From Northwestern University Center for Atom-Probe Tomography
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FIM Image

A field-ion micrograph displaying platelet-shaped molybdenum nitride precipitates with {100}-habit planes in an internally nitrided Fe-2at.% Mo-0.5at.%Sn alloy. Each bright dot represents a single atom in the surface of the FIM tip. The lines of bright dots are the traces of nitride platelets cutting through the approximately hemispherical surface of the apex of the FIM tip, resulting in three sets of lines representing the three {100} habit plane variants. The two concentric circles below the center of the micrograph are the two atomic layers of a platelet tangential to the tip surface, at a (100) pole.

APT image

Within a model Ni-5.2 Al-14.2 Cr at. % superalloy, γ'-precipitation is first detected with atom-probe tomography (APT) after aging for 600 s at 873 K. Each dot within this thin 12 x 5 x 2 nm3 slice from an APT reconstructed volume represents an atom, positioned with sub-nanometer sensitivity, from a specimen aged at 600 s and analyzed along the [001]-direction. The Al and Cr atoms, displayed with red and blue dots, are enlarged in the nanometer-sized γ'-precipitate (R = 0.8 nm) to emphasize the resolution of {002} superlattice planes (d200=0.356 nm) associated with the L12-ordered γ'-phase. The interface between the γ'-precipitate and γ-matrix is delineated clearly with a red 9 at. % Al isoconcentration surface. Approximately, 2/3 of the γ'-precipitate volume is imaged above, and the full precipitate contains 109 detected atoms: 78 Ni (not displayed), 21 Al, and 10 Cr.

TEM of a tip

Transmission-electron micrograph of a 3DAP tomograph tip. The coherency contrast comes from nano-scale Al3Sc precipitates in Al (after aging at 300° C for 5 hours). These fine precipitates lead to high strength at ambient and elevated temperatures. Marsha van Dalen and Richard Karnesky are introducing ternary and quarternary alloying additions to further improve mechanical properties and coarsening resistance.

From Emmanuelle Marquis's Ph.D. Thesis.

TEM of a tip

A challenge for castable Al alloys is that few elements exhibit appreciable solubility in Al. Hence, the volume fraction of any precipitated phases is low (typically less than 1 vol.%). This contrasts from the Ni-based alloys, in which Al and Ti exhibit high solubility in Ni, leading to large volume fractions (usually exceeding 50%).

Analogous to γ' in the Al system are the trialuminides (Al3M, where M is a transition element). In order to achieve superalloy-like performance in Al, the precipitated Al3M must be very small, of the order of nm. Rick and Marsha are addressing this with ternary and quaternary additions to Al3Sc. Keith is investigating Al3Zr-based alloys.

APT of Cu-rich precipitates in steel

Nanometer-sized copper-rich precipitates are an important strengthening element in high-strength low-alloy and low-carbon steels. This 3D atom-probe tomographic reconstruction displays copper-rich precipitates in NUCu-100 steel, designed at Northwestern University to achieve a ultimate tensile strength of 100 ksi (700MPa), for more details see 'Co-precipitation of Copper and Niobium Carbide in a Low Carbon Steel', M.S. Gagliano, PhD Thesis, Northwestern University, 2002. The spatial distributions of individual Cu, Ni, Si, Al, and Mn atoms are shown in a reconstructed volume 2 nm in thickness and with a lateral cross-section of 15 x 14 nm2. It is seen qualitatively that Ni, Al, and Mn are enriched at the locations of the Cu-rich precipitates. For quantitative information on the copper-rich precipitates and the enrichment of Ni, Al, and Mn see 'Interfacial segregation at Cu-rich precipitates in a high-strength low-carbon steel studied on a sub-nanometer scale', D. Isheim, M.S. Gagliano, M.E. Fine, and D.N. Seidman, Acta Materialia Vol. 54(2006) pp. 841-849.

This nugget was featured in Imago's March newsletter.
APT of a catalyst nanowire

Catalyst nanowire interface in three dimensions. (a) 1-nm-thick slices through the nanowire over the region defined by the white bar in b. The diameter of the slices is 10 nm. (b) A 14 × 14 × 23 nm3 reconstruction of an InAs nanowire tip showing Au catalyst particle at the top. (c) One-dimensional composition profile plotted along the growth axis and through the catalyst/nanowire interface. The plotted composition is a radially averaged value within a 4-nm-diameter cylinder centered in the middle of the nanowire. From Local-Electrode Atom-Probe tomography by Danny Perea which appears in Three-Dimensional Nanoscale Composition Mapping of Semiconductor Nanowires.

