The role of atom-probe field ion microscopy in alloy development and phase transformation studies

1994 ◽  
Vol 52 ◽  
pp. 822-823
Author(s):  
M. K. Miller ◽  
R. Jayaram ◽  
K. F. Russell
Keyword(s):  
Grain Boundaries ◽  
Gas Turbines ◽  
Atom Probe ◽  
Solid Solution Hardening ◽  
Alloy Development ◽  
Probe Field ◽  
Hardening Mechanism ◽  
Boron Segregation ◽  
Large Effort

One of the important parameters in the design of new materials is the distribution of the alloyingelements in the microstructure and whether these elements are involved in the formation of precipitates or in segregation to internal interfaces such as grain boundaries. The atom probe field ion microscope is an extremely effective tool for these types of fine scale characterizations. Recently, therehas been a large effort to develop new, more efficient materials for high temperature applications such as gas turbines. A candidate material for this application is NiAl. However, the low temperature ductility of NiAl is extremely small and hinders fabrication. Therefore, attempts have been made to alleviate these problems with the use of microalloying additions such as boron. The atom probe has beenused to determine the location of boron in the microstructure and correlate its distribution with themechanical properties. Atom probe analyses have revealed that the solubility of boron in NiAl is extremely low and most of the excess boron is precipitated in the form of ultrafine MB2 precipitates as shown in Fig. 1. In addition, boron segregation to the grain boundaries has been observed, Fig. 2. Theobserved increase in the yield strength is therefore primarily due to a precipitation hardening mechanism with a contribution from solid solution hardening and this offsets the beneficial effect of the boron at the grain boundaries.

An Atom Probe Field Ion Microscope Investigation Of The Role Of Boron In Precipitates And At Grain Boundaries In NiAl

1991 ◽  
Vol 238 ◽  
Author(s):  
Raman Jayaram ◽  
M. K. Miller
Keyword(s):  
Grain Boundaries ◽  
Atom Probe ◽  
Probe Field ◽  
Analytical Technique ◽  
Boron Segregation ◽  
Boron Doped ◽  
Nial Alloy ◽  
The Matrix ◽  
Boride Phases

ABSTRACTThe high resolution analytical technique of Atom Probe Field Ion Microscopy (APFTM) haseen used to characterize grain boundaries and the matrix of a stoichiometric NiAl alloy doped with 0.04 (100 wppm) and 0.12 at. % (300 wppm) boron. Field ion images revealed boron segregation to the grain boundaries. Atom probe elemental analysis of the grain boundaries measured a boron coverage of up to 30% of a monolayer. Extensive atom probe analyses also revealed a fine dispersion of nanoscale boride precipitates in the matrix. The boron segregation to the grain boundaries was found to correlate with the observed suppression of intergranular fracture. However, the decrease in ductility of boron-doped NiAl is attributed in part to the precipitation hardening effect of the boride phases.

An atom probe field ion microscope analysis of grain boundary chemistry in boron and carbon doped NiAl

1992 ◽  
Vol 50 (2) ◽  
pp. 1220-1221
Author(s):  
Raman Jayaram ◽  
M.K Miller
Keyword(s):  
Grain Boundary ◽  
Enrichment Factor ◽  
Grain Boundaries ◽  
Atom Probe ◽  
Probe Field ◽  
Carbon Doped ◽  
Boron Segregation ◽  
Microanalytical Technique ◽  
Microalloying Elements ◽  
Boundary Chemistry

The low temperature brittleness of nickel aluminides has been a serious impediment to their technological applications. A commonly employed technique to ductilize these materials involves the addition of suitable microalloying elements and correlating grain boundary chemistry with fracture mode. In the well documented case of Ni3Al, boron segregation to grain boundaries is accompanied by suppression of intergranular fracture and a significant increase in ductility. The high resolution microanalytical technique of atom probe field ion microscopy (APFIM) has been used in this study to analyze grain boundaries in order to characterize similar attempts to ductilize NiAl. APFIM specimens were prepared from tensile specimens of stoichiometric NiAl doped with either 0.04 or 0.12 at. % boron or 0.1 at % carbon, respectively. A field ion image of a grain boundary in a B-doped NiAl specimen is shown in Fig. 1. The brightly-imaging spots decorating the boundary were determined by atom probe analysis to be boron atoms. The boron enrichment factor at the boundary depends on the assumed thickness of the segregation as shown in Fig. 2 with an enrichment factor of ∼850 times for a monolayer coverage (i.e. 0.2 nm).

