which is gradually being substituted by vanadium during isothermal annealing. Eventually a plateau in the composition of the precipitate phase is reached. Faster changes in the precipitate chemical composition are observed at the higher temperature in all steels because of the faster vanadium diffusion at 700 °C. At both temperatures, the addition of more vanadium and more carbon to the steel has an accelerating effect on the evolution of the precipitate composition as a result of a higher driving force for precipitation. Addition of vanadium to the nominal composition of the steel leads to more vanadium rich precipitates, with less iron and a smaller carbon-to-metal ratio. Atom Probe Tomography (APT) shows the presence of precipitates with a distribution of carbon-to-metal ratios, ranging from 0.75 to 1, after 10 h of annealing at 650 °C or 700 °C in all steels. These experimental results are coupled to ThermoCalc equilibrium calculations and literature findings to support the Small-Angle Neutron Scattering results. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Atom probe tomography (APT) is routinely used for analyzing property-enhancing particles in the nanometer-size range and below, and plays a prominent role in the analysis of solute clusters. However, the question of how well these small particles are measured has never been addressed because of a lack of a reliable benchmark. Here, to address this critical gap, we use an approach that allows direct comparison of APT and small-angle (X-Ray) scattering (SA(X)S) performed on the same material. We introduce the notion of an effective spatial resolution for the analysis of particles, which, importantly in this context, is very different than the technique's inherent spatial resolution. This effective resolution is highly specific to the system being considered, as well as the analysis conditions. There is no hard limit below which the technique will fail, but particles with a radius of order of ∼ 2 σ = 1 nm, i.e. ∼250 atoms, cannot be accurately measured, even though the particles are detected. This thorough metrological assessment of APT in the analysis of particles allows us to discuss the pulse spread function of the technique and the physics underpinning its limits. We conclude that great care should be taken when analysing solute clusters by APT, in particular when reporting particle size and composition. [ABSTRACT FROM AUTHOR]

17–4 precipitate hardening (PH) stainless steel is used in various applications including in the aerospace, marine, and chemical industries, largely due to its unique combination of corrosion resistance and high strength, which is achieved by the formation of nanoscale Cu-rich precipitates during aging. 17–4 PH has been widely researched for its applicability for laser powder bed fusion (LPBF). However, there are discrepancies in the literature on its heat treatment response, which seem to be linked to compositional variations. Systematic studies of the interplay between these variations and nanoscale precipitation are currently missing. Using atom probe tomography, we present a systematic study of the heat treatment responses of two variants of LPBF 17–4 PH builds fabricated from different powder feedstocks, with significant differences in N contents (High vs Low N 17–4). Both variants formed predominantly δ-ferritic as-built microstructures. The as-built High N 17–4 variant showed a higher volume fraction of austenite which further increased upon solution annealing and quenching. The consequence was no appreciable hardening effect due to the absence of Cu precipitation in either austenite or martensite after aging, degrading the alloy's desirable property profile. Conversely, Low N 17–4 showed no austenite in the as-built condition and a fully martensitic matrix after solution annealing. This variant had the desired aging response; a ∼ 140 HV 5 increase in hardness due to nanoscale Cu precipitation. Our findings describe the deleterious effects of compositional variations incurred during the LPBF process flow and how they can be overcome in 17–4 PH and similar steels. • Atom probe of Cu precipitation in high versus low N laser powder bed fusion 17-4 PH. • Discrepancies in phase transformation pathways systematically linked to composition. • Austenite in high N builds after solution annealing & aging, no bulk precipitation. • Low N builds exhibit desirable, similar to wrought phase transformation behaviour. • Importance of controlling compositional variations for reproducible LPBF properties. [ABSTRACT FROM AUTHOR]

The precipitation kinetics of vanadium carbides and its interaction with the austenite-to-ferrite phase transformation is studied in two micro-alloyed steels that differ in vanadium and carbon concentrations by a factor of two, but have the same vanadium-to-carbon atomic ratio of 1:1. Dilatometry is used for heat-treating the specimens and studying the phase transformation kinetics during annealing at isothermal holding temperatures of 900, 750 and 650 °C for up to 10 h. Small-Angle Neutron Scattering (SANS) and Atom Probe Tomography (APT) measurements are performed to study the vanadium carbide precipitation kinetics. Vanadium carbide precipitation is not observed after annealing for 10 h at 900 and 750 °C, which is contrary to predictions from thermodynamic equilibrium calculations. Vanadium carbide precipitation is only observed during or after the austenite-to-ferrite phase transformation at 650 °C. The precipitate volume fraction and mean radius continuously increase as holding time increases, while the precipitate number density starts to decrease after 20 min, which corresponds to the time at which the austenite-to-ferrite phase transformation is finished. This indicates that nucleation and growth are dominant during the first 20 min, while later precipitate growth with soft impingement (overlapping diffusion fields) and coarsening take place. APT shows gradual changes in the precipitate chemical composition during annealing at 650 °C, which finally reaches a 1:1 atomic ratio of vanadium-to-carbon in the core of the precipitates after 10 h. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Mn-Ni-Si intermetallic precipitates (MNSPs) that are observed in some Fe-based alloys following thermal aging and irradiation are of considerable scientific and technical interest. For example, large volume fractions (f) of MNSPs form in reactor pressure vessel low alloy steels irradiated to high fluence, resulting in severe hardening induced embrittlement. Nine compositionally-tailored small heats of low Cu RPV-type steels, with an unusually wide range of dissolved Mn (0.06–1.34 at.%) and Ni (0.19–3.50 at.%) contents, were irradiated at ≈ 290 °C to ≈ 1.4 × 1020 n/cm2 at an accelerated test reactor flux of ≈3.6 × 1012 n/cm2-s (E > 1 MeV). Atom probe tomography shows Mn-Ni interactions play the dominant role in determining the MNSP f, which correlates well with irradiation hardening. The wide range of alloy compositions results in corresponding variations in precipitates chemistries that are reasonably similar to various phases in the Mn-Ni-Si projection of the Fe based quaternary. Notably, f scales with ≈ Ni1.6Mn0.8. Thus f is modest even in advanced high 3.5 at.% Ni steels at very low Mn (Mn starvation); in this case Ni-silicide phase type compositions are observed. Image 1 [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • High Pressure Torsion of SS304 at 300 °C results in nanocrystalline austenitic microstructure. • Observed Ni-Mn-Si phase at grain boundaries, Cu nanoprecipitates near/along grain boundaries. • Segregation resulted in enrichment of Ni, Mn, Si, and P at grain boundaries. • Precipitation is instigated by segregation along grain boundaries. • Segregation driven by supersaturation of vacancies created by severe plastic deformation. Abstract During irradiation or high-temperature aging, stainless steel can develop precipitates, significantly affecting mechanical properties. In this study atom probe tomography (APT) was used to study grain boundary segregation and secondary phases in a purely austenitic SS304 (a Fe-18Cr-8Ni steel) processed by high-pressure torsion (HPT) at 300 °C. Ni, Mn, Si enriched phase was observed at grain boundaries, and Cu nanoprecipitates were observed along and near phase/grain boundaries. Precipitation is facilitated by deformation assisted segregation along grain boundaries with a mechanism similar to vacancy diffusion in irradiated steels. [ABSTRACT FROM AUTHOR]

