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Complex precipitation behavior of Cu-rich particles (CRPs) was investigated and simulated in continuously cooled and quench-aged super duplex stainless steel. Atom probe tomography (APT) and scanning electron microscopy showed that slow cooling resulted in nonuniform multimodal CRP precipitation and spinodal decomposition, while in the fast cooled and quench-aged conditions, more uniform precipitation of CRPs with no visible spinodal decomposition was found. Depletion of Cu, Ni, and Mn was observed in the ferrite next to the CRPs during growth, but not during dissolution. Some evidence of Ostwald ripening was seen after slow cooling, but in the quench-aged condition, particle coalescence was observed. Large CRPs disappeared next to a ferrite–austenite phase boundary after slow cooling when Cu was depleted due to the diffusion to austenite as also predicted by moving boundary Dictra simulation. Comparing Cu depleted areas next to CRPs analyzed by APT and moving boundary Dictra simulation of CRP–ferrite showed that the effective Cu diffusion coefficient during the early-stage precipitation was about 300 times higher than the Cu diffusion coefficient in ferrite at 475 °C. Using the effective diffusion coefficient and a size-dependent interfacial energy equation, CRP size distribution was successfully predicted by the Langer–Schwartz model implemented in Thermo-Calc Prisma. Applying a short aging time and continuous cooling increased the hardness and decreased the toughness values compared to the solution annealed condition. A nonuniform distribution of Cu in ferrite, the duplex structure, and partitioning of alloying elements among different phases are factors making CRP precipitation in duplex stainless steels complex.

The semiconductor industry has seen tremendous progress over the last few decades with continuous reduction in transistor size to improve device performance. Miniaturization of devices has led to changes in the dopants and dielectric layers incorporated. As the gradual shift from two-dimensional metal-oxide semiconductor field-effect transistor to three-dimensional (3D) field-effect transistors (finFETs) occurred, it has become imperative to understand compositional variability with nanoscale spatial resolution. Compositional changes can affect device performance primarily through fluctuations in threshold voltage and channel current density. Traditional techniques such as scanning electron microscope and focused ion beam no longer provide the required resolution to probe the physical structure and chemical composition of individual fins. Hence advanced multimodal characterization approaches are required to better understand electronic devices. Herein, we report the study of 14 nm commercial finFETs using atom probe tomography (APT) and scanning transmission electron microscopy-energy-dispersive X-ray spectroscopy (STEM-EDS). Complimentary compositional maps were obtained using both techniques with analysis of the gate dielectrics and silicon fin. APT additionally provided 3D information and allowed analysis of the distribution of low atomic number dopant elements (e.g., boron), which are elusive when using STEM-EDS.

The level of chromium plays an essential role in irradiation tolerance of Fe-Cr ferritic alloys. However, conflicting results have been reported regarding the dependence of cavity swelling under irradiation on Cr level and temperature. Here, we have performed a comprehensive set of simultaneous dual-ion (Ni + He) irradiations to high dose (∼30 displacements per atom, dpa) at 400–550 °C on a series of ultra-high purity Fe and Fe-Cr binary alloys (3–14 wt.%Cr). Helium co-implantation rates of 0.1 and 10 appm He/dpa were selected to examine He synergistic effects relevant for fission and fusion reactor conditions, respectively. Cavities were observed in all irradiated samples by transmission electron microscopy. The results show that higher He implantation rate causes a shift in the swelling peak to higher temperatures in both Fe and Fe-Cr alloys. When assuming smaller cavities as biased sinks, the non-monotonic nature of the cavity swelling behavior is related to the ratio of biased to unbiased point defect sink strengths. Cr-enriched precipitates were observed in Fe-14Cr irradiated at 400 °C by atom probe tomography. Our analysis suggests the formation of Cr-enriched precipitates could suppress cavity swelling for Fe-Cr alloys with Cr content above 10 wt%.

Protecting superconducting magnets from neutron irradiation is critically important when demonstrating the utility of spherical tokamaks. Reactive Sintered Borides (RSBs) are promising radiation-dense materials and excellent attenuators of slow (

In this work, the effects of the micro-alloying of Mn, Ni, and Si on the microstructure and mechanical properties of high-carbon pearlite steels were investigated. The results indicated that the addition of solely Ni to high-carbon pearlitic steel can enhance the strength through the refinement of interlamellar spacing, but work-hardening in the ferrite of the pearlite colony may be delayed, leading to a reduction in area. The multiple additions of Ni and the increase in Mn and Si contents in high-carbon pearlitic steel were beneficial to obtaining a balance between ultimate tensile strength and reduction in area. Three-dimensional atom probe tomography results showed Si partitioning into ferrite and Mn and Ni elements partitioning into cementite. The addition of Si inhibited the formation of a continuous network of grain-boundary cementite, leading to high strength and high ductility through optimization of the microstructure.