Effect of Aluminum Level on Boron Clustering in Ni3Al

1988 ◽  
Vol 133 ◽  
Author(s):  
J. A. Horton ◽  
M. K. Miller ◽  
C. T. Liu ◽  
E. P. George ◽  
J. Bentley
Keyword(s):  
Grain Boundaries ◽  
Maximum Size ◽  
Atom Probe ◽  
Probe Field ◽  
Boron Clusters ◽  
Boron Segregation ◽  
Aluminum Level ◽  
Ion Microscopy ◽  
Rapidly Solidified ◽  
Nickel Enrichment

ABSTRACTIn alloys containing 0.24% boron, atom-probe field-ion microscopy (APFIM) revealed the presence of boron clusters in Ni-25 at. % Al and Ni-26 Al but not in Ni-24 Al. The observed boron clusters generally consisted of two to three boron atoms with a maximum size of 10 atoms. Quench rates that ranged from rapid solidification to furnace cooling had little effect on the clustering. The occurrence of the clustering coincides with a higher rate of boron strengthening as measured by an increase in the yield stress per atomic percent boron, and it also coincides with a reduced amount of boron segregation to grain boundaries. The levels of nickel and boron were highly variable on grain boundaries in rapidly solidified material and therefore no consistent indication of nickel enrichment at the grain boundaries associated with boron segregation was found. This result suggests that cosegregation of nickel with boron may not be necessary for the ductilization of Ni3Al by boron, since the rapidly solidified material is also ductilized by boron and exhibits segregation of only boron to the grain boundaries.

scholarly journals Influence of Dislocation-Solute Interactions on The Mechanical Properties of Zirconium-Doped NiAl

1994 ◽  
Vol 364 ◽  
Author(s):  
R. Jayaram ◽  
M.K. Miller
Keyword(s):  
Grain Boundaries ◽  
Fracture Mode ◽  
Atom Probe ◽  
Transgranular Fracture ◽  
Probe Field ◽  
Hardening Mechanism ◽  
The Matrix ◽  
Solute Interactions ◽  
Ductile To Brittle Transition ◽  
Nial Matrix

AbstractAtom probe field ion microscopy (APFIM) has been used to characterize NiAl microalloyed with molybdenum and zirconium. Field ion images and atom probe analyses revealed segregation of zirconium to dislocation strain fields and ribbon-like morphological features that are probably related to dislocations. These results provide direct experimental evidence in support of the suggestion that the tremendous increase in the ductile-to-brittle transition temperature (DBTT) in zirconium-doped NiAl is due to pinning of dislocations by zirconium atoms. Atom probe analyses also revealed segregation of zirconium to grain boundaries. This result is consistent with the change from an intergranular fracture mode in undoped NiAl to a mixture of intergranular and transgranular fracture mode in zirconium-doped NiAl. The NiAl matrix was severely depleted of the solutes molybdenum and zirconium. Small Mo-rich precipitates, detected in the matrix and grain boundaries, are likely to contribute to the significant increase in the room-temperature yield stress of microalloyed NiAl through a precipitation hardening mechanism.

The Microchemistry Studies of Ductile Ll2 Ni-Based Intermetallics

1994 ◽  
Vol 364 ◽  
Author(s):  
Naoya Masahashi
Keyword(s):  
Electron Microscopy ◽  
Auger Electron ◽  
Boron Content ◽  
Atom Probe ◽  
Probe Field ◽  
Composition Fluctuation ◽  
Boron Segregation ◽  
Boron Doped ◽  
Field Ion Microscope ◽  
Stoichiometric Alloy

AbstractAuger electron microscopy (AES) analysis of boron doped Ni3Al have shown boron segregation at grain boundary (GB). Boron segregation was enhanced with increasing bulk boron content independent of stoichiometry, suggesting that hypo-stoichiometric alloy is intrinsically ductile even without boron. A slight Ni cosegregation is confirmed using atom probe field ion microscope (APFIM). In Ni3(Si,Ti), no distinct composition fluctuation was identified between matrix and GB vicinity. These results suggest that atomic bonding atmosphere modification from covalent to metallic in the vicinity of GB is one of factors to modify ductility for Ll2-type intermetallics.