Abstract It is well known the effectiveness of ausforming on increasing the dislocation density of fresh martensite. This work demonstrates, using atom probe tomography, that this increase in the dislocation density has a strong influence on the nucleation of nanoprecipitates during tempering. Therefore, ausforming might be a powerful processing route for the two-fold improvement of ferritic/martensitic steels where creep resistance is of paramount importance. Firstly, ausforming refines the martensitic microstructure (high strength and toughness), and secondly, it increases the number density of thermally stable nanoprecipitates (creep resistance). Graphical abstract Unlabelled Image [ABSTRACT FROM AUTHOR]

Abstract Oxide dispersion strengthened (ODS) FeCrAl alloy (Fe-12Cr-5Al wt%) was neutron irradiated to 1.8 displacements per atom (dpa) at 215, 357, and 557 °C to investigate (Y,Al,O) nano-oxide stability and Cr-rich α ′ precipitate formation using atom probe tomography. The nano-oxide sizes remain unchanged after irradiation, but the compositions are dependent on irradiation temperature due to competition between ballistic dissolution and precipitate reformation. Cr-rich clusters observed after 357 °C irradiation have lower Cr contents (61 at.%) than equilibrium α ′, with a lower number density than wrought FeCrAl alloys. This suggests a suppression of α ′ precipitation due to the high sink strength of ODS FeCrAl. Graphical abstract Unlabelled Image [ABSTRACT FROM AUTHOR]

Abstract The microstructural and compositional evolution of intergranular carbides and borides prior to and after creep deformation at 850 °C in a polycrystalline nickel-based superalloy was studied. Primary MC carbides, enveloped within intergranular γ′ layers, decomposed resulting in the formation of layers of the undesirable η phase. These layers have a composition corresponding to Ni 3 Ta as measured by atom probe tomography and their structure is consistent with the D0 24 hexagonal structure as revealed by transmission electron microscopy. Electron backscattered diffraction reveals that they assume various misorientations with regard to the adjacent grains. As a consequence, these layers act as brittle recrystallized zones and crack initiation sites. The composition of the MC carbides after creep was altered substantially, with the Ta content decreasing and the Hf and Zr contents increasing, suggesting a beneficial effect of Hf and Zr additions on the stability of MC carbides. By contrast, M 5 B 3 borides were found to be microstructurally stable after creep and without substantial compositional changes. Borides at 850 °C were found to coarsen, resulting in some cases into γ′- depleted zones, where, however, no cracks were observed. The major consequences of secondary phases on the microstructural stability of superalloys during the design of new polycrystalline superalloys are discussed. Graphical abstract Image 1 [ABSTRACT FROM AUTHOR]

Abstract A major challenge in the design of oxide dispersion strengthened (ODS) FeCrAl alloys is the optimization of the fine-scale particle size distribution that provides both beneficial mechanical properties and irradiation resistance. To address this obstacle, the nucleation, growth, and coarsening of the fine-scale (Y,Al,O) nanoprecipitates within an ODS FeCrAl powder was studied using atom probe tomography (APT) and small-angle neutron scattering (SANS). Mechanically alloyed Fe 10Cr-6.1Al-0.3Zr + Y 2 O 3 wt.% (CrAZY) powders were heated in-situ from 20 to 1000 °C to capture the nucleation and growth of the nanoprecipitates using SANS. Furthermore, CrAZY powders were annealed at 1000 °C, 1050 °C, and 1100 °C for ageing times from 15 min to 500 h followed by either APT or magnetic SANS to study the structure, composition, and coarsening kinetics of the nanoprecipitates at high temperature. In-situ SANS results indicate nanoprecipitate nucleation and growth at low temperatures (200–600 °C). APT results revealed compositions corresponding to the cubic Y 3 Al 5 O 12 garnet (YAG) stoichiometry with a possible transition towards the perovskite YAlO 3 (YAP) phase for larger precipitates after sufficient thermal ageing. However, magnetic SANS results suggest a defective structure for the nanoprecipitates indicated by deviations of the calculated A-ratio from stoichiometric (Y,Al,O) phases. Particle coarsening kinetics follow n = 6 power law kinetics with respect to particle size, but the mechanism cannot be explained through the dislocation pipe diffusion mechanism. The potential effect of precipitate coarsening during pre- and post-consolidation heat treatments on the irradiation resistance of ODS FeCrAl alloys is discussed with respect to sink strength maximization. Graphical abstract Image 1 [ABSTRACT FROM AUTHOR]