Automotive industries require materials with higher strength, plasticity and crashworthiness, aiming for 3rd generation of advanced high strength steels (AHSS) with medium Mn, Si and minor alloying elements. In this investigation, 3rd generation AHSS were synthesized using a vacuum arc melting furnace with manganese (Mn) and silicon (Si) as major alloying elements as well as minor additions such as Cr, Al, Ni, etc. The steels thus developed were characterized using FE-SEM, XRD, microhardness tester, universal testing machine (UTM) and 3-dimensional Atom Probe Tomography (APT). The alloy steels after casting and homogenization were subjected to hot rolling at 1100 °C, with rolling exit temperature 900 ± 50 °C. The FE-SEM micrographs in SE mode revealed a complex phase microstructure with martensite, ferrite, bainitic ferrite and retained austenite in the specimens obtained after rolling and air cooling. The microhardness of the developed alloys is found in the range of 395–502 VHN in the hot-rolled and air cooled condition of the specimen. The tensile strength of alloys was measured to be in the range of 1412–1614 MPa with elongation of 12.12 %–18.92 %. The analysis of fracture surfaces after tensile tests for developed alloys revealed that Alloy 1 (Fe-4Mn-1.5Si) had dimples indicating ductile fracture while Alloy 2 (Fe-6Mn-1.5Si) has a mixture of dimples and facets, and Alloy 3 (Fe-8Mn-1.5Si) has lower dimples but larger facets, confirming quasi-ductile fracture with a lower ductility limit of 12.12 %. Atom Probe Tomography was performed to study the complex phase structure at nanoscale through re-distribution of carbon and other alloying elements. 3D APT revealed the presence of very fine retained austenite film of thickness ∼4–5 nm and carbon content of 6–8 at.%. This complex phase microstructure obtained after hot rolling and normalizing is made of very fine bainitic ferrite with film type retained austenite providing TRIP effect, in addition martensite and ferrite resulting in high strength. • This research has resulted in the development of a 3rd generation AHSS in the vacuum arc furnace. • A complex phase microstructure was formed with ferrite, bainite, martensite and retained austenite through normalizing • The novel alloys exhibit high tensile strength from 1412 MPa to 1614 MPa with an appreciable elongation from 12 to 19 %. [ABSTRACT FROM AUTHOR]

Irradiation damage and thermal aging greatly affect the phase boundary microstructure and stress corrosion cracking of austenitic stainless steel weld metals (ASSWMs) in water-cooled nuclear reactors. However, the effects of irradiation plus thermal aging (I + A) on the phase boundary segregation and phase changes remain unclear. Phase changes and elemental segregation at the carbide and carbide-free phase boundaries of 308 L ASSWMs after I + A treatment were investigated using atom probe tomography and transmission electron microscopy. The I + A treatment induced Si depletion at the phase interfaces of δ-ferrite/austenite (δ/γ) and δ-ferrite/carbide (δ/C) and also induced Ni enrichment and Cr depletion with concentrations having the order Ni/Cr(δ/γ) > Ni/Cr(δ/C) > Ni/Cr(γ/C). The solute-defect binding model and the vacancy mechanism were applied to explain the phase boundary segregation. Furthermore, the I + A treatment affected microstructural evolution near the phase boundaries; this reduced spinodal decomposition and inhibited G-phase and Ni/Si-rich-cluster formation. The phase separation of δ-ferrite near δ/γ and δ/C phase boundaries differed with the distance from the boundary, forming a gradient microstructure from phase boundaries to δ-ferrite internally. The gradual precipitation of the G-phase was observed beyond about 15 and 10 nm from the δ/γ and δ/C interfaces, respectively; moreover, the growth of α'-phase in the δ-ferrite was accelerated with increasing distance from the δ/γ and δ/C interfaces. [Display omitted] • I + A treatment induced Ni enrichment and Cr depletion at the phase boundaries. • I + A treatment enhanced spinodal decomposition within δ-ferrite, but reduced it near the phase boundary. • The G phases gradually precipitated at ∼ 15 and ∼ 10 nm away from the δ/γ and δ/C interfaces, respectively. • No G phase precipitated near phase boundary because of Ni deficiency for G-phase formation near δ/γ and δ/C interfaces. • The formation of Ni/Si-rich clusters near the phase boundary was inhibited after I + A treatment. [ABSTRACT FROM AUTHOR]