This nugget was featured in Imago's 2006 Calendar.
APT of a Al-Sc-Yb

This LEAP tomography data set is from a dilute Al-Sc-Yb alloy which has been aged at 300°C. Nanosize Al3(Sc1-xYbx) precipitates (L12 structure) improve the strength and creep resistance of Al. Yb segregates to the center of the precipitates while the Sc segregates around the Yb core. The green spheres represent Yb atoms and the blue spheres represent Sc. Blue and green surfaces represent isoconcentration surfaces of Sc and Yb. Al atoms omitted for clarity.

APT of a Al-Sc-Yb

A nanoscale precipitate found in an Al-Sc-Yb alloy specimen analyzed using a Local Electrode Atom Probe (LEAP®) from Imago Scientific Instruments. The <200> planes (spacing ~0.2nm) in the crystalline lattice of the bulk Al structure are seen in ordered rows (green points). The <100> planes (~spacing 0.4 nm) in the precipitate are also clearly visible.

3D APT of a multicomponent steel alloy

A 3-D visual reconstruction of two nanoscale precipitates found in an Fe-Cu multicomponent steel alloy specimen analyzed using a Local Electrode Atom Probe (LEAP®) from Imago Scientific Instruments. The specimen was aged for 1024-hours at 500 degrees Celsius after solution treatment for 40 minutes at 900 degrees Celsius. The isoconcentration surfaces are at 12.0 at.% Ni - 9.5 Al - 3.0 Mn. An enhanced view of individual Cu (in the precipitate cut by the surface of the reconstruction volume) and Fe atoms are displayed delineating both the precipitate core and matrix. The remaining solute atoms (Ni, Al, Si, and Mn) atoms are not shown for clarity.

3D APT of a multicomponent steel alloy

A 3-D visual reconstruction of a grain boundary found in an Fe-Cu multicomponent steel alloy specimen analyzed using a Local Electrode Atom Probe (LEAP®) from Imago Scientific Instruments. The specimen was solution treated for 40 minutes at 900 degrees Celsius and quenched in water at 25 degrees Celsius. An enhanced view of individual C, B, P, and S ions are seen in the bottom right of the figure delineating the grain boundary.

3D APT of a model NiALCr superalloy

γ’-Ni3(Al,Cr) precipitates such as the one imaged above are responsible for the high-temperature strength of Ni-Based Superalloys. The spheroidal γ’-precipitate of radius ca. 9 nm is delineated from the γ-matrix phase by a 10.5 at.% aluminum isoconcentration surface. {110} planes are clearly defined by aluminum (red) and chromium atoms (blue), while Ni atoms are omitted for clarity. This image was obtained using a Local Electrode Atom Probe (LEAP®) from Imago Scientific Instruments

3D APT of high-purity Nb

The study of the surface chemistry of high-purity Nb is extremely important for the advancement of superconducting radio-frequency (SRF) cavities. The figure displays the 3-D reconstruction of Nb oxide on the surface of Nb. The reconstruction contains 300,000 atoms in 51 x 53 x 14 nm3 box. Nb atoms are in magenta, O atoms in cyan.


Heterogeneous nucleation of copper precipitates on a large carbide precipitate in a blast resistant steel. The black dots represent carbon atoms and the red surfaces are 10 at% copper isoconcentration surfaces. Knowledge of the interactions of the different kinds of precipitates in this alloy is important for determining the effects of internal structure on the mechanical properties. Note the heavily distorted nature of the precipitates that nucleated on the carbide, which indicates their nucleation mode. The box dimensions are 66 nm x 68 nm x 149 nm.


NUCAPT has donated their VG100 1DAP/FIM to the Museum of Science and Industry. It will become part of a nanotechnology exhibit they are building. Photo credit: Thom Burdsall.