Overcoming the trade-off between high strength and excellent corrosion resistance of Al-Zn-Mg-Cu alloys is a challenging problem. In this study, a variable-rate non-isothermal retrogression and re-aging (VNRRA) process has been proposed to solve this problem in AA7085 aluminum alloy and is compared with conventional isothermal aging treatments (T6, T77, and T73 tempers) in detail. This improved aging process consists of a slowly heating stage at low temperature, a rapidly heating stage at elevated temperature and an isothermal aging stage at 120 °C, and can synchronously improve the strength and corrosion resistance of Al-Zn-Mg-Cu alloy. Precipitation behaviors, mechanical properties and corrosion resistance have been systematically investgated. Compared with T6 temper, the VNRRA sample exhibits higher hardness and yield strength, which can be attrubuted to the high-density η' precipitates that fully grow up but are not severely coarsened in Al matrix. Meanwhile, the corrosion resistance of the optimal VNRRA specimen is comparable with that of T77-treated specimen, which is closely linked with the discontinuous distribution of Cu-rich GBPs. • The VNRRA treatment acquires a synchronous improvement of strength and corrosion resistance. • The different heating rates lead to grown but not severely coarsened precipitates. • The properties of V-40-200 are comparable with T77 temper, but its pre-aging time is 67% less than T77 temper. • VNRRA may serve as an improved T77 process to be applied in thick components. [ABSTRACT FROM AUTHOR]

Abstract In this paper, G-phase precipitation and the resulting hardening effect on Fe-20Cr-3Ni-1Mn-3Si ferritic alloys by the addition of Ti, Nb, Ta and Zr were individually studied by electron microscopy and atom probe tomography, combined with thermodynamic and first principle calculations. The high resolution scanning electron and transmission electron microscopy observations confirmed that four kinds of Ni 16 M 6 Si 7 (M=Ti, Nb, Ta and Zr) G-phase particles were distributed uniformly in the matrix of the four alloys aged at 560–860 °C. The 3D-APT results revealed the formation of the four different nanoscale precipitates, with the highest number density (6.05 × 1023 m−3) and smallest radius (1.64 ± 0.45 nm) in the Ti added alloy. The nanoscale sized precipitates stability (~3 nm for Ti added alloy; ~5 nm for Nb added alloy and Zr added alloy; ~25 nm for Ta added alloy) was attributed to their particular cube-cube orientation relationships, which led to a very low interfacial energy. The effects of the G-phase on precipitation hardening and quasi steady-state deformation resistance were examined. The 560 °C-aging hardening experiments suggested a rapid precipitation process of the nano-particles. The peak hardness values of the four alloys are in the descending order: Ti ˃˃ Nb > Ta ˃˃ Zr. The 660 °C quasi steady-state deformation experiments showed threshold stresses of 110 and 140 MPa in cases of the Nb and Ti added alloys, which were higher than that of the previously reported B2-NiAl strengthened steels and commercial heat-resistant steels. By using the formation of nanoscale G-phase precipitates, a new ferritic steel family with very high strength and creep resistance has been proposed. Further alloy optimization is in progress. [ABSTRACT FROM AUTHOR]

Abstract Nanoscale precipitation and its influence on the strengthening mechanisms in low-carbon ultra-high-strength steel, hot-rolled at different temperatures and subjected to various isothermal aging conditions, are studied. The steel has a yield strength of ∼1730 MPa and elongation-to-failure of ∼13% under the peak aging condition, of which ∼740 MPa is contributed by precipitation strengthening. The precipitation strengthening mechanisms, including both the shearing mechanism and the Orowan mechanism, are quantitatively analyzed based on the mechanical properties and precipitate properties determined by small-angle neutron scattering, and atom probe tomography (APT). The APT results show that the average Guinier radius of the nanoscale precipitates under the peak aging condition is 1.4 nm at a number density of 6.19 × 1023 m − 3 . These nanoscale precipitates consist of a Cu-enriched core, in which the depletion of Fe and enrichment of Cu change monotonically towards the center of the precipitates, whereas the concentrations of Ni, Al, and Mn exhibit diffused enrichment near the precipitate-matrix interfaces. Until the peak aging, precipitation strengthening mainly arises from shearing mechanism, among which the order and modulus strengthening mechanisms play the most significant role. Beyond peak aging, the shearing mechanism is not valid and the Orowan mechanism is the dominant contributor to the increase in yield strength due to the coarsening of the precipitates. The effect of the matrix microstructure on strength is also addressed and discussed. Graphical abstract Image 1 Highlights • 740 MPa increment in yield strength is obtained through precipitation strengthening. • The precipitates consist of Cu-enriched core encased by Ni(Al,Mn) phase. • Precipitation strengthening is contributed by shear mechanism under and at the peak aging. • Orowan mechanism dominates the increase in yield strength beyond peak aging. [ABSTRACT FROM AUTHOR]