Laser micromachining can serve as a coarse machining step during sample preparation for high-resolution characterization methods leading to swift sample preparation. However, selecting the right laser parameters is crucial to minimize the heat-affected zone, which can potentially compromise the microstructure of the specimen. This study focuses on evaluating the size of heat-affected zone in laser annular milling, aiming to ascertain a minimal scan diameter that safeguards the inner region of micropillars against thermal damage. A computational model based on the finite element method was utilized to simulate the laser heating process. To validate the simulation results, a picosecond pulsed laser is then used to machine the micropillars of Al and Si. The laser-machined samples were subjected to surface and microstructural analysis using Scanning Electron Microscope (SEM) and Electron Backscatter Diffraction (EBSD) scans. The length of heat affected zone obtained from simulations was approximately 6 μ m for silicon and 12 μ m for aluminum. The diameter of micropillars formed with laser machining was 10 μ m for silicon 26 μ m for aluminum. The core of the pillars was preserved with less than one degree of microstructural misorientations making it suitable for further processing for preparing specimens for techniques like APT and TEM. For silicon micropillars, the preserved central region has a diameter of 6 μ m and for aluminum its around 20–24 μ m. Additionally, the study determines the minimum scan diameter that can be achieved using the given laser machining setup across a range of common materials. • Determined minimum scan diameters for laser machining of micropillars with preserved core • Thermal damage during laser micromachining was modeled using finite element method • Si micropillars of diameter 10 μ m with a preserved core produced with laser machining • The modeling approach was extended to a range of engineering materials. [ABSTRACT FROM AUTHOR]

The precipitation mechanism of strengthening phase of a body-centered-cubic (BCC) structured CoFeNi multi-principal element alloy produced by additive manufacturing was studied by transmission electron microscopy (TEM) and atom probe tomography (APT). The hardness of CoFeNi alloy achieved the peak value of 554.79 ± 9.86 HV after aging for 160 h at 400 °C. The CoFeNi alloy exhibited an ultrahigh compressive yield strength and ultimate compressive strength up to 1.8 GPa and 2.3 GPa respectively, whilst maintains a strain of 18.9 %. The microstructure of the alloy exhibited nanoscale lamellar Ni-rich phase with high stability homogeneously distributed in BCC matrix after aging at 400 °C. The novel Ni-rich phase containing about 50 at. % Ni with a hexagonal structure is the mainly precipitation strengthening phase, and has coherent orientation relationship with the BCC matrix in the < 101 > bcc ∥ < 11 2 ¯ 0 > Ni and 111 bcc ∥ { 0 001} Ni. Based on the experimental results, the precipitation mechanisms of the Ni-rich phase were discussed in detail. The current work provides a possible new direction to design high-strength alloy by introducing the novel Ni-rich phase. • An ultra-high strength CoFeNi alloy was prepared by additively manufacturing. • Novel Ni-rich phase precipitated in the alloy without additional alloying element. • The structure and composition of the Ni-rich phase are stable during aging treatment. [ABSTRACT FROM AUTHOR]

Site-specific atom probe tomography coupled with electron back scattering diffraction studies were used for the first time to elucidate the multi-element solute segregation and clustering at austenite-ferrite interface during early stages of phase transformation in Fe-Mn-Si-C steel alloyed with Ti, Mo and Nb. The results have shown the existence of negligible partitioning local equilibrium at interfaces with segregation of C, Mn, Ti and Mo to interfaces having the angle deviation in the range from 2.9 to 12° from Kurdjumov-Sacks orientation relationships (K-S ORs), but either irregular incident planes or the ones not following the matching according to K-S ORs. The segregation of Nb was less common, which was linked to the earlier occupancy of interfaces by Ti and Mo. Variation in solute segregation along the same interfaces is highlighted. Presence of clusters within and in close proximity to the interface is detected. The links between interface orientation, solute segregation, clustering and interphase precipitation are discussed. [Display omitted] • Correlation of solute segregation with crystallography of ferrite/austenite interface. • Strong segregation of Mn, Ti and C to ferrite-austenite interfaces. • Low segregation of Nb due to already occupied sites at interfaces. • Formation of Ti clusters within interfaces as precursors to interphase precipitation. • All incident planes of interfaces were non-coherent or with unusual lattice matching. [ABSTRACT FROM AUTHOR]