Al-Sc-Er alloy, with Sc atoms in purple and Er atoms in gold. The isoconcentration surfaces show that Er partitions to the core of the precipitate and Sc partitions to the precipitate shell. This is described further in Effects of Substituting Rare-Earth Elements for Scandium in a Precipitation-Strengthened Al 0.08 at.% Sc Alloy by Rick and Marsha.

Coalescense dec 2004.gif

Lattice kinetic Monte Carlo simulation by Dr. Zugang Mao showing coagulation and coalescense of L12 ordered precipitates in a model Ni-Al-Cr superalloy. This coarsening mechanism is discussed in The mechanism of morphogenesis in a phase separating concentrated multi-component alloy.


Left: Best-fit ellipsoids to coagulated precipitates in 3DAP data for a Ni-Al-Cr alloy. The coagulation coarsening mechanism is discussed in a recent Nature Materials article and the best-fit ellipsoid algorithm and orientational dependence are described in another recently accepted article

Below: Inverse pole figure of ellipsoid orientation, showing a <110> preference.



The NUCAPT LEAP tomograph is upgraded with a larger detector, faster pulser, and digital FIM. (L-to-R: Dieter Isheim, Aniruddha Biswas, Mark Levesque. Photo credit: Richard Karnesky)


The figure displays a 3-D reconstruction of a Ni-6.24 Al-9.64 Cr at.% alloy aged at 873 K for 2 hours, which contains 72 million atoms and 1150 γ’-precipitates. The number density of precipitates is (7.15 ± 0.21) x 1023 m-3 , with an average radius of (1.11±0.26) nm and an average precipitate edge-to-edge spacing of (3.66±1.33) nm. The data was recorded employing a pulse repetition rate of 200 kHz, a pulse energy of 0.6 nJ, an effective pulse fraction of 20%, a specimen temperature of 40 K, and the target evaporation rate ranged from 0.2 to 7% over the length of the specimen. (Courtesy: Chris Booth-Morrison and Yang Zhou)

Heterogeneos nucleation of Cu precipitates on a grain boundary

This LEAP tomography data set is from a blast resistant steel which has been aged at 550°C and 450°C. Nanosize Cu precipitates are one of the major contributors to the strength of the steel, and as such it is important to understand their nucleation, growth, and coarsening behavior. Heterogeneous nucleation, which is seen here along a grain boundary, changes the behavior from what would be predicted by models for purely homogeneous nucleation. The red represents a 5 at% Cu isoconcentration surface.(Courtesy: Mike Mulholland)

Interprecipitate Distance Distribution algorithm.

The edge-to-edge interprecipitate distance is an important quantity for many physical properties, including the yield strength, conductivity, and coarsening behavior. Because LEAP tomography is able to analyze a large number of precipitates, it can be used to find the interprecipitate distance distribution. The precipitates in this Fe-Cu alloy are fit as ellipsoids and the distances between them are calculated, as described in Direct Measurement of 2-Dimensional and 3-Dimensional Interprecipitate Distance Distributions from Atom-Probe Tomographic Reconstructions

(Courtesy: Richard Karnesky and Dieter Isheim)

Interprecipitate Distance Distribution algorithm.

A proxigram obtained from a LEAP tomographic dataset of a dilute Al-Sc-Lu alloy which has been aged at 300 deg C. Nanometer-sized Al3(Sc1-xLux) precipitates are exploited as a strengthening phase. This proxigram quantifies the core/shell structure which develops in the precipitates, with Lu segregating to the center of the precipitates and Sc forming a shell around the core.

(Courtesy: Matt Krug)

Al-Sc-RE precipitates

Three-dimensional LEAP tomographic reconstructions of Al–0.06 Sc–0.02 Tb and Al–0.06 Sc–0.02 Tm (at.%) aged for: (a) 10 minutes, and (b) 24 hours at 300 °C. Each reconstruction is divided into three sections, with Sc atoms only displayed in the leftmost section, rare earth (RE) atoms only displayed in the center section, and both Sc and RE atoms displayed in the rightmost section. After 10 minutes aging time, nanometer-sized RE-rich Al3(RE1-xScx) precipitates have formed. With continued aging to 24 hours, a core-shell structure is evident in the precipitates, with a RE-rich core surrounded by a Sc-rich shell.

(Courtesy: Matt Krug)