Abstract The addition of minor Mg (~0.4 wt%) to Al-Cu-Li alloy could not only modify the precipitation path but also promote the precipitation of T 1 (Al 2 CuLi) phase, however, the influence of higher Mg addition on the microstructures during ageing is still not clear. In this work, the influence of high Mg addition (>0.4 wt%) on the precipitation sequence, precipitation kinetics and the corresponding strengthening of an Al-Cu-Li alloy has been investigated by atom probe tomography (APT), transmission electron microscopy (TEM), differential scanning calorimetry (DSC) and tensile testing. For an Al-Cu-Li-0.4 wt% Mg alloy in the peak-aged condition, the microstructure contains a high density of fine T 1 precipitates along with some non-negligible θ' phase (Al 2 Cu). When adding larger amount of Mg (0.8 wt%) to the alloy, however, the precipitation of S′ phase (Al 2 CuMg) is strongly accelerated at the expense of T 1 and θ' phases. Much more Mg clusters are observed by APT at the early ageing stages of the high Mg-containing alloy, leading to more rapid hardening response. The precipitation kinetics for T 1 phase become somewhat sluggish due to decreased nucleation sites and shortage of available solutes caused by formation of more S′ precipitates. The precipitation of coarse T 1 and S′ phases is significantly detrimental to the ductility and toughness in the peak-aged condition for the high Mg-containing alloy. [ABSTRACT FROM AUTHOR]

The influence of grain boundary Cr carbides on the intergranular oxidation behavior of a Ni-16Cr alloy is considered using atomistic-to-mesoscale model and atom probe tomography. Cr carbide strongly perturbs the collective reactive dynamics of oxidizing species and alloy elements in the intergranular region. Strong attractive interactions between oxygen and carbide create a driving force for Cr and Ni accumulation in the grain boundary adjacent to the carbide, and for the depletion of Cr and Ni ahead of the oxidation front beyond the carbide. The results shed light on the mechanism of carbide-assisted protection of the alloy against grain boundary corrosion/oxidation. [ABSTRACT FROM AUTHOR]

Abstract We investigate nano-scale irradiation-induced precipitation in a Zr Sn Fe Cr Ni-alloy (Zircaloy-2) by combining atom probe tomography (APT) for chemical detail with scanning transmission electron microscopy (STEM) and high resolution energy dispersive X-ray (EDX) spectroscopy for wider context and complimentary and correlative TEM diffraction techniques for crystallographic relationships. We find that Fe and Cr-rich nano-rods precipitate in Zircaloy-2 following proton irradiation at 350 °C to a low dose of ∼2 dpa. The long-axis of the nano-rods are aligned in a direction 12–15° from the Zr matrix 〈 0001 〉 , align in the basal plane and are of width 1.5–5 nm. Smaller rods are of APT-determined composition Zr 4 (Fe 0.67 Cr 0.33), tending towards Zr 3 (Fe 0.69 Cr 0.31) as the rod volume increases to > ∼400 nm3, in agreement with STEM-EDX determination of composition resembling that of Zr 3 Fe with Cr replacing some of the Fe. The Fe/Cr ratio has been shown to increase with distance from the nearest partially-dissolved Zr(Fe,Cr) 2 phase particle. The nucleation of nano rods has implications for macroscopic irradiation-induced deformation phenomena, irradiation-induced hardening and the evolution of dislocation loops and other defects. Graphical abstract Image 1 [ABSTRACT FROM AUTHOR]

It is well known that deformation prior to artificial aging considerably decreases the strength properties of Al-Cu-Mg-Ag alloys by suppressing the formation of the main strengthening Ω precipitates. This negative effect is the as-yet unresolved obstacle for the wide applications of Al-Cu-Mg-Ag alloys. In this work, preaging prior to deformation is conducted to evaluate its possible influence on improving the typical microstructure and strength of deformed Al-Cu-Mg-Ag alloy. Quantitative transmission electron microscopy (TEM) and atom probe tomography (APT) analysis of the initial solute clustering and subsequent Ω precipitation of the deformed alloy with and without preaging indicate that preaging ensures strong Mg-Ag co-clustering and hence benefits the dense precipitation of Ω phase in deformed Al-Cu-Mg-Ag alloy. Naturally, the strength of 1% stretched Al-Cu-Mg-Ag alloy is obviously enhanced by preaging. [ABSTRACT FROM AUTHOR]

The dispersion hardening effect of Mn(Fe)-containing dispersoids in aluminium alloys has long been ignored since it is difficult to achieve a high number density of fine dispersoids with conventional alloying compositions. This work demonstrates a minor addition of Cd (0.05 at.%) can dramatically enhance the precipitation of α-Al(Mn,Fe)Si dispersoids and therefore the dispersion strengthening of AA3003 alloy. Similar to the 3003 base alloy, a peak hardness in the Cd-containing alloy was obtained after continuous heating to 450 °C. However, an improvement in yield strength by 25% was achieved by the Cd addition. Detailed transmission electron microscopy (TEM) and atom probe tomography (APT) investigations show that the Cd addition has changed the nucleation behaviour of α-Al(Mn,Fe)Si dispersoids from the conventional heterogeneous nucleation on dislocations to a more homogeneous manner. It is found that a high number density of Al-Cd nanoprecipitates formed during heating between 150 and 250 °C. These Al-Cd precipitates attracted Mn and Si atoms to form Mn,Si-rich clusters in/around them, which acted as the precursors for the later nucleation of α-Al(Mn,Fe)Si dispersoids at ∼300 °C. As a result, the number density of dispersoids formed in the Cd-containing alloy after heating to 350–450 °C is about twice as that in the base alloy subjected to the same heat treatment. This work proposes a new approach to enhance the nucleation of α-Al(Mn,Fe)Si dispersoids, which can help to further develop cheap Mn(Fe)-containing dispersoid-strengthened aluminium alloys for high-temperature applications. [ABSTRACT FROM AUTHOR]