[Display omitted] • The topmost surfaces of pristine LaCoO 3 are terminated by A-site La element. • Surface amorphization of LaCoO 3 after OER is induced by formation of La(OH) 3. • Enhanced hydroxide ions incorporation in Ca doped LaCoO 3 is observed directly. • Oxygen vacancies created by Ca doping improve the activity and stability of LaCoO 3. Developing efficient oxygen evolution reaction (OER) electrocatalysts requires a thorough understanding of structure–activity-stability relationships, ideally at the atomic scale. Herein, we employed atom probe tomography and transmission electron microscopy to reveal compositional and structural changes on LaCoO 3 and Ca-doped LaCoO 3 surfaces during OER. We reveal that the topmost surfaces of pristine perovskite are terminated by the A-site element (La). After OER, amorphous La(OH) 3 is formed on the surfaces of LaCoO 3 , which leads to significant activity deterioration. For Ca-doped LaCoO 3 , enhanced intercalation and penetration of hydroxide ions, along with the appearance of Co3+/4+ redox couple, are observed, contributing to its enhanced OER activity and stability. Our study demonstrates how atomic-scale compositional and structural details of electrocatalyst surfaces deepen our understanding of their activity and stability. [ABSTRACT FROM AUTHOR]

A combination of optical imaging (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and atom probe tomography (APT) was used to examine the white etching layer (WEL) and brown etching layer (BEL) formed in the flow lip region of a heavy haul curved rail. These flow lips eventually serve as crack initiating regions, leading to reverse detail fractures. OM distinctly identified the WEL/BEL region based on light contrast, while SEM micrographs identified a fine-grained structure within the WEL with intermittent patches of a deformed pearlitic structure. SEM images of the WEL/BEL indicate that the fraction of cementite patches was higher in the BEL region than in the WEL. TEM investigations revealed the presence of martensite/nano-crystalline ferrite along with newly formed austenite and cementite particles in the WEL and the BEL. The ferrite/martensite grain size was much finer in the WEL than in the BEL. The lath morphology of martensite was observed in the BEL, whereas a mixed morphology of lath and twinned martensite was observed in the WEL. APT studies show no Mn/Si partitioning in WEL/BEL along with C-concentrations ranging from 10 to 15 at.% and up to 20 at.% in the WEL and BEL respectively. The synergistic effect of elevated wheel-rail contact temperatures and severe plastic deformation dictated the overall microstructural evolution of the BELs and WELs on the outer rail surface in the flow lip. • WEL/BEL formed in curved rail flow lips due to repeated wheel-rail interactions. • WEL composed of nano-crystalline ferrite/martensite, cementite, and austenite. • BEL consists of coarser nano-crystalline ferrite/martensite, cementite, and austenite. • TEM reveals lath and twinned martensite morphology in WEL/BEL microstructure. • APT shows C aggregation, absence of Mn/Si partitioning in WEL/BEL. [ABSTRACT FROM AUTHOR]

The present study focuses on the factors underlying the substantially higher yield strength (YS) and ultimate tensile strength (UTS) in laser powder bed fusion (LPBF) processed niobium, as compared to electron beam additive manufacturing (EBAM) or conventionally processed Nb. LPBF builds of pure Nb, with a relative density of 98 %, exhibited an YS of 490 MPa, UTS of 609 MPa, and ductility of 9 % with appreciable strain hardenability. Detailed electron backscatter diffraction analysis revealed a high density of sub-boundaries within the BCC Nb grains. Additionally, the LPBF Nb sample contained ∼1200 ppm of oxygen and ∼380 ppm of nitrogen, part of which segregated to the grain boundaries, as revealed by atom probe tomography (APT). The individual strengthening contributions from grain boundaries, dislocations, and oxygen and nitrogen interstitials have been quantitatively estimated, giving an overall computed YS of 506 MPa, in close agreement with the experimentally measured value of 490 MPa. This quantitative assessment also revealed that solid solution strengthening from oxygen and nitrogen can be of the same order of magnitude as strengthening from dislocations and sub-boundaries in LPBF processed Nb. [ABSTRACT FROM AUTHOR]

The major obstacle to render steelmaking more sustainable is undoubtedly the decarbonization of its process chains. Accompanied by this challenge, the scarcity of high-grade iron ores to be exploited as feedstock is a near reality. This creates a massive dilemma that will force steelmakers to produce green steel from low-grade iron ores. The hydrogen plasma smelting reduction of iron ores (HPSR) emerges as an attractive CO 2 -lean pathway to produce iron, where the ore is exposed to a reducing hydrogen-containing plasma (Ar-10 % H 2) to get simultaneously melted and reduced. Here, we investigate the reduction of low-quality and low-cost model hematite ore samples containing 0.79 wt.% P via HPSR using an electric arc furnace (EAF). The dephosphorization mechanism of the ore was monitored by inspecting the evolving microstructure of the fast-solidified samples, condensed gas on the surface of electrostatic filters installed inside the EAF, as well as quantifying the corresponding P concentration in all constituents (i.e., unreduced oxides, iron and gas). We found that most of the P evaporates already in the beginning of the process (2 min) where the global O concentration in the melt varies from ∼29 to 21 wt.%. The remaining quantities of P, together with other minor gangue-related impurities (especially Si), allocates within the interdendritic domains of the partially reduced samples, as revealed by high-resolution scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX) and atom probe tomography (APT). Complementary thermodynamic modelling underpins the experimental observations, revealing that the evaporation of P is a thermodynamically-driven process, and it is dependent on the oxygen content of the melt. About 97 % dephosphorization was achieved, and only residual amounts of P were found within metallic iron domains, as revealed by APT and chemical analysis of the bulk iron (0.07 wt.% P). Our work aims at providing novel scientific-based perspectives in iron and steelmaking, permitting the production of clean and sustainable iron without the need for secondary metallurgical steps to remove undesired impurities. [Display omitted] [ABSTRACT FROM AUTHOR]