High resolution studies of the solid state amorphization reaction in the ZrCo system with the atom probe/field ion microscope

1994 ◽  
Vol 343 ◽  
Author(s):  
Susanne Schneider ◽  
Ralf Busch ◽  
Konrad Samwer
Keyword(s):  
Solid State ◽  
Single Crystal ◽  
Grain Boundaries ◽  
Amorphous Phase ◽  
Rutherford Backscattering Spectrometry ◽  
Atom Probe ◽  
Nanometer Scale ◽  
Probe Field ◽  
Field Ion Microscope ◽  
State Amorphization

ABSTRACTThe atom probe/field ion microscope is introduced as a new powerful investigation device to study the early stages of the solid state amorphization reaction (SSAR). A bilayer of Zr and Co was condensed under UHV conditions on W wire tips and analyzed in a field ion microscope (FIM) combined with an atom probe (AP). The reaction of Co with Zr has been studied at room temperature. FIM pictures and AP analysis have shown that even at low temperatures an amorphous phase is formed at the Zr/Co interface and in the Zr grain boundaries. In these areas concentration profiles have been taken on a nanometer scale. Most likely, the extended solid solution of Co found in α- Zr grain boundaries causes the formation of the amorphous phase. Further, Rutherford backscattering spectrometry (RBS) suggests that even point defects and dislocations at the surface of an α- Zr single crystal are sufficient to initiate the SSAR between a polycrystalline Co layer vapour- deposited onto that single crystal.

Applications of Atom Probe Microanalysis in Materials Science

MRS Bulletin ◽  
1994 ◽  
Vol 19 (7) ◽  
pp. 27-34 ◽  
Author(s):  
M.K. Miller ◽  
G.D.W. Smith
Keyword(s):  
Grain Boundaries ◽  
Materials Science ◽  
Direct Method ◽  
Light Element ◽  
Atom Probe ◽  
Single Atom ◽  
Probe Field ◽  
Probe Technique ◽  
Wide Range ◽  
Field Ion Microscope

The atom probe field ion microscope is the most powerful and direct method for the analysis of materials at the atomic level. Since analyses are performed by collecting atoms one at a time from a small volume, it is possible to conduct fundamental characterization of materials at this level. The atom probe technique is applicable to a wide range of materials since its only restriction is that the material under analysis must possess at least some limited electrical conductance. Therefore, since its introduction in 1968, the atom probe field ion microscope has been used in many diverse applications in most branches of materials science. Many of the applications have exploited its high spatial resolution capabilities to perform microstructural characterizations of features such as grain boundaries and other interfaces and ultrafine scale precipitation that are not possible with other microanaly tical techniques. This article briefly outlines some of the capabilities and applications of the atom probe. The details of the atom probe technique are described elsewhere.The power of the atom probe may be demonstrated by its ability to see and identify a single atom, which is particularly useful in characterizing solute segregation to grain boundaries or other interfaces. An example of a brightly-imaging solute atom at a grain boundary in a nickel aluminide is shown in Figure 1. In order to conclusively determine its identity, its image is aligned with the probe aperture in the center of the imaging screen and then the selected atom is carefully removed by field evaporation and analyzed in the time-of-flight mass spectrometer. This and many other bright spots in this material were shown to be boron atoms. This example also illustrates the light element analytical capability of the atom probe. In fact, the atom probe may to used to analyze all elements in the periodic table and has had applications ranging from characterizing the distribution of implanted hydrogen to phase transformations in uranium alloys.