Atom probe tomography enables precise quantification of the composition of second phase particles from their early stages, leading to improved understanding of the thermodynamic and kinetic mechanisms of phase formation and quantify structure-property relationships. Here we demonstrate how approaches developed for small-angle scattering can be adapted to atom probe tomography. By exploiting nearest-neighbor distributions and radial distribution function, we introduce a parameter free methodology to efficiently extract information such as particle size, composition, volume fraction, number density and inter-particle distance. We demonstrate the strength of this approach in the analysis of a precipitation-hardened model Al-Zn-Mg-Cu high-strength lightweight alloy. [ABSTRACT FROM AUTHOR]

Atom-probe tomography was performed on the metastable β-Ti alloy, Ti-5Al-5Mo-5V-3Cr wt% (Ti-5553), aged at 300 °C for 0 to 8 h, to precipitate the embrittling isothermal ω phase. Accurate precipitate quantification requires monitoring and controlling suitable charge-state ratios in the mass spectrum, which in turn are closely related to the laser pulse energy used. High ultraviolet laser pulse energies result in significant complex molecular ion formation during field-evaporation, causing mass spectral peak overlaps that inherently complicate data analyses. Observations and accurate quantification of the ω-phase under such conditions are difficult. The effect is minimized or eliminated by using smaller laser pulse energies. With a small laser pulse energy, Ti-rich and solute depleted precipitates of the isothermal ω phase with an oxygen enriched interface are observed as early as after 1 h aging time utilizing the LEAP 5000X S (77% detection efficiency). We note that these precipitates were not detected below a 2 h aging time with the LEAP 4000X Si (58% detection efficiency). The results are compared to the archival literature. The Al concentration in the matrix/precipitate interfacial region increases during aging. Nucleation of the α-phase at longer aging times may be facilitated by the O and Al enrichment at the matrix/precipitate interface (both strong α-stabilisers). The kinetics and compositional trajectory of the ω-phase with aging time are quantified, facilitating direct correlation of the APT data to previously published mechanical testing. [ABSTRACT FROM AUTHOR]

We successfully achieved atomic scale visualization of hydrogen atoms at trapping sites associated with the nano-sized precipitates of titanium carbide and vanadium carbide in ferritic steels using a modified three-dimensional atom probe with a deuterium charge cell. We proposed that the hydrogen trapping sites of fine carbide precipitates were at the (001) broad interface between the precipitate and the ferrite matrix. In this study, the precipitate size dependence in the trapping site and its energy was systematically investigated in vanadium carbide precipitation strengthening steels with various aging times. Hydrogen thermal desorption spectrometry analysis showed that the hydrogen trapping energy in the peak- and over-aged steels was larger than that in the under-aged steel. Atom probe tomography analysis showed the {001} platelets of vanadium carbide were covered by charged deuterium atoms in the peak-aging steel with large trapping energy, whereas no deuterium atoms around the {001} platelets were observed in the under-aged steel with small trapping energy. High-resolution transmission electron microscopy observation showed that misfit dislocations hardly appeared on the (001) surface of the precipitates in the two steels with large and small trapping energies. In contrast, the vanadium–carbon atomic ratios of vanadium carbide precipitates were definitely different between the two steels with large and small trapping energies. The precipitates in the under-aged steel with small trapping energy showed a chemical composition similar to VC, whereas the precipitates in the peak- and over-added steels with large trapping energy showed a chemical composition similar to V 4 C 3 . These results suggested that the origin of the hydrogen trapping site with large trapping energy is not the misfit dislocation core but the carbon vacancy on the (001) broad surface of V 4 C 3 precipitates. [ABSTRACT FROM AUTHOR]

Ferrium® M54® exhibits an excellent UTS/K 1C balance allowing its application in aeronautical structures. This steel belongs to the Co-Ni UHS steels family with M 2 C nanometer-size carbide precipitation during tempering. These steels provide very high strength with a very good fracture toughness thanks to the M 2 C fine precipitation during tempering, but also because coarse particles are dissolved during austenitizing without grain coarsening. The goal of this article is to identify the different carbide populations in M54®. A small addition of Ti in M54® forms a Ti-rich MC carbide precipitation that is stable at high temperature. Consequently, during austenitization at 1060 °C, all other types of coarse carbides are dissolved in the matrix without grain coarsening. As a very small part of the initial carbon content is needed to form MC carbides, efficient and intensive nanometric M 2 C carbide precipitation takes place during tempering, leading to very high final strength. Due to this double precipitation of carbides in M54®, the steel achieves an outstanding UTS/K 1C balance. [ABSTRACT FROM AUTHOR]

Thermal aging of reactor pressure vessel steel welds at elevated temperatures may affect the ductile-to-brittle transition temperature. In this study, unique weld material from a pressurizer, with a composition similar to that of the reactor pressure vessel, that has been in operation for 28 years at 345 °C is examined. Despite the relatively low temperature, the weld becomes hardened during operation. This is attributed to nanometre sized Cu-rich clusters, mainly located at Mo- and C-enriched dislocation lines and on boundaries. The welds have been characterized using atom probe tomography, and the characteristics of the precipitates/clusters is related to the hardness increase, giving the best agreement for the Russell-Brown model. [ABSTRACT FROM AUTHOR]

Abstract The composition evolution of γ′ nanoparticles as a function of aging duration in the Ti-doped CoFeCrNi high entropy alloy was studied by atom probe tomography (APT) and first-principle calculations. The APT results indicate that the evolution behaviors of Co, Fe, and Cr in the Ni 3 Ti-type γ′ nanoparticles are significantly different. Co saturates to a stable concentration in the γ′ nanoparticles rapidly in the initial stage of the precipitation, whereas Fe and Cr atoms are incorporated into the γ′ nanoparticles during the coarsening. The APT results are supported by the first-principle calculations from the perspective of the electronic state. Graphical abstract Unlabelled Image [ABSTRACT FROM AUTHOR]