The influence of Mo on the coarsening behavior of L1 2 -precipitates in chemically complex alloys (CCAs) was thoroughly investigated. Mo addition significantly impacted the morphology, misfit, and microstructural stability of L1 2 -precipitates during aging treatment. Mo incorporation into the B sublattice sites of L1 2 -precipitates (along with Al and Ti) increased their volume fraction and solvus temperature. It also weakened the segregation of solutes between the FCC-matrix and L1 2 -precipitates, resulting in reduced misfit. However, during the aging processing, the misfits in all three CCAs continuously increased. Quantitative analysis revealed that a misfit of approximately 0.5 % yielded cubic morphology of L1 2 -precipitate for CCAs with positive misfits. Further coarsening kinetics studies unveiled a transition from initial matrix-diffusion controlled coarsening to interface-reaction controlled coarsening. Notably, Mo addition prolonged the matrix-diffusion controlled stage and delayed the transition to interface-reaction controlled coarsening. These findings provide valuable insights that can guide future alloy design and heat treatment strategies to optimize the high-temperature structural performance of L1 2 -precipitate CCAs. • The relationship bewteen lattice misfits and L1 2 -precipitates morphology of chemically complex alloys is established. • Incorporation of Mo into L1 2 B-sites increases precipitate volume fraction and solvus temperature. • Mo prolongs matrix-diffusion controlled coarsening of L1 2 -precipitates, delaying transition to interface-reaction control. [ABSTRACT FROM AUTHOR]

The clustering behaviour of a pre-aged Al-Mg-Si alloy during natural ageing (NA) and paint baking (PB) was systematically investigated by hardness measurements and atom probe tomography (APT). The results show that pre-ageing (PA) can effectively retard the negative effect of NA and enhance the paint-baking response even after long-term NA (up to one year). The pre-aged alloy shows a good resistance against clustering within a short NA period of one week, and the capability is enhanced with increasing pre-ageing time. However, the clustering becomes significant after prolonged NA, especially for one year. The increasing number density of clusters containing 10–30 solute atoms contributes most to the hardness increase after prolonged NA. The mechanism about two synergistic processes of 'vacancy trap' and 'vacancy escape' is introduced to explain the phenomenon. The alloy with a prior PA above 2 h exhibits a good PB response even after one-year NA. Such performance is attributed to large-size precipitates (GP zones or pre-β″ precipitates) formed during PA, which can serve as nuclei for β″ due to a similar composition. Moreover, a strength model has been established to predict the different strengthening effect and evaluate contributions from clusters, GP zones and pre-β″/β″ precipitates during multi-stage ageing in the Al-Mg-Si alloy. • Pre-ageing (PA) can retard clustering and facilitate paint baking (PB) response even after one-year natural ageing (NA). • The enhanced NA stability and PB response is due to the generation of GP zone or pre-β″ during PA. • The deteriorated stability after prolonged NA can be ascribed to the vacancy behaviour. • The final hardness after PB largely depends on priorPA time rather than NA period. [ABSTRACT FROM AUTHOR]