On The Effect of Au Addition and the Role of B on Nanocrystallization of Fe-Zr-B Amorphous Alloy

1999 ◽  
Vol 580 ◽  
Author(s):  
Y. Zhang ◽  
N. Wanderka ◽  
U. Czubayko ◽  
F. Zhu ◽  
H. Wollenberger
Keyword(s):  
Amorphous Alloy ◽  
Early Stage ◽  
Primary Crystallization ◽  
Atom Probe ◽  
Chemical Compositions ◽  
Probe Field ◽  
Heterogeneous Distribution ◽  
Nucleation Barrier ◽  
Nucleation Sites

AbstractUsing atom probe field ion microscopy (APFIM) we examined the local chemical compositions of Fe-7Zr-5B-lAu and Fe-14B amorphous alloys in the course of primary crystallization. Au rich clusters are formed during primary crystallization of Fe-7Zr-5B-lAu alloy. However, these clusters do not act as nucleation sites for α-Fe particles. In the early stage of primary crystallization, heterogeneities of Fe and B evolve in the amorphous phase. Heterogeneous distribution of B was found in the as-melt-spun Fe-14B amorphous alloy. During primary crystallization, B is highly supersaturated not only in the nanometer sized α-Fe particles in Fe-7Zr-5B-lAu alloy, but also in those of large diameters in Fe-14B alloy. From the results it is concluded that presence of B lowers the nucleation barrier for primary crystallization.

Imaging atom probe microscopy for segregation studies

1980 ◽  
Vol 295 (1413) ◽  
pp. 133-133 ◽  
Keyword(s):  
Grain Boundaries ◽  
Spatial Resolution ◽  
Image Intensifier ◽  
Atom Probe ◽  
Probe Field ◽  
Low Concentrations ◽  
Quantitative Analyses ◽  
Field Ion Microscope ◽  
Conventional Type ◽  
Imaging Atom Probe

The measurement of low concentrations of elements segregated to or near grain boundaries with a spatial resolution of ca . 1 nm has recently become possible with the introduction of the imaging atom probe (i.a.p.). This development of the original atom probe field ion microscope uses a time-gated image intensifier as the detector of a time-of-flight mass spectrometer and displays an elemental map of ions desorbed from the surface of a field-ion specimen. The sensitivity of the analysis is uniform for both light (e.g. B, C, O) and heavy (e.g. Sn) elements, and concentrations down to 100 pg/g can be detected; accurate quantitative analyses are obtained by using the more conventional type of atom probe.

Phase Transformation and Segregation to Lattice Defects in Ni-Base Superalloys

2007 ◽  
Vol 13 (6) ◽  
pp. 464-483 ◽  
Author(s):  
Didier Blavette ◽  
Emmanuel Cadel ◽  
Cristelle Pareige ◽  
Bernard Deconihout ◽  
Pierre Caron
Keyword(s):  
Grain Boundaries ◽  
Depth Resolution ◽  
Atom Probe ◽  
Atomic Scale ◽  
Probe Field ◽  
Plane Analysis ◽  
Phase Separation Kinetics ◽  
Nickel Base ◽  
Nicral Alloys ◽  
Good Agreement

Nanostructural features of nickel-base superalloys as revealed by atom probe field ion microscopy (APFIM) and atom probe tomography (APT) are reviewed. The more salient information provided by these techniques is discussed through an almost exhaustive analysis of literature over the last 30 years. Atom probe techniques are shown to be able to measure the composition of tiny γ′ precipitates, a few nanometers in size, and to reveal chemical order within these precipitates. Phase separation kinetics in model NiCrAl alloys was investigated with both 3DAP and Monte-Carlo simulation. Results are shown to be in good agreement. Plane by plane analysis of {001} planes of Ni3Al-type γ′ phase makes it possible to estimate the degree of order as well as the preferential sites of various addition elements (Ti, Cr, Co, W, Ta, Re, Ru, etc.) included in superalloys. Clustering effects of Re in the γ solid solution were also exhibited. Due to its ultrahigh depth resolution, the microchemistry of interfaces and grain boundaries can be characterized on an atomic scale. Grain boundaries in Astroloy or N18 superalloys were found to be enriched in B, Mo, and Cr and Al depleted.

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