Correlative atom probe tomography (APT) and transmission electron microscopy (TEM) are used to characterise the microstructure and chemistry of carbide precipitation in M50 bearing steel. This is a prerequisite in establishing relationships between the microstructure and hydrogen embrittlement (HE) resistance. Secondary carbides are the focus of this study, as they play a major role in improving HE-resistance. Secondary carbides are observed in APT, with compositions close to M4C3,M2C and M3C. Correlative TEM measured orientation relationships between the martensite matrix and carbides, enabling the confirmation of M3C cementite precipitates in the corresponding APT reconstruction. Additionally, other precipitates observed in TEM were correlated to the M2C carbides in APT data. The M4C3carbides are found to have a significantly lower volume fraction than the M2C carbides. [ABSTRACT FROM AUTHOR]

Precipitation of α′ in Fe Cr alloys under neutron irradiation is thermodynamically driven while being accelerated by radiation-enhanced diffusion. However, similar alloys under ion irradiation at high dose rates (> 10 − 4 dpa/s) fail to exhibit α′ precipitation. Here, the microstructure of an Fe 18Cr alloy under ion or neutron-irradiation at 300 °C at dose rates from ~ 10 − 7 to 10 − 4 dpa/s was analyzed by atom probe tomography. The steady-state composition content of the clusters depends on the ion irradiation dose and dose rate, confirming the contribution of ballistic mixing in diluting the Cr concentration in non-equilibrium α′ precipitates. [ABSTRACT FROM AUTHOR]

Ferritic-martensitic steels are leading candidates for many nuclear energy applications. However, formation of nanoscale α′ precipitates during thermal aging at temperatures above 450 °C, or during neutron irradiation at lower temperatures, makes these Fe-Cr steels susceptible to embrittlement. To complement the existing literature, a series of Fe-9 to 18 Cr alloys were neutron-irradiated at temperatures between 320 and 455 °C up to doses of 20 dpa. In addition, post-irradiation annealing treatments at 500 and 600 °C were performed on a neutron-irradiated Fe-18 Cr alloy to validate the α-α′ phase boundary. The microstructures were characterized using atom probe tomography and the results were analyzed in light of the existing literature. Under neutron irradiation and thermal annealing, the measured α′ concentrations ranged from ∼81 to 96 at.% Cr, as influenced by temperature, precipitate size, technique artifacts, and, possibly, cascade ballistic mixing. [ABSTRACT FROM AUTHOR]

The early stages of precipitation of the γ ′ phase in a model Co based superalloy (Co-9.1Al-7W (at.%)) have been investigated at 900 °C using electron microscopy and atom probe tomography. Nucleation, growth and coarsening stages have been studied with a focus on the temporal evolution of the precipitate composition in the light of recent theoretical developments on phase separation in multicomponent alloys. The experimental data have been confronted to the theories of nucleation and coarsening recently developed for such alloys, which are valid for non-ideal and non-dilute systems, and predict the temporal evolution of both the matrix and precipitate compositions. The rate constant for the mean size evolution of the particles, as derived from experiments, has been compared to the one predicted by the mentioned coarsening theory that accounts for a more accurate description of the thermodynamics of the phases, as compared with more classical approaches. From this comparison the γ/γ′ interfacial energy was derived and found equal to ∼48 mJ/m 2 The exponents for the temporal evolution of average particles size, number of particles per unit volume were found identical to those for binary alloys during the coarsening regime, as expected, and the temporal evolutions of compositions in both γ and γ′ phases were found to evolve as predicted by theory. Indeed, the W content in the particles, measured from atom probe tomography (APT) experiments, was found to significantly decrease with time and the observed evolution is remarkably well described by the theory and therefore is shown to originate from the competition between diffusion and capillarity. [ABSTRACT FROM AUTHOR]

Carbide precipitation plays a key role in determining mechanical properties of Co-Cr-Mo alloy. Precipitation characteristics of carbides in selective electron beam melting (SEBM)-fabricated Co-Cr-Mo parts have been investigated by atom probe tomography and transmission electron microscopy. We observe co-existence of two types of carbides, i.e. M 23 C 6 and M 6 C, which are formed into continuous carbide thin films along columnar grain boundaries. The carbide thin film is found to precipitate coherently with one γ Co grain while incoherently with another adjacent one. Moreover, columnar carbide chains or clusters consisting of nanometer-sized, cuboidal particles are precipitated coherently with surrounding γ Co phase within interdendritic regions. [ABSTRACT FROM AUTHOR]

The effect of 2.5% pre-stretching on the solute clustering and subsequent precipitation of an initial aged Al-Cu-Mg-Ag alloy is investigated by quantitative transmission electron microscopy (TEM) and atom probe tomography (APT) technique. In present work, 2.5% pre-stretching is found to restrict the dense precipitation of Ω phase, leading to the slower age-hardening response at 180 °C. The dominant Mg-Ag co-clustering, as revealed in non-stretched alloy, becomes weak by 2.5% pre-stretching prior to aging. This suppressed Mg-Ag co-clustering leads to a steep drop of the number density of Mg-Ag co-clusters by 70% and finally fails to induce the formation of high density Ω plates. High density dislocations introduced by pre-stretching also serve as the heterogeneous nucleation sites of θ′ phase and favor an enhanced precipitation of coarse θ′ needles. In addition, pre-stretching also exhibits a negative effect on initial Cu-Mg co-clustering. [ABSTRACT FROM AUTHOR]