The nanoprecipitation of naturally aging Al–5.70Si–2.06Cu–0.29Mg (wt.%) cast alloy and its impact on tensile properties was investigated based on atomic-scale characterization by transmission electron microscopy and atom probe tomographic analyses. Solution treatment led to the dissolution of θ-Al 2 Cu and Q-Al 5 Cu 2 Mg 8 Si 6 phases, along with the spheroidization of the eutectic Si phase of the cast alloy. Upon quenching of the solution-treated alloy, nanoscale Si precipitates with equivalent radii of ∼1.77 nm were formed. Subsequent natural aging resulted in the formation of coherent solute clusters (0.66 ± 0.11 nm in radius), rich in Mg/Si or Cu, which correspond to the precursor phases Q-Al 5 Cu 2 Mg 8 Si 6 and θ-Al 2 Cu. Microhardness of the matrix and the strength of the alloy significantly increased due to the natural aging-induced solute clustering. Analysis of the strengthening mechanism indicated that the enhanced strength of the naturally aged alloy was primarily due to the coherency and modulus strengthening of the dislocation-shearable solute clusters. These clusters suppressed the dynamic strain aging, whereas no significant changes were observed in the strain-hardening behavior. However, natural aging led to the degradation of the alloy ductility due to the presence of shearable solute clusters, which could create slip bands and promote failure in regions with a high fraction of secondary phases within the cast alloy. • Solution treatment causes dissolution of θ/Q and spheroidization of eutectic Si. • Disc-type Si precipitates with Cu/Mg interfacial segregation form during quenching. • Two types of coherent clusters rich in Mg/Si or Cu form during natural aging (NA). • NA improves alloy strength by ∼100 MPa due to dislocation-shearable solute clusters. [ABSTRACT FROM AUTHOR]

Proof for distribution of boron in M 23 C 6 precipitates and prior austenite grain boundaries, and role of boron in reducing the coarsening kinetics of the precipitates and thereby improving the creep strength, are established and quantified in modified 9Cr 1Mo steels using AES, APT, and TEM. The average atomic concentration of B estimated using APT found to be ∼80 times more in the precipitate than its nominal composition in the 100 ppm B containing steel. The necessity to have a small quantity of nitrogen in the steel to take advantage of strengthening by carbo-nitrides along with boron-carbides is also proven from the characterization performed on three different steels after creep tests, one with 500 ppm N with no intentional addition of B (rupture life-44 h for creep test at 650 °C/120 MPa), another with 70 ppm B and 108 ppm N (rupture life-770 h) and the third steel with 100 ppm of B and 20 ppm of N (rupture life-282 h). Based on the results of characterization and the creep tests, maintaining an optimal concentration of around 70-120 ppm B and 90-120 ppm N are recommended for the maximum advantage of the presence of these two micro-alloying elements in this class of steel. [Display omitted] • APT estimates B is ∼80 times higher in the precipitates than Matrix. • APT and AES confirms boron in precipitates replaced by carbon. • Boron segregation occurs in boundaries as well, especially in PAGB. • MX carbo-nitrides influences the enhanced creep life. • Creep life improved by limiting B (70-120 ppm), and N in 90-120 ppm. [ABSTRACT FROM AUTHOR]

The microstructures and nano-scale precipitate phases of Custom 455 stainless steel quenched from 850 °C and over-aged at 480 °C for 256 h have been studied in a quantitative way by using transmission electron microscopy and atom probe tomography. The results show that plate reverted austenite is formed between the martensite laths. In the reverted austenite, a rod-shaped Ni 3 Ti phase particle of about 40 nm long is precipitated at the interphase interface between martensite and reverted austenite, with an adjacent Cu-rich precipitate with a size of ∼20 nm. In the martensite, spherical G-phase particles with a diameter of about 8.0 ± 1.6 nm are precipitated adjacent to the Cu-rich precipitates with a size of about 10.0 ± 2.0 nm. These Cu-rich precipitates in the martensite are much smaller than those in the reverted austenite, but have a ten times higher number density than that in the latter. The orientation relationships between the martensitic matrix, reverted austenite, Ni 3 Ti phase, G-phase and Cu-rich precipitates are: (01−1) M //(1−11) γ //(0004) η //(02−2) G //(111) Cu , [111] M //[011] γ //[2−1−10] η //[111] G //[11−2] Cu. • This is the first to demonstrate that plate reverted austenite is formed in the Custom 455 steel, which causes softening. • Ni 3 Ti phase particle of ∼40 nm is formed at the interface between martensite and reverted austenite with Cu-rich particle. • In the martensite, spherical G-phase particles of ∼8nm in diameter are formed adjacent to Cu-rich precipitates of ∼10nm. • Orientation relationships between matrix, reverted austenite, Ni 3 Ti phase, G-phase and Cu-rich precipitate are determined. [ABSTRACT FROM AUTHOR]

Chemical analysis of shape memory alloys (SMAs) is critically important to characterization due to the high compositional sensitivity of shape memory properties. Chemical analytical techniques must be carefully planned and implemented as they may alter the sample or skew the analysis. Characterization with a complex technique, such as atom probe tomography (APT) used for a nontrivial material like NiTiHf SMAs, is uniquely challenging when determining accuracy of 3D compositional data. APT is a high-resolution alternative for measuring nano-scale compositions and only a few studies have used this technique to examine the 3D nanoscale features of H-phase precipitates within NiTiHf systems. In this study, a Ni 50.5 Ti 34.5 Hf 15 SMA was aged to characterize the H-phase nanoprecipitates and to discuss the influence of aging temperature to promote Ni-enriched H-phase, which is much greater than previously determined within Ni-rich compositions. [Display omitted] [ABSTRACT FROM AUTHOR]

