Effect of Aluminum Level on Boron Clustering in Ni3Al

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.

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The Microchemistry of Grain Boundaries in Ni3Al

MRS Proceedings ◽

10.1557/proc-133-155 ◽

1988 ◽

Vol 133 ◽

Cited By ~ 10

Author(s):

D. N. Sieloff ◽

S. S. Brenner ◽

Hua Ming-Jian

Keyword(s):

Grain Boundary ◽

Grain Boundaries ◽

Atom Probe ◽

High Concentration ◽

Field Ion Microscopy ◽

Boron Clusters ◽

Ion Microscopy

ABSTRACTGrain boundary regions in B-doped as well as B-free Ni3AI were studied by field-ion microscopy and atom probe microanalysis. In the ductile, recrystallized, Ni-rich alloys the segregation of boron was often accompanied by an enrichment of nickel. Such an enrichment was not observed at boundaries in B-free alloys. Boron was also observed to segregate to the boundaries in a 25.2A1 - IB alloy which was reported to contain boron clusters. Such clusters were not observed, instead a high concentration of boron pairs were found.

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

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100130730 ◽

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).

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

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100171845 ◽

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.

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

MRS Proceedings ◽

10.1557/proc-238-445 ◽

1991 ◽

Vol 238 ◽

Cited By ~ 1

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.

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Characterization of Internal Interfaces by Atom Probe Field Ion Microscopy

MRS Proceedings ◽

10.1557/proc-295-247 ◽

1992 ◽

Vol 295 ◽

Cited By ~ 1

Author(s):

M. K. Miller ◽

Raman Jayaram

Keyword(s):

Grain Boundaries ◽

Compositional Analysis ◽

Atom Probe ◽

Probe Field ◽

Field Ion Microscopy ◽

Surrounding Matrix ◽

Wide Range ◽

Ion Microscopy ◽

Field Ion Microscope

AbstractThe near atomic spatial resolution of the atom probe field ion microscope permits the elemental characterization of internal interfaces, grain boundaries and surfaces to be performed in a wide variety of materials. Information such as the orientation relationship between grains, topology of the interface, and the coherency of small precipitates with the surrounding matrix may be obtained from field ion microscopy. Details of the solute segregation may be obtained at the plane of the interface and as a function of distance from the interface for all elements simultaneously from atom probe compositional analysis. The capabilities and limitations of the atom probe technique in the characterization of internal interfaces is illustrated with examples of grain boundaries and interphase interfaces in a wide range of materials including intermetallics, model alloys, and commercial steels.

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An Improved Method for the Preparation and TEM Examination of Sharp Pointed Tips used in APFIM and STM

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100134107 ◽

1990 ◽

Vol 48 (2) ◽

pp. 102-103

Author(s):

E.A. Fischione ◽

P.E. Fischione ◽

J.J. Haugh ◽

M.G. Burke

Keyword(s):

Atom Probe ◽

Preparation Process ◽

Improved Method ◽

Ion Milling ◽

Polishing Process ◽

Probe Field ◽

Scanning Tunnelling ◽

Stm Tips ◽

Tunnelling Microscopy ◽

Ion Microscopy

A common requirement for both Atom Probe Field-Ion Microscopy (APFIM) and Scanning Tunnelling Microscopy (STM) is a sharp pointed tip for use as either the specimen (APFIM) or the probe (STM). Traditionally, tips have been prepared by either chemical or electropolishing techniques. Recently, ion-milling has been successfully employed in the production of APFIM tips [1]. Conventional electropolishing techniques are applicable to a wide variety of metals, but generally require careful manual adjustments during the polishing process and may also be time-consuming. In order to reduce the time and effort involved in the preparation process, a compact, self-contained polishing unit has been developed. This system is based upon the conventional two-stage electropolishing technique in which the specimen/tip blank is first locally thinned or “necked”, and subsequently electropolished until separation occurs.[2,3] The result of this process is the production of two APFIM or STM tips. A mechanized polishing unit that provides these functions while automatically maintaining alignment has been designed and developed.

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