The hierarchical distribution of Cu-rich precipitates (CRPs) and related partitioning and segregation behaviours of solute atoms were investigated in a 1.54 Cu-3.51 Ni (wt.%) low-carbon high-strength low-alloy (HSLA) steel after multistage heat treatment by using the combination of electron backscatter diffraction (EBSD), transmission electron microscopy (TEM) and atom probe tomography (APT). Intercritical tempering at 725 °C of as-quenched lathlike martensitic structure leads to the coprecipitation of CRPs at the periphery of a carbide precipitate which is possibly in its paraequilibrium state due to distinct solute segregation at the interface. The alloyed carbide and CRPs provide constituent elements for each other and make the coprecipitation thermodynamically favourable. Meanwhile, austenite reversion occurs to form fresh secondary martensite (FSM) zone where is rich in Cu and pertinent Ni and Mn atoms, which gives rise to a different distributional morphology of CRPs with large size and high density. In addition, conventional tempering at 500 °C leads to the formation of nanoscale Cu-rich clusters in α-Fe matrix. As a consequence, three populations of CRPs are hierarchically formed around carbide precipitate, at FSM zone and in α-Fe matrix. The formation of different precipitated features can be turned by controlling diffusion pathways of related solute atoms and further to tailor mechanical properties via proper multistage heat treatments. [ABSTRACT FROM AUTHOR]

Atom probe tomography was used to quantitatively assess grain boundary phase compositions and determine local segregation along the grain boundary before and after a 1000 h thermal exposure at 800 °C on an experimental powder processed Ni-base superalloy containing elevated levels of Nb. Due to high levels of refractory alloying elements at the grain boundary, a complex network of σ phase precipitates formed and the interfacial segregation profiles were studied. Although elemental B segregates to grain boundaries and secondary phase interfaces, insufficient levels are present to result in boride formation due to an enhanced solubility of B in the matrix phase. [ABSTRACT FROM AUTHOR]

Nano-scale Ni-Mn-Si-rich precipitates formed in a reactor pressure vessel steel under high neutron fluence have been characterized using highly complimentary atom probe tomography (APT) and scanning transmission electron microscopy with energy dispersive spectroscopy (STEM-EDS) combined with STEM-EDS modeling. Using these techniques in a synergistic manner to overcome the well-known trajectory aberrations in APT data, the average upper limit Fe concentration within the precipitates was found to be ∼6 at.%. Using this knowledge, accurate compositions of the precipitates was determined and it was found that the spread of precipitate compositions was large, but mostly centered around the Γ 2 -and G -phases. The use of STEM-EDS also allowed for larger areas to be examined, and segregation of minor solutes was observed to occur on grain boundaries, along with Ni-Mn-Si-rich precipitates that were smaller in size than those in the matrix. Solute segregation at the grain boundaries is proposed to occur through a radiation induced segregation or radiation enhanced diffusion mechanism due to the presence of a denuded zone about the grain boundary. It is also proposed that the reduced precipitate size at the grain boundaries is due to the structure of the grain boundary. The lack of Ni-Mn-Si precipitates observed in larger Mo-rich precipitates is also discussed, and the absence of the minor solutes required to form the Ni-Mn-Si precipitates results in the lack of nucleation. This is in contrast to cementite phases in which Ni-Mn-Si precipitates have been observed to have formed. It was also determined through this work that the exclusion of all the Fe ions during atom probe analysis is a reasonable approximation. [ABSTRACT FROM AUTHOR]

We address the competitive precipitation and coprecipitation of three types of secondary phases, i.e., Cu-rich precipitates (CRPs), reverted austenite (RA), and alloyed carbide, in a high-strength low-alloy steel with austenite reversion treatment at 675 °C by using electron back-scatter diffraction, transmission electron microscopy, and atom probe tomography. There is a strong competitive diffusion of Ni and Cu participating in austenite reversion and Cu precipitation with the fact that no CRPs are detected in and around the RA. Meanwhile, there is also a strong competitive diffusion of austenite stabilizing element Ni and carbide-forming elements Cr and Mo into the pre-existing C-rich zone, leading to the formation of nonequilibrium alloyed carbide deviating from the stoichiometric composition. On the other hand, the alloyed carbide and CRPs provide constituent elements for each other and make the coprecipitation thermodynamically favorable. The knowledge on the interactive formation of these three features provides versatile access to tailor the distributional morphology of CRPs, RA, and alloyed carbide via a multistage heat treatment and thus realize their beneficial effect on strength and toughness. [ABSTRACT FROM AUTHOR]

The microstructures of a hierarchical-precipitate-strengthened ferritic alloy are characterized, using transmission-electron microscopy (TEM) and atom-probe tomography (APT). The alloy shows duplex precipitates. The primary precipitate with an average edge length of 90 nm consists of NiAl- and Ni 2 TiAl-type phases, while the secondary precipitate with an average radius of 2 nm is a NiAl-type phase. Based on the APT results, the volume fractions of the primary and secondary precipitates were calculated, using the lever rule to be 17.3 and 2.3%, respectively. [ABSTRACT FROM AUTHOR]

A detailed investigation of precipitation of the ordered L1 2 (γ′) phase in a Al 0.3 CrCuFeNi 2 high entropy alloy (HEA), more generally referred to as a complex concentrated alloy (CCA), reveals the role of copper (Cu) on stabilization and precipitation of the ordered L1 2 (γ′) phase. Detailed characterization via coupling of scanning and transmission electron microscopy, and atom probe tomography revealed novel insights into Cu clustering within the face-centered cubic matrix of this HEA, leading to heterogeneous nucleation sites for the γ′ precipitates. The subsequent partitioning of Cu into the γ′ precipitates indicates their stabilization is due to Cu addition. The γ′ order-disorder transition temperature was determined to be ∼930 °C in this alloy, based on synchrotron diffraction experiments, involving in situ annealing. The growth and high temperature stability of the γ′ precipitates was also confirmed via systematic scanning electron microscopy investigations of samples annealed at temperatures in the range of 700–900 °C. The role of Cu revealed by this study can be employed in the design of precipitation strengthened HEAs, as well as in a more general sense applied to other types of superalloys, with the objective of potentially enhancing their mechanical properties at room and elevated temperatures. [ABSTRACT FROM AUTHOR]