Atom probe tomography has been applied to study lithium-induced corrosion of Pulsed-Laser Deposition grown Al 2 O 3 , which is a candidate coating material for breeder blankets for nuclear fusion reactors. Coated Eurofer97 specimens were immersed in static Pb-17Li for 7000 h with samples extracted from the regions near the ceramic-substrate interface to determine the extent of Li penetration. Li-enriched regions, which are non-stoichiometric with respect to any known equilibrium phases predicted by the Li-Al-O phase diagram at 823 K, are reported for the first time in Al 2 O 3. The nature and composition of the Li-enriched features were characterized with nanometre resolution. It was found that the Li content inside these features may increase to a maximum of 35 at%, with the adjacent Al 2 O 3 matrix containing approximately 5–10 at% Li. Based on these results, the corrosion mechanism of amorphous Al 2 O 3 is proposed to be Li substitution of Al atoms. • The near-interface region of the alumina barrier coating on a fusion steel was extracted by focused ion beam milling. • The distribution of Li atoms intruding into an alumina coating is imaged for the first time with atom probe tomography. • Nanoscale region significantly enriched in Li were observed near the ceramic-metal interface. • Their compositions were identified as non-stoichiometric and implied these are non-equilibrium microstructural features. • A possible lithiation mechanism for amorphous alumina was proposed based on composition of the clusters. [ABSTRACT FROM AUTHOR]

Herein, the effect of tempering at 200 °C for 20 min on the mechanical properties of a cold‐rolled and intercritical annealed medium Mn steel is investigated in this study. This effect is mainly dependent on the original annealing condition. For the sample annealed at a relatively low temperature (660 °C), the austenite stability of this sample is further improved significantly after tempering. Thus, the transformation‐induced plasticity (TRIP) effect is severely inhibited during deformation, which leads to a decrease in the properties of the sample. By contrast, for the sample possessing suitable austenite fraction (≈30%) and heterostructure, that is, the sample annealed at 680 °C for 10 min, the simultaneously increased strength and ductility are significantly intrigued by tempering treatment. Electron probe microanalysis and 3D atom probe results reveal that C concentration in austenite is increased due to the C repartition during tempering, which leads to the persistent TRIP effect in a broad strain range during tensile deformation. In addition, the heterogeneous‐deformation‐induced stress of the heterostructured sample is found to be obviously intensified by tempering treatment. Thus, an excellent strength plastic synergistic effect with a product of ultimate tensile strength and total elongation of approximately 70 GPa% is obtained in the tempered sample. [ABSTRACT FROM AUTHOR]

In this study, atom probe tomography and first-principles calculations were used to investigate the influence of Mo addition on multiple precipitates, including isolated NiAl-based precipitates as well as NiAl-based and Cu-rich co-precipitates, in high-strength ferritic steel. The co-NiAl-based precipitates were experimentally confirmed to be nucleated from the abundance of Cu atoms. The addition of Mo accelerated the nucleation process of Cu-rich precipitates and structural transformation of co-precipitates, led to a considerable increase in the nucleation rate of NiAl-based precipitates, and slightly promoted isolated NiAl-based precipitates. The results were discussed from the perspective of lattice misfits and mixing enthalpy. [ABSTRACT FROM AUTHOR]

Biominerals and biomaterials are part of our daily lives, from our skeleton and teeth to coral reefs and carbon-capturing single-cell organisms in the oceans, to engineered ceramics comprising our toothpaste and bone replacements. Many biominerals are hierarchically structured with remarkable material properties that arise from their unique combination of organic and inorganic components. Such structural hierarchy is often formed through a process of biomineralization. However, many fundamental questions remain regarding mineralization events in bones or teeth, and near biomaterials, partly due to the challenges in characterizing three-dimensional (3D) structure and chemical composition simultaneously at the nanometer scale. Atom probe tomography (APT) is a 3D characterization technique that combines both sub-nanometer spatial resolution and compositional sensitivity down to tens of parts per million. While APT is well-established in application to conventional engineering materials, recent years have seen its expansion into biomineralization research. Here, we focus our review on APT applications to biominerals, biomaterials and biointerfaces, providing a high-level summary of findings, as well as a primer on theory and best practices specific to the biomineralization community. We show that APT is a promising characterization tool, where its unique ability to quantify 3D chemical composition is not only complementary to other microscopy techniques but could become an integral part of biomaterial research. With the emerging trends of correlative and cryogenic workflow, notwithstanding the challenges outlined herein, APT has the potential to improve understanding of a broader range of biomaterials, while deriving innovative perspectives on clinical applications and strategies for biomaterial design. Atom probe tomography (APT) is a three-dimensional characterization technique that can provide quantitative elemental and isotopic analysis with sub-nanometer resolution and compositional sensitivity down to tens of parts per million. These capabilities make it uniquely positioned for the analysis of biomineralized materials, both natural and synthetic. Here, we review the various applications of APT to the field of biomineralization, including applications in biominerals, biomaterials, biointerfaces and other biological materials, such as cells or proteins. A brief but comprehensive summary of the relevant technical concepts, limitations, and future perspectives to enable growth in this field are also included. Although APT is relatively new to the field of biomineralization, it has shown the potential to transform our basic understanding of biomineralization mechanisms and better inform biomaterials design. [Display omitted] [ABSTRACT FROM AUTHOR]