Some research showed that the precipitation of η-Ni 3 Al 0.5 Nb 0.5 phase at grain boundary can optimize the mechanical properties and reduce the notch sensitivity of the nickel-based superalloy ATI 718Plus. Therefore, finding the optimum concentration and morphology of η-Ni 3 Al 0.5 Nb 0.5 for different operating conditions is of great importance during the microstructure design process. In this study, the relationship between the mechanical properties as well as notch sensitivity and the η-Ni 3 Al 0.5 Nb 0.5 content in ATI 718Plus was investigated by subjecting the alloy to different heat treatment processes. The stress rupture life of ATI 718Plus was found to improve significantly by decreasing the η-Ni 3 Al 0.5 Nb 0.5 content. However, the notch sensitivity drastically increased when the η-Ni 3 Al 0.5 Nb 0.5 mass percentage dropped below approximately 1.1 wt%. The microstructure of the samples was analyzed by field emission scanning electron microscopy and the phase composition was quantitatively determined by electrolytic phase isolation followed by a micro-chemical and X-ray diffraction analysis. The atomic distribution of elements in the alloy on a nanoscale was determined by 3DAP technique. The phase diagram and time-temperature-transformation curve of the different phase were calculated using the JMatPro6.0 software. Furthermore, the precipitation kinetics of the η-Ni 3 Al 0.5 Nb 0.5 and γ′ phases and the optimum η-Ni 3 Al 0.5 Nb 0.5 mass percentage in 718Plus were discussed. [ABSTRACT FROM AUTHOR]

Microalloying additions to Mg-Zn base alloys can refine precipitation and improve hardening, but their effect on the microstructure at the grain boundary regions are seldom analyzed. Here the grain boundary microstructure is examined in an Mg-4Zn (wt.%) alloy, which has been microalloyed with Ce-Ca. This combination of elements has previously been shown to successfully enhance ductility, texture, and precipitation hardening, compared to binary Mg-Zn. Coarse grain boundary precipitates are found with or without microalloying, but precipitate-free zones (PFZs) for β ′ 1 that surround the boundaries are far narrower with Ce-Ca microalloying additions. Furthermore, fine basal precipitates containing Ca are found uniformly distributed up to the boundary, making those zones devoid of β ′ 1 not truly precipitate-free. Electron microscopy and atom probe analysis of early-stage ageing conditions reveals that Ca readily forms clusters with Zn, and forms fine ordered GP zones, while Zn also segregates to the grain boundaries. The tendency of Ca to homogeneously form clusters and precipitates reduces Ca migration to the grain boundaries, which has a beneficial effect on producing the refined precipitate distributions at the grain boundary regions. [ABSTRACT FROM AUTHOR]

Depending on the particle used to irradiate Fe–Cr alloys, at the same dose and temperature, α′ precipitation may occur or not. This paper aims at explaining the origin of the absence of α′ precipitation under ion irradiation. A Fe–15at.%Cr alloy was irradiated with 2 MeV Fe2+ions at 300°C and analysed using atom probe tomography. For the first time to our knowledge, α′ particles were observed under ion irradiation. The characterisation of the α/α′ decomposition with depth showed that injected Fe strongly reduced α′ precipitation. They might have played a major role in the absence of α′ precipitation under ion irradiation. IMPACT STATEMENT This paper reports the first observation of α′ precipitation in Fe–Cr alloys after heavy ion irradiation and demonstrates that the injected interstitial effect drastically modifies the precipitation behaviour. [ABSTRACT FROM PUBLISHER]

Voids, G phase particles, and Ni-Si rich clusters in proton irradiated dual phase 308L groove filler of a SA508–304 L dissimilar metal weldment are analyzed using advanced characterization techniques. These weldments are often used in light water nuclear reactors and are subject to enhanced corrosion and associated stress corrosion cracking (SCC). Radiation damage is known to accelerate SCC. Ni-Si enriched clusters were observed in proton irradiated γ austenite, while G phase M 6 Ni 16 Si 7 (where M transition metal element) precipitates were observed in proton irradiated δ ferrite. Compositional analysis of the G phase precipitates and Ni-Si clusters from STEM-EDS and APT are compared. Unlike G phase particles in proton irradiated δ ferrite, Ni-Si clusters in proton irradiated γ austenite are not rich in Mn. Both STEM-EDS and APT line-scan profiles of the Ni-Si clusters show that the Fe and Cr concentration gradient between matrix γ austenite and the Ni-Si clusters is not as sharp as those between matrix δ ferrite and G phase. Further, HR-STEM imaging indicates that the lattice parameter of the Ni-Si clusters is commensurate with γ austenite and the clusters do not represent the precipitation of a second phase. Our analysis demonstrates the density and volume fraction of G phase particles and the density of voids scales with proton irradiation damage and the energy to recoils. [ABSTRACT FROM AUTHOR]

The close association between the Ω precipitation and various Ag additions is systematically investigated by quantitative transmission electron microscopy and atom probe tomography analysis. Our results suggest that the precipitation of Ω phase is strongly dependent on Ag variations. Increasing the bulk Ag content favors a denser Ω precipitation and hence leads to a greater age-hardening response of Al-Cu-Mg-Ag alloy. This phenomenon, as proposed by proximity histograms, is directly related to the greater abundance of Ag solutes within Ω precursors. This feature lowers its nucleation barrier and increases the nucleation rate of Ω phase, finally contributes to the enhanced Ω precipitation. Also, it is noted that increasing Ag remarkably restricts the precipitation of θ' phase. [ABSTRACT FROM AUTHOR]