Coarse‐grained composites of refractory ceramics and refractory metals are a novel approach for materials at application temperatures up to 1500 °C. Al2O3 and the refractory metals Nb and Ta are suitable candidates for enhanced thermal shock capability, as they show similar thermal expansion. During fabrication, a key aspect to consider is the possible formation of additional phases upon interaction of the constituent phases as well as through reaction with the environment. X‐Ray diffraction (XRD) and investigations of the microstructure with scanning electron microscopy methods unveil Al2O3–Nb composite to form NbO, whereas for Al2O3–Ta the ternary compound aluminum tantalate (AlTaO4) is found. Thermodynamic calculations show that the changing oxygen solubility in Nb accounts for the formation of NbO, and explain the absence of a corresponding niobate (AlNbO4) phase. AlTaO4 is identified as the disordered tetragonal high‐temperature modification. [ABSTRACT FROM AUTHOR]

To achieve higher strength and good hardenability and at the same time use the positive effects of thermomechanical controlled processing, the concept of Nb and Ti microalloyed steels is increasingly used for high‐strength low‐alloy (HSLA) steels with higher C contents. Herein, how the addition of Ti affects the grain growth and static recrystallization behavior of a Nb microalloyed HSLA steel with a C content of 0.23 wt% is investigated. For this reason, alloys with varying Ti and constant Nb content are produced and investigated by means of annealing and double‐hit deformation experiments. Atom probe tomography measurements reveal that the Nb concentration in the matrix decreases with increasing Ti content. Therefore, the static recrystallization behavior is steadily inhibited with decreasing Ti content, as more dissolved Nb is available for the formation of strain‐induced NbC precipitates. The annealing experiments show that the combined addition of Ti and Nb is most effective against grain coarsening, regardless of whether the Ti content is 90 or 180 ppm. To use the positive properties of Ti against grain coarsening and Nb to inhibit recrystallization, a middle content must be chosen when alloying Ti to HSLA steels with higher C content. [ABSTRACT FROM AUTHOR]

The microstructural properties and strengthening mechanisms in precipitation strengthening Corrax stainless steel manufactured by laser powder bed fusion have been investigated. The as-printed sample initially contains a fully martensitic microstructure. However, aging heat treatment triggered the formation of austenite laths between the martensitic structure. Despite having softer reverted austenite, Corrax showed excellent hardness and strength due to the formation of Ni- and Al-rich, spherical precipitates (with an average size of 4.27 ± 1.20 nm). The atom probe tomography analysis reveals that Cr, Mo and Si are segregated in the Fe-based martensitic matrix, while the Mn diffused to the Al- and Ni-rich precipitates. [ABSTRACT FROM AUTHOR]

Nanoparticles with core–shell motifs are of particular interest because they enable combining multiple functionalities at nanoscale. However, a key challenge in designing such novel structures is to phase-separate the constituents at the core and shell regions, especially in thermodynamically miscible systems. In this study, we report the successful formation of self-organized Cr2O3-Fe2O3 core–shell nanoparticles by adopting a non-equilibrium route of pulsed laser-induced dewetting of an alloyed thin film. In this process, the evolution of nanoparticles takes place from the rupture of the initially flat liquid-phase alloyed film under laser irradiation. A continued laser pulsing results in the ripening of the morphologies at different stages eventually leading to a final droplet shape nanoparticle. Using highly sensitive 3D chemical mapping of individual nanoparticles and thermal simulations, we reveal that thermodynamically-soluble Cr2O3 and Fe2O3 phase-segregate in the core and shell regions, respectively, within ∼ 100 ns during a fast solidification process, leveraging the difference in the cooling rates, surface energies and enthalpy of mixing at high-temperatures. With these results, we present a non-equilibrium laser-assisted pathway that can be used to create core–shell nanostructures with dissimilar characteristics.